Pentagastrin modulation of the neuronal sensitivity of the lateral hypothalamus to noradrenaline and dopamine

Experimental study is dedicated to mechanisms of interaction of pentagastrin and monoamines (noradrenaline and dopamine) at the level of single neurones of the rabbits lateral hypothalamus under alimentary motivation and under saturation. It is shown that pentagastrin can modulate the effects of noradrenaline and dopamine on neuronal impulse activity in hungry and fed up animals, and the character of its action depends on the rabbits initial state. It is suggested that pentagastrin is a factor initiating alimentary motivational excitation, while noradrenaline maintains the latter at the definite level up to obtaining useful result by the animal, when dopaminergic mechanisms participating in the process of reinforcement join the noradrenergic ones.     

Effect of ethanol on central mechanisms of alimentary and defensive motivation in the rabbit

A single intravenous administration of ethanol (0.5 g/kg) to rabbits had different effects on the excitability of feeding and defensive motivational centers of the lateral and ventromedial hypothalamus. Ethanol abolished both inhibitory effects of the dorsal hippocampus and facilitatory action of the midbrain reticular formation on alimentary and defensive motivations. It elicited new power distributions of the main rhythms of general electrical cortical activity in the background and under stimulation of limbic-midbrain structures. Analysis of the activity of organello-specific enzymes in limbic-midbrain neurones revealed disturbances of cellular energetic processes caused by ethanol.     

Integrative properties of parietal cortex neurons of rabbits during the switching of heterogeneous classical conditioned reflexes

The impulsive activity of parietal cortex neurons of rabbits during the elaboration and specialisation of switching-over of alimentary and defensive conditioned reflexes has been studied. There are changes of parietal cortex neurons activity correlated with the stages of switching-over elaboration. The significant differences of the background neurons activity and neurons response to the conditional signal during alimentary and defensive conditioned reflexes have been established. The dominant motivation influences the neurons activity by modulation of background and conditioned activity of neurons. The integrative properties of neurons investigated in switching-over situation are revealed in their ability to summarize the excitation coming to the same sensory input with excitation from different motivational and reinforcement systems.     

Analysis of the impulse activity of the cerebral neurons in rabbits with artificial thirst

Neuronal impulse activity of various brain structures was studied in rabbits in conditions of artificial thirst elicited by intrabrain injection of 0.3-0.5 M NaCl solution (from 5 to 8 mcl). Specific organization was revealed of the impulse flow at drinking motivational excitation, i.e., domination on interval histograms of certain intervals (20-40 and 100-200 ms). Comparative analysis of activity patterns of both different and the same neurones in conditions of natural and artificial thirst showed a resemblance of dominating intervals values that testifies to specificity of the observed neural activity characteristics, reflecting drinking motivational excitation. Thus, an interval code is found corresponding to drinking motivational state. P. K. Anokhin's notions about anticipating reflection of reality find their expression in anticipating reactions of brain neuronal activity.     

Effect of GABA on a temporary connection in a neuronal population of the sensorimotor cortex in rabbits

Evoked activity of sensorimotor cortical neurones in response to stimulation of the pyramidal tract, medial lemniscus and reticular nucleus of the midbrain tegmentum; driving reaction of cortical neurones at stimulation of these brain structures of growing frequency, and conditioned reflexes elaborated by combination of direct stimulation of the sensorimotor cortex and electrocutaneous stimulation were studied in awake nonimmobilized rabbits. Application to the cortex of GABA solutions of low concentration (less than or equal to 1%) emphasizes the evoked neuronal responses, facilitates the appearance of driving reaction and contributes to the manifestation of the temporary connection. Application of GABA solutions of higher concentration (greater than 2%) leads to opposite effects. Positive correlation is found between electrical and behavioural phenomena. The described experimental approach may be used for analysis of various types of influences on temporary connection formation.     

Temporal organization of interneuronal relations in the cerebral cortex of the cat in relation to the level of alimentary motivation

By means of records of multicellular activity, interneuronal relations and their modifications in two cortical zones (Visual and motor) were studied in cats at different levels of alimentary motivation. For quantitative evaluation of interneuronal relations the statistic method of cross-correlation analysis of impulse trains was used in determining the probability of the appearance of the discharge of one neurone after the impulse of the other one. For groups of neurones in both investigated cortical areas, three-neurones microsystems were singled out and their activity was analyzed by temporal parameters of interaction between neurones at the interval of 120 ms, both within one microarea (intraanalyzer connections) and between microareas of two cortical zones. The correlation of temporal parameters of interneuronal connections (temporal delays in the activity of neuronal pairs) changed depending on spatial localization of neurones and functional condition of the animals. The existence is suggested of "informational" (1-30 ms) and "motivational" (90-120 ms) values of interneuronal relations for interanalyser connections.     

Morphophysiologic study of reticulo-cortical pathways in the rabbit

The character of functional connections between the midbrain reticular formation (RF) and the neocortex was studied in rabbits. Unit activity was recorded in sensorimotor cortex by extracellular microelectrode during RF stimulation. Short-latency neuronal reactions were found presumably identified as monosynaptic responses. Results of the studies of anterograde degeneration of myelinic fibers and axonal terminals after electrocoagulation of the RF carried out with the help of electronic microscope allowed to suppose that there were few (less than 0.5 per cent) monosynaptic connections between the RF and the sensorimotor cortex. The main forms of direct connections between these structures were axo-dendritic (situated at the dendritic trunk) and axosomatic synapses at the neurones of the sensorimotor cortex.     

Role of motivational excitations in the integrative activity of individual cerebral neurons

It has been shown that motivational excitation is a factor that changes the functional properties of brain single neurones. On the basis of ascending activating influences of the hypothalamic initiative centres, motivational excitation considerably changes convergent and discriminating properties of the cortical units. It is toward the cortical and subcortical neurones excitated by motivation that excitations evoked by reinforcing stimuli are directed. Under repetitive reinforcing action a certain trace is imprinted in the dynamic architecture of motivational excitation, which is the neuronal basis of the action result acceptor. The apparatus of the action result acceptor, formed after the precedence principle, is precisely the directing factor of the animals' purposeful activity.     

The dynamics of the activating and inhibitory types of cortical neuron synchronization during the realization of a defensive reflex and internal inhibition

In the visual and sensorimotor areas of the neocortex and in the hippocampus of alert nonimmobilized rabbits, in response to combinations of light flashes with electrocutaneous limb stimulation an increase was observed of synchronization in the activity of the near-by neurones by activation by inhibitory type (coincidence of the presence and absence of impulse activity). In response to flashes against the light background--conditioned inhibitor--in the visual cortex synchronization of neurones increased by inhibitory type, and in the sensorimotor cortex and hippocampus changes of synchronization appeared, similar to the action of pain reinforcement but considerably weaker. The increase of synchronization by the activation type took place mainly in the neurones pairs with unidirected increase of impulses frequency and by the inhibitory one--with its decrease. Along with this, in a considerable part of neurones pairs both changes of synchronization appeared at the impulses frequency changes of different direction.     

Effect of the microiontophoretic application of acetylcholine on the formation of conditioned reactions in motor cortex neurons

In alert rabbits the activity of the motor cortex neurones was recorded with simultaneous application of acetylcholine to them in the process of defensive conditioning. Conditioned reorganization, mainly of activation type, were found in 60% of neurones. In most cases conditionally reacting cells were sensitive to acetylcholine. Ionophoretic application of the transmitter promoted the formation of conditioned neuronal responses and increased them in comparison with conditioned reactions evoked in absence of acetylcholine. It is supposed that the influence of acetylcholine on conditioned cellular process is realized due to its action on the state of excitability of the cortical neurones.     

Organization of neuronal responses in the sensomotor cortex during simultaneous stimulation of brain structures

It has been found on alert non-immobilized rabbits that paired stimulations of the medical lemniscus, the midbrain reticular formation and the pyramidal tract in different succession cause in the sensorimotor cortex the formation of a temporary connection by the parameters of single unit activity and evoked potentials. The temporary connection is manifested in dynamics of evoked responses and in the change of electrical activity at the moment of usual presentation of the second stimulus, if it is omitted. The inflow of impulse activity by different paths adds some peculiarities to the organization of the temporary connection. The leading role in the given model situation may belong to the non-specific system.     

Temporal structure of the spike trains of neuronal pairs in the neocortex during calm wakefulness in rabbits

For revealing the conjugation of impulse activity of simultaneously recorded neurones in the visual and sensorimotor areas of rabbits neocortex, histograms were built of cross- and autocorrelation (CCH and ACH) of their discharges sequences. From successions of discharges of the visual cortex neurones, forming pairs of cells acting in correlation, spikes were singled out conjugated with neuronal discharges in the sensorimotor area, and their ACHs were built. In 77% of cases a resemblance was observed of temporal structure of conjugated discharges and real spike sequences, in 23%--there was no such resemblance. Analysis of conjugated discharges ACHs showed that they appeared predominantly periodically (87% of cases). The number of fragments with periodic discharges frequency within delta-frequency range from 3 to 4 Hz prevailed.     

Effect of the enkephalin derivative DAGO on neuronal behavior and activity in the neocortex and hippocampus of rabbits during the acquisition of conditioned defense and inhibitory reflexes

After subcutaneous injection of 25 mkg/kg morphine-like opiate--DAGO a decrease was observed of probabilities of rabbits movements at light flashes--defensive reflex signal. The level of the background neuronal impulse activity became gradually lower in the sensorimotor cortex and the hippocampus and did not change in the visual cortex. Decrease and restoration of responses to the reinforcing stimulus (electrocutaneous limb stimulation) in all studied cortical zones proceeded in one direction while there were significant differences in dynamics of responses to inhibitory and reinforced light flashes depending on the studied cortical zone and biological significance of the stimulus. Appearance is discussed of particular characteristics of neurones systemic organization during learning at change of reinforcement properties under the influence of the studied substance, as well as similarity of some features of mechanisms of internal inhibition elaboration in a defensive situation and of properties of positive reinforcement.     

A comparison of the spike train activity of the cortical neurons and of the spatial synchronization of the EEG

In chronic experiments EEG coherence and conjugation of impulse activity were compared of neurones of the visual and sensorimotor areas of rabbits neocortex simultaneously recorded with the same electrodes. Connection was revealed between the presence and properties of conjugated neurones activity and EEG coherence at various frequencies. At correlated neurones activity a greater EEG coherence was observed on frequencies of 3-4,5 Hz than at the independent activity. At the highest level of the EEG coherence the neurones discharged with less delay of one after the other in pairs, and in their synchronization a common source participated more often than at the lowest level of the EEG coherence.     

EEG-correlates of alimentary behavior in rabbits with different levels of hunger and satiety]

The electrical activity of the rabbit brain at different stages of hunger and satiation was correlated with the animal's behavioral reactions. It has been found that alimentary reactions are attended with the appearance of complex high-amplitude and high-frequency electrical potentials in the lateral hypothalamic area, which increased with the longer duration of the animal's hunger, as well as during search, in response to natural and conditioned alimentary stimuli, and when feeding. As satiation sets in, they fade and disappear after food refusal. It is assumed that this form of activity is an EEG expression of alimentary motivational excitation. Its constituent rhythms reflect the different components of alimentary excitation.     

The organization of the network characteristics of the cells in local and distributed neuronal networks of the cat brain]

In cats with elaborated alimentary instrumental reflexes to light net characteristics of neurones of visual, motor cortex and the hypothalamus lateral nucleus were studied on the basis of revealed interneuronal interactions by means of cross-correlation method of analysis. Different organization of net properties of the cortical neurones in organization of local and distributed neuronal networks was shown, namely: predominance of the divergent characteristics over the convergent ones for cells in local networks and levelling of these relations in distributed nets. Neurones of the lateral hypothalamus nucleus had equal presentation of divergent and convergent properties in organization of local and distributed networks. Net characteristics of neurones of the cortical and subcortical structures were manifested in the background after the elaboration and the extinction of conditioned reflexes. Only small cells of the visual cortex were functionally dependent and changed correlation of net characteristics in local networks at CR extinction.     

Dynamics of caudate nucleus involvement in the process of internal inhibition of the food-getting reflex]

Changes of slow spindle electrical activity (12 to 14 cps) and evoked potentials in the cat caudate nuclei and the motor cortex were studied at different stages of elaboration of differentiation inhibition of a conditioned food-procuring reflex to acoustic stimuli. It has been shown that participation of the caudate nuclei in the inhibitory process begins at the stage of enhancement of food-procuring activity (second stage) and is apparently due to the animal's strong alimentary motivational excitation. At the third stage the inhibitory influence of caudate nuclei on the animal's motor activity in general, and the activity of the motor cortex in particular, develops to the full.     

The dynamics of the interimpulse intervals in the activity of sensorimotor cortex neurons during the acquisition of the food-procuring reflex in the rabbit]

State of hunger is characterized by the presence of definite distribution of interimpulse intervals in the activity of sensorimotor cortical neurones (SMC) of rabbit. Mostly bi- and three-modal distribution of interimpulse intervals in the background activity in hungry animals changes in the process of elaboration of food-procuring habit. As the habit consolidates, the SMC neurones acquire the ability to forestalling actions. Peculiarities are revealed of organization of the SMC neurones impulse stream in response to the action of conditioned signal in the case of abolition or substitution of the reinforcement. Repeated substitutions of reinforcement cause the formation of activity of concordance in the moment of substitute "recognition" despite the absence of alimentary reinforcement.     

Plasticity and its physiological markers in the microsystem of cortical neurons during repeated local stimulation

Separate neuronal microsystems in the sensomotor cerebral cortex are able to exhibit the functional plasticity under conditions of repeated action of acetylcholine applied microiontophoretically. The characteristic properties of dynamics in activity of single cortex neurones are determined mainly by the initial reactivity to transmitter and by the state of nervous cells of the surrounding microsystem. The composition and succession of response components as well the duration of excitatory stage of reaction to acetylcholine serve as physiological markers of plastic properties of neurones in cortical microsystem.     

Neocortex neuron reactions caused by stimulation of the substantia innominata in cats

We investigated neuronal impulse activity in the sensorimotor cortex after substantia innominata (SI) stimulation in cats during the execution of an instrumental conditioned response consisting of placement of a paw on a pedal coupled with alimentary reinforcement. Stimulation of the SI was initiated 1 or 3 sec prior to conditioned stimulation. Background activity of the neurons was inhibited during stimulation of the SI. Preliminary stimulation of the SI one second in advance caused an increase of reactions linked to a subsequent conditioned stimulus and a conditioned-response movement in 32% of the neurons; a 3-sec lead caused increases of such reactions in 33% of neurons. In some cells which originally did not react to the conditioned excitation, a clear reaction did manifest after stimulation. Moreover, stimulation of the SI with a 1-sec lead caused inhibition of impulse reactions in 6% of the cells; with a 3-sec lead, it caused inhibition of impulse reactions in 33% of the cells. The spread of latencies of conditioned-response actions decreased 2- to 3-fold in this case. We discuss the possibility that acetylcholine, which is released by the terminals of cholinergic neurons of the SI, has a facilitating influence on the impulse activity of neocortical neruons.Bogomolets Institute of Physiology, Ukrainian Academy of Sciences, Kiev. Translated from Neirofiziologiya, Vol. 24, No. 1, pp. 11–20, January–February, 1992.