Inhibition of mechanosensory neurons in the crayfish (original) (raw)
Related papers
Journal of Neurophysiology, 1997
Presynaptic inhibition of sensory afferents often manifests fied dactyl sensory afferent (DSA) neurons in a crayfish in vitro itself in intracellular recordings in the form of depolarizing preparation were performed to study modifications of the sensory events known as primary afferent depolarizations (PADs) message occurring before the first central synapse. These afferents (Eccles et al. 1962; Hue and Callec 1983). PADs are known comprised hairs and force-sensitive mechanoreceptors with phasic and phasotonic response characteristics in the terminal segment to be inhibitory because they reduce the size of afferent (dactyl) of the crayfish leg. More than one afferent spike size was spikes in the presynaptic neuron (Eccles et al. 1963; Kenoften observed in intracellular recordings from these afferents, thus nedy et al. 1974; Levine and Murphey 1980) as well as the indicating the presence of electrical coupling between the central amplitude of synaptic potentials in the postsynaptic neuron processes of DSA fibers. Additionally, in identified DSA fibers (Blagburn and Sattelle 1987; Burrows and Laurent 1993; with large spike sizes, primary afferent depolarizations (PADs) of Cattaert et al. 1992). They thus directly affect transmission up to 15 mV were observed, which sometimes triggered antidromic between the first-and second-order elements of the sensory spikes in the afferent. Nevertheless, PADs were clearly inhibitory, system. PADs often result from an increase in membrane because they shunted the afferent spikes. They exhibited the folchloride conductance due to GABAergic synapses. Their lowing properties. First, each PAD was preceded by an afferent spike from a neighboring hair, indicating that the PADs had a reversal potential lies somewhat above resting potential sensory rather than central origin. Second, PADs could follow (Blagburn and Sattelle 1987; Cattaert et al. 1992), and their high frequencies of afferent discharges without failure, a property size is affected by changes in chloride concentrations and suggestive of monosynaptic connections, but because PAD latenthe application of GABAergic agonists or antagonists (Burcies varied by {0.5 ms it is more likely that they were mediated rows and Laurent 1993; Cattaert et al. 1992; Davidoff 1972; by a disynaptic pathway. Third, although PADs were evoked in El Manira and Clarac 1991). an extremely reliable manner, their amplitude varied in a quantal Presynaptic inhibition has often appeared to be closely manner. Most unitary PADs were the result of the release of õ12 linked to the execution of a motor program, such as locomoquanta, the mean quantal content lying between 4 and 5; quantal size was large, Ç1 mV. Fourth, PADs showed facilitation in some tion. A synaptic drive to primary afferents, which is phasefibers, whereas in others they became much smaller when occurring linked to the centrally generated locomotor rhythm, has been at brief intervals. We suggest that PADs may be an efficient and seen in mammals (Gossard et al. 1989) as well as in crustaparsimonious way to limit sensory inflow in space and time, ceans (Cattaert et al. 1990; Sillar and Skorupski 1986). This allowing the crayfish to identify precisely both weak and strong is thought to adapt reflexes to the needs of the ongoing mechanical stimuli. movement (El Manira et al. 1991a,b). In crustacean and insect escape systems, a similar blockade of the afferent input is thought to prevent reafferent signals from the escape I N T R O D U C T I O N movements from eliciting inappropriate reflexes. This block may be of central origin, namely associated with the motor There is evidence in many species that primary sensory command (Kirk and Wine 1984; Krasne and Bryan 1973), afferents are subject to very early modulation, in particular or of proprioceptive origin (Boyan 1988; Fricke and Kenthrough presynaptic inhibition. Such mechanisms have been nedy 1983).
Properties and distribution of anterior VIIIth nerve excitatory inputs to the goldfish Mauthner cell
Brain Research, 1979
The goldfish Mauthner cell (M-cell) is known to initiate a rapid startle response to auditory stimulation~, 9,15. The presumed pathway for this activation is from the sacculus and lagena by way of the posterior branch (VIIIp) of the VIllth nerve. On gross stimulation of this ramus, Furshpan 6 was able to localize a powerful electrotonic component of the compound excitatory postsynaptic potential (EPSP) to the distal lateral dendrite. He further concluded that this input originated from the segregated projection of large myelinated club endings to this area 1°,11,13. However, there is little comparable morphological or electrophysiological evidence on the projections from the anterior branch (VllIa) to the M-celV4,16. As these two nerve branches are thought to transmit functionally distinct sensory information, we have compared the properties and distribution of their excitatory inputs to the M-cell. The results demonstrate that VIIIa input is predominantly chemically mediated and localized on the soma and proximal lateral dendrite.
Neuroscience in the 21st Century, 2013
Elzbieta Jankowska Abbreviations C T and L segments Cervical, thoracic and lumbar spinal cord segments EPSPs Excitatory postsynaptic potentials GABA Gamma aminobutyric acid HRP Horseradish peroxidise IPSPs Inhibitory postsynaptic potentials NA Noradrenaline 5-HT Serotonin VGLUT1 Vesicular glutamate transporter one VGLUT2 Vesicular glutamate transporter two WGA Wheat germ agglutinin Brief History Progress in studies of spinal interneurons has been related to the progress in technical facilities to a much greater extent than in studies of spinal reflexes and in other fields of physiology. Each new technique has opened new possibilities of analysis of these neurons and their networks. Thus, until the 1960s the contribution of spinal interneurons to motor behavior could be deduced primarily indirectly from their actions on motoneurons. However, the situation dramatically changed when it became possible to investigate properties of single functionally identified interneurons, electrophysiological and morphological, as well as immunocytochemical and pharmacological. Recent progress in molecular biology opens further possibilities in studies of these neurons, allowing to trace the origin of their subpopulation from
Crossed reciprocal inhibition evoked by electrical stimulation of the lamprey spinal cord
Experimental Brain Research, 2000
Activation of a motoneuron pool is often accompanied by inhibition of the antagonistic pool through a system of reciprocal inhibition between the two parts of the neuronal network controlling the antagonistic pools. In the present study, we describe the activity of such a system in the isolated spinal cord of the lamprey, when a tonic motor output is evoked by extracellular stimulation (0.5-1 s train of pulses, 20 Hz) of either end of the spinal cord. With two electrodes symmetrically positioned in relation to the midline, stimulation with either of them separately elicited prolonged (1-5 s) ipsilateral ventral root activity. Activity could be abolished by stronger, simultaneously applied, stimulation of the contralateral side of the cord, suggesting that reciprocal inhibition between hemisegments operates when a tonic motor output is generated. Simultaneous stimulation of both sides of the spinal cord with a single electrode with a large tip (300-400 microm in diameter), positioned over the anatomical midline, elicited inconsistent right-side, leftside, or bilateral ventral root responses. A minor displacement (10-20 microm) to the left or right from the midline resulted in activation of ipsilateral motoneurons, whereas the contralateral motoneurons were silent. These findings indicate that a small asymmetry in the excitatory drive to the left and right spinal hemisegments can be further amplified by reciprocal inhibition between the hemisegments. Longitudinal splitting of the spinal cord along the midline resulted in reduced reciprocal inhibition between the hemisegments separated by the lesion. The reduction was proportional to the extent of the split. The inhibition was abolished when the split reached nine segments in length. From these experiments, the longitudinal distribution of the commissural axons responsible for inhibition of contralateral motor output could be estimated.
Reciprocal Innervation through Interneuronal Inhibition
Nature, 1965
After an intravenous injection of L-DOPA (spinal cats), volleys in flexor reflex afferents (FRA) evoke late reflex discharges in ipsilateral flexor and in contralateral extensor motoneurones. A mutual reciprocal inhibition then occurs between the interneuronal pathways mediating late excitation to flexor and extensor motoneurones respectively 9,10. Such a half-centre organization can give rise to alternating activation of flexors and extensors and it has been suggested that the interneuronal network mediating the late reflexes after DOPA constitutes a spinal locomotor centre 9. Evidence is now forthcoming that this interneuronal network is used in stepping in spinal cats 1,2 and also in the mesencephalic cat 4. In the mesencephalic preparation it has been shown that stepping depends on a-y-linkage 12 and the network released after DOPA does indeed give parallel reflex activation of a-and 7-motoneuronesa, 9. It has also been shown that many neuronal pathways, both descending and segmental, with effects on ct-and 7-motoneurones exert similar effects on the interneurones of the reciprocal la inhibitory pathway 6, presumably giving 'a-7-1inkage in reciprocal inhibition '5. If this hypothesis also applies to the 'spinal locomotor centre' then it would be expected that the late reflex activation after DOPA should be accompanied by a facilitation of the reciprocal la inhibitory pathway. The present investigation has indeed shown that such an action does occur. All experiments (14) were made on anaemically decorticated low spinal cats. Conventional techniques were used for intracellular recording from motoneurones and extracellular recording from interneurones. All observations reported were made after intravenous injection of L-DOPA (100 mg/kg) during the period when volleys in the FRA evoked late excitation in motoneurones 9. The evidence for excitatory action on la inhibitory interneurones is threefold. (1) During late activation of flexor and extensor motoneurones (from the ipsiand contralateral FRA respectively) after DOPA there is a concomitant facilitation of transmission in the Ia inhibitory pathway to antagonist motoneurones. This was
Patterns of connectivity of spinal interneurons with single muscle afferents
Experimental Brain Research, 1997
A technique was developed to measure, in the anesthetized and paralyzed cat under artificial ventilation, changes of excitability to intraspinal stimulation simultaneously in two different afferent fibers or in two collaterals of the same afferent fiber. Intraspinal stimulation reduced the threshold of single muscle afferent fibers ending in the intermediate nucleus. This effect was seen with strengths below those required to activate the afferent fiber tested (1.5-12 µA), occurred at a short latency (1.5-2.0 ms), reached a maximum between 15 and 30 ms, and lasted up to 100 ms. The effects produced by graded stimulation applied at the shortest conditioningtesting stimulus time intervals increased by fixed steps, suggesting recruitment of discrete elements, most likely of last-order interneurons mediating primary afferent depolarization (PAD). The short-latency increases in excitability produced by the weakest effective intraspinal stimuli were usually detected only in the collateral closest to the stimulating micropipette, indicating that the stimulated interneurons mediating PAD have spatially restricted actions. The short-latency PAD produced by intraspinal stimuli, as well as the PAD produced by stimulation of the posterior biceps and semitendinosus (PBSt) nerve or by stimulation of the bulbar reticular formation (RF), was depressed 19-30 min after the i.v. injection of 0.5 mg/kg of picrotoxin, suggesting that all these effects were mediated by GABAergic mechanisms. The PAD elicited by stimulation of muscle and/or cutaneous nerves was depressed following the i.v. injection of (-)baclofen, whereas the PAD elicited in the same collateral by stimulation of the RF was baclofen-resistant. The short-latency PAD produced by intraspinal stimulation was not always depressed by i.v. injections of (-)-baclofen.
Brain Research, 1984
Intersegmentally evoked primary afferent depolarization (PAD) was analysed to investigate whether an}' lower lumbar propriospinal neurones are involved in mediating PAD from group I afferents to group I afferents both in the same segments and in Clarke's column. The intersegmental PAD of lower lumbar afferents, as judged by recording dorsal root potentials, was evoked by stimuli applied in the grey matter of L3 and L4 segments. With intraspinal stimuli of I(I,,A or less PAD was evoked from two foci: from within the middle part of the dorsal columns and from the dorsal part of the dorsal horn. Dorsal root potentials evoked from the dorsal horn focus appeared with longer latencies. When the dorsal columns were transected PAD was evoked only from the dorsal horn focus. No PAD appeared upon stimulation of Clarke's column after transection of the dorsal columns even with stronger (2(I/,A) stimuli. Interactions between the actions of the intraspinal stimuli and of different groups of afferents were analysed to define the neuronal pathways via which the intersegmental PAD was evoked. Neurones located within both the lower and the upper lumbar segments were found to be involved. Indications have only been found for a contribution of neurones mediating PAD from afferents other than group I afferents. Lesions of the ipsilateral and contralateral, lateral and ventral funiculi (in addition to the dorsal columns) were made in order to define which of these funiculi are required for the appearance of the intersegmental PAD. The intersegmental PAD coukt be evoked from the dorsal horn when either the contralateral or the ipsilateral funiculi were left intact.
Experimental Brain Research, 1992
1. In the isolated spinal cord and brainstem of the frog, stimulation of the brainstem (BS) with trains of 3-4 pulses at 60-400 Hz produced dorsal root potentials (DRPs). The lowest threshold sites eliciting DRPs were located at the level of the obex up to about 2.5 mm rostrally, 0.5-1.2 mm laterally, between 0.5 and 1.6 mm depth. This region corresponds to the bulbar reticular formation (RF). 2. Stimulation of the RF with strengths below those required to produce DRPs, very effectively inhibited the DRPs produced by stimulation of a neighboring dorsal root (DR-DRPs) as well as the DRPs produced by antidromic stimulation of the central end of motor nerves (VR-DRPs). The inhibition was detectable 20 ms after the first pulse of the conditioning train, attained maximal values between 50 and 100 ms and lasted more than 250 ms. 3. Stimulation of the bulbar RF increased the negative response (N1 response) produced in the motor pool by antidromic activation of motoneurons. The time course of the facilitation of the NI response resembled that of the reticularly-induced inhibition of the VR-DRPs and DR-DRPs. 4. The present series of observations supports the existence of reticulospinal pathways that are able to inhibit the depolarization elicited in afferent fibers by stimulation of other afferent fibers or by antidromic activation of motor axons. This inhibition appears to be exerted on the PAD mediating interneurons and is envisaged as playing an important role in motor control.