Conditioned reflex analysis of functional connections between the hippocampus and limbic system structures

Instrumental defensive conditioned reflex elaborated in dogs to stimulation of the dorsal and ventral hippocampus, also appeared, due to generalization, in response to stimulation of a number of limbic structures. Two types of changes in the generalization effects (estimated by parameters of motor conditioned reaction) were observed in the course of conditioned reflex stabilization: enhancement (in response to stimulation of the lateral hypothalamus, lateral nucleus of septum, limbic cortex) and weakening toward complete disappearance (in response to stimulation of the medial nucleus of amygdala and medial hypothalamus). Manifestation of the generalization phenomenon from the brain structures, which are not involved initially into conditioned activity, suggests the existence of close functional connections between these structures and the hippocampus.     

A collector of evoked potentials]

The collector is an adaptive algorithm for pattern recognition. It proposes new in-line fully-automatic technique to learn and recognize effective patterns of input data stream. Evoked potentials (EP) were recorded by ADDA 100 KHz, 4 channels, and described by 200 points per each EP. The collector recognized different studies of conditioned response (CR) by patterns of EPs in amygdalar central nucleus. In dogs with implanted into the limbic structures concentric electrodes an instrumental CR was elaborated to electrical stimulation of the dorsal hippocampus. Generalization or transfer of this CR was tested by means of electrostimulation of amygdalar basal nucleus. The generalization in the first experiment took place approximately in 86% of cases, in the second one in 52% of cases. In the first experiment the amplitudes of initial negativity and of late positive waves were smaller than those in the second one and in the experiments before conditioning.     

Intralimbic evoked potentials in the formation of an instrumental food conditioned reflex to hippocampal electrostimulation in dogs]

In dogs with the electrodes implanted in the hippocampus, amygdala, septum and hypothalamus an instrumental alimentary conditioned reflex (CR) was elaborated to electrostimulation of the hippocampus. Intralimbic evoked potentials (EPs) were studied during the elaboration and extinction of this reflex and during stimulations of limbic structures conducted with the purpose of CR generalization checking. Late EP components in the lateral hypothalamus and central nucleus of the amygdala changed during CR elaboration and extinction and in the hippocampus during amygdala testing. In both cases the amplitude of trace positivity and of slow negative wave was less, when during stimulation of the structure an instrumental movement was initiated than at its absence.     

The role of the basal ganglia in the reproducibility of instrumental reactions acquired to electrostimulation of the hippocampus

In dogs with electrodes implanted into the brain, a defensive instrumental conditioned reflex (CR) was elaborated to light flashes, stimulation of the dorsal hippocampus (DH) and caudate nucleus (CN) stimulation. Reproducibility of the learned movement was tested for the contralateral DN, CN, nucleus accumbens (AN) and pallid globe (PG). In the second series the percent of the elicited movements was compared to EPs, appearing in response to signal and testing stimulation. The degree was elucidated of structures participation in motivational, signal and executive links of CR. Low degree of AN participation in the executive CR link (2-nd series) and a high degree of AN and PG participation in the signal link (3-d series) were shown. Thus, intrasystemic CR generalization was more effective than the intersystemic one.     

Functional organization of limbic brain structures during conditioned reflex activity in the dog

In experiments on 3 dogs it was shown that instrumental defensive conditioned reflex (CR) to electrical stimulation of the hippocampus is generalized within the limbic system (LS). The rate of generalization depended on the place of testing stimuli in LS. Stimulation of the medial parts of LS at the stage of stabilized initial reflex did not produce the generalized CRs, while they appeared distinctly in response to stimulation of the lateral parts of LS. In the process of elaboration of heterogeneous CRs (defensive and alimentary) to electrical stimulation of the hippocampus, generalized conditioned reactions from some brain structures appeared in both situations to the same degree while from other structures--with considerable differences. These data point to a possible participation in the genesis of the generalized CRs both of signal and reinforcing brain mechanisms.     

Raised excitability produced in cortical neurons by reinforced stimulation of the lateral hypothalamus

Response was recorded in the pyramidal tract (PT) under three experimental situations modelling the shaping of conditioned reflex (CR) during experiments on unrestrained but unanesthetized rabbits. The first paradigm consisted of direct stimulation of two points on the sensorimotor cortex, the second of the same stimuli combine with electrical stimulation (used as additional reinforcement) of the lateral hypothalamus (LH), and the third of LH stimulation in response to a rise occurring in PT response to above control level (modelling instrumental CR). An overall increase in the monosynaptic wave indicative of altered efficacy of synaptic connections was most commonly observed under all these conditions. Increase in the component directly reflecting pyramidal neuronal excitation appeared significantly more pronounced in the second and third than in the first experimental paradigm. The data obtained would point to reinforced efficacy of excitatory synaptic connections as the principal mechanism of CR, while the changed quality of electrical excitability at the membrane of cortical neurons reflects mechanisms underlying the contribution of reinforcement triggered by LH activation in cortical reordering of the motivational/emotional component of reinforcement.Higher Nervous Activity and Neurophysiology Research Institute, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 21, No. 6, pp. 805–811, November–December, 1989.     

The role of the lateral and medial hypothalamus in reproducing food and escape instrumental reactions]

In experiments on two dogs it has been found that testing electric stimulation of the lateral hypothalamus reproduces instrumental movement in case of elaborated alimentary instrumental conditioned reflexes (CR) to a tone and does not reproduce it at elaborated acid-defensive instrumental CR. Under testing electric stimulation of the medial hypothalamus the instrumental movement practically is not reproduced neither in alimentary nor in defensive situation. Appearance of instrumental movement at LH electro-stimulation in alimentary situation is connected with activation of backward conditioned connection from motivation "alimentary" LH centre to representation of this movement in the motor cortex.     

Position-dependent sensitivity and density of taste receptors on the locust leg underlies behavioural effectiveness of chemosensory stimulation

Chemical stimulation of contact chemoreceptors located on the legs of locusts evokes withdrawal movements of the leg. The likelihood of withdrawal depends on the site of stimulation, in addition to the identity and concentration of the chemical stimulus. A significantly higher percentage of locusts exhibit leg avoidance movements in response to stimulation of distal parts of the leg with any given chemical stimulus compared to proximal sites. Moreover, the percentage of locusts exhibiting avoidance movements is correlated with the density and sensitivity of chemoreceptors on different sites of an individual leg. The effectiveness of chemical stimulation also differs between the fore and hind legs, with NaCl evoking a higher probability of leg withdrawal movements on the foreleg. Moreover, sucrose was less effective than NaCl at evoking withdrawal movements of the foreleg, particularly at low concentrations. The gradients in behavioural responses can be partially attributed to differences in the responsiveness and density of the contact chemoreceptors. These results may reflect the different specialization of individual legs, with the forelegs particularly involved in food selection.     

Spontaneous recovery of precise movement and of the postural fixation of the extremities after excision of the somatosensory cortex in dogs

The extirpation of the foreleg area in the somatosensory cortex (SI) in dogs was performed in order to study the role of this area in motor control of the corresponding limb. Stable precise avoidance and escape reactions were established before the cortical lesion. Avoidance reactions disappeared during the first week after the surgery but then they were gradually restored without retraining. At the third weak there was a practically complete recovery of the precision of movements, the ability to fix the leg position and of the duration of successive phases of the reactions. The conclusion was drawn that the initial disturbances of avoidance reactions were most likely the result of diaschisis (shock). The initial disturbances of visually guided instrumental movements and escape reactions were much weaker than those of avoidance reactions (lifting of the foreleg in response to conditioned signal).     

Mechanism of the generalization of a conditioned reflex elaborated to electrostimulation of the brain in dogs

To study functional connections in the limbic system (LS), a model was used of instrumental alimentary CR, elaborated in response to low-frequency hippocampus electrostimulation with testing of its generalization within the LS. The dependence was established of the generalization on activation of corresponding pathways between the signal and tested brain structures, the activation of pathways was estimated by EPs recorded in limbic structures in response to hippocampus stimulation (during CR performance), or vice versa (in generalization trials). It turned out that for the appearance of CR generalization, two-way connections between signal and tested brain structures or connections only to the signal structure are more important. One-way connections from the signal structure to tested ones, judging by data, are not important for appearance of the CR generalization in used model of conditioning.     

Conditioned reflex changes in the intra-analyzer interaction of the afferent inputs from the lateral geniculate body and pulvinar thalami in the cerebral cortex of cats

Paired heterogeneous stimulation of the lateral geniculate body (LGB) and pulvinar (Pulv) as a conditioned stimulus of alimentary instrumental conditioned reflex (CR), resulted in a change of relations between afferent inputs from LGB and Pulv to the visual and associative cortex of cats. At stimulation of LGB preceding by 40 ms, facilitation of the response to testing Pulv stimulation observed in untrained cats, appeared only at the beginning of the learning and was suppressed by the end of elaboration, when the amplitude of the response to the conditioning LGB stimulation greatly increased. In the process of CR elaboration (in the middle of learning), Pulv stimulation preceding by 40 ms facilitated the response to the testing LGB stimulation and simultaneously increased the amplitude of the response to the conditioning Pulv stimulation.     

Organization of the connections of the putamen with the cerebral cortex and hypothalamus]

Connection between the putamen, the brain cortex and the hypothalamus, as well as the role of the former in different aspects of purposive behaviour have been studied in a complex morpho-physiological investigation. In 12 cats, after developing a symmetrical active-defensive conditioned reflex, unilateral electrolysis of the putamen has been performed and the number of conditioned-reflexive reactions have been counted before and after coagulation. The brains have been treated after Nauta--Gygax, Fink--Heimer with additional staining after Kawamura--Niimi. Monosynaptic connections of the putamen with frontal, precentral, postcentral, orbital, parietal cortical areas have been revealed; direct pathways from the putamen to the infundibulum of the grey tuber, to the posterior and lateral hypothalamic nucleus have been demonstrated; participation of the putamen in the formation of active-defensive conditioned reflexes has been stated, as well as in emotional behaviour with a preferable use either the right or the left foreleg.     

The time interval effect on two consecutive LHRH-TRH tests on adult female baboons

To Clarify the relationship between the time interval and pituitary Luteinizing hormone (LH), Follicular stimulation hormone (FSH) and prolactin (PRL) secretion function under LHRH-TRH stimulation, 4 mature female baboons were used. Two consecutive LHRH (100 micrograms)-TRH (250 micrograms) stimulations with a 60 min interval between them was carried out in the early follicular phase, late follicular phase and mid luteal phase in the same baboon in the first menstrual cycle, then carried out with a 120 min interval between tests in the third menstrual cycle. The LH, FSH and PRL were measured by specific radioimmunoassay. The PRL maximum response to the first bolus of TRH was higher than maximum response to the second bolus of TRH. The PRL maximum response to the second TRH at a 120 min interval was higher than the maximum response to the second TRH at a 60 min interval. It seems that the TRH had the dominant effect on PRL releasing but not on PRL Priming. The maximum LH response to the second bolus of LHRH was higher than the maximum response to the first bolus of LHRH. The LH maximum response to the second bolus of LHRH at a 60 min interval was greater than the maximum response at a 120 min interval in the follicular phase but it was the reverse in the luteal phase. The FSH response to the second LHRH was different from the LH response.(ABSTRACT TRUNCATED AT 250 WORDS)     

An analysis of the neuronal processes in the activating brain systems of the rat during the acquisition of an instrumental defense reflex

In chronic experiment, a defensive conditioned reflex was elaborated in rats with electrodes implanted in the reticular oral pons nucleus, cortico-medial group of amygdalar nuclei, ventromedial hypothalamic nucleus and central grey substance of the midbrain. Synchronization of the activity of neuronal groups of emotiogenic formations in the studied brain structures, became enhanced at formation of the conditioned reflex. A dependence was revealed of the level of correlation of limbic neuronal groups activity on functional state of the reticular formation, as well as neurochemical correlation mechanisms. The increase (decrease) of coefficients of correlation of the activity of neuronal ensembles of limbic structures was accompanied by a change of evoked potentials parameters recorded in them.     

The effect of ablation of the caudate nucleus on the alimentary zone of the lateral hypothalamus]

A conditioned food-procuring reaction previously elaborated to an acoustic stimulus was reproduced in chronic experiments on six cats by means of direct electrical stimulation of the posterior parts of the lateral hypothalamus. Folloiwng extensive bilateral electrolytic ablation of the caudate nucleus, conditioned food-procuring reaction to the stimulation of the hypothalamus could not be reproduced for 40 to 70 days. The conditioned foor-procuring reflex to the acoustic stimulus disappeared for 14 to 30 days to be subsequently spontaneously restored. After caudatotomy, a diminution of the average amplitude of background oscillations and of evoked potentials to acoustic stimuli was recorced in the examined zones of the lateral hypothalamus. The part played by the caudate nucleus in the processes of alimentary behaviour activation is discussed.     

The facilitatory influence of anterior cingulate cortex on ON-OFF response of tactile neuron in thalamic ventrobasal nucleus

The structures of limbic system have been found to modulate the auditory, visual and pain afferent signals in the related nuclei of thalamus. One of those structures is anterior cingulate cortex (ACC) that influences nocuous response of the pain-sensitive neurons in the ventropos-tero-lateral nucleus of thalamus. Thus, we inferred that ACC would also modulate tactile information at the thalamic level. To test this assumption, single units were recorded extracellularly from thalamic ventrobasal nucleus (VB). Tactile ON-OFF response and the relationship between different patterns of the responses and the parameters of tactile stimulation were examined. Furthermore, the influence of ACC on the tactile ON-OFF response was studied. ACC stimulation was found to produce a facilitatory effect on the OFF-response of ON-OFF neurons. It lowered the threshold of the off-response of that neuron, and therefore changed the response pattern or enhanced the firing rate of the OFF-response of the neuron. The study on rec     

The facilitatory influence of anterior cingulate cortex on ON-OFF response of tactile neuron in thalamic ventrobasal nucleus

The structures of limbic system have been found to modulate the auditory, visual and pain afferent signals in the related nuclei of thalamus. One of those structures is anterior cingulate cortex (ACC) that influences nocuous response of the pain-sensitive neurons in the ventropostero-lateral nucleus of thalamus. Thus, we inferred that ACC would also modulate tactile information at the thalamic level. To test this assumption, single units were recorded extracellularly from thalamic ventrobasal nucleus (VB). Tactile ON-OFF response and the relationship between different patterns of the responses and the parameters of tactile stimulation were examined. Furthermore, the influence of ACC on the tactile ON-OFF response was studied. ACC stimulation was found to produce a facilitatory effect on the OFF-response of ON-OFF neurons. It lowered the threshold of the off-response of that neuron, and therefore changed the response pattern or enhanced the firing rate of the OFF-response of the neuron. The study on receptive fields of ON-OFF neurons showed that the excitation of the ACC could change an ON-response on the verge of a receptive field into an ON-OFF response. The above results suggest that the ACC modulation sharpens the response of a VB neuron to a moving stimulus within its receptive field, indicating that the limbic system can modulate tactile ascending sensory information.     

Effects of food motivation on spike activity of cat somatic cortex neurons

Spike response to unconditioned electrocutaneous stimulation was investigated in cortical neurons of areas 3 and 4 in untrained hungry cats during heightened excitation motivated by food presentation and when at rest. This reinforcement led to changed background activity level, reduced intensity of the initial stages of spike response, and disappearance of late neuronal response. Neuronal response of the same cortical area to a conditioned stimulus (a clicking sound) during reduced food motivation (the animals being sated during the course of the experiment) was also studied under the effects of instrumental feeding reflex. Coordination between the timing of neuronal response and their corresponding movements was discovered from comparing response pattern accompanying the execution of paw-placing (conditioned reflex and intersignal) movements and those recorded at different levels of food-induced excitation, as well as a similarity between these reactions. It was found that the initial stages of neuronal response to a conditioned signal only occurred during contraction of the brachial biceps muscle, while coordination between their timing and that of EMG changes was dependent on the animal's degree of satiation. Findings indicate the possibility of food-induced excitation substantially influencing spike response pattern in somatic cortex neurons.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 19, No. 6, pp. 725–735, November–December, 1987.     

Comparative study of effect of cortical nucleus of amygdala and pyriform cortex on activity of bulbar respiratory neurons in cats

Comparative microelectrophysiological study of character and peculiarities of effects of the cortical nucleus of amygdala and of the periamygdalar area of pyriform cortex on impulse activity was performed on the same single functionally identified respiratory medullar neurons. A high reactivity of bulbar respiratory neurons to stimulation is established in both studied limbic structures. There is established the qualitatively different character of their response reactions at stimulation of the cortical amygdala nucleus and the periamygdalar cortex. The cortical amygdala nucleus has been shown to produce both facilitating and inhibitory effects (with predominance of the activating one) on activity of medullar respiratory neurons (without topographical orderliness). The effect of periamygdalar cortex at stimulation of various parts was characterized by topographic differentiation. The suppressing reactions of neurons in the majority of cases were recorded at stimulation of the rostral area of periamygdalar cortex, whereas the excitatory reactions-at stimulation of its caudal part. Functional organization of respiratory control of the studied limbic system structures is discussed.     

Septal nuclei in the regulation of vago-sensitive neurons activity of the solitary nucleus in cats

The descending influences of the septal nuclei (lateral nucleus--LSN and bed nucleus stria terminalis--BNST) on activity of viscero-sensory neurons of the nucleus of tractus solitarius (NTS) identified by stimulation of cervical part of the n. vagus were investigated in the cat anaesthetised by chloraloze-nembutal combination. It was found that out of 70 units recorded in the NTS area 50 were identified as those of primary and secondary input vagal neurons. Influence of single, paired and frequency stimulation on the septal structures was studied on these neurons. It was revealed that 30% (15 un) reacted by phase-specific response to the single stimulation of the septal nuclei. The latent period of initial excitation was in the range 5-25 ms. During the paired stimulation these neurons were not able to react to the second stimulus for the equal 10-300 ms. It was revealed that 34% (17 un) of the identified vagal neurons reacted by a tonic change of their spontaneous activity. The increase of frequency stimulation to 20 Hz evoked different changes of the rhythmical activity of the vagal neurons (increase, diminishing or inhibition). The study of interaction between central and peripheral signals in the solitary neurons induced blocking influence of descending septal discharge on the vagal test response. It is possible that the septal downward impulses reach the vago-sensitive solitary neurons indirectly through other structures of the limbic brain (amygdala, hypothalamus) and participate in modulation of the spontaneous activity of these neurons.