Stimulation Of Lateral Hypothalamus Research Articles

Effects of midbrain reticular formation, hippocampal, and lateral hypothalamic stimulation upon recovery from neophobia and taste aversion learning

In a neophobia paradigm midbrain reticular formation (MRF) electrical stimulation applied after consumption of a novel flavor produced a time-dependent disruption in recovery from neophobia (learned safety), while hippocampal and lateral hypothalamic stimulation had no disruptive effects. In a learned aversion paradigm neither MRF nor hippocampal or lateral hypothalamic stimulation applied after the illness experience produced a disruptive effect. In conjunction with previously reported effects of amygdala stimulation [12] the data support the existence of separate information processing systems mediating learned aversion and learned safety.

Effects of hippocampal and lateral hypothalamic electrical stimulation on hippocampal cholinergic mechanisms in BALB/c inbred mice

Electrical stimulation of the hippocampus (HPC) and of the lateral hypothalamus (LH) were found to have the same 24 h delayed effect on choline acetyltransferase activity. Since previous experiments demonstrated that these treatments had the same effect on memory storage processes, the present finding and earlier neurochemical investigations suggest that HPC and LH stimulation might act through a common hippocampal cholinergic mechanism.

Operant discriminative conditioning of vertical eye movements in the midpontine pretrigeminal cat

In the acute midpontine pretrigeminal cat, either upward or downward eye movements above a certain preset amplitude were reinforced by electrical stimulation of the lateral hypothalamic (LHT) reward area, which did not induce a significant eye movement by itself. During the course of the reinforcement procedure, eye movements greatly increased. In a yoked control test where LHT stimulation was delivered to a cat, independently of its own eye movements, no significant enhancement of the eye movements was observed. However, when reinforcement was given contigently on each large eye movement, eye movement rat became much higher. When cats were trained for an operant discrimination between an S + (light-off or light-on) and an S − (light-on or light-off), 5 cats acquired clearly differential responses to the S + and S −. They also learned a discrimination reversal. Furthermore, removal of the visual cue eliminated differential responses during the reinforcement and nonreinforecement periods. These data strongly suggest that, in this preparation, a real learning process in the form of a visual discrimination is maintained and an operant conditioning of eye movements with hypothalamic stimulation was achieved without feedback from the peripheral nerves or caudal central nervous system.

Effect of food and water deprivation on hippocampal self-stimulation and poststimulation feeding

Barpressing for electrical stimulation of the dorsolateral hippocampus was facilitated by both food and water deprivation. These results were not simply attributable to a nonspecific effect of deprivation on self-stimulation; food deprivation but not water deprivation produced an increase in barpressing for lateral hypothalamic stimulation. Feeding elicited by dorsolateral hippocampal stimulation increased after food deprivation, but was not affected by water deprivation. These findings suggest a dissociation between the reinforcing consequences of hippocampal stimulation and the effects of hippocampal stimulation on feeding. In addition, there seems to be at least some degree of independence between the neural mechanisms underlying hippocampal reward and those underlying hypothalamic reward.

Effect of hypothalamic stimulation on mesencephalic neurons

The purpose of this study was to determine the effect of electrical stimulation of the lateral hypothalamus and preoptic area on second- and higher-order neurons in the ventral tegmental area of the mesencephalon. Single-unit responses were recorded by tungsten microelectrodes in anesthetized cats. Lateral hypothalamic stimulation caused short- and long-latency excitation as well as antidromic activation of ventral tegmental area neurons. However, half of the responsive neurons exhibited a suppression of firing, or inhibition, following stimulation. The short latency of onset of the suppression obtained in some of these neurons suggests the possibility that, in addition to a descending excitatory hypothalamic outflow, descending monosynaptic inhibitory pathways to the ventral tegmental area are also present.

New approach of the cardio-vascular depressive mechanism during lateral hypothalamic stimulation.

Paraventricular nucleus stimulation acts directly on the alpha- and beta-adrenoreceptors in heart and arterioles, eliciting arterial hypotension and cardiac chronotropism and inotropism decrease. Efferent pathways follow sympathetic nervous fibres through the medulla and the thoraco-lumbar ganglionic chain. The role of the alpha- and beta-adrenoreceptors in these depressive reactions is discussed.

Interaction between morphine and reinforcing lateral hypothalamic stimulation

The interaction between morphine and lateral hypothalamic self-stimulation in rats was investigated in three experiments. In nonaddicted animals injections of moderate doses of morphine (8 mg/kg) resulted in a short-lasting increase in the self-stimulation threshold. Injections of low doses (2 mg/kg) did not alter the self-stimulation threshold significantly. In addicted animals self-stimulation thresholds were significantly lower 2 h compared to 22 h after injection of 200 mg/kg morphine hydrochloride (calculated as the salt). A 16 mg/kg injection of morphine in non-addicted rats suppressed self-stimulation. However, when the animals were administered noncontingent priming stimulation and were hand-shaped toward the lever whenever they left it, they continued to lever-press throughout the entire 90-min postinjection testing period. The animals that were neither primed nor shaped (and therefore remained unstimulated), however, showed a significantly better recovery when tested 90 min after the injection; i.e., their response rate was higher than that of the primed and shaped animals, which were engaged in bar-pressing throughout the entire testing procedure.

EFFECT OF ADRENERGIC BLOCKADE AND DEXAMETHASONE ON THE ALDOSTERONE RESPONSE TO BRAIN STIMULATION IN THE RHESUS MONKEY

The increase in aldosterone and plasma renin activity (PRA) observed after stimulation of extrahypothalamic sites within the brain of the rhesus monkey was prevented by the prior administration of the beta-adrenergic blocking agent propranolol. alpha-Adrenergic blockade by phentolamine had no inhibiting effect. Propranolol only partially reduced the response of aldosterone to lateral hypothalamic stimulation in spite of inhibition of PRA; a partial reduction in aldosterone was also obtained from this site after dexamethasone treatment without any effect on PRA. It was concluded that the increase in aldosterone observed after extra-hypothalamic stimulation was mediated mainly through the renin-angiotensin mechanism whereas in the case of the hypothalamus, release of ACTH was also a contributory factor.

Aftereffects of rewarding lateral hypothalamic brain stimulation and feeding behavior

The aftereffects of rewarding lateral hypothalamic brain stimulation are shown to depress the speed with which rats will initiate consumption of various foods. The strength of this depression was positively correlated (r xy = 0.60) with the rate of self-stimulation on that electrode. Seemingly paradoxical relations between this finding and other known characteristics of lateral hypothalamic stimulation are discussed.

Stimulation bound ingestive behavior: A view from the tail

Applying a sustained but mild pressure to a rat's tail (tail-pinch) induces many of the same responses as does electrical stimulation of lateral hypothalamus (such as eating, gnawing, maternal and sexual behaviors) and in a higher percentage of cases. Some of the parallels include the stimulus bound character of the behavior, the propensity of tail-pinched animals to switch goals and response patterns, and a common response to manipulations such as gastric loading, diazepam injection, and flavor-associated poisoning. A major difference involves the failure of tail pinch to induce or facilitate water ingestion. Similarities and differences between effects of tail-pinch and electrical brain stimulation on ingestive behavior are assessed and the hypothesis is advanced that a common theme may be a preferential facilitation of nigro-striatal dopamine system function, promoting a heightened sensitivity and responsivity to most survival-oriented and/or prepotent environmental stimuli.

An analysis of barbiturate-induced eating and drinking in the rat

Systemic injections of pentobarbital and phenobarbital induced nondeprived animals to eat and to drink. The feeding was not secondary to osmotic changes brought on by drinking, and the drinking was not dependent upon eating. Responses to pentobarbital were quantitatively and qualitatively different from behaviors elicited by lateral hypothalamic stimulation.

A dose-response study of anorectic drug effects on food intake, self-stimulation, and stimulation-escape

A comparison was made of the short-term effects in rats of 3 anorectic drugs (amphetamine, fenfluramine, and phenylpropanolamine) on food intake and responses to obtain brain stimulation and to escape from automatic brain stimulation. At a dose which decreased food intake, amphetamine increased self-stimulation, but not stimulation-escape. Fenfluramine decreased both self-stimulation and stimulation-escape. Phenylpropanolamine, on the other hand, decreased self-stimulation, but not stimulation-escape. Even though all 3 drugs decreased food intake, each of them had different effects on hypothalamic self-stimulation and stimulation-escape. Only the actions of phenylpropanolamine were in agreement with the hypothesis that lateral hypothalamic reward and aversion reflect the animal's tendency to eat, suggesting that other aspects of reinforcement are also involved in lateral hypothalamic stimulation and were affected differently by these drugs.

Inhibitory potentials produced in cortical cells by stimulation of the lateral hypothalamus in rabbits

(1) Intracellular potentials were recorded from pyramidal tract (PT) and non-pyramidal tract (non-PT) cells of the frontal cortex in urethane-anesthetized rabbits and the effects of electrical stimulation of the lateral hypothalamus (LH) were examined on the ipsilateral side. (2) Latencies of antidromic spikes of PT cells evoked by stimulation of the medullary pyramidal tract (PYR) had a unimodal distribution with the mean at 4.0 msec. The mean conduction velocity of the pyramidal tract fibers was 10.5 m/sec. (3) Prolonged IPSPs were produced in PT and non-PT cells by single shock stimulation of LH (LH-IPSP). They were significantly longer lasting than those produced by PYR stimulation (PYR-IPSP). (4) The latencies of LH-IPSPs ranged from 1.7 to 25.0 msec and were divided into two groups. The latencies of PYR-IPSPs had a unimodal distribution ranging from 2.5 to 30 msec. (5) In a few non-PT cells, a sequence of brief depolarization and prolonged hyperpolarization occurred in response to LH stimulation. (6) In some non-PT cells, EPSPs which occasionally resulted in spike discharges were observed after LH stimulation. However, no excitation of PT cells was observed by LH stimulation.

Influences of hypothalamic stimulation upon septal and hippocampal electrical activity in the cat

Spontaneous patterns of hippocampal EEG and septal cell activity were studied in immobilized cats, and the influences of high frequency stimulation of medial hypothalamus (MH) and lateral hypothalamus (LH) were determined. Septal cells were divided into 3 classes on the basis of their discharge patterns: (1), rhythmic bursting (2), non-rhythmic bursting and (3), non-bursting, and the relationship of these discharge patterns to hippocampal theta rhythm was analyzed. Rhythmic bursting cells displayed close frequency and phase relations to hippocampal theta rhythm and were located chiefly in the diagonal band of Broca. Cells of the other two categories were found both within and outside of the diagonal band region. High frequency stimulation of medial hypothalamus evoked theta rhythm in hippocampus and bursts of repetitive firing at theta frequency from rhythmic bursting septal cells, whereas lateral hypothalamic stimulation desynchronized hippocampal EEG activity and disrupted rhythmic bursting patterns in the septum. The majority (59%) of rhythmic bursting cells ceased bursting and fired continuously at an increased rate during high frequency stimulation of lateral hypothalamus, while other (33%) rhythmic bursting cells ceased bursting and were either completely inhibited or fired at a markedly reduced rate. Of the rhythmic bursting cells tested with high frequency stimulation of lateral hypothalamus 73% responded with short latencies (1.7–4.5 msec). No rhythmic bursting cells were found which responded to medial hypothalamic stimulation at fixed latencies. Brain stem-hypothalamic pathways which mediate these differential effects upon septum and hippocampus are discussed.

Posttrial hippocampal, amygdaloid, and lateral hypothalamic electrical stimulation: effects on short- and long-term memory of an appetitive experience.

Water-deprived rats were given 150 licks of a 10% sucrose solution, followed 4 sec later by 30 sec of low-intensity electrical brain stimulation applied through bipolar electrodes implanted bilaterally in the dorsal hippocampus, amygdala, or lateral hypothalamus. Retention of the licking experience was then tested either 90 sec or 24 hr after the 150-lick experience by measuring the number of licks taken on an empty drinking tube. Rats that received hippocampal stimulation licked the empty tube less than controls did during the 24-hr, but not during the 90-sec, retention test. These data suggest that the hippocampus may be critically involved in processes (e.g., consolidation) mediating long-term, but not short-term, memory. Compared with controls, rats that received amygdala stimulation did not exhibit any changes in licking at either retention test. Rats that received lateral hypothalamic stimulation showed more licking compared with controls during the 90-sec, but not the 24-hr, retention test. Subsequent tests suggested that facilitation of short-term memory may have been influenced by stimulation-induced motivational changes.

Grooming in the rat as an aftereffect of lateral hypothalamic stimulation.

Grooming occurred as an aftereffect of electrical stimulation at hypothalamic sites that elicited locomotion, drinking, or eating as stimulus-bound behaviors. Removal of food or water, which caused rats to switch from one stimulus-bound behavior to another, produced little or no change in the grooming aftereffect. Stimulation with pulse showed that the absolute refractory period for the neurons responsible for the occurrence of grooming is approximately 1 msec. This value is longer than those reported for drinking, eating, and locomotion. Finally, it was found that with some electrodes, low levels of stimulation elicited grooming directly, during the stimulation; at higher levels grooming occurred only as an aftereffect. It is concluded that grooming is activated through neurons separate from those that produce drinking, eating, or locomotion and that its occurrence as an aftereffect may be due to an interaction between short-lasting inhibitory and longer lasting excitatory effects of the stimulation.

Hippocampal electrical correlates of free behavior and behavior induced by stimulation of two hypothalamic-hippocampal systems in the cat

Bilateral dorsal and ventral hippocampal and anterior and posterior neocortical electrical activity was recorded in 11 cats during free behavior situations and during stimulation of medial and lateral hypothalamic systems which influence hippocampal electrical activity and behavior in distinct and contrasting ways. Behavioral states characterized by alertness, attentiveness, scanning, or investigatory activity were accompanied by hippocampal theta rhythm and by desynchronization of neocortical electrical activity. Behavioral states characterized by relaxed wakefulness, inattentiveness, or drowsiness were accompanied by high voltage irregular patterns of electrical activity in the hippocampus with no organized theta rhythms. Specific behaviors (alerting, orienting, scanning, or investigatory) emerging from relaxed behavioral states occurred concomitantly with hippocampal theta rhythm. Electrical stimulation of the medial hypothalamic system at 100 Hz elicited hippocampal theta rhythm and specific behaviors of alerting, orienting, scanning, and investigatory activity. In contrast, lateral hypothalamic stimulation at 100 Hz caused low voltage desynchronization of hippocampal electrical activity accompanied by postural stability and fixation of gaze. The relation of hippocampal theta rhythm to behavior is discussed in terms of brain stem-hypothalamic-hippocampal systems.

Effects of anterior medial forebrain bundle lesions on self-stimulation with two different operant responses

Rats immobilized in a restraining cage were trained to move their tails back and forth using lateral hypothalamic stimulation as reinforcement. The same rats were also trained to bar press in an ordinary cage for the same reinforcement. Following lesions in the medial forebrain bundle anterior to the stimulation site the stimulation no longer appeared to be positively reinforcing when the animals were tested on the tail movement task. When these subjects were tested on bar pressing, the stimulation still appeared to be reinforcing. Various interpretations of the data, including the possibilities that the lesions changed the rats' emotional responsiveness, and that a different set of fibers within the medial forebrain bundle mediates the reinforcement of each of the two tasks were considered.

Pattern of drinking and feeding produced by hypothalamic norepinephrine injection in the satiated rat

Injection of norepinephrine into the perifornical region of the anterior hypothalamus elicited both drinking and feeding in satiated rats. Analysis of these behaviors revealed the following: (1) Both responses were dose-dependent, occurring at doses at least as low as 0.5 μg. (2) The drinking response (1–4 ml) had a latency of around 1.5 min and a duration 2–3 min. It was followed within a minute or two by eating (2–4 g) that lasted approximately 20 min. It was also followed within a minute or lasted approximately 60 min. (3) Satiation from the ingestion process appeared to be a primary factor in terminating the elicited feeding response, whereas a time-related factor was important in terminating the elicited drinking. (4) These ingestive responses produced by noradrenergic stimulation of the anterior perifornical hypothalamus were found to bear striking similarities to the rat's natural feeding behavior and premeal component of his natural food-associated drinking behavior. (5) These noradrenergically elicited responses could not be observed with lateral hypothalamic stimulation, while only feeding was elicited by ventromedial hypothalamic stimulation. (6) The drinking induced by central noradrenergic stimulation, in contrast to that induced by peripheral beta-adrenergic stimulation, was unaffected by nephrectomy.

Conditioned suppression of behavior maintained by intracranial stimulation as a function of stimulation intensity.

Conditioned suppression was demonstrated in two experiments with rats lever pressing on a fixed-ration 1 schedule for lateral hypothalamic intracranaial stimulation (ICS)'n Experiment I, conditioned suppression of responding for low-intensity ICS was obtained with a moderate intensity of foot shock, In Experiment II, low and high intensities of ICS were alternated within the same session and the same animal The suppression that was exhibited with low intensity ICS was minimal or absent with high-intensity stimulation, despite the pairing of foot shock with each warning stimulus. Conditioned suppression was a function of ICS intensity, and was independent of response rates. The inverse relationship between ICS intensity and degree os suppression is consistent with a motivational analysis of conditioned suppression. Previous reports of resistance to suppression of behaviors maintained by ICS may now be attributed to the use of high-intensity stimulation.