Damage to the nucleus accumbens shell but not core impairs ventral tegmental area stimulation-induced feeding.

Food intake is regulated not only by homeostatic requirements but also by emotional factors (e.g. palatability of food, alleviation of emotional tension etc.). The nucleus accumbens (Acb) is a part of the mesolimbic dopaminergic system which is responsible for a positive emotional aspect of various homeostasis-relevant stimuli. In the present work, we tested the Acb involvement in feeding behaviour using an experimental paradigm specifically designed to assess motivational vs motor aspect of food ingestion. In rats, feeding was evoked by electrical stimulation of the midbrain ventral tegmental area (a somatodendritic region of mesolimbic system) and assessed quantitatively with the use of the latency to feed/stimulation frequency curve-shift paradigm before and after electrolytic lesion of Acb. An impairment of stimulation-induced feeding manifesting as an elevation of the reaction threshold and a rightward, parallel shift of the stimulation frequency/reaction latency curve in the range of frequency which is sensitive to motivational aspects of food occurred after lesions localized mainly in the Acb shell. The lesions situated mainly in the Acb core were ineffective. The results obtained indicate that the Acb shell connected with the limbic system but not the motor-related Acb core affects motivational aspects of feeding behaviour.

Microinjection of procaine into the pedunculopontine tegmental nucleus suppresses hippocampal theta rhythm in urethane-anesthetized rats.

It was found that the cholinergic component of the pedunculopontine tegmental nucleus (PPN) is involved in the generation of theta rhythm in the hippocampus. However, it is still not known how important PPN is in the brainstem theta-generating system, where the nucleus reticularis pontis oralis is regarded as a primary generator. In the present experiment, performed on urethane-anesthetized rats, we studied the effect on the tail pinch-elicited hippocampal theta of unilateral inactivation of PPN by means of direct procaine microinjection. Procaine induced ipsilateral suppression of theta rhythm, manifested as desynchronization of hippocampal EEG, a shift of the fast Fourier transformation (FFT) power peak toward lower frequencies, and a reduction of FFT peak magnitude at theta band. Hippocampal field activity returned to normal (both its FFT peak frequency and magnitude) within 30 min after the injection. The results obtained indicate that PPN is critical for hippocampal theta generation but it may not be involved in encoding theta frequency.

Stress-induced changes in peripheral natural killer cell cytotoxicity in pigs may not depend on plasma cortisol.

The study examined cortisol (COR) involvement in stress-related changes in natural killer cell cytotoxicity (NKCC). The relationship between blood COR level, phasic changes in NKCC, and the number of large granular lymphocytes (LGL) was examined in pigs during the course of 4-h immobilization stress (IMB) and for 6 days after its termination. NKCC was determined using 18-h 51Cr-release assay, LGL number was assessed with a standard hematological method, and plasma COR level was measured by radioimmunoassay. The blood level of COR was increasing during IMB (max 446Delta% at the second hour) and decreased after its termination (max -59Delta% on day 2). Changes in NKCC level and LGL number were biphasic; i.e., an initial increase in both measures (NKCC max 24Delta%, LGL max 18Delta%) in an early phase of stress (0-1h) was followed by their subsequent decrease (NKCC max -35Delta%, LGL max -41Delta%) in the late phase (3-4 h) of stress, which persisted for several days after termination of IMB. Thus, in the early phase of stress, there was a positive correlation between NKCC, LGL number, and COR levels (all elevated); a positive correlation between the measures also occurred after termination of IMB (all decreased). A negative correlation between COR and NKCC, which might be indicative of COR-related immunosuppression, was found only in the late (3-4 h) phase of stress. It is concluded that COR may be only one of multiple factors (possibly antagonistic) determining an actual immune response during stress.

Peripheral blood natural killer cell cytotoxicity after damage to the limbic system in the rat.

The present work was aimed at examining the possible involvement of different parts of the septal area (dorsal, medial, lateral, and septohypothalamic nucleus), the basolateral amygdala, and the bed nucleus of the stria terminalis (BNST) in the regulation of the cytotoxic activity of NK cells (NKCC). The experimental approach included performing electrolytic (or sham) lesions in the tested brain areas and to measuring the peripheral blood NKCC (chromium-51 release assay), the number of leukocytes and lymphocytes, and the plasma corticosterone levels both before and at different time points after the lesion. Lesions were also induced in the three extralimbic structures: the paraventricular hypothalamic nucleus (PVN), the dorsal caudate-putamen, and the cerebellum. To test for a possible effect on NKCC of stress associated with blood collection, anesthesia, cranial surgery, and passing electric current through the brain the proper control experiments were also performed. Lesions of the medial septum and BNST caused gradual depression of NKCC, which peaked on the 10th day after the lesion, followed by a recovery to the baseline on days 21 (medial septum) and 42 (BNST) postinjury. In the respective sham-lesioned groups, mere insertion of electrodes into the medial septum and BNST evoked transient enhancement of NKCC (on the 3rd postlesion day), probably resulting from mechanical stimulation of the nervous tissue. Destruction of the other limbic and extralimbic structures appeared ineffective. After PVN lesions NKCC remained unchanged, despite an approximately 60% decrease in the basal corticosterone level. No adverse effects of the experimental and surgical procedures on NKCC, leukocyte and lymphocyte number, and corticosterone level were found, indicating that electrolytic lesions and other stereotaxic techniques can be safely used to study the brain-immune system interactions. The results obtained raise the question about the interrelationship between the medial septum and the hippocampal formation, BNST, the medial amygdala, and the hypothalamus (both medial and lateral) as a possible circuit involved in the regulation of cellular immune functions.

Anatomical correlates of the lateral hypothalamic influence on waking-sleep relationship in the rat.

Restricted electrolytic lesions of the lateral hypothalamus (LH) evoke sleeplessness in the rat. The present study was aimed to analyze a possible anatomical substrate of the LH hyposomnia within the hypothalamus. In a group of electrolytically lesioned LH rats the intensity of sleep disturbances, assessed on the basis of EEG records from the neocortex and the hippocampus, was confronted with the localization and the extent of destruction of the LH area and with the topography of known fiber systems of the medical forebrain bundle (MFB). In separate experiments the effects of the destruction of LH cell bodies by means of bilateral ibotenic acid (IBO) injections and inhibition of LH neuronal elements by bilateral muscimol (MUSC) administration were also tested. It was found that pronounced hyposomnia follows electrolytic but not IBO lesions of the LH/MFB area. The effective LH damage might have been localized at every level of its antero-posterior axis, from the preoptic area up to the posterior hypothalamus, suggesting involvement of fiber system(s) rather than a localized group of neuronal pericaria. The most effective lesions transsected projections descending from the preoptic/anterior hypothalamic area, olfactory structures, ventral striatum and the central amygdaloid nucleus as well as fibers connecting LH with the brainstem reticular formation, many of them using GABA as a neurotransmitter. Bilateral MUSC injections caused a dose-dependent, bicuculline-reversible, increase in waking time, most pronounced at a dose of 50 ng, which ressembled the effect of the electrolytic lesion. These results indicate that LH hyposomnia is not attributable to the damage to the intrahypothalamic neurons and suggest the participation of GABA-ergic transmission in LH in waking-sleep regulation.

Effect of unilateral injection of MK-801 into the area of A10 cells on feeding evoked by stimulation of homologous area in the contralateral hemisphere.

It was found previously that unilateral electrolytic and 6-OHDA lesions of the ventral tegmental area (VTA) and unilateral intra-VTA injection of bicuculline resulted in facilitation of behavioral responses evoked by electrical stimulation of the symmetrical VTA area in the contralateral hemisphere. We postulated that "the contralateral facilitation effect", which may reflect the yet unexplored mechanism of immediate compensation after acute unilateral brain injury, is attributable to the A10 DA neurons and their regulatory inputs. The present study was aimed at examining the possible involvement of NMDA-mediated glutamatergic transmission in VTA in the "contralateral facilitation effect". The behavioral model of the VTA stimulation-induced feeding in rats was used. Latency to eat was measured as a function of stimulation frequency before and after unilateral intra-VTA injection of non-competitive NMDA receptors antagonist, MK-801, (doses 0.0, 1.25 and 2.5 micrograms). MK-801 caused a dose-dependent augmentation of feeding evoked by stimulation of the contralateral VTA, which manifested as a decrease in the reaction frequency threshold and a leftward shift of the latency/frequency curve. Dose 2.5 micrograms replicated the facilitatory effect of electrolytic and 6-OHDA lesions. The results are interpreted in terms of MK-801-evoked depression of excitatory glutamatergic tone over A10 DA cells and compensatory increase in DA release in the contralateral hemisphere.

Facilitatory effect of unilateral lesion of the ventral tegmental area on locomotor response to stimulation of the contralateral ventral tegmental area: involvement of GABAergic transmission.

It was found previously that in the rat, unilateral electrolytic lesion of the ventral tegmental area (VTA) facilitated feeding induced by electrical stimulation of the homologous VTA tissue in the contralateral hemisphere. In the present work, VTA stimulation-induced locomotor response was tested in male Wistar rats using a latency to move/stimulation frequency curve shift paradigm in order to check for functional generality of the "contralateral facilitation effect" and also with the aim of elaborating an easy and reliable behavioral model to study this phenomenon. In a further step, the hypothesis was tested that enhancement of function of the intact VTA results from elimination of tonic GABAergic influence derived normally from the lesioned VTA. GABA(A) (bicuculline, doses 0, 0.5 and 5.0 ng) and GABA(B) (phaclofen, doses 0, 500 and 1000 ng) receptors antagonists, and for comparison, a GABA(A) receptor agonist (muscimol, doses 0, 12.5, 25. 0 and 50.0 ng), were injected unilaterally to VTA and their effect on locomotor response elicited by electrical stimulation of the contralateral VTA was tested in a latency/frequency paradigm. It was found that similar to feeding, locomotor response evoked by unilateral electrical stimulation of the VTA was facilitated after contralateral VTA lesion which manifested as a decrease of the locomotion threshold and a leftward shift of the function relating latency to move to stimulation frequency. The effect was immediate, long-lasting and specific to the VTA destruction; lesions outside the VTA area caused gradual impairment of the locomotor response to stimulation. The facilitatory effect of the electrolytic lesion could be replicated by bicuculline, which significantly facilitated stimulation-induced behavior. Phaclofen exerted slight facilitating influence only at a low dose. No effect of muscimol on the locomotion threshold was found. We conclude that "the contralateral facilitation effect" at the level of VTA reflects the interhemispheric regulation of activity of the dopaminergic (DA) cells in which GABA(A)-mediated interhemispheric communication plays a significant role.

Augmentation of ventral tegmental area stimulation-induced feeding by both stimulation and lesion of the contralateral ventral tegmental area in the rat.

Unilateral lesions of the ventral tegmental area (VTA) facilitate behavioral responses (feeding and exploration) induced by electrical stimulation of the VTA in the contralateral hemisphere. It was hypothesized that this facilitation may result from a lesion-induced compensatory increase in dopamine transmission in the intact hemisphere. In the present study we tested on the functional level the hypothesis that the activity of bilateral mesocorticolimbic systems is inversely related. For this purpose we compared the effect of unilateral subthreshold activation with the effect of subsequent unilateral lesion of VTA on feeding response evoked by electrical stimulation of the contralateral VTA. In male Wistar rats implanted with bilateral VTA electrodes stimulation-induced feeding was tested in a latency to feed-stimulation frequency curve-shift paradigm. One electrode was used for induction of feeding reaction and the other electrode was used for concurrent stimulation (with the subthreshold current) and subsequent electrolytic lesioning of the contralateral VTA. It was found that both contralateral stimulation and subsequent lesion performed through the same electrode facilitated a feeding response that manifested as a decrease in the reaction's threshold and a leftward shift of the latency-frequency curve. The paradoxical similarity of the effects of the stimulation and lesion is discussed in terms of functional organization of the mesocorticolimbic system and adaptive changes in dopaminergic transmission.

Effect of lateral hypothalamic lesion on sleep-waking pattern and EEG power spectra in the rat.

Bilateral, electrolytic lesion of the lateral hypothalamus (LH) in rats produces hyposomnia and qualitative EEG changes which are difficult to assess by conventional visual inspections of electroencephalograms. In the present study the spectral analysis of EEG was applied in LH-lesioned rats and confronted with a standard visual scoring method. One-hour samples of hippocampal and cortical EEG were taken from the light part of the circadian cycle before and after electrolytic or sham LH damage. In half of the LH-lesioned rats a power spectral analysis was performed using a Fast Fourier Transform routine at 1 Hz bands from 0.5 to 25 Hz; in the other half, as well as in the sham-lesioned group, EEG records were visually scored for the amount of waking, slow wave sleep and paradoxical sleep. Significant hyposomnia effects were found in LH-lesioned rats. Power spectral analysis of hippocampal EEG revealed a significant increase in power density at 4-6 Hz and a reduction at 7-10, 14-17, 19-22 and 23-24 Hz. In neocortical EEG there was a significant increase in power density at 5-6 Hz band and a reduction at 7-8 Hz. The results are discussed in the context of the effects of selective destruction of the specific neurotransmitter systems occupying the LH area.

Bilateral lesions of the pedunculopontine tegmental nucleus affect feeding induced by electrical stimulation of the ventral tegmental area.

The pedunculopontine tegmental nucleus (PPN) is anatomically connected with dopaminergic cells in the ventral mesencephalon, which are known to participate in the regulation of various adaptive appetitive behaviours. In the present experiment we studied a possible involvement of PPN in feeding elicited by stimulation of the ventral tegmental area (VTA). It was found that bilateral electrolytic lesioning of the PPN affected VTA-elicited feeding. However, the effects were diverse and showed dependence on the localization of the lesion within the PPN area. Lesions localized anteriorly in the PPN impaired VTA feeding whereas those involving the middle portion of the nucleus facilitated electrically elicited food ingestion. A precise alignment of the lesion and the area activated at the site of stimulation appeared crucial for the effect of the lesion. The results indicate that PPN belongs to the central feeding circuitry and it contains both activating and inhibiting elements directed to the ventral tegmental area.

Electrolytic lesions of the lateral hypothalamus influence peripheral blood NK cytotoxicity in rats.

Bilateral electrolytic lesions of the lateral hypothalamic (LH) area in Wistar rats result in a time-dependent blood NK cytotoxicity changes as measured by the 51Cr-release (for entire cell population) and agarose (for a single-cell) assays. NK activity against YAC-1 and K-562 cells shifts from depression through enhancement to another depression on the 2nd, 5th and 21st post-lesion day, respectively, as compared to both LH sham-operated animals and the pre-lesion baselines. This effect is not attributable to malnutrition and dehydration resulting from ingestive impairments evoked by LH lesions. No significant change in NK cytotoxicity was found after destruction of the medial hypothalamus (MH). The results indicate that LH, under normal conditions, which may be considered as a dynamogenic and stressogenic hypothalamic area is essential for proper regulations of NK cytotoxicity at both population and single-cell level.

Daily pattern of EEG activity in rats with lateral hypothalamic lesions.

The experiment was aimed to further elucidate the phenomenon of sleep suppression observed earlier after electrolytic lesions of the lateral hypothalamus (LH). In male Wister rats the amounts of waking (W), slow wave sleep (SWS) and paradoxical sleep (PS) were counted in 1 h samples of EEG taken from the light and dark parts of the circadian cycle, as well as in the whole 12 h diurnal records before lesioning and after electrolytic or sham lesions of LH. Significant increase of W with a simultaneous reduction of SWS and PS was found in 1h and 12h diurnal records; no effect of the lesion on nocturnal EEG was observed. The results suggest that lesion-induced sleep suppression concerns the light part of the day when rats are naturally less active, and that 1h samples of diurnal EEG may be sufficient to diagnose LH insomnia. No correlation was found between the magnitude of waking-sleep disturbances and the intensity of ingestive impairments (aphagia, adipsia, body weight loss) evoked by LH lesions which suggests that LH insomnia may be a result of disruption of a mechanism directly involved in the regulation of waking-sleep cycle rather than a secondary effect of other lesion-induced impairments.

Unilateral damage to the ventral tegmental area facilitates feeding induced by stimulation of the contralateral ventral tegmental area.

Unilateral lesions of the ventral tegmental area (VTA) facilitated feeding induced by electrical stimulation of the homologous VTA tissue in the contralateral hemisphere. The lesions shifted the function relating latency to begin feeding to stimulation frequency to the left simultaneously causing a reduction of frequency threshold for feeding reaction. Facilitation of feeding was immediate (with a peak on the 2nd postlesion day) and in some animals persisted up to the end of the 2-week experimental period. No facilitation of VTA stimulation-induced feeding was found in the control animals in which comparable lesions were performed in the contralateral lateral hypothalamus or the antero-dorsal thalamus which suggests that the effect was site specific. Individual differences in the magnitude and duration of the facilitatory effect on feeding may be related to the variability in the medio-lateral localization of the lesions. The results are interpreted in terms of compensatory increase in the dopaminergic transmission and/or decrease of the GABA-ergic inhibitory tone in the contralateral hemisphere after unilateral lesion to the mesencephalic dopaminergic systems. A possible involvement of the noradrenergic transmission is also discussed.

Facilitory effect of delta 9-tetrahydrocannabinol on hypothalamically induced feeding.

Six male Lewis rats were tested for the effect of delta 9-tetrahydrocannabinol (delta 9-THC) on feeding evoked by electrical stimulation of the lateral hypothalamus. Treatment with delta 9-THC (0.4 mg/kg IP) decreased frequency threshold for feeding by 20.5% (+/- 4.3), causing a leftward shift in the function relating stimulation frequency to the latency to begin eating 45-mg food pellets upon stimulation onset; there was no change in the asymptotic performance that was approached with sufficiently high stimulation frequencies. Naloxone (1 and 2 mg/kg) reduced the facilitory effect of delta 9-THC, but did so at doses that can inhibit feeding in the no-drug condition. These data are consistent with evidence implicating endogenous opioids in feeding, and suggest (but do not confirm) that the facilitation of feeding by delta 9-THC may be mediated by endogenous opioids. The facilitation of stimulation-induced feeding by doses of delta 9-THC that have been found to facilitate brain stimulation reward is consistent with evidence suggesting common elements in the brain mechanisms of these two behavioral effects of medial forebrain bundle stimulation.

The EEG activity after lesions of the diencephalic part of the zona incerta in rats.

Neocortical and hippocampal EEG activity was recorded in 23 rats subjected to the bilateral electrolytic lesions of the diencephalic zona incerta (ZI). The aim was to find whether damage to ZI can replicate insomnia and disturbances in cortical EEG desynchronization and hippocampal theta rhythm found after lesions of the lateral hypothalamic (LH) area. No effect of the ZI lesions on waking-sleep cycle was found. The amplitude and frequency of cortical waves and hippocampal theta rhythm during waking were changed only in some rats. These changes were small, short-lasting and bidirectional (toward and increase or decrease in different subjects). Both the amplitude and frequency of paradoxical sleep theta were depressed in part of animals. Thus the marked EEG changes after LH lesions can not be attributed to simultaneous damage of the adjacent subthalamic region. However, the ZI seems to constitute a part of a larger system regulating cortical arousal and hippocampal theta rhythm.

Disturbances in sleep-waking pattern and cortical desynchronization after lateral hypothalamic damage: effect of the size of the lesion.

The effect of electrolytic lesions of varying size within the anterior part of the lateral hypothalamus (LH) on neocortical activity and quantitative sleep-waking relations was studied in male Wistar rats. It was found that extensive LH lesions caused simultaneously an abolishment of cortical desynchronizing reactions and an electroencephalographic insomnia. More restricted damage left the qualitative pattern of cortical EEG unchanged, but still produced substantial reduction in the amount of sleep. Pronounced EEG disturbances coexisted with relatively mild behavioral deficits. It is concluded that a constellation of the LH syndrome symptoms is critically dependent on the variations of lesion parameters.

Morphological substratum of lateral hypothalamic aphagia and adipsia: a mapping study in the rat.

The purpose of the experiment was to map an area involved in the regulation of food and water intake within the region of the lateral hypothalamus (LH), the adjacent subthalamus and antero-ventral midbrain. The strategy was to make a series of electrolytic lesions, varying in size and localization and to correlate the size of the damage to particular structures occupying the region with the presence and intensity of ingestive disturbances. The highest correlation was found between the presence and duration of aphagia and adipsia and the size of damage to the tuberal part of LH. Even large lesions localized anteriorly or posteriorly to this region gave only moderate ingestive deficits. Surprisingly, total or almost total disruption of the nigro-striatal bundle at the level of the anterior or posterior LH evoked only slight, if any, disturbances in food and water ingestion. No correlation was found between the duration of aphagia and adipsia and the size of damage to zona incerta, fields of Forel, capsula interna, lemniscus medialis, ventral tegmental area and substantia nigra. Our results did not confirm pharmacological data concerning dopamine depletion-induced aphagia and adipsia. It seems that the role of the nigro-striatal system for LH ingestive impairments is still to be cleared up.

Differential effect of the damage to the lateral hypothalamic area on hippocampal theta rhythm during waking and paradoxical sleep.

Hippocampal theta rhythm was analyzed in rats subjected to bilateral, electrolytic lesions of the lateral hypothalamic (LH) region at different levels of its rostro-caudal axis. It was found that damage to the LH disturbed the hippocampal theta activity both during waking and paradoxical sleep. The main effect consisted in the lowering of the theta frequency. Typically, a decrease of frequency was accompanied by an increase of amplitude during waking, and an amplitude fall during paradoxical sleep. Extensive lesions increased the amount of rhythmic slow activity during waking and induced long trains of immobility-related theta. The general picture of impairments of the hippocampal theta rhythm in particular subjects depended on the size of the lesion and, to some extent, also on its localization within the LH. It is concluded that LH region contains systems of fibers which transmit impulses from the brain stem reticular formation to the prosencephalic structures generating the rhythmicity of theta.

The effect of lateral hypothalamic lesions on spontaneous EEG pattern in rats.

Neocortical and hippocampal EEG was recorded in ten rats subjected to bilateral lesions of the lateral hypothalamus at different levels of its rostro-caudal axis. In nine rats the damage evoked a marked increase of waking time with a simultaneous reduction of the percentage of large amplitude irregular activity related to slow wave sleep in the first eight postlesion days. There was also a decrease in the amount of paradoxical sleep. Enhanced waking coexisted with behavioral somnolence. The most extensive hypothalamic lesions produced qualitative changes of EEG concerning mainly the frequency of hippocampal theta rhythm. Control lesions within the subthalamic region did not influence either qualitative or quantitative EEG pattern. It is concluded that limited lesions of the lateral hypothalamus did not destroy a sacient number of reticular activating fibers to disturb a cortical desynchronizing reaction. The increased amount of waking pattern may be due to serotonergic deafferentation of the neocortex. Dissociation of behavioral and EEG indices of the level of arousal imply the existence of separate neuronal systems for both aspects of activation.