Frederic Libersat - Academia.edu (original) (raw)

Papers by Frederic Libersat

Research paper thumbnail of Current Biology 2008

Research paper thumbnail of On predatory wasps and zombie cockroaches: Investigations of "free will" and spontaneous behavior in insects

Communicative & integrative biology, 2010

Accumulating evidence suggest that nonhuman organisms, including invertebrates, possess the abili... more Accumulating evidence suggest that nonhuman organisms, including invertebrates, possess the ability to make non-random choices based purely on ongoing and endogenously-created neuronal processes. We study this precursor of spontaneity in cockroaches stung by A. compressa, a parasitoid wasp that employs cockroaches as a live food supply for its offspring. This wasp uses a neurotoxic venom cocktail to 'hijack' the nervous system of its cockroach prey and manipulate specific features of its decision making process, thereby turning the cockroach into a submissive 'zombie' unable to self-initiate locomotion. We discuss different behavioral and physiological aspects of this venom-induced 'zombified state' and highlight at least one neuronal substrate involved in the regulation of spontaneous behavior in insects.

Research paper thumbnail of Force-sensitive mechanoreceptors of the dactyl of the crab: single-unit responses during walking and evaluation of function

Journal of neurophysiology, 1987

The activities of individual force-sensitive mechanoreceptors of the dactyl (terminal leg segment... more The activities of individual force-sensitive mechanoreceptors of the dactyl (terminal leg segment) of the crab, Carcinus maenas, have been recorded during free walking. These receptors have also been mechanically and electrically stimulated in freely moving animals to directly evaluate their function in locomotion. All force-sensitive mechanoreceptors fired during the stance phase of walking and were silent during swing. Receptor discharges showed regular phase relationships to bursts in motor neurons of leg muscles. Crabs walk laterally and use the legs of one side either in trailing to actively push the animal to the opposite side, or in leading, to less forcefully pull the animal in that direction. Individual force-sensitive mechanoreceptors differed in their patterns of activity during trailing or leading according to their location on the dactyl. Units of proximal receptors fired more vigorously when used in trailing than in leading. Discharges in trailing were also increased b...

Research paper thumbnail of Synaptic Reorganization Induced by Selective Photoablation of an Identified Neuron

The maintenance of synaptic strength and specificity in the CNS may depend on interactions among ... more The maintenance of synaptic strength and specificity in the CNS may depend on interactions among postsynaptic den- drites. We examined the effect of removing a neuron on synap- tic organization. A single identified postsynaptic neuron in the adult cercal system of the cockroach was removed with pho- toablation. After a 30 d recovery period, the synaptic connec- tivity and morphology

Research paper thumbnail of Octopamine partially restores walking in hypokinetic cockroaches stung by the parasitoid wasp Ampulex compressa

Journal of Experimental Biology, 2007

Research paper thumbnail of Olfactory learning-induced increase in spine density along the apical dendrites of CA1 hippocampal neurons

Hippocampus, 2004

We have previously shown that rule learning of an olfactory discrimination task is accompanied by... more We have previously shown that rule learning of an olfactory discrimination task is accompanied by increased spine density along the apical dendrites of piriform cortex pyramidal neurons. The purpose of the present study was to examine whether such olfactory learning task, in which the hippocampus is actively involved, induces morphological modifications in CA1 pyramidal neurons as well. Rats were trained to discriminate positive cues in pairs of odors for a water reward. Morphological modifications were studied in Golgi-impregnated neurons with light microscopy, 1 and 3 days after training completion. Spine densities were measured on the proximal region of apical dendrites and on basal dendrites after rule learning. Three days after training completion, the mean spine density on apical dendrites in neurons from trained rats was significantly higher by 20.5% than in neurons from pseudo-trained and naive animals, which did not differ from each other. By contrast, there was no significant difference in spine density of basal dendrites among the three groups. As length and diameter of spiny dendritic segments did not change after learning, the learning-related increase in spine density in neurons from trained rats may reflect a net increase in the number of excitatory synapses in the hippocampus following olfactory rule learning.

Research paper thumbnail of Olfactory learning-related NCAM expression is state, time, and location specific and is correlated with individual learning capabilities

Hippocampus, 2005

The notion that long-term synaptic plasticity is generated by activity-induced molecular modifica... more The notion that long-term synaptic plasticity is generated by activity-induced molecular modifications is widely accepted. It is well established that neural cell adhesion molecule (NCAM) is one of the prominent modulators of synaptic plasticity. NCAM can be polysialylated (PSA-NCAM), a reaction that provides it with anti-adhesion properties. In this study we have focused on NCAM and on its polysialylated state, and their relation to learning of an olfactory discrimination task, which depends on both the piriform (olfactory) cortex and hippocampus. We trained rats to distinguish between pairs of odors until rule learning was achieved, a process that normally lasts 6 -8 days. At four time points, during training and after training completion, synaptic NCAM and PSA-NCAM expression were assessed in the piriform cortex and hippocampus. We report that NCAM modulation is specific to PSA-NCAM, which is upregulated in the hippocampus one day after training completion. We also report a correlation between the performance of individual rats in an early training stage and their NCAM expression, both in the piriform cortex and hippocampus. Since individual early performance in our odor discrimination task is correlated with the performance throughout the training period, we conclude that early NCAM expression is associated with odor learning capability. We therefore suggest that early synaptic NCAM expression may be one of the factors determining the capability of rats to learn.

Research paper thumbnail of Sensory Arsenal on the Stinger of the Parasitoid Jewel Wasp and Its Possible Role in Identifying Cockroach Brains

PLoS ONE, 2014

The parasitoid jewel wasp uses cockroaches as live food supply for its developing larva. To this ... more The parasitoid jewel wasp uses cockroaches as live food supply for its developing larva. To this end, the adult wasp stings a cockroach and injects venom directly inside its brain, turning the prey into a submissive 'zombie'. Here, we characterize the sensory arsenal on the wasp's stinger that enables the wasp to identify the brain target inside the cockroach's head. An electron microscopy study of the stinger reveals (a) cuticular depressions innervated by a single mechanosensory neuron, which are presumably campaniform sensilla; and (b) dome-shaped structures innervated by a single mechanosensory neuron and 4-5 chemosensory neurons, which are presumably contact-chemoreceptive sensilla. Extracellular electrophysiological recordings from stinger afferents show increased firing rate in response to mechanical stimulation with agarose. This response is direction-selective and depends upon the concentration (density) of the agarose, such that the most robust response is evoked when the stinger is stimulated in the distal-to-proximal direction (concomitant with the penetration during the natural stinging behavior) and penetrating into relatively hard (0.75%-2.5%) agarose pellets. Accordingly, wasps demonstrate a normal stinging behavior when presented with cockroaches in which the brain was replaced with a hard (2.5%) agarose pellet. Conversely, wasps demonstrate a prolonged stinging behavior when the cockroach brain was either removed or replaced by a soft (0.5%) agarose pellet, or when stinger sensory organs were ablated prior to stinging. We conclude that the parasitoid jewel wasp uses at least mechanosensory inputs from its stinger to identify the brain within the head capsule of the cockroach prey.

Research paper thumbnail of Dual locomotor activity selectively controlled by force- and contact-sensitive mechanoreceptors

Neuroscience Letters, 1986

The crab Carcinus maenas walks laterally: moreover, as soon as leg contact with the support is lo... more The crab Carcinus maenas walks laterally: moreover, as soon as leg contact with the support is losl, it starts swimming. In free-moving animals, discharges from individual force-and contact-mechanoreceptors located in the terminal segment of the last pair of walking legs have been recorded. These receptors are active during the stance phase of walking and remain silent during swimming. Selective electrical stimulation of their allerent fibers during swimming inhibits this behaviour. The possible role of such sensory information in selecting different motor patterns is discussed.

Research paper thumbnail of Mechanisms of Dendritic Maturation

Molecular Neurobiology, 2004

The highly complex geometry of dendritic trees is crucial for neural signal integration and the p... more The highly complex geometry of dendritic trees is crucial for neural signal integration and the proper wiring of neuronal circuits. The morphogenesis of dendritic trees is regulated by innate genetic factors, neuronal activity, and external molecular cues. How each of these factors contributes to dendritic maturation has been addressed in the developing nervous systems of animals ranging from insects to mammals. The results of such investigations have shown that the contribution of intrinsic and extrinsic factors and activity, however, appear to be weighted differentially in different types of neurons, in different brain areas, and especially in different species. Moreover, it appears that dozens of molecules have been found to regulate dendritic maturation, but it is almost certain that each molecule plays only a specific role in this formidable cooperative venture. This article reviews our current knowledge and understanding of the role of various factors in the establishment of the architecture of mature dendritic trees.

Research paper thumbnail of In situ visualization and photoablation of individual neurons using a low cost fiber optic based system

Journal of Neuroscience Methods, 1996

This paper describes a low-cost system for in situ visualization and photoablation of single neur... more This paper describes a low-cost system for in situ visualization and photoablation of single neurons. The system includes a fiber optics light source equipped with a filter port, a blue excitation filter and a yellow barrier filter, and a light guide which terminates with a focusing lens. This system is inexpensive, easy to use, and requires minimal maintenance. Given its price, this system is readily accessible and has the potential of becoming standard equipment for in situ visualization and killing of individual neurons.

Research paper thumbnail of New vistas on the initiation and maintenance of insect motor behaviors revealed by specific lesions of the head ganglia

Journal of Comparative Physiology A, 2006

In insects, thoracic pattern generators are modulated by the two head ganglia, the supraesophagea... more In insects, thoracic pattern generators are modulated by the two head ganglia, the supraesophageal ganglion (brain) and the subesophageal ganglion, which act as higher-order neuronal centers. To explore the contribution of each head ganglion to the initiation and maintenance of speciWc motor behaviors in cockroaches (Periplaneta americana), we performed speciWc lesions to remove descending inputs from either the brain or the subesophageal ganglion or both, and quan-tiWed the behavioral outcome with a battery of motor tasks. We show that 'emergency' behaviors, such as escape, Xight, swimming or righting, are initiated at the thoracic level independently of descending inputs from the head ganglia. Yet, the head ganglia play a major role in maintaining these reXexively initiated behaviors. By separately removing each of the two head ganglia, we show that the brain excites Xight behavior and inhibits walking-related behaviors, whereas the subesophageal ganglion exerts the opposite eVects. Thus, control over speciWc motor behaviors in cockroaches is anatomically and functionally compartmentalized. We propose a comprehensive model in which the relative permissive versus inhibitory inputs descending from the two head ganglia, combined with thoracic aVerent sensory inputs, select a speciWc thoracic motor pattern while preventing the others.

Research paper thumbnail of Parasitoid wasp affects metabolism of cockroach host to favor food preservation for its offspring

Journal of Comparative Physiology A, 2005

Unlike predators, which immediately consume their prey, parasitoid wasps incapacitate their prey ... more Unlike predators, which immediately consume their prey, parasitoid wasps incapacitate their prey to provide a food supply for their offspring. We have examined the effects of the venom of the parasitoid wasp Ampulex compressa on the metabolism of its cockroach prey. This wasp stings into the brain of the cockroach causing hypokinesia. We first established that larval development, from egg laying to pupation, lasts about 8 days. During this period, the metabolism of the stung cockroach slows down, as measured by a decrease in oxygen consumption. Similar decreases in oxygen consumption occurred after pharmacologically induced paralysis or after removing descending input from the head ganglia by severing the neck connectives. However, neither of these two groups of cockroaches survived more than six days, while 90% of stung cockroaches survived at least this long. In addition, cockroaches with severed neck connectives lost significantly more body mass, mainly due to dehydration. Hence, the sting of A. compressa not only renders the cockroach prey helplessly submissive, but also changes its metabolism to sustain more nutrients for the developing larva. This metabolic manipulation is subtler than the complete removal of descending input from the head ganglia, since it leaves some physiological processes, such as water retention, intact.

Research paper thumbnail of Multiple feedback loops in the flying cockroach: excitation of the dorsal and inhibition of the ventral giant interneurons

Journal of Comparative Physiology A, 1989

Research paper thumbnail of Localization of the site of effect of a wasp's venom in the cockroach escape circuitry

Journal of Comparative Physiology A: Sensory, Neural, and Behavioral Physiology, 1999

The parasitic wasp Ampulex compressa stings a cockroach Periplaneta americana in the neck, toward... more The parasitic wasp Ampulex compressa stings a cockroach Periplaneta americana in the neck, toward the head ganglia (the brain and subesophageal ganglion). In the present study, our aim was to identify the head ganglion that is the target of the venom and the mechanisms by which the venom blocks the thoracic portion of the escape neuronal circuitry. Because the escape responses elicited by a wind stimulus in brainless and sham-operated animals were similar, we propose that the venom eect is on the subesophageal ganglion. Apparently, the subesophageal ganglion modulates the thoracic portion of the escape circuit. Recordings of thoracic interneuron responses to the input from the abdominal giant interneurons showed that the thoracic interneurons receive synaptic drive from these interneurons in control and in stung animals. Unlike normal cockroaches, which use both fast and slow motoneurons for producing rapid escape movements, stung animals activate only the slow motoneuron. However, we show that in stung animals, the fast motoneuron still can be recruited with bath application of pilocarpine, a muscarinic agonist. These results indicate that the descending control from the subesophageal ganglion is presumably exerted on the premotor thoracic interneurons to motoneurons connection of the thoracic escape circuitry.

Research paper thumbnail of Morphometric analysis of dendritic remodeling in an identified motoneuron during postembryonic development

The Journal of Comparative Neurology, 2002

A detailed quantitative description of modifications in neuronal architecture is an important pre... more A detailed quantitative description of modifications in neuronal architecture is an important prerequisite to investigate the signals underlying behaviorally relevant changes in neuronal shape. Extensive morphological remodeling of neurons occurs during the metamorphosis of holometabolous insects, such as Manduca sexta, in which new adult behaviors develop postembryonically. In this study, a morphometric analysis of the structural changes of an identified Manduca motoneuron, MN5, was conducted by sampling its metric parameters at different developmental stages. The remodeling of MN5 is divided into three main phases. The regression of most larval dendrites (1) is followed by the formation of dendritic growth-cones (2), and subsequently, adult dendrite formation (3). In contrast, the cell body and link segment surface increase during dendritic regression and regrowth, indicating that different cell compartments receive different signals, or respond differently to the same signal. During dendritic growth-cone formation, the growth of the cell body and the link segment are arrested. Sholl and branch frequency analysis suggest two different modes of dendritic growth. During a first growth-cone-dependent phase, new branch formation occurs at all dendrites. The maximum path length of the major dendritic tree changes little, whereas branch order increases from 20 to 45. Changes in total dendritic length are correlated with strong changes in the number of nodes but with minor changes in the average dendritic segment length, indicating a mode of growth similar to that induced by steroid hormone application to cultured motoneurons. The second phase is growth-cone-independent, and branching is limited to high order dendrites.

Research paper thumbnail of Comparative analysis of dendritic architecture of identified neurons using the Hausdorff distance metric

The Journal of Comparative Neurology, 2000

Dendritic trees often are complex, three-dimensional structures. Comparative morphologic studies ... more Dendritic trees often are complex, three-dimensional structures. Comparative morphologic studies have not yet provided a reliable measure to analyze and compare the geometry of different dendritic trees. Therefore, it is important to develop quantitative methods for analyzing the three-dimensional geometry of these complex trees. The authors developed a comparison measure based on the Hausdorff distance for comparing quantitatively the three-dimensional structure of different neurons. This algorithm was implemented and incorporated into a new software package that the authors developed called NeuroComp. The authors tested this algorithm to study the variability in the three-dimensional structure of identified central neurons as well as measuring the structural differences between homologue neurons. They took advantage of the uniform dendritic morphology of identified interneurons of an insect, the giant interneurons of the cockroach. More specifically, after establishing a morphometric data base of these neurons, the authors found that the algorithm is a reliable tool for distinguishing between dendritic trees of different neurons, whereas conventional metric analysis often is inadequate. The authors propose to use this method as a quantitative tool for the investigation of the effects of various experimental paradigms on three-dimensional dendritic architecture.

Research paper thumbnail of Wasp Voodoo Rituals, Venom-Cocktails, and the Zombification of Cockroach Hosts

Integrative and Comparative Biology, 2014

Research paper thumbnail of Dynamics of olfactory learning-induced up-regulation of L1 in the piriform cortex and hippocampus

European Journal of Neuroscience, 2005

L1 is a cell adhesion molecule implicated in the formation of neural circuits and synaptic plasti... more L1 is a cell adhesion molecule implicated in the formation of neural circuits and synaptic plasticity. We have examined the sequence and time-frame in which modifications in the synaptic expression of L1 occur in the piriform cortex and hippocampus in the course of rule learning of an olfactory discrimination task. Rats were trained to choose the correct odour in a pair to be rewarded with drinking water. Such training requires 6-8 days on average before rats reach maximal performance. We observed a learning-induced L1 upregulation that occurred at an early training stage in the piriform cortex but only after rule-learning establishment in the hippocampus. We suggest that the dynamics of L1 up-regulation may reflect the functional role of these brain regions in olfactory rule learning.

Research paper thumbnail of Olfactory learning-induced morphological modifications in single dendritic spines of young rats

European Journal of Neuroscience, 2005

Learning-related morphological modifications in single dendritic spines were studied quantitative... more Learning-related morphological modifications in single dendritic spines were studied quantitatively in the brains of young Sprague-Dawley rats. We have previously shown that olfactory discrimination rule-learning results in transient physiological and morphological modifications in piriform cortex pyramidal neurons. In particular, spine density along the apical dendrites of neurons from trained rats is increased after learning. The aim of the present study was to identify and describe olfactory learning-induced modifications in the morphology of single spines along apical dendrites of the same type of neurons. By using laser-scanning confocal microscopy, we show that 3 days after training completion spines on neurons from olfactory discrimination trained rats are shorter as compared to spines on neurons from control rats. Further analysis revealed that spine shortening attributed to olfactory discrimination learning derives from shortening of spine head and not from shortening of spine neck. In addition, detailed analysis of spine head volume suggests that spines with large heads are absent after learning. As spine head size may be related to the efficacy of the synapse it bears, we suggest that modifications in spine head dimensions following olfactory rule-learning enhance the cortical network ability to enter into a 'learning mode', in which memories of new odours can be acquired rapidly and efficiently.

Research paper thumbnail of Current Biology 2008

Research paper thumbnail of On predatory wasps and zombie cockroaches: Investigations of "free will" and spontaneous behavior in insects

Communicative & integrative biology, 2010

Accumulating evidence suggest that nonhuman organisms, including invertebrates, possess the abili... more Accumulating evidence suggest that nonhuman organisms, including invertebrates, possess the ability to make non-random choices based purely on ongoing and endogenously-created neuronal processes. We study this precursor of spontaneity in cockroaches stung by A. compressa, a parasitoid wasp that employs cockroaches as a live food supply for its offspring. This wasp uses a neurotoxic venom cocktail to 'hijack' the nervous system of its cockroach prey and manipulate specific features of its decision making process, thereby turning the cockroach into a submissive 'zombie' unable to self-initiate locomotion. We discuss different behavioral and physiological aspects of this venom-induced 'zombified state' and highlight at least one neuronal substrate involved in the regulation of spontaneous behavior in insects.

Research paper thumbnail of Force-sensitive mechanoreceptors of the dactyl of the crab: single-unit responses during walking and evaluation of function

Journal of neurophysiology, 1987

The activities of individual force-sensitive mechanoreceptors of the dactyl (terminal leg segment... more The activities of individual force-sensitive mechanoreceptors of the dactyl (terminal leg segment) of the crab, Carcinus maenas, have been recorded during free walking. These receptors have also been mechanically and electrically stimulated in freely moving animals to directly evaluate their function in locomotion. All force-sensitive mechanoreceptors fired during the stance phase of walking and were silent during swing. Receptor discharges showed regular phase relationships to bursts in motor neurons of leg muscles. Crabs walk laterally and use the legs of one side either in trailing to actively push the animal to the opposite side, or in leading, to less forcefully pull the animal in that direction. Individual force-sensitive mechanoreceptors differed in their patterns of activity during trailing or leading according to their location on the dactyl. Units of proximal receptors fired more vigorously when used in trailing than in leading. Discharges in trailing were also increased b...

Research paper thumbnail of Synaptic Reorganization Induced by Selective Photoablation of an Identified Neuron

The maintenance of synaptic strength and specificity in the CNS may depend on interactions among ... more The maintenance of synaptic strength and specificity in the CNS may depend on interactions among postsynaptic den- drites. We examined the effect of removing a neuron on synap- tic organization. A single identified postsynaptic neuron in the adult cercal system of the cockroach was removed with pho- toablation. After a 30 d recovery period, the synaptic connec- tivity and morphology

Research paper thumbnail of Octopamine partially restores walking in hypokinetic cockroaches stung by the parasitoid wasp Ampulex compressa

Journal of Experimental Biology, 2007

Research paper thumbnail of Olfactory learning-induced increase in spine density along the apical dendrites of CA1 hippocampal neurons

Hippocampus, 2004

We have previously shown that rule learning of an olfactory discrimination task is accompanied by... more We have previously shown that rule learning of an olfactory discrimination task is accompanied by increased spine density along the apical dendrites of piriform cortex pyramidal neurons. The purpose of the present study was to examine whether such olfactory learning task, in which the hippocampus is actively involved, induces morphological modifications in CA1 pyramidal neurons as well. Rats were trained to discriminate positive cues in pairs of odors for a water reward. Morphological modifications were studied in Golgi-impregnated neurons with light microscopy, 1 and 3 days after training completion. Spine densities were measured on the proximal region of apical dendrites and on basal dendrites after rule learning. Three days after training completion, the mean spine density on apical dendrites in neurons from trained rats was significantly higher by 20.5% than in neurons from pseudo-trained and naive animals, which did not differ from each other. By contrast, there was no significant difference in spine density of basal dendrites among the three groups. As length and diameter of spiny dendritic segments did not change after learning, the learning-related increase in spine density in neurons from trained rats may reflect a net increase in the number of excitatory synapses in the hippocampus following olfactory rule learning.

Research paper thumbnail of Olfactory learning-related NCAM expression is state, time, and location specific and is correlated with individual learning capabilities

Hippocampus, 2005

The notion that long-term synaptic plasticity is generated by activity-induced molecular modifica... more The notion that long-term synaptic plasticity is generated by activity-induced molecular modifications is widely accepted. It is well established that neural cell adhesion molecule (NCAM) is one of the prominent modulators of synaptic plasticity. NCAM can be polysialylated (PSA-NCAM), a reaction that provides it with anti-adhesion properties. In this study we have focused on NCAM and on its polysialylated state, and their relation to learning of an olfactory discrimination task, which depends on both the piriform (olfactory) cortex and hippocampus. We trained rats to distinguish between pairs of odors until rule learning was achieved, a process that normally lasts 6 -8 days. At four time points, during training and after training completion, synaptic NCAM and PSA-NCAM expression were assessed in the piriform cortex and hippocampus. We report that NCAM modulation is specific to PSA-NCAM, which is upregulated in the hippocampus one day after training completion. We also report a correlation between the performance of individual rats in an early training stage and their NCAM expression, both in the piriform cortex and hippocampus. Since individual early performance in our odor discrimination task is correlated with the performance throughout the training period, we conclude that early NCAM expression is associated with odor learning capability. We therefore suggest that early synaptic NCAM expression may be one of the factors determining the capability of rats to learn.

Research paper thumbnail of Sensory Arsenal on the Stinger of the Parasitoid Jewel Wasp and Its Possible Role in Identifying Cockroach Brains

PLoS ONE, 2014

The parasitoid jewel wasp uses cockroaches as live food supply for its developing larva. To this ... more The parasitoid jewel wasp uses cockroaches as live food supply for its developing larva. To this end, the adult wasp stings a cockroach and injects venom directly inside its brain, turning the prey into a submissive 'zombie'. Here, we characterize the sensory arsenal on the wasp's stinger that enables the wasp to identify the brain target inside the cockroach's head. An electron microscopy study of the stinger reveals (a) cuticular depressions innervated by a single mechanosensory neuron, which are presumably campaniform sensilla; and (b) dome-shaped structures innervated by a single mechanosensory neuron and 4-5 chemosensory neurons, which are presumably contact-chemoreceptive sensilla. Extracellular electrophysiological recordings from stinger afferents show increased firing rate in response to mechanical stimulation with agarose. This response is direction-selective and depends upon the concentration (density) of the agarose, such that the most robust response is evoked when the stinger is stimulated in the distal-to-proximal direction (concomitant with the penetration during the natural stinging behavior) and penetrating into relatively hard (0.75%-2.5%) agarose pellets. Accordingly, wasps demonstrate a normal stinging behavior when presented with cockroaches in which the brain was replaced with a hard (2.5%) agarose pellet. Conversely, wasps demonstrate a prolonged stinging behavior when the cockroach brain was either removed or replaced by a soft (0.5%) agarose pellet, or when stinger sensory organs were ablated prior to stinging. We conclude that the parasitoid jewel wasp uses at least mechanosensory inputs from its stinger to identify the brain within the head capsule of the cockroach prey.

Research paper thumbnail of Dual locomotor activity selectively controlled by force- and contact-sensitive mechanoreceptors

Neuroscience Letters, 1986

The crab Carcinus maenas walks laterally: moreover, as soon as leg contact with the support is lo... more The crab Carcinus maenas walks laterally: moreover, as soon as leg contact with the support is losl, it starts swimming. In free-moving animals, discharges from individual force-and contact-mechanoreceptors located in the terminal segment of the last pair of walking legs have been recorded. These receptors are active during the stance phase of walking and remain silent during swimming. Selective electrical stimulation of their allerent fibers during swimming inhibits this behaviour. The possible role of such sensory information in selecting different motor patterns is discussed.

Research paper thumbnail of Mechanisms of Dendritic Maturation

Molecular Neurobiology, 2004

The highly complex geometry of dendritic trees is crucial for neural signal integration and the p... more The highly complex geometry of dendritic trees is crucial for neural signal integration and the proper wiring of neuronal circuits. The morphogenesis of dendritic trees is regulated by innate genetic factors, neuronal activity, and external molecular cues. How each of these factors contributes to dendritic maturation has been addressed in the developing nervous systems of animals ranging from insects to mammals. The results of such investigations have shown that the contribution of intrinsic and extrinsic factors and activity, however, appear to be weighted differentially in different types of neurons, in different brain areas, and especially in different species. Moreover, it appears that dozens of molecules have been found to regulate dendritic maturation, but it is almost certain that each molecule plays only a specific role in this formidable cooperative venture. This article reviews our current knowledge and understanding of the role of various factors in the establishment of the architecture of mature dendritic trees.

Research paper thumbnail of In situ visualization and photoablation of individual neurons using a low cost fiber optic based system

Journal of Neuroscience Methods, 1996

This paper describes a low-cost system for in situ visualization and photoablation of single neur... more This paper describes a low-cost system for in situ visualization and photoablation of single neurons. The system includes a fiber optics light source equipped with a filter port, a blue excitation filter and a yellow barrier filter, and a light guide which terminates with a focusing lens. This system is inexpensive, easy to use, and requires minimal maintenance. Given its price, this system is readily accessible and has the potential of becoming standard equipment for in situ visualization and killing of individual neurons.

Research paper thumbnail of New vistas on the initiation and maintenance of insect motor behaviors revealed by specific lesions of the head ganglia

Journal of Comparative Physiology A, 2006

In insects, thoracic pattern generators are modulated by the two head ganglia, the supraesophagea... more In insects, thoracic pattern generators are modulated by the two head ganglia, the supraesophageal ganglion (brain) and the subesophageal ganglion, which act as higher-order neuronal centers. To explore the contribution of each head ganglion to the initiation and maintenance of speciWc motor behaviors in cockroaches (Periplaneta americana), we performed speciWc lesions to remove descending inputs from either the brain or the subesophageal ganglion or both, and quan-tiWed the behavioral outcome with a battery of motor tasks. We show that 'emergency' behaviors, such as escape, Xight, swimming or righting, are initiated at the thoracic level independently of descending inputs from the head ganglia. Yet, the head ganglia play a major role in maintaining these reXexively initiated behaviors. By separately removing each of the two head ganglia, we show that the brain excites Xight behavior and inhibits walking-related behaviors, whereas the subesophageal ganglion exerts the opposite eVects. Thus, control over speciWc motor behaviors in cockroaches is anatomically and functionally compartmentalized. We propose a comprehensive model in which the relative permissive versus inhibitory inputs descending from the two head ganglia, combined with thoracic aVerent sensory inputs, select a speciWc thoracic motor pattern while preventing the others.

Research paper thumbnail of Parasitoid wasp affects metabolism of cockroach host to favor food preservation for its offspring

Journal of Comparative Physiology A, 2005

Unlike predators, which immediately consume their prey, parasitoid wasps incapacitate their prey ... more Unlike predators, which immediately consume their prey, parasitoid wasps incapacitate their prey to provide a food supply for their offspring. We have examined the effects of the venom of the parasitoid wasp Ampulex compressa on the metabolism of its cockroach prey. This wasp stings into the brain of the cockroach causing hypokinesia. We first established that larval development, from egg laying to pupation, lasts about 8 days. During this period, the metabolism of the stung cockroach slows down, as measured by a decrease in oxygen consumption. Similar decreases in oxygen consumption occurred after pharmacologically induced paralysis or after removing descending input from the head ganglia by severing the neck connectives. However, neither of these two groups of cockroaches survived more than six days, while 90% of stung cockroaches survived at least this long. In addition, cockroaches with severed neck connectives lost significantly more body mass, mainly due to dehydration. Hence, the sting of A. compressa not only renders the cockroach prey helplessly submissive, but also changes its metabolism to sustain more nutrients for the developing larva. This metabolic manipulation is subtler than the complete removal of descending input from the head ganglia, since it leaves some physiological processes, such as water retention, intact.

Research paper thumbnail of Multiple feedback loops in the flying cockroach: excitation of the dorsal and inhibition of the ventral giant interneurons

Journal of Comparative Physiology A, 1989

Research paper thumbnail of Localization of the site of effect of a wasp's venom in the cockroach escape circuitry

Journal of Comparative Physiology A: Sensory, Neural, and Behavioral Physiology, 1999

The parasitic wasp Ampulex compressa stings a cockroach Periplaneta americana in the neck, toward... more The parasitic wasp Ampulex compressa stings a cockroach Periplaneta americana in the neck, toward the head ganglia (the brain and subesophageal ganglion). In the present study, our aim was to identify the head ganglion that is the target of the venom and the mechanisms by which the venom blocks the thoracic portion of the escape neuronal circuitry. Because the escape responses elicited by a wind stimulus in brainless and sham-operated animals were similar, we propose that the venom eect is on the subesophageal ganglion. Apparently, the subesophageal ganglion modulates the thoracic portion of the escape circuit. Recordings of thoracic interneuron responses to the input from the abdominal giant interneurons showed that the thoracic interneurons receive synaptic drive from these interneurons in control and in stung animals. Unlike normal cockroaches, which use both fast and slow motoneurons for producing rapid escape movements, stung animals activate only the slow motoneuron. However, we show that in stung animals, the fast motoneuron still can be recruited with bath application of pilocarpine, a muscarinic agonist. These results indicate that the descending control from the subesophageal ganglion is presumably exerted on the premotor thoracic interneurons to motoneurons connection of the thoracic escape circuitry.

Research paper thumbnail of Morphometric analysis of dendritic remodeling in an identified motoneuron during postembryonic development

The Journal of Comparative Neurology, 2002

A detailed quantitative description of modifications in neuronal architecture is an important pre... more A detailed quantitative description of modifications in neuronal architecture is an important prerequisite to investigate the signals underlying behaviorally relevant changes in neuronal shape. Extensive morphological remodeling of neurons occurs during the metamorphosis of holometabolous insects, such as Manduca sexta, in which new adult behaviors develop postembryonically. In this study, a morphometric analysis of the structural changes of an identified Manduca motoneuron, MN5, was conducted by sampling its metric parameters at different developmental stages. The remodeling of MN5 is divided into three main phases. The regression of most larval dendrites (1) is followed by the formation of dendritic growth-cones (2), and subsequently, adult dendrite formation (3). In contrast, the cell body and link segment surface increase during dendritic regression and regrowth, indicating that different cell compartments receive different signals, or respond differently to the same signal. During dendritic growth-cone formation, the growth of the cell body and the link segment are arrested. Sholl and branch frequency analysis suggest two different modes of dendritic growth. During a first growth-cone-dependent phase, new branch formation occurs at all dendrites. The maximum path length of the major dendritic tree changes little, whereas branch order increases from 20 to 45. Changes in total dendritic length are correlated with strong changes in the number of nodes but with minor changes in the average dendritic segment length, indicating a mode of growth similar to that induced by steroid hormone application to cultured motoneurons. The second phase is growth-cone-independent, and branching is limited to high order dendrites.

Research paper thumbnail of Comparative analysis of dendritic architecture of identified neurons using the Hausdorff distance metric

The Journal of Comparative Neurology, 2000

Dendritic trees often are complex, three-dimensional structures. Comparative morphologic studies ... more Dendritic trees often are complex, three-dimensional structures. Comparative morphologic studies have not yet provided a reliable measure to analyze and compare the geometry of different dendritic trees. Therefore, it is important to develop quantitative methods for analyzing the three-dimensional geometry of these complex trees. The authors developed a comparison measure based on the Hausdorff distance for comparing quantitatively the three-dimensional structure of different neurons. This algorithm was implemented and incorporated into a new software package that the authors developed called NeuroComp. The authors tested this algorithm to study the variability in the three-dimensional structure of identified central neurons as well as measuring the structural differences between homologue neurons. They took advantage of the uniform dendritic morphology of identified interneurons of an insect, the giant interneurons of the cockroach. More specifically, after establishing a morphometric data base of these neurons, the authors found that the algorithm is a reliable tool for distinguishing between dendritic trees of different neurons, whereas conventional metric analysis often is inadequate. The authors propose to use this method as a quantitative tool for the investigation of the effects of various experimental paradigms on three-dimensional dendritic architecture.

Research paper thumbnail of Wasp Voodoo Rituals, Venom-Cocktails, and the Zombification of Cockroach Hosts

Integrative and Comparative Biology, 2014

Research paper thumbnail of Dynamics of olfactory learning-induced up-regulation of L1 in the piriform cortex and hippocampus

European Journal of Neuroscience, 2005

L1 is a cell adhesion molecule implicated in the formation of neural circuits and synaptic plasti... more L1 is a cell adhesion molecule implicated in the formation of neural circuits and synaptic plasticity. We have examined the sequence and time-frame in which modifications in the synaptic expression of L1 occur in the piriform cortex and hippocampus in the course of rule learning of an olfactory discrimination task. Rats were trained to choose the correct odour in a pair to be rewarded with drinking water. Such training requires 6-8 days on average before rats reach maximal performance. We observed a learning-induced L1 upregulation that occurred at an early training stage in the piriform cortex but only after rule-learning establishment in the hippocampus. We suggest that the dynamics of L1 up-regulation may reflect the functional role of these brain regions in olfactory rule learning.

Research paper thumbnail of Olfactory learning-induced morphological modifications in single dendritic spines of young rats

European Journal of Neuroscience, 2005

Learning-related morphological modifications in single dendritic spines were studied quantitative... more Learning-related morphological modifications in single dendritic spines were studied quantitatively in the brains of young Sprague-Dawley rats. We have previously shown that olfactory discrimination rule-learning results in transient physiological and morphological modifications in piriform cortex pyramidal neurons. In particular, spine density along the apical dendrites of neurons from trained rats is increased after learning. The aim of the present study was to identify and describe olfactory learning-induced modifications in the morphology of single spines along apical dendrites of the same type of neurons. By using laser-scanning confocal microscopy, we show that 3 days after training completion spines on neurons from olfactory discrimination trained rats are shorter as compared to spines on neurons from control rats. Further analysis revealed that spine shortening attributed to olfactory discrimination learning derives from shortening of spine head and not from shortening of spine neck. In addition, detailed analysis of spine head volume suggests that spines with large heads are absent after learning. As spine head size may be related to the efficacy of the synapse it bears, we suggest that modifications in spine head dimensions following olfactory rule-learning enhance the cortical network ability to enter into a 'learning mode', in which memories of new odours can be acquired rapidly and efficiently.