Abdominal positioning interneurons in crayfish: projections to and synaptic activation by higher CNS centers (original) (raw)
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Abdominal positioning interneurons in crayfish: participation in behavioral acts
Journal of Comparative Physiology A, 1989
Intracellular recording, stimulation, and Lucifer dye injections were used to characterize abdominal positioning interneurons from the neuropile of the second through sixth abdominal ganglia of the crayfish, Procambarus clarhii. Motor outputs of these cells were recorded with extracellular electrodes placed on various flexion and extension roots along the nerve cord. In a n effort to assess the functional relationships between the postural interneurons in the abdomen and those known to exist in the circumesophageal connectives (CECs), a stimulus pulse train was delivered to each of the CECs while monitoring the intracellular responses of the impaled interneurons. Abdominal positioning interneurons were grouped into four general categories based on their responses to CEC stimulation: 1) those that projected their axons directly through the CECs; 2) those that were remotely activated to spiking; 3) those locally activated to produce EPSPs or IPSPs; and 4) those that were not affected by CEC stimulation.
Extensor motor neurons of the crayfish abdomen
Journal of Comparative Physiology ? A, 1975
The somata of five deep extensor motoneurons of the third abdominal ganglion of the crayfish (Procambarus clarkii) were located and identified. The positions of these somata within the ganglion and their distal distribution to muscles have been mapped and were constant. The soma of the extensor inhibitor was noted to touch the soma of the flexor inhibitor. Three of the excitatory neurons were clustered near their exit route. Sensory and cord routes of activation of the extensor motoneurons were also found and were constant from preparation to preparation. Sub-threshold recording showed that these motoneurons exhibited radically different types of post-synaptie response to stimuli at different sites in the nervous system. No interaction between extensor motoneurons or between the extensor and flexor motoneurons was observed.
Neural basis of a simple behavior: Abdominal positioning in crayfish
Microscopy Research and Technique, 2003
Crustaceans have been used extensively as models for studying the nervous system. Members of the Order Decapoda, particularly the larger species such as lobsters and crayfish, have large segmented abdomens that are positioned by tonic flexor and extensor muscles. Importantly, the innervation of these tonic muscles is known in some detail. Each abdominal segment in crayfish is innervated bilaterally by three sets of nerves. The anterior pair of nerves in each ganglion controls the swimmeret appendages and sensory supply. The middle pair of nerves innervates the tonic extensor muscles and the regional sensory supply. The superficial branch of the most posterior pair of nerves in each ganglion is exclusively motor and supplies the tonic flexor muscles of that segment. The extension and flexion motor nerves contain six motor neurons, each of which is different in axonal diameter and thus produces impulses of different amplitude. Motor programs controlling each muscle can be characterized by the identifiable motor neurons that are activated. Early work in this field discovered that specific central interneurons control the abdominal positioning motor neurons. These interneurons were first referred to as "command neurons" and later as "command elements." Stimulation of an appropriate command element causes a complex, widespread output involving dozens of motor neurons. The output can be patterned even though the stimulus to the command element is of constant interval. The command elements are identifiable cells. When a stimulus is repeated in a command element, from either the same individual or from different individuals, the output is substantially the same. This outcome depends upon several factors. First, the command elements are not only identifiable, but they make many synapses with other neurons, and the synapses are substantially invariant. There are separate flexion-producing and extension-producing command elements. Abdominal flexion-producing command elements excite other flexion elements and inhibit extensor command elements. The extension producing elements do the opposite. These interactions insure that interneurons of a particular class (flexion-or extension-producing) synaptically recruit perhaps twenty others of similar output, and that command elements promoting the opposing movements are inhibited. This strong reciprocity and the recruitment of similar command elements give a powerful motor program that appears to mimic behavior.
Discharge Patterns of Neurones Supplying Tonic Abdominal Flexor Muscles in the Crayfish
Journal of Experimental Biology, 1967
1. The discharge patterns of tonic flexor motoneurones in the crayfish abdomen have been investigated by simultaneous recording from several nerve roots. The five flexor motoneurones supplying each segment are serially homologous, smaller units have higher discharge frequencies, and the excitability of a given unit is generally higher in more caudal ganglia. 2. Even the smallest axons are capable of generating substantial muscle tension at their spontaneous discharge frequencies. Tension development is extremely tonic. Single motor impulses are without effect, latencies are long, and the frequency/tension relation is steep. 3. The inhibitory axon to each flexor discharges during ‘extension’ reflexes, but has no visible effect upon relaxation time, or upon the response to subsequent excitation. Inhibitory impulses do not relax previously unexcited muscle. 4. Phase histograms for the discharge of pairs of homologous or non-homologous efferent axons across a single ganglion, within the...
Journal of Comparative Physiology A, 1995
Voltage-dependent variability in the shape of synaptic responses of the LDS interneuron, an identified nonspiking cell of crayfish, to mechanosensory stimulation was studied using intracellular recording and current injection techniques. Stimulation of the sensory root ipsilateral to the interneuron soma evoked a large depolarizing synaptic response. Its peak amplitude was decreased and the time course was shortened when the LDS interneuron was depolarized by current injection. When the cell was hyperpolarized, the peak amplitude was increased and the time course was prolonged. Upon large hyperpolarization, however, the amplitude did not increase further while the time course showed a slight decrease. The dendritic membrane of the LDS interneuron was found to show an outward rectification upon depolarization and an inward rectification upon large hyperpolarization. Current injection experiments at varying membrane potentials revealed that the voltage-dependent changes in the shape of the synaptic response were based on an increase in membrane conductance due to the rectifying properties of the LDS interneuron. Stimulation of the contralateral root evoked a small depolarizing potential comprising an early excitatory response and a later inhibitory component. Its shape also varied depending on the membrane potential in a manner similar to that of the synaptic response evoked ipsilaterally.
Inhibition of mechanosensory neurons in the crayfish
Journal of Comparative Physiology ? A, 1983
1. Electrical stimulation of the ventromedial (VM) abdominal nerve cord region in crayfish causes inhibition of afferent EPSPs in many near-field mechanosensory interneurons (MSIs). This inhibition occurs without any detectable change in interneuronal membrane potential or conductance (Figs. I and 2). In an earlier report this region was shown to contain multisegmental proprioceptive interneurons that receive input from walking legs and swimmerets. 2. IPSPs evoked in one identified mechanosensory interneuron (Interneuron A) by VM stimulation, are too brief to account for the full period of EPSP suppression (Fig. ). 3. In five recordings from unidentified MSIs, EPSPs that normally decrement during repetitive low frequency stimulation were able to facilitate during sustained periods of inhibition (Fig. ). This suggests a differential effect of VM-evoked inhibition on two homosynaptic processes, depression and facilitation. 4. Stimulation of VM causes primary afferent depolarization (PAD) in mechanosensory afferents (MSAs) (Fig. ). 5. Statements 1-4 are consistent with our view that presynaptic inhibition of MSAs arises in part from activity in central interneurons driven by input from thoracic walking legs as well as other segmental appendages. 6. Stable, short latency PAD, is correlated onefor-one with action potentials in the interganglionic connective. This suggests that some final in-Abbreviations: MSI mechanosensory interneuron; MSA mechanosensory afferent; VM ventro-medial cord region; PAD primary afferent depolarization; NF near field; CPR caudal photoreceptor; MG medial giant; LG lateral giant