A biological model of the excitation of a second order sensory neurone

Summary Computer simulation of a relatively simple model can reproduce the main characteristics of the firing patters of some nerve cells. The abdominal stretch receptor of the crayfish has provided an analogous biological model. Synaptic input impulses were simulated by randomly distributed, short lasting transmembrane current pulses. Under these experimental conditions the stretch receptor neurone largely behaved as predicted by the computer simulations.     

The monosynaptic connection: the modulating effect of opioid peptides on the plasticity of presynaptic neurons and identified synapses]

Study of opioid peptides (leucine-enkephalin and methionine-enkephalin) action on plastic properties of the system of monosynaptically connected neurones LPa7--LPa3, PPa3 and LPa8--LPa3, PPa3 was conducted in the snail brain. It has been shown that all three links in the system studied (presynaptic neurone, postsynaptic neurone and synapse) manifest one and the same type of plasticity--habituation to rhythmic stimulation. Enkephalins have a modulating action on plastic properties of the presynaptic neurone and synapse: they retard the habituation of the presynaptic neurone to intracellular stimulation and retard the development of habituation at synaptic level. However, changes in the character of postsynaptic response in the presence of enkephalins are not a direct consequence of their influence on plastic properties of the presynaptic neurone. Besides, enkephalines reduce the effectiveness of synaptic transmission in the given system: they reduce EPSP duration in the postsynaptic neurone.     

Giant polyfunctional neuron of the edible snail

The structure of the receptive field of LPa3 neurone and its connection with the periphery were studied on semi-intact preparations of the snail Helix pomatia. It was found that: 1) The mechano-sensitive receptive field (excitatory) of the LPa3 neurone occupies nearly the whole surface of the snail's skin and internal organs. But latencies of LPa3 reactions to mechanical stimulation, the whole field may be divided into four zones: 50 to 60 ms, 100 ms, 130 to 140 ms and 200 to 250 ms. 2) Blockade of synaptic transmission with magnesium or cobalt has shown that relaying of the signal from the mantle receptors to the LPa3 neurone takes place in the peripheral nervous system. 3) Cobalt ionophoresis showed that the LPa3 neurone gives off processes to the right and left pallial nerves, the anal nerve and, occasionally, to the cutaneous nerve. During simultaneous intracellular recording from the LPa3 neurone and extracellular from the above nerves, action potentials are in every case recorded at first in the neurone body, and then, with a 20 to 30 ms delay, in the nerves. This means that the LPa3 neurone processes joining the nerves are axons. It is suggested that the sensory inputs and wide branching structures output of the LPa3 neurone axons make it an integrating polyfunctional system.     

A hybrid computer model of stochastic activity of the neurone

The authors describe a hybrid computer neurone model intended for the investigation of stochastic transformations effected by neurones in correlation to some of their physiological parameters. The model is designed so as to give the best possible characterization of the internal dynamics of a neurone with minimum limiting conditions. It allows the generation of suitable input stochastic processes or operates with input processes obtained experimentally in the living neurone and it carries out basic statistical tests of the output stochastic process.     

Identified motor neuron closing the neurostome as a component of the defensive reaction of Helix pomatia

In the suboesophagal complex of Helix pomatia, a neurone (LPa33) was identified as a member of the system of neurones which trigger the defensive behaviour, one of the most responsive components of which is the reaction of the pneumostome closing. Spike activity of the LPa33 unit triggers the pneumostome closing in the form of a coordinated reaction of certain pneumostome muscles, which compose the neurone motor field. It is suggested that neurone LPa33 innervates separate muscles of its motor field directly with its axones.     

Organization of the sensory input of command neurons

Dynamics of habituation of synaptic responses to tactile stimulation of the snail skin was used as a criterion for defining organization of the receptive field of an escape behaviour command neurone. It was shown that every command neurone had its own specific nonhabituating area of the receptive field while the size of the field was common to all command neurones - it comprised the whole skin surface. The receptive field of a command neurone system is not homogeneous in structure. Areas corresponding to ecologically significant regions can be singled out by the maximal response amplitude and low rate of habituation.     

The physiological construction of the neurone concept (1891-1952)

Steps in the physiological construction of the neurone concept are described. Early ideas on the function of the nerve cell led to later polemics on the neurone doctrine and the speculative attitude of histophysiology. Researches of Sherrington and Adrian emerged from a specific British context, and confronted American oscillography and Berger rhythm. At the end of various polemics, the neurone was constructed by the intracellular technique and the use of concepts borrowed from other sub-disciplines. Analysis of these paths demonstrates underlying disciplinary interactions as essential factors.     

Neural responses to depth-motion stimulation in a horizontally sensitive interneurone in the optic lobe of the blowfly (Phormia terraenovae)

The neural responses to depth-motion stimulation have been investigated in a higher-order interneurone in the optic lobe of the blowfly. The optical stimulus was generated by an outline square or elements of a square moving in real depth. Extracellular, single-unit recording and signal-averaging techniques show that this neurone is velocity coding assuming different delay constants for the excitatory and inhibitory processes. There is no systematic response to the second derivative but a partial response in the excitatory range to the third derivative of motion. The neurone responses to motion in the horizontal direction but not in the vertical direction. When there is simultaneous motion in the preferred and non-preferred directions the neurone reacts systematically with excitation to motion in depth toward the eye, and with inhibition during motion away from the eye. This response is restricted to the frontal part of the eye while in the periphery excitation and inhibition cancel each other. The status of this neurone in the process of motion perception is discussed.     

Auditory neurones in the brain of the cricket Gryllus bimaculatus (De Geer): Ascending interneurones

Two types of auditory interneurone which ascend from the prothoracic ganglion to the brain in the cricket Gryllus bimaculatus (De Geer) are described. Intracellular recordings were made from the axons of the neurones in the brain under closed-field stimulus conditions and the recorded cells then stained with either cobalt or Lucifer Yellow. Both neurone types—the Plurisegmental ascending low frequency neurone 1 (PALF1), and the Plurisegmental ascending high frequency neurone 1 (PAHF1)—show response characteristics which would make them well suited to encoding the conspecific calling and courtship songs respectively. Further, the projection areas of both neurone types in the brain overlap those of previously identified intraganglionic interneurones, particularly in the anterior-ventral protocerebrum, and it is suggested that an auditory neuropile may exist in this region.     

The formation of the area centralis of the retinal ganglion cell layer in the chick

In adult domestic chickens, the neurones in the retinal ganglion cell layer are very unevenly disposed such that there is a sixfold increase in neurone density from the retinal edge to the retinal centre. The formation of the high ganglion-cell-density area centralis was studied on chick retinal wholemounts from the 8th day of incubation (E8) to 4 weeks after hatching (4WAH). The density of viable neurones and the number and the distribution of pyknotic neurones in the ganglion cell layer were estimated across the whole retina. Between E8 and E10, the distribution of neurones in the ganglion cell layer was anisodensitic with 53,000 mm-2 in the centre compared to 34,000 mm-2 in the periphery of the retina. Thereafter, a progressively steeper gradient of neurone density developed, which decreased from 24,000 mm-2 in the retinal centre to 6000 mm-2 at the retinal periphery by 4WAH. Neuronal pyknosis in the ganglion cell layer was observed between E9 and E17. From E11 onwards, consistently more pyknotic neurones were found in the peripheral than in the central retina. It was estimated that over the period of cell death approximately twice as many neurones died per unit area in the retinal periphery than in the centre. Retinal area measurements and estimation of neurone densities in the ganglion cell layer after the period of neurone generation and neurone death indicated differential retinal expansion, with more expansion in the peripheral than in the central retina. These observations allow us to conclude that the formation of the area centralis of the chick retina involves (1) slightly higher cell generation in the retinal centre, (2) higher rate of cell loss in the retinal periphery and (3) differential retinal expansion.     

A model of localized iconic memory, replicable and associative, using time sharing and 3 neuronal communication modes

A model is proposed for the functioning of an iconic memory involving several layers of neurones. A small group of neurones in one layer project their terminations over the terminations of a single neurone of the superior layer. According to the communication mode (emission or reception), a neurone in one layer can memorize the state of the terminations of a neurone of the superior layer, or impose on the latter the state of its own terminations. In the comparison mode, an emitting neurone compares its state to another emitting neurone and, in case of sufficient similarity, switches to the reception mode (associative recall). The first layer, corresponding to short-term memory, communicates with the cells involved in the representation of the perceived image. This model makes possible the establishment of a correspondence between a percept and a neurone, the replication of memorized configurations, the restructuration of memory and, starting with a percept or a memorized item, the integral associative recall of all similar memorized items.     

Injection of glyoxylate ions from the recording microelectrode for the fluorescent microscopic detection of neuronal monoamines

To make it sure that a physiological experiment is carried out on the monoaminergic neurone, we propose to fill the intracellular recording glass microelectrode with 2 M solution of potassium glyoxylate, with pH 6.0. After the experiment is over, glyoxylate ions are injected ionophoretically into the neurone, and then the specimen is dried in the air and heated to obtain fluorescence of a cellular monoamine, if it is present in the cell. Some details of the method are described.     

Non-spiking local interneurones mediate abdominal extension related descending control of uropod motor neurones in the crayfish terminal abdominal ganglion

The role of non-spiking local interneurones in the synaptic interactions between abdominal extension-evoking descending interneurones and uropod motor neurones in the terminal abdominal ganglion of the crayfish Procambarus clarkii (Girard) was investigated electrophysiologically. Continuous electrical stimulation of the lateral region of the 3rd-4th abdominal connective that included abdominal extension evoking interneurones excited the opener motor neurones and inhibited the closer, reductor motor neurone. Spikes from a single descending interneurone evoked consistent and short latency (0.8–0.9 ms) excitatory postsynaptic potentials (e.p.s.ps) in the opener motor neurones, and evoked rather long-latency (1.5–2.7 ms) inhibitory postsynaptic potentials (i.p.s.ps) in the reductor motor neurone. Many non-spiking interneurones also received depolarizing p.s.ps (0.8–2.5 ms in latency) that were usually faster than i.p.s.ps of the reductor motor neurone if both neurones were recorded sequentially in the same preparation. Non-spiking interneurones received convergent inputs from several descending interneurones and made inverting connection with the reductor motor neurone. Elimination of descending inputs to a particular non-spiking interneurone could reduce the inhibitory response of the reductor motor neurone. These observations strongly suggested that descending inhibitory inputs to the closer, reductor motor neurone were mediated by non-spiking interneurones. Furthermore, some non-spiking interneurones made output connections with the opener motor neurones. The disynaptic pathway through non-spiking interneurones is significant to control and modulate the opening pattern of the uropod during abdominal extension. Accepted: 27 December 1996     

Inhibitory effects of dipeptides containing tryptophan on the excitability on the giant neuron of the giant African snail (Achatina fulica, Ferussac)]

Besides an inhibitory effect of L-Lys-L-Phe-L-Tyr and L-Phe-L-Tyr, L-Phe-L-Trp showed the same effect on the excitability of a giant neurone (the TAN, tonically autoactive neurone) identified in suboesophageal ganglia of Achatina futica Férussac. The critical concentration of L-Phe-L-Trp to produce the effect was 10(-5)--3 X 10(-5) kg/1. The inhibitory effect of this substance was relatively slow and independent no chloride ions, as well as in the case of L-Phe-L-Tyr. L-Trp-L-Phe, Gly-L-Trp and L-Trp-Gly did not show any effect on the same neurone. The I-V curve of the TAN's neuromembrane, measured by the injection of a transmembrane triangular current, were not modified markedly by L-Phe-L-Trp at 4 X 10(-4) kg/1. The pattern of the TAN's spike firing produced by the depolarizing current injection were not influenced by this substance.     

THE EFFECT OF SPIKE ACTIVITY VERSUS SYNAPTIC ACTIVATION ON THE METABOLISM OF RIBONUCLEIC ACID IN A MOLLUSCAN GIANT NEURONE

—Previous experiments on a giant neurone (R2) from Aplysia californica have shown that a prolonged electrical stimulation of ganglionic nerves, strong enough to elicit post-synaptic spikes in the giant neurone, caused a marked increase in the uptake of labelled nucleosides into the neuronal RNA. The results described in the present paper very strongly indicate that these effects of synaptic activation were not due to the discharge of spikes in the giant neurone itself. Spikes which were directly elicited in the giant neurone by current pulses injected into the cell through an intracellular microelectrode had no significant effect on RNA labelling. Weak stimulation of ganglionic nerves, eliciting post-synaptic potentials but few spikes in the giant neurone, produced a small but significant increase of RNA labelling.     

An assessment of the manifestation of the functional connections between brain structures]

Responses of hypothalamic neurons to single (1/s, 20 impulses) stimulation of the prefrontal (area 8), cingulum (area 24), periamygdaloideus (RPA) cortex and hippocampus (field CA3) were studied on experimental cats anesthetized with ketamine. The routine elaborated for IBM PC/AT 386 provided: 1) selection of such neurone reaction with the latent period variation less than its length per the set value (5-20%); 2) selection of repeated neurone reactions with the same variability of latent periods from 20 cortical stimuli; 3) ranging of neurone reactions according to these indices. Quantitative estimation of the priority ranges made it possible to determine the profundity of the functional relations between the cerebral structures.     

Information processing at a central synapse suggests a noise filter in the auditory pathway of the noctuid moth

1. The central projections of the A1 afferent were confirmed via intracellular recording and staining with Lucifer Yellow in the pterothoracic ganglion of the noctuid moths, Agrotis infusa and Apamea amputatrix (Fig. 1). Simultaneous recordings of the A1 afferent in the tympanal nerve (extracellularly) and in the pterothoracic ganglion (intracellularly) confirm the identity of the stained receptor as being the A1 cell. 2. The major postsynaptic arborizations of interneurone 501 in the pterothoracic ganglion were also demonstrated via intracellular recording and staining (Fig. 2). Simultaneous recordings of the A1 afferent (extracellularly) and neurone 501 (intracellularly) revealed that each A1 spike evokes a constant short latency EPSP in the interneurone (Fig. 2Bi). Neurone 501 receives only monaural input from the A1 afferent on its soma side as demonstrated by electrical stimulation of each afferent nerve (Fig. 2Bii). EPSPs evoked in neurone 501 by high frequency (100 Hz) electrical stimulation of the afferent nerve did not decrement (Fig. 2Biii). These data are consistent with a monosynaptic input to neurone 501 from the A1 afferent. 3. The response of neurone 501 to a sound stimulus presented at an intensity near the upper limit of its linear response range (30 ms, 16 kHz, 80 dB SPL) was a plateau-like depolarization, with tonic spiking activity which continued beyond the end of the tone. The instantaneous spike frequency of the response was as high as 800 Hz, and was maintained at above 600 Hz for the duration of the tone (Fig. 3). 4. The relationship between the instantaneous spike frequency in the A1 afferent and that recorded simultaneously in neurone 501 is linear over the entire range of A1 spike frequencies evoked by white noise sound stimuli (Fig. 4). Similarly, the relationship between instantaneous spike frequency in the A1 afferent and the mean depolarization evoked in neurone 501 is also linear for all A1 spike frequencies tested (Fig. 5). No summation of EPSPs occurred for A1 spike frequencies below 100 Hz.(ABSTRACT TRUNCATED AT 250 WORDS)     

Organization of motoneurones in the prothoracic ganglion of the cockroach Periplaneta americana (L.).

The location within the prothoracic ganglion of neurone somata with axons in identified peripheral nerves is examined by the cobalt iontophoresis technique. Axons are filled with cobalt by diffusion through their cut ends and the cobalt is then precipitated as the black sulphide inside the neurone. It is assumed that neurones with axons in peripheral nerves and somata in central ganglia are either motor or neuro-secretory. Fifteen nerves are examined and maps of the location of somata with axons in each nerve are presented. The axon distribution in peripheral nerves of three common inhibitory neurones is described. Dendritic morphology of one common inhibitory neurone and two coxal depressor motoneurones is illustrated. It is proposed that some individual neurones can be reliably identified from their soma dimensions and location within the ganglion. The number of motoneurones with somata in the prothoracic ganglion and their homology with cells in the other thoracic ganglia are discussed.     

Reformation of specific neuromuscular connections during axolotl limb regeneration: evidence that the first contacts are correct

Retrograde neuronal tracing with horseradish peroxidase was used to determine the position in the spinal cord of the motor neurone pools of a proximal (biceps) and a distal (extensor digitorum) limb muscle at various times during axolotl limb regeneration. It was found that from the earliest stages of muscle redifferentiation (as judged by light and electron microscopic analysis) the vast majority of axons innervating the regenerating muscles came from cells within the bounds of the normal motor neurone pool for each muscle. A few incorrect projections were noted in that the regenerating proximal muscle was sometimes innervated by some cells caudal to its normal motor neurone pool. The results are discussed in terms of mechanisms that may be operating in the regenerating limb to ensure that specific neuromuscular connections are made.     

Neuronal mechanisms of learning in an in vitro Aplysia preparation: sites other than the sensory-motor neuron synapse are involved

Classical conditioning of the gill withdrawal reflex can be demonstrated in two different in vitro Aplysia preparations. The data obtained show that as conditioning of the gill withdrawal reflex proceeds there are changes in synaptic efficacy at the central sensory-motor neurone synapse. These changes in synaptic efficacy, however, are not necessary nor are they sufficient for the observed changes in gill reflex behaviour. Changes must be occurring at other loci within the nervous system to mediate the associative learning. We hypothesized, based on data obtained from one type of in vitro preparation, that changes occur in the ability of the motor neurone to elicit a gill withdrawal response as a result of classical conditioning training. In order to test this hypothesis we depolarized an identified gill motor neurone before and after classical conditioning and found that the motor neurone's ability to elicit a gill movement was facilitated following classical conditioning training. In control preparations that received an explicitly unpaired stimulus paradigm (which does not lead to classical conditioning of the reflex) there was a decrease in the efficacy of a gill motor neurone to elicit a gill withdrawal response. There are a number of possible sites within the integrated central (CNS) and peripheral (PNS) nervous systems where changes could occur to bring about the alterations in motor neurone efficacy. Our results suggest that changes in neuronal activity which underlie learning occur at multiple sites within the nervous system and that a complete understanding of the mechanisms of associative learning can only be obtained when all of these sites are taken into account.