Functional properties of interneurons of the masticatory reflex

Interneurons of the supratrigeminal nucleus, transmitting effects from the sensory and motor branches of the trigeminal nerve to motoneurons of the muscles of mastication were investigated. Two groups of interneurons with different functional connections were found. The first group (A) contains neurons excited during stimulation of the sensory branches and the motor nerve to the digastric muscle (A₁), neurons excited during stimulation of sensory branches and high-threshold afferents of the motor nerve to the masseter muscle (A₂), and neurons excited only by low-threshold afferents of the motor nerve to the masseter muscle (A₃). Neurons of the second group (B) were activated only by sensory fibers of the trigeminal nerve. It is postulated that interneurons of group A transmit inhibitory effects to motoneurons of antagonist muscles of the lower jaw. Group B interneurons participate in the transmission of excitatory influences to motoneurons of the digastric muscle.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 2, pp. 150–157, March–April, 1972.     

The role of sensory input in motor neuron sprouting control

Primary sensory neurons project to motor neurons directly or through interneurons and affect their activity. In our previous paper we showed that intramuscular sprouting can be affected by changing the sensory synaptic input to motor neurons. In this work, motor axon sprouting within a peripheral nerve (extramuscular sprouting) was induced by nerve injury at such a distance from muscle so as not to allow nerve-muscle trophic interactions. Two different procedures were carried out: (1) sciatic nerve crush and (2) sciatic nerve crush with homosegmental ipsilateral L3-L5 dorsal rhizotomy. The number of regenerating motor axons innervating extensor digitorum longus muscle was determined by in vivo muscle tension recordings and an index of their individual conduction rate was obtained by in vitro intracellular recordings of excitatory postsynaptic end-plate potentials in muscle fibers. The main findings were: (1) there are more regenerated axons distally from the lesion than parent axons proximally to the lesion (sprouting at the lesion); (2) sprouting at the lesion was negatively affected by homosegmental ipsilateral dorsal rhizotomy; (3) the number of motor axons innervating extensor digitorum longus muscle extrafusal fibers counted proximally to the lesion increased following nerve injury and regeneration but this did not occur when sensory input was lost. A transient innervation of extrafusal fibers by &#110 motor neurons may explain the increase of motor axons counted proximally to the lesion.     

The role of sensory input in motor neuron sprouting control

Primary sensory neurons project to motor neurons directly or through interneurons and affect their activity. In our previous paper we showed that intramuscular sprouting can be affected by changing the sensory synaptic input to motor neurons. In this work, motor axon sprouting within a peripheral nerve (extramuscular sprouting) was induced by nerve injury at such a distance from muscle so as not to allow nerve-muscle trophic interactions. Two different procedures were carried out: (1) sciatic nerve crush and (2) sciatic nerve crush with homosegmental ipsilateral L3-L5 dorsal rhizotomy. The number of regenerating motor axons innervating extensor digitorum longus muscle was determined by in vivo muscle tension recordings and an index of their individual conduction rate was obtained by in vitro intracellular recordings of excitatory postsynaptic end-plate potentials in muscle fibers. The main findings were: (1) there are more regenerated axons distally from the lesion than parent axons proximally to the lesion (sprouting at the lesion); (2) sprouting at the lesion was negatively affected by homosegmental ipsilateral dorsal rhizotomy; (3) the number of motor axons innervating extensor digitorum longus muscle extrafusal fibers counted proximally to the lesion increased following nerve injury and regeneration but this did not occur when sensory input was lost. A transient innervation of extrafusal fibers by gamma motor neurons may explain the increase of motor axons counted proximally to the lesion.     

Local innervation patterns of the metathoracic flexor and extensor tibiae motor neurons in the cricket Gryllus bimaculatus

To elucidate neural mechanisms underlying walking and jumping in insects, motor neurons supplying femoral muscles have been identified mainly in locusts and katydids, but not in crickets. In this study, the motor innervation patterns of the metathoracic flexor and extensor tibiae muscles in the cricket, Gryllus bimaculatus were investigated by differential back-fills and nerve recordings. Whereas the extensor tibiae muscle has an innervation pattern similar to that of other orthopterans, the flexor has an innervation unique to this species. The main body of the flexor muscle is divided into the proximal, middle and distal regions, which receive morphologically unique terminations from almost non-overlapping sets of motor neurons. The proximal region is innervated by about 12 moderate-sized excitatory motor neurons and two inhibitory neurons while the middle and distal regions are innervated by three and four large excitatory motor neurons, respectively. The most-distally located accessory flexor muscle, inserting on a common flexor apodeme with the main muscle, is innervated by at least four small excitatory (slow-type) and two common inhibitory motor neurons. The two excitatory and two inhibitory motor neurons that innervate the accessory flexor muscle also innervate the proximal bundles of the main flexor muscle. This suggests that the most proximal and distal parts of the flexor muscle participate synergistically in fine motor control while the rest participates in powerful drive of tibial flexion movement.     

Transformation of the afferent tactile signal into a motor command in the cat motor cortex

Activity of 112 neurons of the precruciate motor cortex in cats was studied during a forelimb placing reaction to tactile stimulation of its distal parts. The latent period of response of the limb to tactile stimulation was: for flexors of the elbow (biceps brachii) 30–40 msec, for the earliest reponses of cortical motor neurons about 20 msec. The biceps response was observed 5–10 msec after the end of stimulation of the cortex with a series of pulses lasting 25 msec. Two types of excitatory responses of the neurons were identified: responses of sensory type observed to each tactile stimulation of the limb and independent of the presence or absence of motion, and responses of motor type, which developed parallel with the motor response of the limb and were not observed in the absence of motion. The minimal latent period of the responses of motor type was equal to the latent period of the sensory responses to tactile stimulation (20±10 msec). Stimulation of the cortex through the recording microelectrode at the site of derivation of unit activity, which increased during active flexion of the forelimb at the elbow (11 stimuli at intervals of 2.5 msec, current not exceeding 25 µA), in 70% of cases evoked an electrical response in the flexor muscle of the elbow.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 9, No. 2, pp. 115–123, March–April, 1977.     

Penis-retractor muscle of Aplysia: excitatory motor neurons

Cobalt axonal iontophoresis and intracellular recordings were used to identify a cluster of several motor neurons innervating the penis-retractor muscle of Aplysia. Intracellularly recorded motor neuron action potentials elicited direct, one-for-one, constant latency excitatory junctional potentials (ejps) in individual muscle fibers. The axons of motor neurons could be recorded extracellularly in the penis-retractor nerve and stimulation of the nerve backfired the motor neurons. Perfusion of the ganglion, the muscle, or both with solutions of either increased Mg++/decreased Ca++ or increased Ca++ sea water indicated that the presumed motor neuron impaled was not a sensory cell and that interneurons were not intercalated in the pathway. Innervation of muscle fibers was found to be functionally polyneuronal and diffuse. The ejps were found to undergo marked facilitation with repetitive motor-neuron stimulation. The motor neurons were isolated in a distinct cluster in the right pedal ganglion. Their electrical activity was characterized by spontaneous irregular action potentials and a moderate input of postsynaptic potentials.     

The abdominal motor system of the crayfish, Cherax destructor. I. Morphology and physiology of the superficial extensor motor neurons

Using extracellular and intracellular stimulation, recording and dye-filling, we identified and studied the superficial extensor motor neurons of the crayfish, Cherax destructor. Functional associations of each neuron were characterised by recording its responses to sensory and abdominal cord inputs, its extensor muscle innervation pattern and its relationships with other neurons. Two clear associations were found among the six neurons of each segment. A medium-sized excitor (no. 3), that innervates a substantial percentage of extensor muscle fibres, and the largest excitor (no. 6), recruited during peak, excitation, were inhibited by input from unknown interneurons that excited the common inhibitor (no. 5). Likewise, these excitors received excitatory input when the inhibitor was silent. Another medium-sized neuron (no. 4) that innervates many muscle fibres was co-active with one of the small excitors (no. 2). The two medium-sized neurons were never active at the same time, and these two groupings may be determined by pre-motor interneurons. The implications of these findings for our understanding of motor control in this system are discussed. Accepted: 21 June 1998     

Pathways mediating abdominal phasic flexor muscle activity in crayfish with chronically cut nerve cords

1. Nerve cord transection abolishes the ability of crayfish (Procambarus clarkii) to produce tailflips in response to gradually applied tactile or proprioceptive stimulation of the abdomen, but this ability eventually returns. To determine the time-course of this return and to analyze its underlying neural pathways, we made behavioral observations, electromyographic recordings from abdominal phasic flexor muscles, and intracellular recordings from motoneurons in crayfish with cord lesions between the thorax and the abdomen.
2. Abdominal stimulation activated the phasic flexor muscles in the rostral 5 abdominal segments and their homologs in the 6th segment, the posterior telson flexor muscles. Nearly one-quarter of cord-transected animals responded to the stimuli with phasic flexor muscle activity by one week after the lesion, and almost 90% were responsive by 3 weeks.
3. Regeneration of axons across the lesion played little or no role in the recovery of phasic flexor muscle responsiveness. In addition, the lateral giant axons were not activated by the gradually applied stimuli that triggered phasic flexor muscle contractions. These results suggest that non-giant pathways confined to the abdominal nervous system become functional following chronic cord transection.
4. Retransection of the nerve cord below the original lesion showed that smaller subsets of the abdominal cord, including a single ganglion, could develop the ability to generate phasic flexor muscle contractions in response to gradually applied stimuli.
5. Phasic flexor motoneurons in cord-transected animals could be excited by stimulation of afferents throughout the abdomen. The sensory pathways producing this activation appear to project through the nerve cord without much cross-over between left and right sides.

     

Multisegmental motor activity in the segmentally restricted gin trap behavior in Manduca sexta pupae

Stimulation of sensory neurons innervating hairs in the gin traps on the abdomen of Manduca sexta pupae evokes a rapid bending of the abdomen that is restricted to one or more of the three articulating posterior segments. However, electrical stimulation of the gin trap sensory nerve in an isolated abdominal nerve cord evokes characteristic motor neuron activity in every abdominal segment. To determine if the segmentally distributed motor activity also occurred in intact animals and how it contributed to the segmentally restricted reflex movement, mechanical stimulation of the sensory hairs in intact animals was used to evoke reflex responses that were recorded as electromyograms synchronized with video recordings of the behavior. Motor activity was monitored during movements to determine if there was activity in many segments when the movement was restricted to one segment. Coordinated muscle activity was evoked throughout the abdomen in response to stimulation of any of the three gin traps, even when movement was restricted to one segment. Differences in the timing of ipsilateral and contralateral motor activity among segments allowed the closing of gin traps to be segmentally restricted. These findings suggest that the neural circuit underlying the gin trap reflex is distributed throughout the abdominal nerve cord. This network generates a complex, yet coordinated, motor pattern with muscular activity in many abdominal segments that produces a localized bending reflex. Accepted: 10 January 1997     

Synaptic responses produced in lobster abdominal postural motor neurons by mechanical stimulation of the swimmeret

1. Intracellular recordings were obtained from the somata of identified abdominal postural motor neurons in lobster to examine their subthreshold and suprathreshold responses to tactile stimulation of the swimmeret. 2. Pressure stimulation of the swimmeret surface evoked abdominal extension by producing tonic spiking in the extensor excitors and the synergistic flexor inhibitor (f5) and hyperpolarizing responses in the extensor inhibitor and antagonistic flexor excitors. These responses often continued for several seconds following the termination of the stimulus. The receptive fields of these motor responses extended over most of the swimmeret surface. 3. More localized tactile stimulation of the swimmeret surface elicited EPSPs in f5 and the extensor excitors, and IPSPs in the flexor excitors. The amplitude of these synaptic potentials decreased as the stimulus intensity was reduced. 4. Stimulation of feathered hair (both sexes) and smooth hair (female only) sensilla produced responses characteristic of extension whereas bristly spines on the male accessory lobe excited only two flexor excitors without affecting any of the other postural motor neurons. 5. Summed synaptic responses recorded from the motor neurons differed in their amplitudes and latencies according to the type of mechanoreceptor stimulated-cuticular receptors, feathered hairs or smooth hairs. Stimulation of the swimmeret cuticle produced the strongest responses (shortest latency, largest amplitude), while feathered hair stimulation initiated the weakest responses (longest latency, smallest amplitude). 6. The relatively long latencies (greater than 35 ms) and the complex form of the EPSPs and IPSPs indicate the involvement of multisynaptic interneuronal pathways in the reflex arcs.     

Studies on the Distribution of Factor I and Acetylcholine in Crustacean Peripheral Nerve

Extracts of whole nerve (chelipeds of Cancer magister) cause inhibition of impulse generation of the crayfish stretch receptor preparation, similar to that produced by gamma-aminobutyric acid (GABA). This is not found with extracts containing only sensory or sensory and motor fibers. Extracts of inhibitory fibers inhibit the stretch receptor discharge—indicating an inhibitory action equivalent to that of up to 30,000 micrograms of GABA per gm. wet weight of inhibitor fiber. This high value is taken as an indication that the inhibitory substance in crab inhibitory fibers is not identical with gamma-aminobutyric acid. Whole nerves were found to contain 1.7 to 6.7 µg. acetylcholine per gm. nerve tissue (clam ventricle and frog rectus abdominis muscle). No acetylcholine could be detected in extracts of motor and inhibitory fibers. The acetylcholine content of sensory fibers can account for the acetylcholine activity of whole nerve extract. It is concluded that the factor I of crustacean nerve is an exclusive property of the inhibitory fibers. The results support the assumption that factor I is the transmitter substance of inhibitory neurons in these animals. The absence of acetylcholine in motor fibers indicates that this substance does not function as a transmitter of motor impulses in Crustacea, and explains the previously observed failure of the substance to elicit motor responses in these animals. The function of acetylcholine in sensory fibers is not yet clarified.     

Differentiation of Nerve Terminals in the Crayfish Opener Muscle and Its Functional Significance

Junctional potentials (jp's) recorded from superficial distal fibers of the crayfish opener muscle are up to 50 times larger than jp' in superficial central fibers when the single motor axon that innervates the muscle is stimulated at a frequency of 1/sec or less. At 80/sec, in contrast, central jp's are up to four times larger than those observed in distal fibers. The tension produced by single muscle fibers of either type is directly proportional to the integral of the time-voltage curve minus an excitation-contraction coupling threshold of 3 mv. Distal fibers therefore produce almost all the total muscle tension at low frequencies of stimulation and central fibers add an increasingly greater contribution as their nerve endings begin to facilitate in response to increased rate of motor discharge. Differentiation of muscle membrane characteristics (input resistance, space constant, time constant) cannot account for these differences in facilitation ratios. The mechanism of neuronal differentiation is not based upon the size or effectiveness of transmitter quanta, since equal sized jp's have equal variances;: mjp sizes and variances are also equal. No differences were found between fiber types in rates of transmitter mobilization, density of innervation, or the relationship between transmitter release and terminal depolarization. Single terminals on distal fibers were found to release transmitter with a greater probability than central terminals. More effective invasion of distal terminals by the nerve impulse at low frequencies can account for the difference.     

Effect of substances blocking calcium channels (verapamil,D-600, manganese ions) on transmitter release from motor nerve endings in frog muscle

Experiments on isolated frog nerve-muscle preparations showed that manganese ions (0.4–5.0 mM) inhibit evoked transmitter release by reducing the quantum composition of the end-plate potentials, and they intensify spontaneous transmitter release to a certain extent by increasing the frequency of miniature potentials. Verapamil (1 · 10^–6–5·10^–5 g/ml) and D-600 (2.5·10^–5 g/ml), by contrast with manganese ions, do not inhibit evoked release, but also intensify spontaneous release of the transmitter. All the agents tested prevent the potentiating effect of imidazole (3 mM). During repetitive stimulation, verapamil disturbs action potential generation in the motor nerve. Manganese ions had no such action. It is concluded that between the calcium channels of motor nerve endings and the calcium channels of heart muscle or the neuron soma there are molecular differences, expressed as sensitivity to the blocking action of verapamil and D-600.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 9, No. 4, pp. 415–422, July–August, 1977.     

Sensitivity of transformed (phasic to tonic) motor neurons to the neuromodulator 5-HT

Long-term adaptation resulting in a 'tonic-like' state can be induced in phasic motor neurons of the crayfish, Procambarus clarkii, by daily low-frequency stimulation [Lnenicka, G.A., Atwood, H.L., 1985b. Long-term facilitation and long-term adaptation at synapses of a crayfish phasic motoneuron. J. Neurobiol. 16, 97-110]. To test the hypothesis that motor neurons undergoing adaptation show increased responses to the neuromodulator serotonin (5-HT), phasic motor neurons innervating the deep abdominal extensor muscles of crayfish were stimulated at 2.5 Hz, 2 h/day, for 7 days. One day after cessation of conditioning, contralateral control and conditioned motor neurons of the same segment were stimulated at 1 Hz and the induced excitatory post-synaptic potentials (EPSPs) were recorded from DEL(1) muscle fibers innervated by each motor neuron type. Recordings were made in saline without and with 100 nM 5-HT. EPSP amplitudes were increased by 5-HT exposure in all cases. Conditioned muscles exposed to 5-HT showed a 2-fold higher percentage of increase in EPSP amplitude than did control muscles. Thus, the conditioned motor neurons behaved like intrinsically tonic motoneurons in their response to 5-HT. While these results show that long-term adaptation (LTA) extends to 5-HT neuromodulation, no phenotype switch could be detected in the postsynaptic muscle. Protein isoform profiles, including the myosin heavy chains, do not change after 1 week of conditioning their innervating motor neurons.     

Development of the gin trap reflex inManduca sexta: a comparison of larval and pupal motor responses

1. Responses of motor neurons in larvae and pupae of Manduca sexta to stimulation of tactile sensory neurons were measured in both semi-intact, and isolated nerve cord preparations. These motor neurons innervate abdominal intersegmental muscles which are involved in the production of a general flexion reflex in the larva, and the closure reflex of the pupal gin traps. 2. Larval motor neurons respond to stimulation of sensory neurons innervating abdominal mechanosensory hairs with prolonged, tonic excitation ipsilaterally, and either weak excitation or inhibition contralaterally (Figs. 4A, 6). 3. Pupae respond to tactile stimulation of mechanosensory hairs within the gin traps with a rapid closure reflex. Motor neurons which innervate muscles ipsilateral to the stimulus exhibit a large depolarization, high frequency firing, and abrupt termination (Figs. 2, 4B). Generally, contralateral motor neurons fire antiphasically to the ipsilateral motor neurons, producing a characteristic triphasic firing pattern (Figs. 7, 8) which is not seen in the larva. 4. Pupal motor neurons can also respond to sensory stimulation with other types of patterns, including rotational responses (Fig. 3A), gin trap opening reflexes (Fig. 3B), and 'flip-flop' responses (Fig. 9). 5. Pupal motor neurons, like larval motor neurons, do not show oscillatory responses to tonic current injection, nor do motor neurons of either stage appear to interact synaptically with one another. Most pupal motor neurons also exhibit i-V properties similar to those of larval motor neurons (Table 1; Fig. 10). Some pupal motor neurons, however, show a marked non-linear response to depolarizing current injection (Fig. 11).     

Peptidergic innervation of leg muscles of the cockroach,Periplaneta americana (L.), and a possible role in modulation of muscle contraction

FMRFamide-related peptides of insects are particularly important because of their possible function as neurohormones and neuromodulators on a wide variety of tissues. Part of this study was an investigation of the immunofluorescent staining of motor nerves which arise in the metathoracic ganglion, examined in wholemount using an antiserum that recognizes extended -RFamide peptides (generally recognized to be of the FMRFamide family). This antiserum revealed immunochemical staining of numerous cell bodies in the metathoracic ganglion and of axons in peripheral nerve 5, a large nerve which contains both motor and sensory fibres. Axons staining positive for FMRFamide-related peptides were traced in nerve 5 as far as the femur-tibia joint, and into the first (sensory-motor) and third (motor only) ramus of nerve 5. Reverse-phase HPLC with radioimmunoassay revealed a peak of FMRFamide-related peptide activity in nerve 5 that was coincident with a peak found when thoracic ganglia were processed in the same fashion. A physiological assay was devised to test the ability of various non-native peptides to alter the characteristics of contraction of skeletal muscles of the legs. Using neurally evoked contractions of coxal depressor muscles of the metathoracic leg it was determined that several non-native peptides could potentiate muscle contractions.The results of this study suggest that muscles of the legs receive innervation by identifiable, FMRFamide-related peptide-containing neurons and that the release of peptide(s) at the muscle may be yet another method of modulating the mechanics of muscle contraction.Abbreviations D _f fast depressor motor neuron - D _s slow depressor motor neuron - DU M dorsal unpaired median - FaRPs FMRFamide related peptides - FEFe fast extensor of the femur - FFFe fast flexor of the femur - FITC fluorescein isothiocyanate - FPC fast promotor of the coxa - FPT fast flexor of the pretarsus - I _1–3 inhibitory motor neurons - LMS leucomyosuppressin, N5 nerve 5 - N5r1 first ramus of nerve 5 - PBS phosphate buffered saline - PLCl posterior lateral cluster - RIA radioimmunoassay - SETi slow extensor of the tibia - SFTi slow flexor of the tibia - TFA trifluoroacetic acid - VMCl ventral median cluster     

Motor patterns during kicking movements in the locust

Locusts (Schistocerca gregaria) use a distinctive motor pattern to extend the tibia of a hind leg rapidly in a kick. The necessary force is generated by an almost isometric contraction of the extensor tibiae muscle restrained by the co-contraction of the flexor tibiae (co-contraction phase) and aided by the mechanics of the femoro-tibial joint. The stored energy is delivered suddenly when the flexor muscle is inhibited. This paper analyses the activity of motor neurons to the major hind leg muscles during kicking, and relates it to tibial movements and the resultant forces.During the co-contraction phase flexor tibiae motor neurons are driven by apparently common sources of synaptic inputs to depolarized plateaus at which they spike. The two excitatory extensor motor neurons are also depolarized by similar patterns of synaptic inputs, but with the slow producing more spikes at higher frequencies than the fast. Trochanteral depressors spike at high frequency, the single levator tarsi at low frequency, and common inhibitors 2 and 3 spike sporadically. Trochanteral levators, depressor tarsi, and a retractor unguis motor neuron are hyperpolarized.Before the tibia extends all flexor motor neurons are hyperpolarized simultaneously, two common inhibitors, and the levator trochanter and depressor tarsi motor neurons are depolarized. Later, but still before the tibial movement starts, the extensor tibiae and levator tarsi motor neurons are hyperpolarized. After the movement has started, the extensor motor neurons are hyperpolarized further and the depressor trochanteris motor neurons are also hyperpolarized, indicating a contribution of both central and sensory feedback pathways.Variations in the duration of the co-contraction of almost twenty-fold, and in the number of spikes in the fast extensor tibiae motor neuron from 2–50 produce a spectrum of tibial extensions ranging from slow and weak, to rapid and powerful. Flexibility in the networks producing the motor pattern therefore results in a range of movements suited to the fluctuating requirements of the animal.     

Excitatory neurotransmitters in the tentacle flexor muscles responsible for space positioning of the snail olfactory organ

Recently, three novel flexor muscles (M1, M2 and M3) in the posterior tentacles of the snail have been described, which are responsible for the patterned movements of the tentacles of the snail, Helix pomatia. In this study, we have demonstrated that the muscles received a complex innervation pattern via the peritentacular and olfactory nerves originating from different clusters of motoneurons of the cerebral ganglia. The innervating axons displayed a number of varicosities and established neuromuscular contacts of different ultrastructural forms. Contractions evoked by nerve stimulation could be mimicked by external acetylcholine (ACh) and glutamate (Glu), suggesting that ACh and Glu are excitatory transmitters at the neuromuscular contacts. Choline acetyltransferase and vesicular glutamate transporter immunolabeled axons innervating flexor muscles were demonstrated by immunohistochemistry and in Western blot experiments. Nerve- and transmitter-evoked contractions were similarly attenuated by cholinergic and glutamatergic antagonists supporting the dual excitatory innervation. Dopamine (DA, 10^?5 M) oppositely modulated thin (M1/M2) and thick (M3) muscle responses evoked by stimulation of the olfactory nerve, decreasing the contractions of the M1/M2 and increasing those of M3. In both cases, the modulation site was presynaptic. Serotonin (5-HT) at high concentration (10^?5 M) increased the amplitude of both the nerve- and the ACh-evoked contractions in all muscles. The relaxation rate was facilitated suggesting pre- and postsynaptic site of action. Our data provided evidence for a DAergic and 5-HTergic modulation of cholinergic nerves innervating flexor muscles of the tentacles as well as the muscles itself. These effects of DA and 5-HT may contribute to the regulation of sophisticated movements of tentacle muscles lacking inhibitory innervation.     

Neuromuscular relationships in the abdomen of the Californian shore crab Pachygrapsus crassipes

There are two pairs of muscles in each abdominal segment of the crab; one pair of flexors and one pair of extensors. In the early larval stages the muscles have short sarcomeres--a property of fast fibers--and high thin to thick filament ratios--a property of slow fibers. In the adult the abdominal muscles are intermediate and slow, since they have fibers with intermediate and long sarcomeres, high thin to thick filament ratios, low myofibrillar ATPase activity, and high NADH diaphorase activity. The different fiber types are regionally distributed within the flexor muscle. Microelectrode recordings from single flexor muscle fibers in the adult showed that most fibers are supplied by three excitatory motor axons, although some are supplied by as many as five efferents. One axon supplies all of the flexor muscle fibers in its own hemisegment, and the evoked junctional potentials exhibit depression. This feature together with the innervation patterns of the fibers are similar to those reported for the deep flexor muscles of crayfish and lobsters. Therefore, in the adult crab, the abdominal flexor muscles have some features in common with the slow superficial flexors of crayfish and other features in common with the fast deep flexor muscles.     

微循环研究常用部位的肽能和胺能神经支配

以逆行追踪与免疫细胞化学相结合法,探讨了大鼠提睾肌、盲肠系膜和耳廓等微循环研究常用部位的神经肽Ｙ（ＮＰＹ）、降钙素基因相关肽（ＣＧＲＰ）、甲啡吠（Ｍ－ＥＮＤ）和５－羟色胺（５－ＨＴ）等肽能和胺能神经的支配。结果表明：支配提睾肌的运动和感觉神经元分别含有５－ＨＴ和ＣＧＲＰ。支配提睾肌血管、盲肠系膜及其血管的交感神经元,一部分含有ＮＰＹ,一部分含有Ｍ－ＥＮＫ;支配耳廓局部的运动和感觉神经元均含有ＣＧＲ