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At least 235 records · Page 13Linked to original sources
PubMed1975

Habituation of mechanoreceptive interneurons in the crayfish.

The effect of repetition of sensory stimuli was studied on the responses of mechanoreceptive interneurons in the optic tract of the crayfish (Procambarus bouvieri (Ortmann)). The number of spikes recorded from a given unit gradually decreased during a train of stimuli. The decrease showed a negative exponential time course, with a curvature dependent upon the frequency of stimulation, the intensity of stimuli, and the hour of the day. Habituation is selective for the intensity and rate of stimulation, and the particular spot of receptive field stimulated. Locomotor excitation results in a dimminution of the rate of decay. The effect of a single train of stimuli when leading to pronounced habituation may persist for periods longer than 24 hr.

Animals↗
PubMed1975

Integration in the crayfish antennal neuropile: topographic representation and multiple-channel coding of mechanoreceptive submodalities.

(1) Response patterns of interneuron populations in the antennal neuropile of the crayfish have been investigated by extracellular recordings made with a single electrode. Mechanical stimuli of the antennae are divided into submodalities and topographically represented. The submodalities include large movements of the entire antenna, directional aspects of movements and vibrations, and vibratory stimulation up to click repetition rates of 100. (2) Interneuron output is always patterned, ranging from simple bimodal types to complex multimodal patterns that extend over 40 msec. The interneuron output is "noisy" due to short- and long-term fluctuations in sensitivity producing temporal fluctuations in both output probability and output patterns. The response latencies both within and between populations cluster around several fixed latencies. (3) The axons of a group of neurons, sensitive to the same submodality, are located together and consequently can be recorded with a single electrode. Responses from the interneurons composing a population are similar in response to nonoptimal stimulation, but are synchronized and of high probability to optimal stimulation.

Animals↗
PubMed1975

Physical and physiological properties of the crayfish antennal flagellum.

(1) Mechanoreceptors in the crayfish antennae are divided into four functional categories: vibration (13%), bidirectional displacement (19%), unidirectional displacement (45%), and position (23%) receptors. The distribution of receptors along the length of the flagellum follows a logarithmic progression, decreasing from about 40% at the base to less than 5% at the tip. (2) Vibratory stimulation of the antennae was found to induce a traveling wave. Because of an impedance gradient along the length of the flagellum, the traveling wave moves most efficiently from base to tip. The wave was observed to travel at an average velocity of 6.0 m/sec. (3) Large deflections of the tip are not uniformly transferred to the base, but decrease logarithmically. This due to the existence of the impedance gradient. (4) Receptor output probability was found to be greatest when low frequency/high intensity stimulation was applied to the flagellar base. (5) Characteristics of large (2 cm) posterior-going deflections of the flagellar tip that are effective in producing response differences are displacement: (a) amplitude, (b) velocity, and (c) acceleration.

Animals↗
PubMed1976

Synaptic development in the crayfish opener muscle.

Nerve terminal regions in walking leg opener muscles of several crayfish of different ages (0 to 245 days after hatching) were examined by means of electron microscopy. This muscle is innervated by two axons (excitatory and inhibitory) and at maturity contains three classes of synapse: excitatory and inhibitory neuromuscular synapses, and inhibitory axo-axonal synapses. The muscle itself is initially a syncytium, which gradually becomes subdivided into distinct "muscle fibers" as the animal matures. Innervation was not found in the opener muscle just before or just after hatching, but was present in restricted locations on the inner side of the muscle within a few days of hatching. As the muscle enlarged and became subdivided, innervation appeared in various other locations. Synaptic contacts were located in young stages soon after hatching, and in later stages. Morphological differences characteristic of excitatory nerve terminals could be found even at the earliest stages of innervation. Both excitatory and inhibitory synapses, but particularly the former, showed evidence of progressive enlargement to a final size within the first two months, and no evidence for further enlargement of existing synapses thereafter. Synaptic maturation also involved the appearance of presynaptic "dense bodies" though to be regions at which transmitter substance is preferentially released. Nerve terminals at different levels of maturation were observed in opener muscles of young crayfish. Clear evidence for differential maturation of the three types of synapse present in this muscle was obtained. The inhibitory neuromuscular synapses attained their final average size and developed their dense bodies sooner than the excitatory neuromuscular synapses. The inhibitory axo-axonal synapses were the last to appear and to mature.

Age Factors↗
PubMed1978

Developmental abnormalities of identifiable neurons in the crayfish Procambarus simulans.

We report anomalies of lateral giant neurons in field-caught animals. In one case, both lateral giant neurons arising from the fifth abdominal ganglion did not terminate in the next-most anterior ganglion, but rather continued to the third abdominal ganglion. In another case, an additional large neuron arising in the fifth abdominal ganglion coursed in a posterior direction. All othe CNS structures appeared normal in animals having either anomaly.

Animals↗
PubMed1979

Central inhibition of an identified mechanosensory interneuron in the crayfish.

Inhibitory input from crayfish mechanoreceptors is mediated polysynaptically to sensory interneurons. An identifiable sensory interneuron, the caudal photoreceptor (CPR), has been used as a model system to characterize inhibitory intermediate cells. A survey of the abdominal connectives, by antidromic stimulation, has identified eleven inhibitory cells, some of which also function as ascending sensory interneurons. These results indicate that lateral interactions within networks of mechanosensory interneurons form an integral part of the information processing mechanisms.

Animals↗
PubMed1979

Functional characterization of the neurodepressing hormone in the crayfish.

The effect of the neurodepressing hormone (NDH) was studied on different identified motoneurons in the abdominal ganglia of the crayfish Procambarus bouvieri (Ortmann). Although differences in sensitivity were apparent, all the neurons tested responded to NDH with a reduction in spontaneous firing rate, which lasted as long as NDH was present, and, depending on the concentration and time of action of the hormone, for even longer periods. NDH activity was determined in the various parts of the central nervous system of the crayfish, being highest in the eyestalk, gradually diminishing away from the eyestalk, with a cephalo-caudal gradient, being lowest in the abdominal ganglia. High levels of NDH activity were detected in the blood. After eyestalk ablation, NDH concentration steadily diminishes in the blood and central nervous system, until virtually disappearing after 4 days; from day 5 onwards, the activity is recovered up to its original levels. NDH synthesis takes place with a time constant of approximately 3 hr in cultured isolated segments of central nervous system, being highest in the eyestalk.

Animals↗
PubMed1979

Photomechanical migrations of pigment granules along the retinula cells of the crayfish.

The light-dependent migrations of proximal pigment granules along the photoreceptors of the crayfish compound-eye were studied in isolated retinas and eyestalks. The extent and kinetics of movement in each direction were found quantitatively equivalent to those observed in the organ in situ. These and other features make these cells to appear as intrinsically independent pigmentary effectors, directly responsive to light. During dark adaptation (DA) the pigment migrates away from the cell nucleus and accumulates along the axon in two distinct steps. Each step constitutes half of the total distance of about 180 microns and proceeds at 0.30 micron/sec. Only prolonged metabolic impairment inhibited the first phase, while the second was blocked by hypoxia, cyanide, colchicine, and D2O. The maintenance of a full DA position was also shown to be highly dependent upon metabolism. Light incidence on DA eyes is followed by an apparently monophasic expansion of the pigment from the axon towards the perikaryl region at 0.38 micron/sec. This movement was not affected by any of the foregoing agents and seems to be a passive relaxation process. Cytochalasin B had no effect on either motion. The migration in either direction has an exponential time course and is temperature dependent. Electron microscopy revealed two separate patterns of cytoplasmic organization corresponding to the cell areas where the two phases of DA occur. In the region close to the nucleus the pigment appears irregularly scattered, whereas in the axon the granules are situated arond a thick longitudinal bundle of microtubules. These results suggest the existence of two different mechanisms of pigment granule translocation operating in two separate regions of the retinula cell.

Animals↗
PubMed1980

GABA inactivation at the crayfish neuromuscular junction.

Changes in the effective membrane resistance of the abductor muscle of the dactylopodite of the caryfish were used to indicate changes in the GABA concentration in the synaptic cleft. Following bath application of GABA (10(-5) to 5 X 10(-5) M), the muscle membrane resistance decreased and then increased slowly over the next few minutes. Renewing the solution or stirring the bath restored the GABA effect. Higher GABA concentrations produced a large stable decrease in membrane resistance. An active uptake system for GABA in the junctional region is suggested by the observation that the slow increase in membrane resistance following GABA application was decreased by cooling to 2 degrees C or by the addition of known GABA uptake blockers such as L-DABA, beta-guanidinopropionic acid, or nipecotic acid. The transport inhibitors, PCMBS and chlorpromazine, produced irreversible decreases in muscle membrane resistance, which precluded examining their effects on GABA inactivation. The decrease in GABA effect was not dependent on the external sodium concentration or on the degree of receptor activation. Nipecotic acid, which blocked GABA inactivation, did not affect the decay of the neurally evoked inhibitory junctional potential.

Animals↗
PubMed1980

L-proline as a glutamate antagonist at a crustacean neuromuscular junction.

The fast as well as the slow contractions of the adductor muscle in the claw of Procambarus clarkii are inhibited by L-proline. This inhibition is dose dependent and decreases with increasing frequency of stimulation of the "slow" fiber. Contractions caused by perfusing the adductor muscle with L-glutamate solutions are also inhibited by L-proline. The inhibiting potency of L-proline is small; the effective concentration of this amino acid is 50--100 times that of the L-glutamate applied. It was postulated that the inhibitory effect of L-proline is based on competition for excitatory receptor sites of L-glutamate, which causes depolarization and contraction, and L-proline, which lacks these actions. Theoretical considerations suggested a linear relationship between the stimulating L-glutamate and the just-inhibiting L-proline concentrations. Experimental evidence supported this model.

Animals↗
PubMed1980

Excitatory Neuromuscular transmission in crayfish: calcium dependence is unaffected by picrotoxin.

Picrotoxin, 1 X 10(-5)M to 1.6 X 10(-3)M, had little or no effect on the amplitude of intracellularly recorded excitatory junctional potentials (EJPs) at extracellular calcium concentrations [Ca2+]0 ranging from 0.5 to 15 mM. The slope of the log EJP vs. log[Ca2+]0 relationship was approximately 1 with or without picrotoxin. The reduction EJP amplitude resulting from the addition of 5 X 10(-5)M GABA was largely reversed by 10(-5)M picrotoxin.

Animals↗
PubMed1981

Release of 3H-gamma-aminobutyric acid (GABA) by inhibitory neurons of the crayfish.

Inhibitory neurons innervating the muscle receptor organ (MRO) of crayfish were used to study the uptake and release of tritiated GABA. MROs that have been directly exposed to 3H GABA for 60--75 min release radioactivity during low-frequency electrical stimulation. When ganglia containing the inhibitory cell bodies are exposed to 3H GABA, the isotope travels along a pathway unique to the inhibitory axon, at rates that range between 160 and 240 mm per day. Electrical stimulation of inhibitory axons whose cell bodies have been exposed to 3H GABA for 4--5 hr produces release of isotope from isolated MROs. Low calcium, high magnesium exposure prevents the stimulus-dependent release of radioactivity. Thin layer chromatographic analyses indicate that GABA comprises at least a major fraction of the radioactivity collected from stimulated preparations. A number of unidentified radioactive compounds are usually present with GABA, and it is suggested that most of these are catabolites of GABA.

Animals↗
PubMed1981

Interneurons of the crayfish brain: the relationship between dendrite location and afferent input.

This study was undertaken to examine the relationship between the structure and function of the descending interneurons of the crayfish brain. In particular, the dendritic fields were examined to ascertain if the location of an interneuronal dendrite in any of the six cerebral hemineuromeres (which subserve specific sensory modalities) is a necessary or sufficient condition to determine the functional and/or synaptic input to the interneuron. If a neuron projects a dendrite to a hemineuromere of the deutocerebrum or tritocerebrum, the neuron derives sensory input from the corresponding afferent root in 95% of our observations. Most of these inputs (86%) contain at the least a monosynaptic component. Conversely, if a cell derives monosynaptic input from any one of three of the four deutocerebral and tritocerebral roots tested, it has a corresponding dendrite (in 98% of our observations) in the appropriate hemineuromere. Input from the contralateral antennal nerve is an exception to this rule. The presence of a dendrite in the protocerebrum is not sufficient for predicting detectable visual input, but every instance of detectable visual input is associated with a protocerebral dendrite. Polysynaptic inputs are frequently (42%) not associated with corresponding dendrites. In neurons that were repeatedly dye filled in different animals, we observed significant variation only in the number and precise location of the smaller secondary and tertiary neurites. This variation rarely influenced the subset of sensory lobes innervated by the neuron.

Afferent Pathways↗
PubMed1981

Cyclic AMP, 5-HT, and the modulation of transmitter release at the crayfish neuromuscular junction.

In this study it was found that several agents which elevate cAMP levels in cells also increase dramatically the quantity of transmitter released from crayfish excitatory nerve terminals in response to a stimulus. With respect to time course and magnitude, the increase produced by one of these agents, the cyclic nucleotide phosphodiesterase inhibitor Squibb 20,009 (SQ 20,009), is unlike any reported for such a drug at a synapse. Additionally, SQ 20,009 potentiated the facilitation of transmitter release produced by serotonin (5-HT) at this synapse. These results establish a possible role for cAMP in the control and modulation of transmitter release at the crayfish neuromuscular junction (NMJ). They further suggest that 5-HT functions here by activation of a presynaptically located adenylate cyclase.

Animals↗