The organization of instrumental food-procuring movements in rats]

The roles of the lateral hypothalamus, basolateral nucleus of the amygdalar complex, the second field of the frontal cortex, and ventromedial thalamic nucleus in organization of the fast ballistic food-procuring movements were studied in albino rats. Sequences of uni- and bilateral destruction of the brain structures were assessed by photorecording. Movement-related neuronal activity in these structures was recorded in freely moving animals. A specific involvement of each of the above listed structures in organization of food-procuring movements was shown. The lateral hypothalamus seems to participate in initiation of the motor program and its efficient realization, the basolateral amygdala appears to produce activatory, training, and stabilizing effects. The second field of the motor cortex leads in movement acquisition (i.e., in memorizing) and decision making about triggering the program. The idea about the relay role of the thalamic motor nucleus is supplemented by understanding of its more complex integrative function.     

Neuronal reactions in field 2 of the frontal cortex, related to organization and performance of food-procuring movements in rats

Movement-related electrical reactions of neuronal units localized in field 2 of the frontal cortex were studied in albino rats performing fast food-procuring movements under conditions of unrestrained behavior. According to the temporal characteristics of the changes in the neuronal spike activity, three types of reactions were classified: (i) activation that forestalled the movement initiation for 1.0–1.5 sec; (ii) activation or inhibition forestalling this beginning for 0.20–0.26 sec; and (iii) activation in the course of a performed movement. Considerations about the involvement of the neurons of various cortical layers in the mechanisms of programing, switching on, and current control of the efficiency of performance of food-procuring movements are proposed, and the role of the frontal cortex in these processes is discussed.     

Role of the amygdalar complex in programing of fast food-procuring movements in rats

Effects of uni- and bilateral electrolytic destruction of the basolateral nuclei of the amygdalar complex on the main parameters of fast food-procuring movements of albino rats were studied in the course of rearrangement of the motor programs; modifications of the parameters were observed both throughout the entire experiment and within each experimental day. The accuracy of the movements was significantly modified, which was manifested in an increase in the number of trials necessary for successful food capturing. An increase in the duration and a decrease in the frequency of the movements were also observed. The studied parameters underwent no complete recovery even on the tenth experimental day. Thus, the basolateral nuclei of the amygdalar complex occupy an important position in the system responsible for rearrangement of motivated automatized movements; when these nuclei are Injured, their function cannot be completely compensated by other brain structures.     

Fast ballistic food-procuring movements in rats: Phenomenology and probable controlling mechanisms

Parameters of fast ballistic food-procuring movements were studied in albino rats. With the use of video and photorecording, the number of attempts used by an animal, to get the food globula, duration of the movements, and their phasic structure were analyzed within the whole learning period and certain experimental days. When the motor skill had been formed, programed ballistic components characterized by hard-to-modify parameters and components with a considerable impact of reverse afferentation in their formation and performance were analyzed. The experimental data are interpreted in terms of the expediency of using the operant motor reactions performed by rats getting food from a narrow manger as a model of voluntary motor activity in electrophysiological, behavioral, neurochemical, and morphological studies. The regularities in formation of motor programs, initiation, realization, and control of the movements, and central mechanisms of these phenomena are discussed.     

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.     

Impulse activity of neurons in the lateral hypothalamus during microionophoretic administration of melatonin and noradrenaline in rats

Microionophoretic administration of melatonin into the perineuronal space of lateral hypothalamic neurons in WAG and Fischer-344 rats decreased the firing rate and regularized activity of the cells. Moreover, the effects of melatonin completely blocked the activation of neurons and changes in their pulse activity produced by norepinephrine. The effects of melatonin on neuronal activity in behaviorally active stress-resistant WAG rats were more pronounced than in behaviorally passive stress-predisposed Fischer-344 rats. These data suggest that stress-protective activity of melatonin is associated with inhibition of the pulse activity of neurons in emotiogenic structures of the brain and changes in neuronal sensitivity to norepinephrine.     

Intrahypothalamic connections of the lateral hypothalamus

Using the axon degeneration method by R. Fink and L. Heimer, organization of intrathalamic connections between various areas of the lateral hypothalamus have been studied after unisided electrolitic lesion. At any location of the injury foci, similar patterns are observed in ipsilateral distribution of degenerating fibers along the whole lateral preoptico-hypothalamic area. The most massive degeneration is observed in the zone where the medial forebrain bundle (MFB) fibers run. The degenerating fibers spread forward--into the septal area, and backward--into the mesencephalic part of the brain. The rostral and caudal parts of the lateral hypothalamus, taking part in formation of the MFB collateralies towards the thalamus, are connected with various thalamic nuclei. Massive preterminal degeneration in the perifornical zone and single argerophile granules in the medial hypothalamus convincingly demonstrate an important role of the intermediate zone for connections of its medial and lateral parts with each other. The conclusion that the intrahypothalamic connections of the lateral hypothalamus are realized within the MFB system supports the modern notion on a close connection of the lateral hypothalamus with the system of longitudinal diffuse bundles of fibers of the medial anterocerebral pathway that run through it.     

Neuronal activity related to spontaneous and capsaicin-induced rhythmical jaw movements in the rat

Intraoral capsaicin induced rhythmical jaw movements (RJM) in anesthetized rats. Neurons in the trigeminal spinal nucleus caudalis or the cortico-peduncular (CP) axons were extracellularly recorded. Capsaicin excited dose-dependently most caudalis neurons, which were activated by stimulation of the oral cavity and/or the tooth pulp and activated during spontaneous or induced RJM. Ten of 55 CP axons were antidromically activated by stimulation of the contralateral trigeminal motor nucleus. All antidromic and 29 other CP axons discharged prior to the spontaneous RJM, but most of them did not during capsaicin-induced RJM. These neuronal activities possibly initiate spontaneous RJM although the activities of caudalis neurons are necessary for capsicin-induced RJM.     

Rhythmical jaw movements and lateral ponto-medullary reticular neurons in rats

Neuronal activity in the lateral reticular formation was investigated in urethane-anesthetized rats. Stimulation of anterior and posterior cortical areas induced two types of rhythmical jaw movements (RJM). The effects of stimulation of these cortical areas, the peripheral nerves, and the trigeminal motor nucleus on these neurons and their activity during the RJM were analyzed. The smallest percentage of neurons receiving anterior cortical input received peripheral input, and most neurons with posterior cortical input received peripheral input. Sixty per cent of reticular neurons showed the rhythmical firing closely related to the RJM. Therefore, these neurons may participate in masticatory pattern formation.     

A retinal projection to the lateral hypothalamus in the rat

Summary This study presents evidence for a retinal projection to neurons in the lateral hypothalamic area (LHA) of the albino rat. In Golgi-Kopsch material dendrites from LHA-neurons are observed to extend through the supraoptic commissures into the optic tract. The presence of dendrites in the optic tract is confirmed by electron microscopy. Numerous axon terminals are observed forming asymmetric synaptic contacts with these dendritic profiles. Following bilateral enucleation, many of the preterminal axons and terminals in synaptic contact with dendrites in the optic tract demonstrate dark degeneration. After intraocular injection of horseradish peroxidase, there is marked labeling of preterminal axons and terminals in the optic tract. These observations indicate that LHA neurons receive a direct retinal projection from terminals making synaptic contact with dendrites of LHA-neurons extending into the optic tract.     

Role of the lateral hypothalamus in sleep

Sleep and Biological Rhythms -     

Correlation of the unit activity of the right and left lateral hypothalamus in food motivation

Correlation between activities of neurons in the right and left lateral hypothalamus of a rabbit recorded during quiet wakefulness, after 24-h food deprivation, and after satiation was studies by plotting cross- and autocorrelation histograms. A predominant order in correlated bilateral discharges of hypothalamic neurons was revealed in hungry animals: in a significantly greater number of cases (59%) the left-side discharges led the right-side ones with time delays to 200 ms (peaks at 30 and 160 ms). The opposite order of discharges was less common (21%). In the state of hunger, the probability of appearance of theta-range frequencies in correlated neuronal discharges increased (from 11 to 29%).     

Inference of a stable dispersion relation for electrocortical activity controlled by the lateral hypothalamus

A second test is undertaken for a theory of linear wave motion in electrocortical waves, under lateral hypothalamic control via regulation of damping. This test invokes a general property of linear systems, namely that wave motion with characteristic natural frequencies implies fixed phase velocities associated with each wavelength, independent of the changes in hypothalamic input. A means of testing the invariance of this dispersion relation at the point of recording is derived from a simplified biophysical model for waves in a dipole layer. The method avoids some problems implicit in direct spatio-temporal wave analysis. Results confirm that the model under test is internally consistent, and is also consistent with other findings concerning the origin and spatial nature of the EEG.     

Organization of a program of automatized food-procuring movement in rats

With the use of techniques of video- and photorecording, local destruction of the brain structures, and recording of the spike responses, roles of the suprasegmental brain structures in organization and control of automatized food-procuring movements were studied in rats under conditions of unrestrained behavior. It is shown that there are several neuronal populations in the prefrontal cortex related to programing, initiation, and current control of the efficacy of performance of food-procuring movements. The lateral hypothalamus is considered a motivational structure. It acts as the source providing an increase in the excitability and further support of the excitation level in the structures, which are links of the systems controlling food-procuring movements. The lateral hypothalamus is also involved in a system providing formation and final application of motor programs.     

A linear theory for global electrocortical activity and its control by the lateral hypothalamus

A linear model for electrocortical waves and their control by the lateral hypothalamus is proposed. It is argued that such a linear model is not in contradition to non-linearity of neural elements on the microscopic scale. Telencephalic structures are treated as a mass of linked oscillators generating activity with a number of resonant modes. The lateral hypothalamus is regarded as controlling damping of activity in the telencephalic mass, and therefore exerting a specific parametric control over all signal processing in the cortical networks. An initial test is proposed to assess the constancy of telencephalic natural frequencies, with variation in lateral hypothalamic damping.