Locus Coeruleus and Tuberomammillary Nuclei Ablations Attenuate Hypocretin/Orexin Antagonist-Mediated REM Sleep.

Hypocretin 1 and 2 (Hcrts; also known as orexin A and B), excitatory neuropeptides synthesized in cells located in the tuberal hypothalamus, play a central role in the control of arousal. Hcrt inputs to the locus coeruleus norepinephrine (LC NE) system and the posterior hypothalamic histaminergic tuberomammillary nuclei (TMN HA) are important efferent pathways for Hcrt-induced wakefulness. The LC expresses Hcrt receptor 1 (HcrtR1), whereas HcrtR2 is found in the TMN. Although the dual Hcrt/orexin receptor antagonist almorexant (ALM) decreases wakefulness and increases NREM and REM sleep time, the neural circuitry that mediates these effects is currently unknown. To test the hypothesis that ALM induces sleep by selectively disfacilitating subcortical wake-promoting populations, we ablated LC NE neurons (LCx) or TMN HA neurons (TMNx) in rats using cell-type-specific saporin conjugates and evaluated sleep/wake following treatment with ALM and the GABAA receptor modulator zolpidem (ZOL). Both LCx and TMNx attenuated the promotion of REM sleep by ALM without affecting ALM-mediated increases in NREM sleep. Thus, eliminating either HcrtR1 signaling in the LC or HcrtR2 signaling in the TMN yields similar effects on ALM-induced REM sleep without affecting NREM sleep time. In contrast, neither lesion altered ZOL efficacy on any measure of sleep-wake regulation. These results contrast with those of a previous study in which ablation of basal forebrain cholinergic neurons attenuated ALM-induced increases in NREM sleep time without affecting REM sleep, indicating that Hcrt neurotransmission influences distinct aspects of NREM and REM sleep at different locations in the sleep-wake regulatory network.

Role of the lateral hypothalamus in submandibular salivary secretion during feeding in rats.

To evaluate the role of the lateral hypothalamic area (LH) in the masticatory-salivary reflex, we investigated submandibular salivary secretion and the electromyographic (EMG) activity of the jaw-closer masseter muscle in sham-operated rats and rats with unilateral LH lesions. One week prior to surgery and recording, the rats were given daily experience of eating pellets; powder; or hard, medium or soft mash, all of which were composed of laboratory chow. Salivary secretion was induced during eating and grooming behavior. During eating, the powdered food induced the highest salivary flow rate, and the soft (wet) mash induced the lowest salivary flow rate. Conversely, the amount of food consumed (dry weight) was greatest when soft mash was provided and lowest when the powder or pellets (a dry diet) were provided. The EMG activity of the masseter muscle during eating was greatest during consumption of the pellets and weakest during consumption of the powder. LH lesions that were ipsilateral to the examined submandibular gland reduced salivary secretion to about 20-30% of the control value, whereas contralateral LH lesions reduced it to about 40-50% of the control value. Neither masseter muscle EMG activity nor food consumption was markedly affected by the presence of an LH lesion. These results suggest that the texture of food, especially its water content, affects the flow rate of saliva and that the LH is heavily involved in the masticatory-salivary reflex.

Neurochemical and behavioral analyses of the lateral hypothalamic syndrome: a look back.

Philip Teitelbaum is one of the great physiological psychologists of his generation. His early research clarified key issues regarding the effects of electrolytic lesions of the ventromedial or ventrolateral hypothalamus on food intake in rats, a subject of paramount interest during the 1950s and 1960s. Perhaps best known were his extensive studies of the lateral hypothalamic syndrome in rats, which focused on the complex and changing array of symptoms after experimental brain damage. It soon became clear from later work that his research interests were not in the brain's control of food intake but in the effects of lesions to fragment behavior and thereby allow investigators to view its components. He was the foremost proponent of the use of exquisite behavioral analysis to reveal details in movement that allowed insights into brain function, and that approach - old fashioned physiological psychology made modern and at its finest - has infiltrated the entire field of experimental psychology, including studies of ingestive behavior, even while the new field of behavioral neuroscience emerged. He extended his analytic approach to neurological issues such as autism in humans, a promising arena that fully occupied his attention during the later phases of his career. But his influence on his scientific colleagues went well beyond his careful and powerful thinking; his articles and books have been models of clarity and concision. I write in behalf of a grateful field to salute his many great contributions.

The natriuretic effect of oxytocin blocks medial tuberomammillary polydipsia and polyuria in male rats.

Lesions of the tuberomammillary complex, a neuroanatomical system closely related to the hypothalamic supraoptic and paraventricular nuclei, induce strong polydipsia in male rats. It was recently demonstrated that this increase in water intake is immediate, persistent, follows circadian rhythms and appears to be related to sodium regulation. The present study found that urine osmolality was significantly lower in tuberomammillary-lesioned animals vs. their respective controls at 8:00 h after surgery. Therefore, the aim of the present study was to examine the natriuretic effect of intraperitoneal oxytocin (OT) administration on medial ventral tuberomammillary nucleus (E3) polydipsia and polyuria of lesioned and control male rats. At 24:00 h post-lesion, OT blocked the hyperdipsic and polyuric responses of E3-lesioned animals but not those of non-lesioned controls, which did however significantly increase their water intake. Moreover, urinary osmolality and sodium excretion increased in E3 -lesioned animals that received OT but not in lesioned controls receiving physiological saline (992 +/- 187.19 vs. 215.83 +/- 23.39 mOsm/kg; 1.68 +/- 0.13 vs. 0.47 +/- 0.1 mEq/L). At 48:00 h post-lesion, OT administration also induced a higher intake of water and of simultaneously offered hypertonic NaCl (1.5%) in E3-lesioned animals. These results are interpreted in terms of the hypothalamic systems involved in sodium and water homeostasis.

The lateral hypothalamus and anterior hypothalamic nucleus differentially contribute to rats' defensive responses in the elevated plus-maze and shock-probe burying tests.

Lesions or pharmacological inhibition of the lateral septum reduce rats' open-arm avoidance in the elevated plus-maze and their burying behavior in the shock-probe test. The current study examined whether hypothalamic areas that receive direct input from the lateral septum also influence open-arm avoidance and defensive burying. Bilateral infusions of the GABA-A receptor agonist muscimol (20 ng) into the lateral hypothalamus selectively increased rats' open-arm avoidance without affecting shock-probe burying. In contrast, infusions of muscimol into the anterior hypothalamic nucleus suppressed burying without affecting rats' open-arm avoidance. These dissociations suggest that the lateral hypothalamus contributes to the exploration of potentially threatening environments, whereas the anterior hypothalamus influences defensive responses to proximal discrete threat stimuli.

Distinct effects of anterior pyriform cortex and the lateral hypothalamus lesions on protein intake in rats.

Several specific locations in brain, including pyriform cortex and hypothalamus, are associated with regulation of food intake. Although lesions of these locations significantly alter food intake, their involvement in the selection of macronutrients is not well characterized. In this study, we examined distinct effects of anterior pyriform cortex (APC) and lateral hypothalamus (LH) lesions on protein intake in rats. The APC or LH of male adult rats were lesioned by treatment with kainic acid, and the rats were then given free access to two kinds of casein diets containing high (60%) and low (5%) protein. Total energy content of these diets was kept constant by changing the carbohydrate content. Following the APC lesions, body weight and food intake decreased, but returned to control levels on day 13 and day 4, respectively. APC lesions did not change the ratio of protein intake. In contrast, LH lesions disturbed body weight gain and the selection of a high protein diet for at least two weeks, although food intake returned to control levels by day 2. Our results suggest that LH, but not APC, may play an important role in the selection of protein intake in rats.

Dipsogenic potentiation by sodium chloride but not by sucrose or polyethylene glycol in tuberomammillary-mediated polydipsia.

The aim of this study was to examine the dipsogenic mechanisms involved in the recently discovered tuberomammillary (TM)-mediated polydipsia. Rats with bilateral electrolytic lesions of each TM subnucleus underwent several dipsogenic treatments, both osmotic and volemic. Animals with ventral (E2) or medial TM lesions (E3 or E4) showed a potentiated hyperdipsic response to hypertonic sodium chloride administration but not to sucrose or polyethylene glycol treatments. The increase in response to sodium chloride was significantly greater in groups E3/E4 and E2 than in the non-lesioned group and in animals with polydipsia induced by lesion of the median eminence. As previously reported, hyperphagia was induced by lesion to ventral TM nuclei (E1 or E2), confirming a possible role for the TM complex in food intake. However, lesions in medial nuclei (E3 or E4) did not produce this increase in food intake. These results are interpreted in relation to the hypothalamic systems involved in food and water intake.

Effects of lesions of the bed nucleus of the stria terminalis, lateral hypothalamus, or insular cortex on conditioned taste aversion and conditioned odor aversion.

The effects of permanent forebrain lesions on conditioned taste aversions (CTAs) and conditioned odor aversions (COAs) were examined in 3 experiments. In Experiment 1, lesions of the bed nucleus of the stria terminalis had no influence on CTA or COA acquisition. Although lesions of the lateral hypothalamus induced severe hypodipsia in Experiment 2, they did not prevent the acquisition of CTAs or COAs. Finally, in Experiment 3, lesions of the insular cortex retarded CTA acquisition but had no influence on COA acquisition. The implications of these findings are discussed with regard to the forebrain influence on parabrachial nucleus function during CTA acquisition.

Indomethacin attenuates hyperthermia produced by anterior coronal lateral hypothalamic knife cuts.

Electrolytic lesions of the lateral hypothalamus (LH) and coronal knife cuts of fibers anterior to the LH produce an elevation in core body temperature, or hyperthermia. Prostaglandin has been shown to mediate hyperthermia produced by electrolytic LH lesions. The present study characterizes the time course and the role of prostaglandin in mediating knife-cut-induced hyperthermia. Results show that the prostaglandin synthesis inhibitor indomethacin significantly attenuates hyperthermia produced by the knife cuts, suggesting that prostaglandin is involved in mediating this temperature increase. A disruption of axonal fibers that project from the LH to the preoptic area is postulated to be responsible for the temperature increase. There was no effect of knife cuts on food intake and body weight loss, which were also measured, suggesting that this fiber system is not involved in feeding behavior.

Opposing roles of the nucleus accumbens and anterior lateral hypothalamic area in the control of sexual behaviour in the male rat.

Opposing roles have been implicated for the nucleus accumbens (NAc) and anterior portion of the lateral hypothalamic area (aLHA) in the regulation of sexual behaviour in male rats based on in vivo neurochemical correlates. The present study provides functional evidence supporting this hypothesis by examining the effects of lesions to these structures on copulation, noncontact erection and receptive female preference. Sexually naïve male Long-Evans rats received either bilateral 1.0- micro L injections of NMDA (10 micro g/ micro L/side) or vehicle (shams) into either the aLHA or the NAc. During repeated tests of copulation most of the sham-lesioned males, but few of the aLHA-lesioned and NAc-lesioned males, copulated to ejaculation. Most of the NAc-lesioned males also failed to intromit, whereas the majority of the aLHA-lesioned males intromitted repeatedly. During exposure to an inaccessible receptive female behind a wire-mesh screen, aLHA-lesioned males displayed facilitation of noncontact erections, whereas NAc-lesioned males displayed impaired noncontact erections. Conversely, during simultaneous exposure to inaccessible receptive and nonreceptive females in different compartments, all males spent more time in the proximity of the receptive female. These findings indicate that the aLHA plays an inhibitory role in the regulation of sexual arousal and an excitatory role in the regulation of ejaculation. Conversely, the NAc plays an excitatory role in the regulation in sexual arousal.

Lesions of the lateral hypothalamus impair pilocarpine-induced salivation in rats.

In the present study we investigated the effects of electrolytic lesions of the lateral hypothalamus (LH) in the salivation induced by intracerebroventricular (i.c.v.) or intraperitoneal (i.p.) injection of the cholinergic agonist pilocarpine. Rats with sham or LH lesions and stainless steel cannulas implanted into the lateral ventricle (LV) were used. In rats anesthetized with urethane (1.25mg/kg of body weight) saliva was collected using pre-weighed cotton balls inserted in the animal mouth during a period of 7 min following i.c.v. or i.p. injection of pilocarpine. Injection of pilocarpine (1mg/kg of body weight) i.p. in sham-operated rats (6h, 2, 7, and 15 days after the surgery) induced salivation (497+/-24, 452+/-26, 476+/-30, and 560+/-75 mg/7 min, respectively). The effects of i.p. pilocarpine was reduced 6h, 2 and 7 days after LH lesions (162+/-37, 190+/-32, and 229+/-27 mg/7 min, respectively), not 15 days after LH lesions (416+/-89 mg/7 min). Injection of pilocarpine (120 micro g/micro l) i.c.v., in sham-operated rats (6h, 2, 7, and 15 days after the surgery) also produced salivation (473+/-20, 382+/-16, 396+/-14, and 427+/-47 mg/7 min, respectively). The salivation induced by i.c.v. pilocarpine was also reduced 6h, 2 and 7 days after LH lesions (243+/-19, 278+/-24, and 295+/-27 mg/7 min, respectively), not 15 days after LH lesions (385+/-48 mg/7 min). The present results show the participation of the LH in the salivation induced by central or peripheral injection of pilocarpine in rats, reinforcing the involvement of central mechanisms on pilocarpine-induced salivation.

Lesions in lateral hypothalamic areas increase splenocyte apoptosis.

OBJECTIVE: The lateral hypothalamic area (LHa) is involved in various functions such as feeding, drinking, sexual and reward behavior, among others. Recently, we demonstrated that the LHa can regulate cellular immunity in the spleen. In experiments involving the LHa, it was noticed that the spleen shrinks noticeably after LHa destruction. To explore this phenomenon further, the effect of LHa lesioning on splenocyte apoptosis was investigated. METHODS: Male Wistar-King-Aptekman rats underwent bilateral lesioning of their LHa and consequent spleen weights, splenocyte numbers and apoptosis were measured. For the detection of splenocyte apoptosis, both ELISA, which measures DNA fragmentation within the splenocytes, and flow cytometry, which measures the percentage of apoptotic lymphocytes in the spleen, were used. RESULTS: In the LHa-lesioned rats, spleen weights and the number of splenocytes decreased significantly within 24 h. Additionally, in the spleen, lymphocyte apoptosis significantly increased compared to the control after 6 h. CONCLUSION: These results suggest that the LHa may play a role in immunoregulation by affecting lymphocytes in the spleen through apoptosis and may be relevant to the pathway of stress-induced apoptosis.

Infusion of neurotoxic doses of N-methyl-D-aspartate into the lateral hypothalamus in rats produces stomach erosions, hyperthermia, and a disruption in eating behavior.

The present study examined whether damage to intrinsic lateral hypothalamic (LH) neurons induced by microinfusions of N-methyl-D-aspartate (NMDA) would produce effects similar to those seen after electrolytic LH lesions. In Experiment 1, rats receiving electrolytic (1.2 mA anodal current, 10 s) LH lesions displayed motor impairments, whereas those receiving NMDA (20 microg/microl) infusions did not. Both electrolytic lesions and NMDA infusions were associated with eating deficits, hyperthermia, and gastric erosion formation 24 hr after surgery. In Experiment 2, either 20 microg/microl or 10 microg/microl NMDA destroyed LH cells and produced dose-dependent gastric mucosal erosions as well as similar increases in body temperature. These results indicate that an alteration in the acute activity of intrinsic LH neurons plays a role in the production of gastric mucosal injury and hyperthermia and lend support to other studies implicating a role of LH neurons in eating behavior.

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.

Sensorimotor impairment and recovery of function in brain-damaged rats: reappearance of symptoms during old age.

Following unilateral lesions in the posterior-lateral hypothalamic area, rats displayed impaired orienting behavior to tactile stimuli placed on the contralateral side of the body, whereas sham-operated animals showed no sensorimotor impairment. Recovery from this impairment occurred during the first postoperative month. As the animals became senescent, there was a reinstatement of contralateral sensorimotor impairment in the brain-damaged animals. Although preliminary, these data may have important implications for the study of aging-dependent neurological and psychiatric disorders.

A role for the dopaminergic nigrostriatal bundle in the pathogenesis of altered brain glucose consumption after lateral hypothalamic lesions. Evidence using the 14C-labeled deoxyglucose technique.

The pattern of altered brain glucose consumption which results from unilateral electrolytic lesions of the lateral hypothalamic area in albino rats is first described. Glucose consumption was estimated using the 2-deoxy-D-[14C]glucose tracer technique, which allows for the in vivo determination of the rates of glucose consumption of individual structures within the brain. Unilateral lesions resulted in a decrease of the glucose consumption of a number of structures rostral and ipsilateral to the lesion compared with that of the corresponding structures on the contralateral side. The lesion-associated depression of glucose consumption was greatest in sulcal prefrontal cortex, frontal cortex, parietal cortex, and caudatoputamen. No structure caudal to the lesion was affected. The deficit appeared acutely (2 h postoperatively) and persisted virtually unchanged for at least 14 days after the lesions had been made. Unilateral 6-hydroxydopamine lesions of the substantia nigra resulted in a decrease of the glucose consumption of a few of the ipsilateral structures which had been affected after the lateral hypothalamic lesions, most significantly in the ipsilateral caudatoputamen. In addition, the decreased glucose consumption of the ipsilateral caudatoputamen which had occurred after the lateral hypothalamic lesions disappeared when 1 mg/kg apomorphine hydrochloride was intravenously administered to the lesioned animals 14 days postoperatively. Thus, the decrease of ipsilateral caudatoputamen glucose consumption observed after unilateral electrolytic lateral hypothalamic lesions was (1) reproduced by 6-hydroxydopamine lesions of the substantia nigra and (2) reversed by intravenous apomorphine. Destruction of the ascending dopaminergic nigrostriatal bundle at the level of the lateral hypothalamus may have accounted for the reduced caudatoputamen glucose consumption which had been observed after lateral hypothalamic lesions.