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)     

Changes in firing behaviour of an insect motor neurone during development and following experimental surgery

The firing behaviour of an identified neurone in the cricket was studied using extracellular recording from the axon. In the last nympal instar (preadult developmental stage), the contralateral dorsal longitudinal motor neurone (CDLM) showed spontaneous activity and was excited by air puffs to the head and cerci and by single shocks to the anterior nerve cord. In the normal adult the CDLM did not exhibit these properties. However, responses which were characteristic of the last instar appeared in the adults which had been subjected to any one of the following surgical procedures: (1) central nervous system injuries which separated the CDLM arborization and axon from the soma; (2) operations which injured the central nervous system without cutting the CDLM; and (3) operations which damaged the cuticle only. Since cuticle damage alone was as effective as the more extensive operations, it is suggested that a sufficient cause for the appearance of nymphal firing behaviour in the adult CDLM is cuticle damage. The factor associated with cuticle damage which mediates the changes in activity of the CDLM neurone is not known, but its action does not require the mediation of the CDLM soma.     

Modelling nonlinear integration of synaptic signals by neurones

Neurones with active conductance on dendrites integrate synaptic signals and modulate generation of axon spikes in a nonlinear way. Owing to experimental difficulties, modelling provides invaluable insight for the comprehension of neurone behaviour particularly when dendrites are excitable. We used experimental data obtained for the Anterior Gastric Receptor neurone (AGR neurone), which controls the lobster gastric mill activity, to derive a set of partial differential equations for the membrane voltage. Simulation showed that upon varying the intensity of stimulation on the dendrite, the response pattern between dendrites and axon activity continuously changes. In addition, when only half of the dendritic tree is active, axon firing exhibits regular oscillations and bursting activity. We discuss these results in relation with the experimental work done on the AGR neurone.     

Behavioral specialization of cortical and hypothalamic neurons in the rabbit

Behavioural specialization was analyzed of hypothalamic and limbic neurones, with their activity recorded in rabbits during food-acquisition behaviour. The neurones with activity changed during staying of the animal in a definite place of the cage or during behavioural acts, characteristic of a specific behaviour in the cage, are considered as specialized in relation to the most "new" systems, acquired by the rabbit directly during learning of the given behaviour. Neurones with the activity changed with rabbit's turns, i.e. connected with behavioural acts, which the rabbit has not specially learnt, are considered specialized in relation to more "old" inborn systems. Neurones, in which no constant connection with any part of the studied behaviour was observed, are related to the most "ancient" systems. Comparison of the number of hypothalamic and limbic neurones of different groups showed that in the cortex there were some more neurones specialized in relation to behavioural acts, which were formed directly during learning of the rabbit in the experimental cage.     

Vital investigation of the genome activity and neuronal synaptic plasticity in snail in the course of learning

Vital investigation of genome activity and its role in mechanisms of long-term synaptic plasticity formation were studied in LP11 neuron (command neurone of defence behaviour) during sensitisation (simple form of learning) in semi-intact preparation of snail Helix lucorum. Genome activity was investigate by means of specific fluorescent dye SYTO 16 and image analysis system. It was found that application of sensitizing stimulation (10% quinine solution) onto the snail head initiate two-phase changes in neural responses evoked by tactile or chemical stimulation. Depression of neural responses was obtained during short-term phase (during 1 hour after sensitization) and facilitation of neural responses--during long-term phases (over 1 hour). At the same time (15-20 min after learning), a significant increase in SYTO 16 fluorescent level was found in nucleus site LP11 neurone. Initial SYTO 16 fluorescence level was registered in 4-5 hours after sensitization. If the sensitization was produced during actinomycin D application (inhibitor of RNA synthesis, 20 microM) then facilitation of neural responses evoked by sensory stimulation were suppressed during long-term phase of sensitization and was the same as in control sensitized snails during short-term phase of learning. Increase in SYTO 16 fluorescence level in nucleus region site of LP11 neurone was completely prevented in sensitization during actinomycin D application. If actinomycin D was applied 30 min after sensitization (1 hour after first sensitizing stimulation) then synaptic facilitation and fluorescent dynamics was the same as in control sensitized snails. Our experimental data showed that nociceptive sensitization development was followed by quick (15-20 min) DNA activation and long-term synaptic facilitation (1 hour after sensitization), while induction of the processes was suppressed by inhibitor of RNA synthesis during short time interval (during 1 hour of learning).     

The effects of two novel objects on the behavior of singly caged adult rhesus macaques.

Six female and six male adult rhesus macaques were given sticks and nylon balls as an attempt at simple cage enrichment. A latin square design was used to compare behavior during separate 4-week periods with each object and during a control period with no object. Frequency and duration of 15 different behaviors were recorded. Resting was the most common activity which decreased slightly in duration when the stick or nylon ball was present (P less than 0.02). The mean duration of stick use was longer than that of the nylon ball (P less than 0.01). No other behaviors changed significantly, including the frequency of abnormal behaviors such as self-abuse, stereotypic acts, and bizarre postures. Generally, these objects were used infrequently and led to few changes in the behavior of singly-caged adult rhesus macaques. However, they did appear to stimulate activity for some individuals.     

Role of a goal in determining neuronal activity of the motor and visual areas of the rabbit cortex

In experiments on alert rabbits neuronal activity of the motor and visual cortical areas was studied in behavioural acts (BA) of grasping of a piece of plastics (P) and carrot (C) from consequently presented cups of the feeder; the animal had an opportunity to seize a C piece only after grasping and taking away from the previous cup the P piece. "Visual environment" in which BA were realized were identical; P and C pieces were identical in form and visual characteristics. Records were made of unit activity (201 cells), animal's movements (photoelectric method), EMG of the m. masseter; in parallel videorecords of behaviour were carried out. BA of P and C pieces grasping were identical in electromyo- and actographic characteristics; motor composition of these BA did not differ. 61 neurones were activated in both BA, 5--only in BA of P piece grasping, 22--only in BA of C piece grasping, i. e. 30% of neurones were activated only in one of the compared BA. Characteristics of activations, appearing in both acts could be significantly different: different frequency, connection with different stages of the compared BA. The obtained data are determined by changes of the motor and receptive fields of neurones in one BA in comparison to another, and are considered as an evidence supporting the suggestion that appearance of cortical neurones' activations in behaviour depends on BA goal and is not strictly determined by the parameters of movements and environment.     

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.     

Electrical activity in the vagus nerves and some medullary nuclei in rats: Changes induced by endotoxin action and hyperthermia evoked by an increase in ambient temperatures

Acute experiments on rats showed that intraperitoneal administration of 5 μg/kg of a bacterial toxin (pyrogenal) increases the afferent impulsation frequency in the cervical segments of vagus nerves, VN (multifiber recording), and frequency of the multineuronal activity in the solitary tract nucleus (STN); these changes were observed during the whole period of recording (10–160 min following toxin injection). Enhancement of the efferent impulsation in the VN and neuronal activity in the dorsal nucleus of the vagus nerve (DNVN) could be observed only 120–130 min after toxin administration. Under these conditions rectal temperature in experimental animals was 1.5° higher than that in control rats throughout the period of recording. Following subdiaphragmatic vagotomy, the afferent impulsation frequency in the cervical VN decreased about four times and kept on decreasing during the whole period of registration. Pyrogenal introduction evoked no changes in the direction of reactions to vagotomy. Under these conditions, body temperature of these animals was 2.5°C higher than in control vagotomized rats by the final stage of recording. Animal heating in a chamber caused no changes in the afferent impulsation frequency and resulted in a decrease in the frequency of VN efferent discharges. Involvement of the VN in the maintenance of temperature homeostasis during fever induced by the endotoxin action and by hyperthermia due to a rise in ambient temperature is discussed. Neirofiziologiya/Neurophysiology, Vol. 32, No. 2, pp. 112–119, March–April, 2000.     

Mechanisms of association learning in the post-synaptic neurone

A general mechanism for association learning in neurones is presented based on the biochemistry and electrophysiology of synaptic receptor regions. The mechanism involves the voltage sensitive generation of second messengers in the post-synaptic neurone, and their subsequent influence on the sensitivity of the local receptor region. The mechanism is examined in detail using a computer model of the reaction dynamics of two important synaptic receptors; the adrenergic receptor and the NMDA-type glutamate receptor. The computer model simulates concentration changes of several molecules in the post-synaptic neurone following an input to a receptor. It also models changes in membrane potential caused by the cell firing, and allows for the impact of these potential changes on second messenger generation within the cell. Finally the model incorporates two possible mechanisms whereby high concentrations of second messenger can lead to long-lasting changes in receptor sensitivity. The model demonstrates an enhancement of synaptic response when previous inputs to the same receptor region have occurred when the cell was firing. Using the model, long term potentiation (LTP) of the glutamate response is demonstrated following a high frequency input to the glutamate receptor. A neurone with ten glutamate receptors is simulated and demonstrates that individual neurones should be capable of recognising patterns of input activity when those patterns have repeatedly occurred at times of major cellular activity.     

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.     

Proprioceptive feedback in locust kicking and jumping during maturation

Campaniform sensilla monitor the forces generated by the leg muscles during the co-contraction phase of locust (Schistocerca gregaria) kicking and jumping and re-excite the fast extensor (FETi) and flexor tibiae motor neurones, which innervate the leg muscles. Sensory signals from a campaniform sensillum on the proximal tibia were compared in newly moulted locusts, which do not kick and jump, and mature locusts which readily kick and jump. The activity pattern of FETi during co-contraction was mimicked by stimulating the extensor tibiae muscle. Less force was generated and the spike frequency of the sensory neurone from the sensillum was significantly lower in newly moulted compared to mature locusts. Depolarisation of both FETi and flexor motor neurones as a result of sensory feedback was consequently less in newly moulted than in mature locusts. The difference in the depolarisation was greater than the decrease in the afferent spike frequency suggesting that the central connections of the afferents are modulated. The depolarisation could generate spikes in FETi and maintain flexor spikes in mature but not in newly moulted locusts. This indicates that feedback from the anterior campaniform sensillum comprises a significant component of the drive to both FETi and flexor activity during co-contraction in mature animals and that the changes in this feedback contribute to the developmental change in behaviour.Abbreviations aCS anterior campaniform sensillum - ETi extensor tibiae - FETi fast extensor tibiae motor neurone - FlTi flexor tibiae - pCS posterior campaniform sensillum     

An approach to the study of neural activity during behaviour in insects

A method is described for easily recording neural activity from the central nervous system of a suspended cockroach while the animal can still walk, groom, and perform other acts. Recordings revealed that some giant fibre units are active during spontaneous walking. The preparation should be especially useful in further studies of the neural basis of behaviour.     

A Statistical Analysis of the Continual Activity of Single Cortical Neurones in the Cat Unanaesthetized Isolated Forebrain

Statistical analyses are applied to records obtained under conditions of spontaneous activity. These demonstrate that all the cells examined are similar in the respect that their signals are composed of an approximately Poissonian shower gated on and off at random instants. A mathematical model is developed on this basis which characterises the signal of any one neurone with a number of simple parameters. The manner in which these parameters change under various types of stimulation is studied. It is found that the average frequency inside the sections of Poisson shower remains unchanged in all cases examined. Implications as to the types of network involved are discussed.     

Tonic component of the conditioned reflex process and its functional role

Tonic background activity of 266 neurones in the hippocampus and different neocortical areas was studied in freely moving rabbits in the process of defensive and food instrumental conditioned performance and during switching-over of instrumental and classical food and defensive reflexes. Associations of CS and reinforcement evoke background activity changes in most of recorded cortical neurones preceding the development of other conditioned manifestations. Conditioned reflex was performed only after reaching the background firing rate of almost every examined neurone optimal for its realization. The performance of different conditioned reflexes was associated with different background activity levels of cortical neurones. The above mentioned data form the experimental basis for the identification of the tonic component in conditioned process which reflects tonic character of temporary connection formation and function.     

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.     

Physiological properties of sympathetic preganglionic neurones in the thoracic intermediolateral nucleus of the cat

Extracellular spikes were recorded from cell bodies of sympathetic preganglionic neurones in spinal segments T1-T3 of the cat. Each neurone was identified by its antidromic response to electrical stimulation of the sympathetic chain and was found in histological sections to lie within the intermediolateral nucleus. Physiological properties studied in detail included basal activity, spike configuration, and latency of antidromic activation. Also studied, in tests with paired stimuli, were the threshold interstimulus interval evoking two responses, as well as changes in amplitude and latency of the second spike which occurred at intervals near this threshold. Approximately 60% of the units studied were spontaneously active, the rest were silent. Spontaneous activity was characterized by a slow (mean = 3.1 +/- 2.6 (SD) spikes/s), irregular pattern of discharge. With approximately one-third of the cases there was a periodic pattern of discharge in phase with oscillations in blood pressure. This correlation of phasic activity suggests that many of the units studied were involved specifically in cardiovascular function. Silent and spontaneously active units could not be differentiated on the basis of latency of antidromic activation or threshold interstimulus interval; mean latency for the two groups was 7.2 +/- 4.9 ms, mean threshold interval was 6.4 +/- 4.7 ms. Thus, with the exception of basal activity, the physiological properties studied failed to indicate more than a single population of neurones. These results therefore suggest that the sympathetic preganglionic neurones in the intermediolateral nucleus subserving varied autonomic functions share overlapping physiological properties, and that functional differentiation of these neurones may be based on differences in synaptic inputs.     

Male urine signals social rank in the Mozambique tilapia (Oreochromis mossambicus)

Background  

The urine of freshwater fish species investigated so far acts as a vehicle for reproductive pheromones affecting the behaviour and physiology of the opposite sex. However, the role of urinary pheromones in intra-sexual competition has received less attention. This is particularly relevant in lek-breeding species, such as the Mozambique tilapia (Oreochromis mossambicus), where males establish dominance hierarchies and there is the possibility for chemical communication in the modulation of aggression among males. To investigate whether males use urine during aggressive interactions, we measured urination frequency of dye-injected males during paired interactions between size-matched males. Furthermore, we assessed urinary volume stored in the bladder of males in a stable social hierarchy and the olfactory potency of their urine by recording of the electro-olfactogram.     

Behavioural changes are related to moult regulation in the cockroach, Periplaneta americana

Abstract. Larval holometabolous insects show changes in behaviour (e.g. start of wandering and spinning) in specific periods of the moulting cycle in relation to definite ratios of juvenile hormone and moulting hormone (ecdysone). In hemimetabolous insects no such changes in behaviour are known. It should be investigated whether the cockroach Periplaneta americana shows changes in locomotor activity and in food and water consumption in relation to periods of ecdysone production during the last larval stage. Within a mean duration of the last larval stage of 30 days there were two periods of reduced locomotor activity: on day 9 and between days 13 and 17. From days 12–13 food consumption decreased by c . 40% up to the day 18. Water consumption decreased between days 9 and 18 by about 55%. Peaks of ecdysone production appeared after these changes of behaviour in each case. Therefore in larval Periplaneta ecdysone seems not to trigger these behavioural changes.     

Effects of hypothalamic releasing hormones and biogenic amines on identified neurones in the circumoesophageal ganglia of the water snail (Planorbis corneus)

1. The effect of locally applied releasing hormones, thyrotropin-releasing hormone (TRH) and luteinizing-hormone-releasing hormone (LHRH) and the putative neurotransmitters, acetylcholine (ACh) and dopamine (DA), on the neuronal excitability of identified invertebrate giant dopaminergic neurone (GDN) and serotoninergic neurone (5-HT) (Planorbis corneus) were investigated by intracellular recording in vitro. 2. The membrane potential of GDN was of the order of -60 to -70 mV. The microiontophoretically applied substances produced membrane depolarization as well as spike activation. Their order of efficacy was as follows: TRH greater than ACh greater than DA greater than LHRH. 3. The effects of the tested TRH, ACh, LHRH and DA on serotoninergic neurones were less pronounced. 4. During ACh depolarization the membrane resistance of GDN was found to be strongly reduced, whereas TRH produced only a small reduction in membrane resistance. 5. Dihydro-beta-erythroidin (DHE) added to the bath solution reversibly blocked ACh depolarization without influencing TRH depolarization. Concentrations of atropine sulfate required to block the ACh depolarization were higher by at least 100 order of magnitude. 6. These effects are discussed in relation to the immunoreactive TRH detected earlier in the central nervous system of invertebrates and vertebrates. The results are consistent with the postulate that TRH acts as a neuromodulator and/or neurotransmitter on invertebrate and vertebrate neurones.