Modulation of pyramidal response in the rat sensorimotor cortex after combined stimulation of the lateral hypothalamus and the sensorimotor cortex

It was shown during experiments on unrestrained rats that rhythmic stimulation of the pyramidal tract produced a statistically significant increase in the functional activity of neuronal populations of the sensorimotor cortex, manifesting as potentiation of the primary, positive phase of pyramidal cortical response. Combined rhythmically matched stimulation of the pyramidal tract and of the lateral hypothalamus leads to statistically significant enhancement in potentiation of the positive phase of pyramidal cortical response compared with effects produced independently of hypothalamic involvement. When stimulation of the pyramidal tract and the lateral hypothalamus are combined with stimulation applied at the same periodicity to the sensorimotor cortex, a further statistically significant enhancement in potentiation of the positive phase of pyramidal cortical response is seen in addition to the potentiating effect produced by hypothalamic stimulation.Institute for Brain Research of the All-Union Scientific Center of Mental Health, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 18, No. 3, pp. 367–373, May–June, 1986.     

Changes in pyramidal tract response to direct stimulation of the sensomotor cortex of the rabbit during formation of a conditioned reflex

Changes of pyramidal tract (PT) response were analyzed, reflecting the final result of cortical interaction in the process of combinations of direct stimulations of cortical surface in nonimmobilized and unanaesthetized rabbits. It has been shown that in a situation, modelling conditioning, changes take place of the first direct component--the D-component--of the PT response (reflecting the excitability of the PT neurones), as well as changes of the successive indirect synaptic component--I-component (reflecting the excitability of presynaptic cortical elements and of intracortical synaptic connections). I-component changes were significantly more expressed. In most cases the I-component of the response was increased. The obtained data testify to an increase of synaptic efficiency in the process of temporary connection formation and to possible change (increase or reduction) of excitability of PT neurones.     

Cerebral-evoked responses elicited by direct stimulation of the lateral spinothalamic tract in the human

The authors recorded cerebral-evoked responses elicited by direct stimulation of the human lateral spinothalamic tract (LST) during percutaneous cordotomy to investigate central conduction of noxious stimuli. These responses consisted of four negative potentials, peak latency being 3.8 (N1), 8.4 (N2), 12.2 (N3) and 21.9 (N4) ms respectively. N1 showed wide distribution over the scalp and was considered to be of subcortical origin. N2-N4 were distributed in both the temporal and central area. The different distribution pattern of N2-N4 from conventional somatosensory-evoked potential suggested a different projection of LST from the medial lemniscus system.     

The late excitatory responses of the motor cortex neurons in the cat to stimulation of the pyramidal tract

Under conditions of partial suppression of GAMKA-dependent cortical inhibition in the motor cortex of anesthetized cats, a weak electrical stimulation of the pyramidal tract evoked the late slow (50-200 ms) excitatory reactions in the motor cortex neurons similar to those previously recorded under the same conditions in response to stimulation of the parietal cortex. This finding favors the proposal that the late excitatory component of the cortico-cortical response reflects the repetitive activation of cortical neurons due to excitation spread via the system of cortical recurrent excitatory collaterals.     

Modulation of the thalamocortical responses of the sensorimotor cortex during stimulation of the lateral hypothalamus in rabbits in ontogeny

It has been demonstrated that rhythmic stimulation of the relay thalamic nucleus in rabbits at the second half of the first month of postnatal life does not significantly affect the amplitude of the second and third positive components (PC-2 and PC-3) of the positive phase of the thalamocortical responses. Combination of rhythmic stimulation of this nucleus and that of lateral hypothalamic structures is accompanied by a significant increase of the amplitude of both positive components of the thalamocortical responses, the degree of potentiation of PC-3 being higher than that of PC-2. The described potentiation is most evident at the third week of postnatal development of rabbits.     

Role of the lateral hypothalamus and prefrontal cortex in organization of voluntary movements

Roles of the lateral hypothalamus and prefrontal cortex in organization and control of automatized food-procuring movements were studied in rats under conditions of unrestrained behavior with the use of video- and photorecording techniques, destruction of the brain structures, and recording of single neuron impulse responses. The lateral hypothalamus is considered a link in the control system for food-procuring movements, which provides formation of the motor program. The role of the prefrontal cortex is regarded as related to programing and initiation of food-procuring movements and current control of efficiency of their performance. Positions of the lateral hypothalamus and prefrontal cortex within an ensemble of the motor centers, which organizes voluntary movements, are discussed.     

Dendritic action potentials of pyramidal tract neurons in the cat sensorimotor cortex

The intracellular activity of pyramidal tract neurons was studied during electrical stimulation of ventrolateral and ventroposterolateral thalamic nuclei in acute experiments on cats immobilized by myorelaxants. Somatic action potentials were observed and spontaneous spikes were also produced by single and rhythmic stimulation of the thalamic nuclei at the rate of 8–14 Hz, by iontophoretic application of strychnine, and by intracellular depolarizing current pulses. These potentials had a relatively low and variable amplitude of 5–60 mV and are presumed to be dendritic action potentials. It is postulated that these variable potentials arise in the dendrites of pyramidal neurons with multiple zones generating such activity. No interaction was observed where somatic and dendritic action potentials occur simultaneously. The possible functional role of dendritic action potentials is discussed.I. S. Beritashvili Institute of Physiology, Academy of Sciences of the Georgian SSR, Tbilisi. Translated from Neirofiziologiya, Vol. 18, No. 4, pp. 435–443, July–August, 1986.     

Optical recording of the in vivo piriform cortex responses to electrical stimulation of the lateral olfactory tract in the rat

Using a voltage-sensitive styryl dye, optical recordings ofthe piriform cortex responses to bipolar electrical stimulationsof the rat lateral olfactory tract (LOT) were taken. Surgicalprocedures were performed on Wistar SPF male rats anaesthetizedwith equithesine. Anaesthesia was continued during the recording.In addition the animals were curarized and artificially ventilated.Piriform cortex was stained with RH795. Cortical fluorescencewas recorded with a 124-element photodiode array using epi-illuminationwhile electrical stimulations were delivered to the LOT. Mappingof the piriform activity indicated a very large overlap of therecorded responses. Nevertheless, some differences in locationof recorded responses were observed and seemed to correlatewith the location of the stimulation electrode on the LOT. Theresults are discussed in relation to the anatomy and histologyof the olfactory bulb projections to the piriform cortex.     

Responses of pyramidal tract and corticorubral neurons to stimulation of lateral hypothalamic structures in cats

Responses of pyramidal tract neurons and corticorubral and unidentified neurons in the pericruciate area of the cortex to electrical stimulation in the posterior, tuberal, and anterior zones of the lateral hypothalamus and also to electrodermal stimulation of all four limbs were studied in cats anesthetized with chloralose. The proportion of pyramidal tract, corticorubral, and unidentified neurons which responded to hypothalamic stimulation was 73.3, 55.7, and 79.1% respectively. Data on the possibility of monosynaptic activation of some pyramidal tract neurons and unidentified cells were obtained. The presence of less stable and longer-latency responses of corticorubral neurons indicated the absence of a monosynaptic pathway for realization of ascending hypothalamic influences on neurons of the cortical extrapyramidal system. Some cortical neurons responded to stimulation of more than one zone of the hypothalamus. Pyramidal tract neurons and corticorubral neurons with axon collaterals running into the region of the hypothalamus were discovered for the first time. It was shown that most neurons of the pericruciate area of the cortex to which the ascending influence of the hypothalamus is directed have a large bilateral receptive field and respond to electrodermal stimulation of several limbs.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 14, No. 3, pp. 298–306, May–June, 1982.     

Functional asymmetry of the frontal cortex and lateral hypothalamus of cats during food instrumental conditioning

The synchronism and latency of auditory evoked potentials (EP) recorded in symmetric points of the frontal cortex and lateral hypothalamus of cats were measured at different stages of instrumental food conditioning and after the urgent transition to 30% reinforcement. Correlation coefficients between EPs in the cortex and hypothalamus were high (with left-side dominance) at the beginning of the experiments, when food motivation was high, and during the whole experiments in cases of high-probability of conditioned performance. Analysis of early positive P55-80 EP component showed that at all conditioning stages the peak latency of this component was shorter in the left cortical areas than in symmetrical points, whereas in the hypothalamus the shorter latency at the left side was observed at the stage of unstable conditioned reflex, and at the stage of stable reflex the latency of the studied component was shorter at the right side. During transition to 30% reinforcement, the latency was also shorter in the right hypothalamus. It is suggested that the high left-side correlation between the hypothalamus and cortex was associated with motivational and motor component of behavior rather than reflected the emotional stress induced by transition to another stereotype of food reinforcement (30%).     

Reactions of cat motor cortex neurons to stimulation of the pyramidal tract and ventroposterolateral thalamic nuclei

Responses of neurons of motor cortex evoked by stimulations of pyramidal tract (PT) and ventroposterolateral (VPL) nucleus of thalamus were studied in cats immobilized by Myorelaxin. Antidromic spikes were found in 22.6% and in 9.9% of cortical cells when PT and VPL were stimulated, respectively. Fast- and slow-conducting PT-neurones could be differentiated according to antidromic excitation latencies. PT stimulation evoked EPSPs in 46.3% of studied neurones and VPL stimulation--in 48.2% ones. Monosynaptic EPSPs were identified in responses of fast- and slow-conducting PT-units and of neurones projecting in VPL; mechanisms and functional role of such reactions are discussed. Di- and polysynaptic IPSPs were evoked in 74.5% of units by PT stimulation and in 94.4%--by VPL stimulation. Three groups of IPSPs were classified with durations to 120, 130-280 and more than 300 ms. Duration of PT-evoked IPSPs was higher in cortical neurones from surface layers and VPL-evoked ones--in units localized in deep layers.     

Beta-lipotropin and beta-endorphin in compensation mechanisms of function after damage of the lateral hypothalamus

Possibility of restoration of food intake and other related functions impaired after lesion of lateral hypothalamus was studied on 45 male albino non-strain rats divided into 3 groups with 15 per each. Neuropeptides beta-lipotropin (beta-LPT) and its derivative beta-endorphin were used as compensation factors. The parameters recorded were: volume of food and water intake, diuresis, body weight and temperature, frequencies of rest periods, comforting forms of behavior and orienting-exploratory activity. The results revealed that lesion of lateral hypothalamus resulted in the formation of specific central and peripheral syndrome responsible for the impairment of food intake and other related functions. Intracerebroventricular injections of beta-LPT and beta-endorphin facilitated compensation of impaired functions caused by lesion of lateral hypothalamus. The data were analyzed on the basis of the systems approach to the organism's physiological functions.