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PubMed1987

Synaptic responses of red nucleus neurons in the alert cat to cortical and cerebellar inputs.

Postsynaptic potentials of neurons of the red nucleus (RN), evoked to stimulation of the sensorimotor region of the cerebral cortex and cerebellar nucleus interpositus, were studied in chronic experiments on alert cats by means of an intracellular recording technique. Movements of the animals were restricted by rigid fixation (through a special device previously attached to the head) of the animal's head on the frame of the stereotaxic apparatus. Rubrospinal neurons were identified according to their antidromic activation in response to stimulation of the rubrospinal tract at the decussation level. A decrease in the critical level of depolarization necessary for spike generation was shown to be a characteristic peculiarity for mono- and polysynaptic reaction of the RN neurons in the alert animals. A rare possibility of recording separate EPSPs, the presence of burst discharges of rubrospinal neurons as well as a higher activity of RN interneurons was observed.

Animals↗
PubMed1987

Electrophysiology of ascending, possibly cholinergic neurons in the rat laterodorsal tegmental nucleus: comparison with monoamine neurons.

In urethane-anesthetized rats single neuronal activity was recorded in the laterodorsal tegmental nucleus (LDT), which has a dense complement of cholinergic neurons, and in the dorsal raphe and locus coeruleus for comparison. Most LDT neurons responded antidromically to stimulation of either one or more of several rostral loci, and gave rise to broad spikes. They showed various properties very similar to those of monoaminergic neurons. Others generated brief spikes. The former may be cholinergic. The most frequent response of broad-spike LDT neurons to noxious stimulation was phasic excitation, which tended to become weak or disappear upon repetition.

Animals↗
PubMed1977

Comparative study of perceived pain and nociceptive flexion reflex in man.

The purpose of this study was to compare the amplitude of the flexion reflex of the biceps femoris muscle (BF) with the intensity of the painful sensation elicited by a nociceptive stimulation resulting from application of constant-current either on the sural nerve or on the skin in its distal receptive field. Experiments were carried out on 15 normal volunteers. It was observed that: (1) Stimulation of the sural nerve (either on or through the skin) elicits two different reflex responses in the BF: the first (RII) is of short latency, low threshold and corresponds to a tactile reflex. The second (RIII) is of longer latency and higher threshold, and corresponds to a nociceptive reflex. The threshold of RIII was found to be the threshold of a pain sensation. (2) Stimulation of the skin elicits only a late nociceptive (RIII) response in the BF. The threshold of this response was also found to be that of pain. (3) The threshold of both pain and RIII were found to be higher for sural nerve stimulation (10 mA) than for cutaneous stimulation (5 mA). It was suggested that the large diameter cutaneous fibers could have an inhibitory effect of both pain and the nociceptive reflex. This was supported by the results obtained during a selective ischemic block of the largest diameter fibers in the sural nerve, when a 10 mA stimulation was applied to the nerve. In this case, a decrease of the RII reflex was observed in BF, together with an increase of both RIII and pain sensation. Functional implications of these results are discussed.

Adult↗
PubMed1984

Medullary locomotor strip and column in the cat.

Responses of lateral medullary neurons to microstimulation of two points in the locomotor strip--rostral and caudal to the obex--were recorded intracellularly in mesencephalic decerebellated uncurarized cats. Excitatory and inhibitory postsynaptic potentials and orthodromic action potentials occurred up to 20 ms after a single stimulus. A number of cells responded to stimulation of a locomotor point by a repetitive discharge, and in some cells synaptic responses were evoked by contralateral stimulation. The responsive neurons were scattered among other cells in the lateral medullary tegmentum. At least one-third of neurons with synaptic responses to stimulation of the rostral locomotor point were antidromically invaded from the caudal one. The characteristic length of these descending axons was between 4 and 9 mm, although there were longer axons too. The lateral medullary cells which give synaptic responses to stimulation of the locomotor strip form the locomotor column located medial to the strip, and a portion of these cells send their axons to the strip. It is suggested that the activity is propagated polysynaptically along the column through axonal collaterals of its neurons. One can assume that when repetitive stimulation achieves a threshold for locomotion such as propagation occurs without decrement. As a result, spinal stepping generators are activated.

Animals↗
PubMed1985

Bilateral corticosubthalamic nucleus projections: an electrophysiological study in rats with chronic cerebral lesions.

The present study sought to determine the distribution of the cortical areas giving rise to the corticosubthalamic nucleus projections, using extracellular stimulating and recording techniques in rats with and without chronic lesions. In acute rats, cortical stimulation induced a powerful excitation in 87% of the subthalamic nucleus cells recorded. This response was obtained from stimulation over a large extent of the cortex since nearly all the ipsilateral cortex and the rostral two-thirds of the contralateral side was found to influence the activity of the subthalamic nucleus neurones. An excitatory response quite similar to that induced by cortical stimulation was recorded in the subthalamic nucleus after striatal or internal capsule stimulations. Therefore in order to eliminate the possibility of recording a polysynaptic excitation, similar experiments were performed in rats bearing various chronic lesions. With either ipsilateral or contralateral cortical stimulations, there was no major consequence of these lesions on the type or characteristics of the response recorded or on the percentage of responding cells. The cortical origin of the excitation of the subthalamic neurones was further supported by the results of experiments performed in chronically decorticated rats. It is concluded that (1) the subthalamic nucleus receives an excitatory cortical input, (2) this control comes from ipsilateral and contralateral cortical areas and (3) it only involves direct corticosubthalamic nucleus fibres. The subthalamic nucleus is, together with the striatum, the only basal ganglia nucleus known to receive afferents from extensive regions of the cortex. By its two main afferents (cortex and external segment of the pallidum), the subthalamic nucleus is in a position to compare direct cortical informations with cortical informations processed at the striatopallidal complex level.

Animals↗
PubMed1990

Neural mechanisms underlying the action of primer pheromones in mice.

Our electrophysiological experiments in female mice have provided evidence that electrical stimulation of the accessory olfactory bulb orthodromically excites a subpopulation of tuberoinfundibular arcuate neurons by way of the amygdala. The present study shows that half of such neurons are identified as dopaminergic by examining the effectiveness of infusing 6-hydroxydopamine and 5,7-dihydroxytryptamine locally into the median eminence in blocking their antidromic response. Further attention is focused on excitatory amino acid receptors within the amygdala and the amygdaloid pathway that mediate the accessory bulb-induced excitation of tuberoinfundibular arcuate neurons. The excitatory transmission was reversibly blocked by intra-amygdala infusion (3 nmol) of the excitatory amino acid antagonists kynurenic acid, D,L-2-amino-5-phosphonovalerate, gamma-D-glutamylaminomethylsulphonate and D,L-2-amino-4-phosphonobutyrate. Intra-amygdala infusions (3 nmol) of N-methyl-D-aspartate and kainate markedly enhanced the firing activity of tuberoinfundibular arcuate neurons with excitatory inputs from the accessory bulb, whereas similar infusions of quisqualate were without effect Intra-stria terminalis infusions of the local anaesthetic lignocaine completely abolished the excitatory transmission in all the cells tested. Furthermore, tuberoinfundibular arcuate neurons stimulated from the accessory bulb were also orthodromically stimulated from the stria terminalis with a shorter latency. These studies demonstrate that the projections of the accessory olfactory bulb activate excitatory amino acid receptors within the amygdala and subsequently the stria terminalis route, thereby causing excitation of tuberoinfundibular dopaminergic arcuate neurons. This functional pathway can account for the reproductive effects so far described as a consequence of vomeronasal chemoreception.

Amino Acids↗
PubMed1994

Indirect nucleus accumbens input to the prefrontal cortex via the substantia nigra pars reticulata: a combined anatomical and electrophysiological study in the rat.

The nucleus accumbens is a major component of the ventral striatum through which most of the limbic affiliated cortical areas gain access to the basal ganglia circuitry. In this study, the organization of the pathways linking the nucleus accumbens to the thalamus, via the substantia nigra pars reticulata, was examined in the rat using anatomical and electrophysiological methods. Use of anterograde and retrograde transport of wheatgerm agglutinin conjugated to horseradish peroxidase has established that the core of the nucleus accumbens innervates a dorsal region of the substantia nigra pars reticulata which projects to subfields of the mediodorsal and ventral medial thalamic nuclei. These subfields consist of the rostral pole of the mediodorsal nucleus with the exception of its central segment and a region of the ventral medial nucleus, medial to the mammillothalamic tract. Confirming the existence of a nucleus accumbens nigrothalamic link, we have observed that electrical or chemical stimulation of the nucleus accumbens induces an inhibition of the spontaneous discharges of the nigral cells which project to the mediodorsal and ventral medial thalamic nuclei. Finally, the cortical projections of the thalamic subfields involved in the nucleus accumbens nigrothalamic circuit were determined using the anterograde and retrograde axonal transport of wheatgerm agglutinin conjugated with horseradish peroxidase. These subfields innervate mainly the prelimbic and to a lesser degree the orbital areas of the prefrontal cortex. The present data show that the substantia nigra pars reticulata is a major link between the core of the nucleus accumbens and the prefrontal cortex and provide further evidence for the concept of a parallel architecture in the basal ganglia thalamocortical circuits of the ventral striatum.

Action Potentials↗
PubMed1995

Effects of upper cervical spinal cord stimulation on neurons in the lumbosacral enlargement of the cat: spinothalamic tract neurons.

Extracellular microelectrode recordings were made from deep spinothalamic tract neurons in the lumbosacral spinal cord of cats anaesthetized with chloralose and paralyzed with gallamine triethiodide. The effects of upper cervical spinal cord stimulation were tested on 43 spinothalamic tract neurons, by stimulation of the ipsilateral dorsolateral funiculus at C3 and rostral C1 using five or six shocks at 333 Hz. The strength of cervical stimulation was adjusted so that the C3 shock was above threshold for antidromic activation of spinocervical tract neurons but the same strength of shock applied at C1 was below threshold for the same neurons. Four of the 43 spinothalamic cells (9%) were not influenced by upper cervical stimulation. The remaining 39 spinothalamic tract cells (91%) were all excited from the upper cervical cord. Twenty-seven of these (63%) were excited more strongly from C3 than from C1, 4 (9%) were excited more strongly from C1 than from C3, and the remaining eight cells (19%) showed no significant differences between their responses to stimulation at C1 and C3. There were no obvious differences between those spinothalamic tract neurons showing differential effects from C1 and C3 and those showing no such effects. The neuronal systems possibly responsible for the differential effects from C3 and C1 on spinothalamic tract neurons are discussed. We conclude that the most likely candidate system for the greater excitation from C3 compared with C1 is the subset of spinocervical tract neurons with axon collaterals in the lumbosacral enlargement and that the spinothalamic tract is a further ascending path, in addition to the postsynaptic dorsal column path, that receives excitatory input from spinocervical axon collaterals. The greater excitation from C1 compared with C3 is interpreted as due to excitation from C1 and a mixture of excitation and inhibition from C3. The responsible neuronal systems seem likely to be either the spinocervical neurons with axon collaterals operating on the spinothalamic tract via inhibitory interneurons, or cells in the lateral cervical nucleus with axons descending to the lumbosacral cord.

Animals↗
PubMed1989

Excitation and suppression of primary auditory fibres in the pigeon.

Spike potentials were recorded from single fibres in the auditory nerve of the pigeon. In fibres with recognizable responses to sound, spontaneous activity and properties of responses to tonal stimuli were studied in quiet background conditions. Mean spontaneous rate in the sample of fibres was 35 spikes/s. Tuning of spike response to tones was manifest as a single peak in rate at each sound pressure level (SPL) in the frequency-intensity plane. The majority of fibres showed only excitation of spike rate above spontaneous rate. Post stimulus time histograms (PSTs) in such cases were typical of excitatory responses, previously described in birds and mammals showing pronounced adaptation and post-stimulus suppression of spike rate. In most cases of excitation-only responses, however, slopes of rate functions depended on stimulus frequency. Close to characteristic frequency (CF), slopes tended to decrease with increasing SPL, whereas away from CF, slopes tended to increase with SPL. In a minority of excitation-only responses, slopes of rate functions were parallel. In some fibres, tones adjacent to the response area caused overt suppression of spontaneous firing. For these fibres, the slopes of rate functions were more-strongly frequency-dependent, being negative at low SPL when rate suppression occurred. Suppression of spontaneous activity at low SPL was non-monotonic and quite different from suppression of spike rate at stimulus intensities above rat saturation. In PSTs of suppressed spontaneous activity, rebound occurred at the termination of the tone. The results clarify previous observations of suppression of primary auditory responses in birds. We conclude that responses in the majority of auditory fibres in the pigeon are the product of opposing excitatory and suppressive influences in the cochlea, generated by single tones in quite.

Acoustic Stimulation↗
PubMed1994

Reinforcement learning control.

Reinforcement learning refers to improving performance through trial-and-error. Despite recent progress in developing artificial learning systems, including new learning methods for artificial neural networks, most of these systems learn under the tutelage of a knowledgeable 'teacher' able to tell them how to respond to a set of training stimuli. Learning under these conditions is not adequate, however, when it is costly, or even impossible, to obtain this kind of training information. Reinforcement learning is attracting increasing attention in computer science and engineering because it can be used by autonomous systems to learn from their experiences instead of from knowledgeable teachers, and it is attracting attention in computational neuroscience because it is consonant with biological principles. Recent research has improved the efficiency of reinforcement learning and has provided some striking examples of its capabilities.

Animals↗