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F B Krasne

Publications and source records attributed to F B Krasne.

At least 37 records · Page 2Linked to original sources
PubMed1985

Intracellular analysis of the innervation of a crayfish sensory interneuron by regenerating afferents.

Mechanoreceptors of the crayfish tail fan have peripheral somata and send their axons to the last (sixth) abdominal ganglion via five bilateral pairs of nerve roots (R1-R5). Comparisons were made between normal crayfish and regenerate preparations in which R4 had been cut and directed back to an extensively denervated sixth abdominal ganglion; 8 to 15 weeks postoperatively, an identified target interneuron (A) in this ganglion was impaled, and its response to water currents, electrical excitation of R4, and stimulation of individual sensory hairs supplying axons to R4 was studied along with several other properties of the pre- and post-synaptic neurons. Normal levels of excitability in A to R4 stimulation were achieved within six weeks as judged by extracellular criteria. Subsequent intracellular analysis revealed that few differences exist between regenerated and normal inputs: probability of (re-) connection, unitary EPSP amplitude and time course distributions, resting membrane potentials, and critical firing levels were comparable in the two groups; input impedance, however, may have been lower in regenerates. Compound electrically elicited EPSPs were similar in amplitude, rise time, and half amplitude width, but differed slightly in latency to onset (regenerates greater than normals). This was accounted for by differences in conduction time to the ganglion in regenerates, and central delay estimates suggest that connections in both groups are monosynaptic. The body root (R1) providing input to A that remained intact in the regenerate preparations increased in efficacy; over 12 postoperative weeks the response of A to R1 activation by water drops steadily increased and at 12 weeks unitary increments to ascending electrical stimulation of R1 were significantly larger than in normals. The response to giant interneuron activation demonstrated that recurrent inhibitory inputs were normal in regenerates. In addition, synaptic depression, normally responsible for behavioral habituation in this system, was comparable across groups. Further, protection from habituation was observed in both normals and regenerates if R4 stimulation was preceded by giant interneuron activation, thus indicating that normal presynaptic inhibitory inputs to the regenerated afferent terminals have also successfully regenerated.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1984

Crayfish escape behavior: production of tailflips without giant fiber activity.

The giant interneurons of the crayfish nerve cord are well-known mediators of fast tail flexions, "tailflips," that propel animals through the water away from danger. More recent studies have revealed an additional nongiant generator of tailflips. In contrast to giant tailflips, which are stereotyped, nongiant tailflips have variable form. The operating principles and portions of the neural circuitry governing nongiant tailflips were here investigated. Whereas fast flexor motor neurons (FFs) receive excitatory postsynaptic potentials (EPSPs) with large unitary components just prior to giant tailflips, excitation of the FFs during nongiant tailflips is due to summation of many small EPSPs, and these build up for about 60 ms prior to the tailflip; we call the period of excitation prior to FF firing the preflexion phase and the period during which FFs fire, the flexion phase of the tailflip. Even FFs that will not fire during a given tailflip become depolarized during preflexion and flexion periods. Throughout the preflexion and flexion periods there is activity in dorsal nerve cord axons (DCAs) that lie below the giants. Many DCAs are interneurons that excite FFs at short latency. Some DCAs fire uniquely during the preflexion phase, while some fire only during the flexion phase. Which DCAs fire is highly variable, and in some cases firing of particular DCAs can be correlated with particular forms of tailflips. Two identified DCAs, 12 and 13, that fire during the flexion phase were studied. These interneurons originate and receive their synaptic input in the second and third abdominal ganglia, respectively, and project to the last ganglion exciting FFs caudal to their ganglion of origin en route. Their pattern of synaptic input prior to and during nongiant tailflips is indistinguishable from that of FFs. Their input to FFs is weak, but when they fire they tend to promote intersegmental synchrony of FFs in the segments they feed. It appears likely to us that nongiant tailflips are synthesized from a small library of component tailflip movements that can be combined to produce a variety of complete tailflips and that the component movements are produced by a limited group of premotor interneurons, of which 12 and 13 are members.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1983

Serotonin and octopamine have opposite modulatory effects on the crayfish's lateral giant escape reaction.

Serotonin and octopamine have opposite effects on a simple behavioral response, the crayfish's lateral giant escape reaction. Specifically, serotonin depresses the lateral giants' responsiveness, whereas octopamine enhances it. Both effects are largely confined to the disynaptic pathway from the sensory afferents to the lateral giants, although, occasionally, small effects are also seen in the monosynaptic pathway to the lateral giants. One specific locus of the octopaminergic effect is the synapse between the afferents and the largest of the sensory interneurons in the disynaptic pathway, interneuron A. Serotonin, however, does not have a consistent effect at this synapse. Although serotonin and octopamine modulate the excitability of the escape response, neither monoamine appears to significantly alter the rate at which this response habituates.

Animals↗
PubMed1982

Resistance of a crayfish sensory interneurone to hyperinnervation by acceptable afferents.

1. Intact normal innervation of muscle fibres and other peripheral targets usually prevents regenerating nerves from forming synapses with the targets. Whether intact innervation similarly prevents synapse formation on central target neurones has rarely been tested. This question was examined here for interneurone A of the crayfish last abdominal ganglion. 2. Interneurone A normally receives synaptic input from mechanoreceptor neurones distributed over the side of the tailfan ipsilateral to interneurone A's axon and unilateral dendrites. When the five nerve roots carrying mechanoreceptor axons of one side are cut and central and peripheral ends of one or more are sutured together, regeneration and reinnervation of interneurone A occurs over some two to six weeks. If peripheral ends of roots from the 'wrong' (contralateral) side of the body are sutured to ipsilateral central stumps, they also form connexions with interneurone A. When roots from the two sides of the body are simultaneously tied to a central stump, functional connexion formation occurs equally well for afferents from both sides. Therefore, roots of the two sides seem to be equivalent in their ability to reinnervate interneurone A. 3. If peripheral ends of roots from one side of the tailfan are tied to roots on the intact opposite side of the body, the cut axons appear to grow into the last ganglion but usually do not form functional synapses there. The intact innervation therefore seems to exclude further innervation by other acceptable afferents. 4. It is known that mechanoreceptors are added to the tailfan at moult. Exclusion of extra innervation often broke down partially in animals that moulted during the present experiments. This suggests the possibility that synapse formation or exchange may be controlled by moult-inducing hormones.

Animals↗
PubMed1982

Segmental giant: evidence for a driver neuron interposed between command and motor neurons in the crayfish escape system.

1. The giant command neurons for tailflip escape behavior in crayfish have been thought to excite the nongiant fast flexor (tailflip producing) motor neurons (FFs) via monosynaptic connections. We show here that excitation of FFs instead occurs via a bilateral pair of segmental giant neurons (SGs) interposed between the command axons and FFs in each segment. 2. Anatomically, the SGs appear to make numerous contacts with ipsilateral command axons and FFs and fewer contacts contralaterally. In contrast, the command axons have only sparse direct connections to the FFs. An SG has an axon in the ipsilateral first ganglionic root and may be a modified swimmeret motor neuron. 3. Each SG is depolarized well beyond threshold by the firing of an ipsilateral command axon and is depolarized to near threshold by the firing of a contralateral command axon. The synapses between command axons and SGs are electrical and probably rectifying. 4. Each FF is excited to a level near firing threshold by the SG ipsilateral to its axon and is excited weakly by the contralateral SG. The synapses between SGs and FFs are electrical and nonrectifying. 5. Variations in excitatory postsynaptic potentials (EPSPs) recorded in FFs during prolonged, high-frequency firing of the command axons can be accounted for by refractoriness of SG spikes, as opposed to refractoriness of dendritic branch spikes as had previously been delivered. 6. These findings illustrate the limitations of conventional tests for monosynapticity. 7. The functional significance of having driver neurons interposed between command neurons and motor neurons is discussed.

Animals↗
PubMed1981

Different command neurons select different outputs from a shared premotor interneuron of crayfish tail-flip circuitry.

In the crayfish a bilateral pair of interneurons (the 13's) are involved in the generation of two types of tail-flip escape responses, one mediated by giant neurons and the other by nongiant circuitry. The 13's make a variety of output connections with the motoneurons and with other interneurons involved in tail flipping. The motoneuronal outputs include strong synapses on telson flexor motoneurons, whose activity during tail flips mediated by lateral giant fibers would be maladaptive. The lateral giants always drive the 13's, but also drive inhibitory neurons that prevent the undesirable outputs of the 13's while permitting their adaptive outputs to be expressed. It is often adaptive for tail flips initiated by nongiant circuitry to utilize the telson flexor muscles that 13 strongly excites. During such tail flips 13 is often fired, and this firing is important in driving the telson flexors.

Action Potentials↗
PubMed1981

The crayfish lateral giants as command neurons for escape behavior.

The lateral giants (LGs) of the crayfish have often been described as command neurons. Recently, questions have arisen as to the definition of command neurons and as to whether the LGs are necessary for tailflips. We find that in an isolated abdomen preparation the LGs are necessary; temporarily blocking the LGs by hyperpolarization eliminates the tailflip flexor muscle output normally elicited by stimulation of the sensory afferents. However this demonstration of the LGs' necessity does not establish the LGs as the decision point of the behavior, for the LGs might be driven by a large input from a preceding decision neuron. We have checked for such an input by plotting the size of the EPSP produced in the hyperpolarized LG by various stimulus levels near spike threshold. We find no evidence for a large driving input near spike threshold. We conclude that the LGs have most of the features of command neurons.

Afferent Pathways↗
PubMed1981

Interneurons between giant axons and motoneurons in crayfish escape circuitry.

1. Crayfish giant fibers are generally believed to generate tailflip movements by means of direct connections to two classes of phasic flexor muscle motoneurons, the motor giants (MoGs) and the nongiant fast flexor motoneurons (FFs). It is shown here that the giants also stimulate a network of interneurons that make connections with the FFs. 2. This network includes an intraganglionic neuron, the segmental giant (SG), in each abdominal hemisegment and a number of intersegmental neurons, two of which (I2 and I3) were studied in detail. 3. The SGs are driven reliably by the giant fibers and they in turn drive the FFs of their hemisegment about as effectively as do the giant fibers themselves; it is possible that the giant fibers excite the FFs mainly by way of the SGs. The SGs also have an efferent first root axon whose peripheral targets we have been unable to determine. 4. I2 and I3 originate in the second and third abdominal ganglia, respectively, and descend to the last ganglion. In their ganglia of origin they are reliably driven by the giant fibers and by the SGs. In addition, I2 weakly excites I3 and both receive weak, apparently direct, excitatory input from FFs as well as less direct excitatory and inhibitory input from unidentified afferent sources. Both weakly excite most FFs in ganglia behind the one in which they originate. This excitation adds to that produced directly by giant fibers and SGs and, we believe, is sometimes decisive in causing FF firing. Their firing also causes inhibition involved in suppressing effects of reafference, as do the giant fibers themselves. 5. I3 strongly excites the motoneurons of certain tail fan muscles (the ventral and posterior telson flexors). However, the contraction of these muscles would be maladaptive during some giant fiber-mediated tailflips. Accordingly, when the giant fibers, which always recruit I3, fire, they cause an inhibition of the motoneurons that nullifies the excitatory input from I3. At a formal level this means that the giants, viewed as command neurons, not only drive but also alter or modulate the subordinate motor pattern-generating network that they control. 6. Tailflips that are less stereotyped than those mediated by giant fibers are known to occur without participation of the giants. It is suggested that the presence of complex circuitry mediating between giant fibers and FFs may be related to the use of portions of this circuitry as well as the FFs themselves in production of nongiant tailflips.

Animals↗
PubMed1978

Extrinsic control of intrinsic neuronal plasticity: an hypothesis from work on simple systems.

All advanced nervous systems use plastic properties of neurons for learning, remembering and achieving other information processing feats. Recent findings on a variety of relatively simple nervous systems or reduced parts of more complex ones suggest the notion that, in addition to having neurons with intrinsically plastic properties, nervous systems also have mechanisms for controlling the development, expression, and maintenance of changes in their inherently malleable neurons. This hypothesis has important implications for understanding both the brain's learning machinery and also aspects of nervous system organization not obviously related to learning.

Afferent Pathways↗
PubMed1977

Regenerating afferents establish synapses with a target neuron that lacks its cell body.

When the axons of crayfish tail-fan mechanoreceptor neurons are severed, the axons regenerate into the central nervous system and after 2 to 6 weeks reestablish functional contacts with their standard interneuronal target cells. Removal of the cell body and hence the genes of the largest of these interneurons does not interfere with the successful reestablishment of synapses between it and its afferents.

Action Potentials↗
PubMed1977

Survival of functional synapses on crustacean neurons lacking cell bodies.

Previous workers have demonstrated that some crustacean neurons remain capable of spike propagation and transmitter release and replenishment for months after removal of their perikarya. Here, it is shown that postsynaptic reactions to chemical synaptic input can also persist for months after removal of the soma of the postsynaptic neuron. Interneuron A of the crayfish abdominal cord receives chemically transmitting terminals of ipsilateral tactile afferents of the tail fan. The neuron's soma lies contralateral to its axon and dendrites at the caudal margin of the last abdominal ganglion. The region containing the soma was removed. Interneuron A unambiguously identified by receptive field, location, and size, survived and continued to respond sensitively to tactile input in better than 50% of the cases examined for more than 8 weeks. Cobalt filling of the active fiber in several 8-week-old preparations ruled out the possibility that the severed neurite had reconnected with a foreign soma.

Animals↗
PubMed1977

Protection from habituation of the crayfish lateral giant fibre escape response.

1. Habituation of the lateral giant fibre escape response in the crayfish to repetitive tactile stimuli is believed to result from homosynaptic depression at the first synapse of the reflex, between tactile afferents and interneurones. Normally, habituation of escape responses to repeated innocuous stimuli is presumed to be adaptive. Experiments reported here were undertaken to determine whether habituation would occur under circumstances when it would presumably be maladaptive - in particular, when tactile receptors are stimulated by an animal's own tail-flip movements.2. Experiments were carried out on the crayfish isolated abdominal nerve cord, which contains the lateral giant reflex pathway.3. Compound e.p.s.p.s elicited in the lateral giant by electrical stimulation of tactile afferents decline by from 25 to 36% over a series of eleven trials at 1/5 sec (control series).4. To determine whether such a decline would occur when sensory afferents are stimulated during a ;tail-flip', stimuli were given as in the control series but each stimulus occurred 20 msec after direct electrical stimulation of a medial giant or lateral giant escape-command fibre at which time tail flexion movements of an intact animal would be in progress. Under these conditions% e.p.s.p. decline over 11 trials at 1/5 sec was only 16-45% of that occurring on the control series.5. This protective effect starts at about 10 msec after escape command neurone firing, is maximal at 20 msec, and thereafter declines, remaining weakly detectable at 100 msec. This time course is commensurate with that required for execution of a tail-flip movement. Thus, sensory afferent-to-lateral giant transmission is protected from depression if stimuli occur when a tail-flip movement is or should be occurring.6. Giant fibre spikes do not superimpose facilitation upon a depressed reflex pathway, nor accelerate rate of recovery from depression; rather, protection is attributable to actual prevention of development of the depressed state.7. Protection was also examined at the first synapse of the reflex, where the depression responsible for habituation is believed to occur, by recording intracellularly in the largest of the first-order interneurones (interneurone A) of the pathway. In absence of protection, ten stimuli presented at 1/4 sec caused a mean decline of 32% in the e.p.s.p. in interneurone A. When such stimuli followed directly evoked escape command neurone firing by 20 msec this decline was reduced by 59-100%.8. We suggest that protection serves to prevent crayfish from habituating to stimuli produced by their own tail-flip movements.

Action Potentials↗
PubMed1977

Presynaptic inhibition: the mechanism of protection from habituation of the crayfish lateral giant fibre escape response.

1. Mechanism of protection from habituation of the lateral giant escape reflex of the crayfish was studied. Experiments were designed to determine whether presynaptic inhibition of primary afferents for the reflex occurs following escape command neurone firing, and if so, whether it could account for protection of the first synapse from depression. 2. Synaptic transmission between afferents and interneurone A of the escape reflex is strongly inhibited following giant fibre spikes. 3. Giant fibre firing results in post-synaptic inhibition of interneurone A. However, inhibition of afferent input to interneurone A consistently outlasts both i.p.s.p.s and post-synaptic conductance increases in the neurone; the inhibition, therefore, is probably not exclusively post-synaptic. 4. Giant fibre firing results in excitability changes in sensory afferent terminals as measured by the amplitude of antidromic compound action potentials to focal electrical stimuli applied in the region of afferent terminals in the last abdominal ganglion. The time course of this effect parallels those of protection and inhibition of the first synapse. 5. The magnitude and time course of protection and inhibition of transmission to interneurone A parallel each other closely. Both processes considerably outlast measurable signs of post-synaptic inhibition. 6. We conclude that following giant fibre activity the first synapse of the lateral giant reflex is presynaptically inhibited and the presynaptic inhibition is responsible for the protection effect described in the preceding paper.

Action Potentials↗
PubMed1975

Habituation and inhibition of the crayfish lateral giant fibre escape response.

1. Decrement of the lateral giant fibre escape response was studied in intact, restrained, crayfish and in those with the ventral nerve cord transected at the thoracic-abdominal level. 2. Taps (delivered at rates of 1 per 5 min to the abdomen) depressed responsiveness to about 50% of its inital value in 10 trials, for both intact and operated animals. 3. With additional stimulation, responsiveness dropped to near zero for both groups. Recovery was negligible 2 h later, but nearly complete after an additional 24 h rest. 4. Protection against response decrement in this situation was obtained by directly activating the cord giant fibres 30 msec prior to the tactile stimulus. The directly-elicited giant fibre spikes which follow the tactile stimulus do not influence the course of response decrement. 5. The results establish the decrement as centrally mediated habituation, and minimize the role of receptor alterations or descending neuronal influences in the behavioural change. 6. A comparison is made between the properties of hibituation and the homosynaptic depression of afferent to interneurone synapses that is presumed to be the physiological mechanism of habituation in this situation.

Animals↗
PubMed1975

Extrinsic modulation of crayfish escape behaviour.

Extrinsic systems were shown to control the excitability of the neurones which mediate tail-flip escape in the crayfish. Restraint suppresses the escape mediated by giant fibres and some, but not all, categories of non-giant mediated escape; autotomy of claws increases the excitability of non-giant mediated escape without affecting the lateral giant reflex. The effects of restraint on the lateral giant reflex result from inhibition rather than reduced facilitation. The inhibition descends from thoracic and higher levels, and the lateral giant escape command neurone appears to be its primary target. Inhibition may serve to shift the control of escape behaviour from short latency 'reflex' systems to more flexible 'voluntary' ones which can produce responses at times most opportune for successful escape.

Action Potentials↗
PubMed1973

Habituation: regulation through presynaptic inhibition.

During tail-flip escape responses of crayfish, synaptic transmission at the habituation-prone synapses of the lateral giant reflex pathway is presynaptically inhibited. This prevents transmitter release and all subsequent postsynaptic actions and spares the reflex from becoming habituated to stimuli produced by an animal's own escape movements. These observations demonstrate the existence of a control circuit whose adaptive function is to regulate the malleability of inherently plastic synapses. They also suggest that regulation of plasticity could be a common use of presynaptic inhibition.

Action Potentials↗