Mituhiko Hisada

Neuroanatomy of the terminal (sixth abdominal) ganglion of the crayfish, Procambarus clarkii (Girard)

SummaryWe studied the neuroanatomy of the terminal (sixth abdominal) ganglion in the crayfish Procambarus clarkii with silver-impregnated sections and nickel fills. We describe the fiber tracts, commissures and neuropilar areas, and give the topological relationships of motoneurons and intersegmental interneurons with reference to their neuropilar landmark structures.All five anterior abdominal ganglia have an almost identical number of 600–700 neurons with a similar pattern of distribution. Each contains a single neuromere with a common plan of neuropil organization. In contrast, the terminal ganglion consists of two neuromeres which appear to be derived from the intrinsic sixth abdominal and ‘telson’ ganglion. The basic organization of each neuromere parallels that of the third abdominal ganglion in the appearance and arrangement of fiber tracts and commissures, although some modifications occur. The fusion of two neuromeres is represented by the duplication of segmentally homologous neurons, MoGs and LGs, whose topological relationships to the neuropil structures are similar to those of the anterior ganglion.We also discuss the origin of the telson and its ganglion (the seventh abdominal neuromere), and dispute the classical theory that the telson derives from a ‘postsegmental region.’

Local spikeless interaction of motoneuron dendrites in the crayfishProcambarus clarkii girard

Summary1.Spikeless communication between dendrites of crayfish motoneurons was demonstrated by intracellular current injection.2.Subthreshold depolarization of one motoneuron (Add MN) innervating the adductor exopodite, one of the closer muscles of the uropod, increased the spontaneous discharge rate of another motoneuron (Red MN No. 1) innervating another closer muscle, reductor exopodite.3.Hyperpolarization of the Add MN caused a decrease in the spike frequency of the Red MN No. 1.4.The effects are graded and dependent on the membrane potential changes in the current-injected cells.5.Spikeless communication was also observed between opener motoneurons. Such communication was observed only between synergistic motoneurons and not between antagonistic ones.6.Regions in the Add MN in which current injection effectively changed the Red MNs activity were always distant from the spike-initiating region, and confined to the distal dendritic branches.7.The amplitude of e.p.s.p.s recorded from the Red MN No. 1 in response to antidromic spikes of the Add MN was increased by hyperpolarization and decreased by depolarization at the site of recording. The spikeless, graded interaction appears to be mediated by chemical transmission via a monosynaptic connection.8.It is concluded that the crayfish uropod motoneurons function not only as simple output elements but also as complex integrative elements by forming local circuits at restricted dendritic regions.

Functional characteristics of local non-spiking interneurons as the pre-motor elements in crayfish

SummaryControl of the crayfish uropod motoneurons by the unilateral-type local non-spiking interneurons (LNSNs) in the terminal (sixth) abdominal ganglion was studied with intracellular recording and current injection.1.Current injected into LNSNs affected the spike activity of uropod motoneurons in a graded manner. The effects depended on both the duration and the intensity of current pulses.2.Simultaneous intracellular recordings from an LNSN and an opener motoneuron showed that LNSNs could change the motoneuron membrane potential by their own membrane potential change without generating spikes.3.In fifty-nine cases, we penetrated LNSNs which affected uropod motoneurons bidirectionally. Hyperpolarization of 23 LNSNs decreased and that of other 36 LNSNs increased the spontaneous discharge rate of an identified reductor exopodite motoneuron (Red MN) No. 1. Depolarization had the opposite effect in either case.4.It is suggested that at least one chemical synapse should be intercalated between the LNSN and the motoneuron. although whether their connection is monosynaptic or not still remains open to future study.5.Twenty-four penetrated LNSNs co-actively controlled the synergistic set of motoneurons. Other 23 LNSNs also controlled the antagonistic set in addition to the synergistic set of motoneurons in a reciprocal way, and other 21 LNSNs in a co-activating way.6.The possible role of unilateral-type LNSNs in the motor control, especially in the non-rhythmical, episodic movement such as uropod steering, is discussed.

Statocyst control of the uropod movement in response to body rolling in crayfish

Summary1.The steering movement of crayfish uropods in response to body rolling was analysed quantitatively.2.The uropod on the upper side is spread out while the other one on the lower side is closed. Opening of one uropod was always accompanied by closing of the other. Positional changes of both uropods in response to body rolling were measured at 13 body positions. The response curve followed an approximate sine function in an intact animal3.In a single-statocyst animal, increase of receptor activity in the intact statocyst caused opening of the ipsilateral uropod and closing of the contralateral one, while decrease of receptor activity had no effect on the uropod position.4.A response curve obtained by algebraic summaion of two response curves in the animals with right and left statolith removed respectively was consistent with that of an intact animal with both statocysts.5.It was concluded that each statocyst can produce bilateral uropod movement only in a limited range of roll angle since the receptor activity increases only when the statocyst hairs are deflected toward the inside of the sensory crescent. Bilateral uropod movement in an intact animal is produced by simple summation of inputs from the right and left statocysts.6.Unilateral statolith removal caused an asymmetrical configuration of the uropods in the resting (0°) body position. The uropod on the operated side opened and that on the opposite side closed. This asymmetry was normalized day by day and the original symmetrical configuration was finally restored about 7 days after operation.

Functional polarization of statocyst receptors in the crayfishProcambarus clarkii Girard

SummaryDirectionality of response in the statocyst receptors of the crayfish (Procambarus clarkii Girard) was investigated by artificially deflecting individual statocyst hairs in various directions. 1.The hairs attached to the receptors are aligned in a crescent on the statocyst floor. Hair deflection toward the center of the crescent elicited maximal excitatory responses in the majority of the receptors. Hair deflection in the opposite direction elicited maximal suppressive responses.2.It was concluded that most of the statocyst receptors are functionally polarized toward the center of the crescent. The plane of functional polarization was consistent with that of morphological polarization.3.The receptors could be classified into two types; tonic (42%) and phasic (50%), according to the time course of the excitatory responses. The remainder (8%) could not be classified as either of these, showing intermediate responses.4.Some (ca. 40%) of the phasic-type receptors responded transiently regardless of the direction of hair deflection. It is suggested that the role of those receptors without any plane of functional polarization, is different from that of the other receptors in producing equilibrium responses.

Physiological and morphological characterization of anaxonic non-spiking interneurons in the crayfish motor control system

Spike activation of the motoneurons innervating uropod muscles in crayfish is controlled by anaxonic interneurons located within the terminal (the 6th abdominal) ganglion. These neurons do not generate spikes either spontaneously at the resting potential level or in response to current injection of either polarity. Yet the change in the membrane potential of these non-spiking interneurons caused an increase or decrease in the discharge frequency of motoneuron spikes, depending upon the direction of the membrane potential change. These non-spiking interneurons within the terminal ganglion presumably integrate various descending command signals and select the adequate information to be gated to the motoneurons.

Projection of statocyst sensory neurons associated with crescent hairs in the crayfish Procambarus clarkii Girard

SummaryThe central projection of statocyst sensory neurons associated with the crescent hairs of the crayfish Procambarus clarkii was investigated. Cobalt fills of statocyst nerves revealed that they entered the brain as the two discrete fiber bundles and terminated in different portions of the brain. One terminates in the ipsilateral half of the brain and the other in the contralateral half. The latter was further subdivided into two discrete components.The relationship between the location of statocyst receptors in the different regions of the crescent and their central projection pattern was investigated by the extracellular cobalt marking method. The results showed that the two fiber bundles, which projected to the ipsilateral and contralateral halves of the brain respectively, originated from different regions of the crescent. Ipsilaterally projecting neurons had their origin mainly in the posterior hairs of the sensory crescent whereas contralaterally projecting ones in the anterior hairs of the sensory crescent.

The topological organization of primary afferents in the terminal ganglion of crayfish, Procambarus clarkii

SummaryThe central projections of primary afferents in the terminal ganglion of the crayfish can be seen when an axonal filling with nickel chloride with subsequent silver intensification was used for identification. We describe here the topological relationships of the projections to the landmark structures of the neuropil.The terminal ganglion has five pairs of sensory nerves associated with the mechanosensory hairs and internal proprioceptors. The projection fields of the primary sensory neurons in the nerves Rl and R2 are almost entirely restricted to the ipsilateral half of the ganglion, whereas those of the nerves R3, R4 and R5 cross the midline to form three sensory commissures, A6SCI, A7SCI and A7SCII. The projection fields are segregated from each other, although all are restricted to the ventral neuropil which lies under the ventral intermediate tract (VIT). The intersegmental projections that ascend via the connective ipsilateral to their origins could be observed. This pattern of projection correlates well with the receptive fields exhibited by several mechanosensory interneurons on the body surface of the final segment.

Afferent response patterns of the crayfish statocyst with ferrite grain statolith to magnetic field stimulation

Summary1.Magnetic field stimulation to simulate the rotation of the crayfish statocyst has been performed to determine the response characteristics of the statocyst hair cells. Ferrite grains were introduced about one month before the experiment as a replacement for the natural statoliths to effect magnetic pulling.2.Several types of response discharge could be recognized. Excitatory response types included tonicon, tonic-on-off, phasic-on, and phasic-on-off types. Inhibitory types can be divided into tonic-inhibition with off-excitation and phasic-inhibition with offinhibition.3.Statocyst afferent neurons could be classified into several groups depending on the direction of the preferred sensitivity within the simulated rotation plane tested. Among 21 units examined, 9 units showed a single preferred direction with excitatory response and were thus unidirectional units; 3 units were bidirectional, and 5 units were multidirectional. There were 2 bidirectional inhibitory units and 2 multidirectional inhibitory units.4.Analysis of the response pattern suggests that the central nervous system in the crayfish should be capable of averaging responses of more than one unit among the statocyst afferent neurons to detect the coincidence of discharge frequency change in order to obtain the positional information.

Statocyst interneurons in the crayfishProcambarus clarkii Girard

Summary1.Four pairs of descending interneurons which were excited by the statocyst were identified in the ventral nerve cord of the crayfishProcambarus clarkii Girard.2.These statocyst interneurons showed directional sensitivity: interneuron C1 responded to head-up and same-side-down tilting of the body, C2 to head-up and -down and same-side-down tilting whereas I2 to head-down and same-side-up tilting. I1 responded to tilting in all directions.3.They ran all through the ventral nerve cord from the brain to the terminal (6th abdominal) ganglion and directly projected on the latter. The conduction velocity of interneuron C1 was 3.8 ±1.3 m/s.4.They were located in particular areas in the cross section of the ventral nerve cord. Interneuron C1 was almost always found in Wiersmas area 74 in the circumesophageal commissure and area 78 in the 5–6 abdominal connective. Interneurons C2, I1 and I2 were found in areas 66 and 80, 62 and 77 and 68 and 80 (84) respectively.5.Statolith removal experiment revealed that interneurons C1 and C2 received input from the statocyst contralateral to the axons in the nerve cord. I2 received input from the ipsilateral statocyst. I1 received input from the statocyst on either side.6.The connection between the statocyst sensory neuron and the interneuron was studied by electrical stimulation of the sensory neurons. The result indicated that it was organized in a parallel way, one being monosynaptic and the other polysynaptic.7.They showed phaso-tonic response to body tilting. The spike discharge rate in the tonic component represented the angle of body tilt.8.It was concluded that the direction and magnitude of the body tilt were represented by the combination of excited interneurons in both connectives and the spike discharge rate of each excited interneuron respectively.9.The statocyst interneurons also received visual input and proprioceptive input from the walking legs.