Lateral hypothalamic lesions and activity of the sympathetic nervous system

Differences in carbachol dose, pain condition, and sex following lateral hypothalamic stimulation

Lateral hypothalamic (LH) stimulation produces antinociception in female rats in acute, nociceptive pain. Whether this effect occurs in neuropathic pain or whether male-female sex differences exist is unknown. We examined the effect of LH stimulation in male and female rats using conditions of nociceptive and neuropathic pain. Neuropathic groups received chronic constriction injury (CCI) to induce thermal hyperalgesia, a sign of neuropathic pain. Nociceptive rats were naive for CCI, but received the same thermal stimulus following LH stimulation. To demonstrate that CCI ligation produced thermal hyperalgesia, males and females received either ligation or sham surgery for control. Both males and females demonstrated significant thermal hyperalgesia following CCI ligation (p<0.05), but male sham surgery rats also showed a significant left-right difference not present in female sham rats. In the second experiment, rats randomly assigned to CCI or nociceptive groups were given one of three doses of the cholinergic agonist carbachol (125, 250, or 500 nmol) or normal saline for control, microinjected into the left LH. Paw withdrawal from a thermal stimulus (paw withdrawal latency; PWL) was measured every 5 min for 45 min. Linear mixed models analysis showed that males and females in both pain conditions demonstrated significant antinociception, with the 500-nmol dose producing the greatest effect across groups compared with controls for the left paw (p<0.05). Female CCI rats showed equivalent responses to the three doses, while male CCI rats showed more variability for dose. However, nociceptive females responded only to the 500-nmol dose, while nociceptive males responded to all doses (p<0.05). For right PWL, only nociceptive males showed a significant carbachol dose response. These findings are suggestive that LH stimulation produces antinociception in male and female rats in both nociceptive and neuropathic pain, but dose response differences exist based on sex and pain condition.

Modulation of solitary taste neurons by electrical stimulation of the ventroposteromedial nucleus of the thalamus in the hamster

Taste neurons in the nucleus of the solitary tract (NST) not only send axons to the parabrachial nuclei (PbN), but also receive descending projections from gustatory nuclei in the forebrain in rodents. The parvicellular portion of the ventroposteromedial nucleus of the thalamus (VPMpc) receives projections from the bilateral PbN and transmits taste information to the gustatory cortex. Here, we examined the influence of bilateral stimulation of the VPMpc on taste-responsive neurons in the NST. Extracellular single unit activity was recorded from the urethane-anesthetized hamster. Taste responses were confirmed by delivery of four basic tastants to the anterior tongue. After identifying a taste neuron in the NST, the VPMpc was stimulated bilaterally. Thirty seven out of 83 neurons were orthodromically activated following VPMpc stimulation: 30 were excited and seven were inhibited. Among these cells, seven were excited and one was inhibited bilaterally. In addition, four NST neurons were antidromically invaded from the ipsilateral VPMpc. The effect of VPMpc activation on taste-driven responses was tested on 8 of 30 cells that were excited, and all seven cells that were inhibited by the VPMpc stimulation. The VPMpc stimulation enhanced responses to the effective taste stimuli or suppressed the taste-evoked activities in all eight and seven cells tested, respectively, parallel to the type of the inputs which they received from the VPMpc. These results suggest that a subset of taste neurons in the NST is under the influence from the bilateral VPMpc and that the VPMpc activation modulates taste responses of these cells.

Amylin causes anorexigenic effects via the hypothalamus and brain stem in chicks

This study was conducted to determine the effects of amylin on appetite-related processes in chicks. Broiler chicks were centrally and peripherally injected with amylin, and feed and water intake were quantified. Feed intake was reduced after both central and peripheral amylin, but water intake was not affected. To determine if the hypothalamus and brainstem were involved in the anorexigenic effect, chicks were centrally and peripherally injected with amylin, and c-Fos immunoreactivity was quantified in the lateral hypothalamus (LH), ventromedial hypothalamus (VMH), area postrema (AP) and the nucleus of the solitary tract (NTS). Amylin decreased c-Fos immunoreactivity in the LH, did not affect the VMH, and increased c-Fos immunoreactivity in the AP and NTS. To determine if alimentary transit time was affected, chicks received central amylin and were gavaged with chicken feed slurry containing a visible marker. Amylin-treated chicks had increased alimentary canal transit time. Chicks also responded to central amylin with increased anxiety-related behaviors and increased plasma corticosterone concentration. These results demonstrate that amylin affects feeding, alimentary canal transit, and behavior through hypothalamic and brainstem mechanisms in chicks.

Brown adipose tissue: function and physiological significance

The function of brown adipose tissue is to transfer energy from food into heat; physiologically, both the heat produced and the resulting decrease in metabolic efficiency can be of significance. Both the acute activity of the tissue, i.e., the heat production, and the recruitment process in the tissue (that results in a higher thermogenic capacity) are under the control of norepinephrine released from sympathetic nerves. In thermoregulatory thermogenesis, brown adipose tissue is essential for classical nonshivering thermogenesis (this phenomenon does not exist in the absence of functional brown adipose tissue), as well as for the cold acclimation-recruited norepinephrine-induced thermogenesis. Heat production from brown adipose tissue is activated whenever the organism is in need of extra heat, e.g., postnatally, during entry into a febrile state, and during arousal from hibernation, and the rate of thermogenesis is centrally controlled via a pathway initiated in the hypothalamus. Feeding as such also results in activation of brown adipose tissue; a series of diets, apparently all characterized by being low in protein, result in a leptin-dependent recruitment of the tissue; this metaboloregulatory thermogenesis is also under hypothalamic control. When the tissue is active, high amounts of lipids and glucose are combusted in the tissue. The development of brown adipose tissue with its characteristic protein, uncoupling protein-1 (UCP1), was probably determinative for the evolutionary success of mammals, as its thermogenesis enhances neonatal survival and allows for active life even in cold surroundings.

Hypothalamus of the human fetus

The organization of the human hypothalamus was studied in 31 brains aged from 9 weeks of gestation (w.g.) to newborn, using immunohistochemistry for parvalbumin, calbindin, calretinin, neuropeptideY, neurophysin, growth associated protein GAP43, synaptophysin and glycoconjugate, 3-fucosyl-N-acetyl-lactosamine. Morphogenetic periods 9-10 and 11-14 w.g. are characterized by differentiating structures of the lateral hypothalamic zone, which give rise to the lateral hypothalamus (LH) and posterior hypothalamus. The perifornical nucleus differentiates at 18 w.g., from LH neurons which remain anchored in the perifornical position while most of the LH cells are displaced laterally. A transient supramamillary nucleus was apparent at 14 w.g. but not after 16 w.g. As the ventromedial nucleus differentiated at 13-16 w.g., three principal parts; the ventrolateral, the dorsomedial and the shell were revealed by distribution of calbindin, calretinin and GAP43 immunoreactivity. Morphogenetic periods 15-17, 18-23 and 24-33 w.g. are characterized by differentiation of the hypothalamic core, in which calbindin positive neurons revealed the medial preoptic nucleus at 16 w.g. abutted laterally by the intermediate nucleus. The dorsomedial nucleus was clearly defined at 10 w.g. and consisted of compact and diffuse parts, an organization that was lost after 15 w.g. Differentiation of the medial mamillary body into lateral and medial was seen at 13-16 w.g. Morphogenetic period after 34 w.g. was marked by differentiation of midline zone structures including suprachiasmatic, arcuate and paraventricular nuclei. The findings of the present study provide for a better understanding of the structural organization of the adult human hypothalamus, produce new evidence for homologies with the better studied rat hypothalamus and underpin staging system for fetal human hypothalamic development.

Paradoxical [correction of parodoxical] effect of orexin A: hypophagia induced by hyperthermia

This experiment tested the effect of the sympathetic and thermogenic activation induced by orexin A on eating behavior. The food intake, firing rate (FR) of the sympathetic nerves to interscapular brown adipose tissue (IBAT), IBAT and abdominal temperatures (T(IBAT) and T(ab)), and heart rate (HR) were monitored in 24 h-fasting male Sprague-Dawley rats for 15 h after food presentation. Orexin A (1.5 nmol) was injected into the lateral cerebral ventricle 6 h before food presentation while FR, T(IBAT) and T(ab), and HR were also monitored. The same variables were controlled in rats receiving orexin A contemporaneously to food presentation. Two other groups of control animals were tested with the same procedure, however orexin A was substituted by saline. The results showed that food intake was significantly lower in the group receiving orexin A 6 h before food presentation in comparison to all the other groups. FR, T(IBAT) and T(ab), and HR were significantly higher in the rats receiving orexin A with respect to rats receiving saline. These findings demonstrate that orexin A, so-called for its orexigen action, can also induce hypophagia. On the other hand, orexin A always induces an activation of the thermogenesis. These results suggest a revision of the role played by orexin A in the control of food intake, assigning to this peptide a primary role in the thermoregulation. The possibility that orexin A can induce hypophagia is well demonstrated by this experiment, so that the scientific community should use a different name for this peptide. An appropriate name could be 'hyperthermine' A.

Regulation of feeding behavior, gastric emptying, and sympathetic nerve activity to interscapular brown adipose tissue by galanin and enterostatin: the involvement of vagal-central nervous system interactions

Galanin and enterostatin, which are distributed in both the central nervous system and the gastrointestinal tract, regulate the feeding behavior. In the first set of experiments, we investigated the effects of galanin and enterostatin, injected into the third ventricle, on food intake, gastric emptying, and the sympathetic activity of nerves innervating interscapular brown adipose tissue in rats. Galanin dose-dependently increased the intake of a high-fat diet after overnight starvation, but it did not affect low-fat diet intake. In contrast, enterostatin suppressed the intake of the high-fat diet, while intake of the low-fat diet was not affected. Galanin significantly and dose-dependently suppressed gastric emptying rate. However, gastric emptying showed no response to enterostatin. Galanin produced a dose-dependent suppression of sympathetic firing rate. In rats fed a high-fat diet, the injection of enterostatin showed a dose-dependent increase in firing rate. In contrast, animals fed a chow diet showed almost no response. In the second set of experiments, we investigated the role of the hepatic vagus nerve in modulating the peripheral response to enterostatin in rats. Intraperitoneal (i.p.) enterostatin reduced the intake of a high-fat diet. Immunohistochemical identification indicated that the Fos protein was present in the nucleus tractus solitarius, and parabrachial, paraventricular, and supraoptic nuclei after IP enterostatin. These responses to i.p. enterostatin were blocked by hepatic vagotomy. These results suggest that galanin and enterostatin coordinate to regulate feeding behavior, gastric emptying, and sympathetic activity to interscapular brown adipose tissue via central and peripheral sites of action, one of which was the interaction which was found to exist through the vagal system.

Modulation of natural killer cell activity affected by electroacupuncture through lateral hypothalamic area in rats

Electroacupuncture (EA) has been reported to modulate natural killer cell (NK cell) activities. Also it is well known that hypothalamus directly mediates the effects of EA on analgesia. Especially lateral hypothalamic area (LHA) is related to splenic NK cell activities. In order to investigate the relationship between hypothalamus and effects of EA on NK cell activity, lesions have been made bilaterally at LHA of Spraque-Dawley rats. Subsequently, NK cell cytotoxities of normal and lesioned rats were measured with (51)Cr release immunoassay after EA stimulation for 2 and 14 days. NK cell activity of EA group was significantly higher than sham group. In addition, lesions abolished effects of EA on NK cell activity. These results strongly suggest that LHA is closely related to increase of NK cell activity induced by EA.

Organization of human hypothalamus in fetal development

The organization of the human hypothalamus was studied in 33 brains aged from 9 weeks of gestation (w.g.) to newborn, using immunohistochemistry for parvalbumin, calbindin, calretinin, neuropeptide Y, neurophysin, growth-associated protein (GAP)-43, synaptophysin, and the glycoconjugate 3-fucosyl- N-acetyl-lactosamine. Developmental stages are described in relation to obstetric trimesters. The first trimester (morphogenetic periods 9-10 w.g. and 11-14 w.g.) is characterized by differentiating structures of the lateral hypothalamic zone, which give rise to the lateral hypothalamus (LH) and posterior hypothalamus. The PeF differentiates at 18 w.g. from LH neurons, which remain anchored in the perifornical position, whereas most of the LH cells are displaced laterally. A transient supramamillary nucleus was apparent at 14 w.g. but not after 16 w.g. As the ventromedial nucleus differentiated at 13-16 w.g., three principal parts, the ventrolateral part, the dorsomedial part, and the shell, were revealed by distribution of calbindin, calretinin, and GAP43 immunoreactivity. The second trimester (morphogenetic periods 15-17 w.g., 18-23 w.g., and 24-33 w.g.) is characterized by differentiation of the hypothalamic core, in which calbindin- positive neurons revealed the medial preoptic nucleus at 16 w.g. abutted laterally by the intermediate nucleus. The dorsomedial nucleus was clearly defined at 10 w.g. and consisted of compact and diffuse parts, an organization that was lost after 15 w.g. Differentiation of the medial mamillary body into lateral and medial was seen at 13-16 w.g. Late second trimester was marked by differentiation of periventricular zone structures, including suprachiasmatic, arcuate, and paraventricular nuclei. The subnuclear differentiation of these nuclei extends into the third trimester. The use of chemoarchitecture in the human fetus permitted the identification of interspecies nuclei homologies, which otherwise remain concealed in the cytoarchitecture.

Taste responses of neurons of the hamster solitary nucleus are enhanced by lateral hypothalamic stimulation

Gustatory responses in the brain stem are modifiable by several physiological factors, including blood insulin and glucose, intraduodenal lipids, gastric distension, and learning, although the neural substrates for these modulatory effects are not known. Stimulation of the lateral hypothalamus (LH) produces increases in food intake and alterations in taste preference behavior, whereas damage to this area has opposite effects. In the present study, we investigated the effects of LH stimulation on the neural activity of taste-responsive cells in the nucleus of the solitary tract (NST) of the hamster. Bipolar stimulating electrodes were bilaterally implanted in the LH, and the responses of 99 neurons in the NST, which were first characterized for their taste sensitivities, were tested for their response to both ipsilateral and contralateral LH stimulation. Half of the taste-responsive cells in the NST (49/99) were modulated by LH stimulation. Contralateral stimulation was more often effective (41 cells) than ipsilateral (13 cells) and always excitatory; 10 cells were excited bilaterally. Six cells were inhibited by ipsilateral stimulation. A subset of these cells (n = 13) was examined for the effects of microinjection of DL-homocysteic acid (DLH), a glutamate receptor agonist, into the LH. The effects of electrical stimulation were completely mimicked by DLH, indicating that cell somata in and around the LH are responsible for these effects. Other cells (n = 14) were tested for the effects of electrical stimulation of the LH on the responses to stimulation of the tongue with 0.032 M sucrose, NaCl, and quinine hydrochloride, and 0.0032 M citric acid. Responses to taste stimuli were more than doubled by the excitatory influence of the LH. These data show that the LH, in addition to its role in feeding and metabolism, exerts descending control over the processing of gustatory information through the brain stem.

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.

Intracerebroventricular administration of the beta(3)-adrenoceptor agonist CL 316243 causes Fos immunoreactivity in discrete regions of rat hypothalamus

Intracerebroventricular (i.c.v.) administration of the beta(3)-AR agonist BRL37344 causes dose dependent decreases in food intake in rats suggesting a role for beta(3)-AR in the central control of feeding. We have conducted experiments investigating the effects of i.c.v. administration of the selective beta(3)-AR agonist CL316243 on Fos expression to determine whether beta(3)-AR stimulation affects neurones within specific brain nuclei. Significantly higher numbers of Fos positive cells were found in the rats treated i.c.v. with CL316243 compared with control rats in the paraventricular hypothalamus, lateral hypothalamic area, ventromedial hypothalamic nucleus and dorsal hypothalamic area. Pre-treatment with the selective beta(3)-AR antagonist SR59230A resulted in a significant decrease in the number of Fos positive cells in all those areas compared with rats treated with CL316243 alone. These experiments demonstrate that i.c.v. administration of selective beta(3)-AR agonist causes neuronal activation in hypothalamic areas important in the central regulation of appetite via a beta(3)-AR mediated effect.

Ventilatory and metabolic responses to cold and hypoxia in conscious rats with discrete hypothalamic lesions

We tested the hypothesis that hypothalamic nuclei involved in thermoregulatory control could represent a site of integration of the metabolic and ventilatory response to cold and hypoxia. Electrolytic lesions were performed bilaterally under stereotaxic guide, either within the anterior or posterior hypothalamic areas of adult rats. One week later, oxygen consumption (VO2) and ventilation (VE) were measured in the conscious animals during warm (27 degrees C) or cold (12 degrees C) conditions, in normoxia (21% O2) or hypoxia (10% O2), and compared to measurements obtained in control rats, which were either intact or sham-operated. VO2, VE, and body temperature did not differ between lesioned and control rats during warm normoxia. In cold and hypoxia, singly or combined, VE/VO2 was higher in the lesioned rats, because of higher VE. The differences in the cold were mostly confined to rats with anterior lesions, whereas differences in hypoxia were mostly in rats with posterior lesions. We conclude that the integrity of the anterior and posterior hypothalamic areas is important for the proper coupling of metabolism and ventilation during cold or hypoxic stimuli.

Lateral hypothalamic lesion induces sympathetic stimulation and hyperthermia by activating synthesis of cerebral prostaglandins

This experiment tests the effect of intracerebroventricular (icv) injection of lysine acetylsalicylate on the sympathetic and thermogenic changes induced by lesion of the lateral hypothalamus (LH). The firing rate of the nerves innervating interscapular brown adipose tissue (IBAT), along with IBAT and colonic temperatures (TIBAT and Tc) were monitored in urethane-anaesthetized male Sprague-Dawley rats lesioned in the LH. These variables were measured before and after an icv injection of 1mg lysine acetylsalicylate. The same variables were also monitored in: a) lesioned rats with icv administration of saline; b) sham-lesioned animals with icv injection of lysine acetylsalicylate; c) sham-lesioned rats with icv injection of saline. In an additional experiment, the same variables were monitored after an icv injection of lysine acetylsalicylate or saline in rats with LH lesion performed 48 h before the icv injection. The results show that lysine acetylsalicylate injection reduces the increases in firing rate, TIBAT and Tc induced by LH lesion. These findings suggest that cerebral prostaglandin synthesis plays a key role in the sympathetic and thermogenic changes following LH lesion.

Effect of galanin and enterostatin on sympathetic nerve activity to interscapular brown adipose tissue

The effects of galanin and enterostatin on sympathetic activity have been examined in rats using electrophysiological techniques. Galanin, in doses of 25-300 pmol, and enterostatin, in doses of 0.5-10 nmol, were injected into the third ventricle of anesthetized male Sprague-Dawley rats in 1-microliter volumes. Galanin produced a dose-dependent suppression (ranging between 20 and 80%) of sympathetic firing rate of nerves innervating interscapular brown adipose tissue. In rats fed a chow diet, injection of enterostatin produced only a transient 10% rise in firing rate which returned to baseline within 10-15 min. In contrast, animals fed a high-fat diet showed a dose-dependent increase in firing rate lasting for 60 min. The results of this experiment are consistent with the hypothesis that food intake and sympathetic nervous system activity have a reciprocal relationship. The implications of this relationship are discussed.

Nitric oxide reduces the thermogenic changes induced by lateral hypothalamic lesion

The experiment described here tests the effect of intracerebroventricular (icv) injection of nitric oxide (NO) precursors, such as L-arginine (L-arg) and nitroprusside (NP), on the thermogenic changes induced by lesion of the lateral hypothalamus (LH). The firing rate of the nerves innervating interscapular brown adipose tissue (IBAT), along with IBAT and colonic temperatures (TIBAT and TC) were monitored in urethane-anaesthetized male Sprague-Dawley rats lesioned in the LH. These variables were measured before and after an icv injection of 4 mumol L-arg or 400 nmol NP. The same variables were also monitored in: a) lesioned rats with icv administration of saline; b) sham-lesioned animals with icv injection of L-arg or NP; c) sham-lesioned rats with icv injection of saline. The results show that L-arg or NP injection reduces the increases in firing rate. TIBAT and TC induced by LH lesion. These findings suggest that NO plays a key role in the thermogenic changes following LH lesion.

Glucagon injected in the lateral hypothalamus stimulates sympathetic activity and suppresses monoamine metabolism

Glucagon injected in the lateral hypothalamus stimulates sympathetic activity and suppresses monamine metabolism. The central hypothesis underlying this study is that there is a reciprocal relationship between food intake and sympathetic activity to IBAT. This hypothesis was tested by using intrahypothalamic microinjections of glucagon, a peptide that has been reported to decrease food intake. Sympathetic nerve activity to interscapular brown adipose tissue (IBAT) was measured as electrophysiological discharges of sympathetic nerves to IBAT. The microinjection of glucagon into the lateral hypothalamus (LH) increased sympathetic nerve activity by +103.8 +/- 35.0% (mean +/- S.E.M.) from pre-injection basal level by 30 min after injection. There was a gradual return to baseline. Micro-injection of glucagon into the LH depressed food intake. Monoamine metabolism was measured by using a microdialysis probe attached to a guide cannula for microinjection of glucagon into the LH. After microinjection of glucagon, the dialysates were collected over 30 min intervals and assayed for norepinephrine (NE), serotonin (5-HT), dopamine (DA) and their metabolites (3-methoxy-4-hydroxyphenylglycol (MHPG); 5-hydroxyindole-3-acetic acid (5-HIAA); and 3,4-dihydroxyphenylacetic acid (DOPAC). Glucagon suppressed both NE and MHPG concentrations in the lateral hypothalamus (LH), and the concentration of DOPAC was also decreased. There was no change of 5-HT concentration but 5-HIAA levels were reduced by glucagon treatment. These data show that glucagon injected in the LH stimulates sympathetic activity and suggest that this may have occurred by suppression of norepinephrine, dopamine and serotonin turnover in the LH of freely moving rats. These data support the hypothesis of a reciprocal relationship between food intake and sympathetic activity.

The lateral hypothalamic area revisited: neuroanatomy, body weight regulation, neuroendocrinology and metabolism

This article reviews findings that have accumulated since the original description of the syndrome that follows destruction of the lateral hypothalamic area (LHA). These data comprise the areas of neuroanatomy, body weight regulation, neuroendocrinology, neurochemistry, and intermediary metabolism. Neurons in the LHA are the largest in the hypothalamus, and are topographically well organized. The LHA belongs to the parasympathetic area of the hypothalamus, and connects with all major parts of the brain and the major hypothalamic nuclei. Rats with LHA lesions regulate their body weight set point in a primary manner and not because of destruction of a "feeding center". The lower body weight is not due to finickiness. In the early stages of the syndrome, catabolism and running activity are enhanced, and so is the activity of the sympathetic nervous system (SNS) as shown by increased norepinephrine excretion that normalizes one mo later. The LHA plays a role in the feedback control of body weight regulation different from ventromedial (VMN) and dorsomedial (DMN). Tissue preparations from the LHA promote glucose utilization and insulin release. Although it does not belong to the classical hypothysiotropic area of the hypothalamus, the LHA does affect neuroendocrine secretions. No plasma data on growth hormone are available following electrolytic lesions LHA but electrical stimulation fails to elicit GH secretion. Nevertheless, antiserum raised against the 1-37 fragment of human GHRF stains numerous perikarya in the dorsolateral LHA. The plasma circadian corticosterone rhythm is disrupted in LHA lesioned rats, but this is unlikely due to destruction of intrinsic oscillators. Stimulation studies show a profound role of the LHA in glucose metabolism (glycolysis, glycogenesis, gluconeogenesis), this mechanism being cholinergic. Its role in lipolysis appears not to be critical. In general, stimulation of the VMN elicits opposite effects. Lesion studies in rats show altered in vitro glucose carbon incorporation into several tissue fractions both a few days, and one mo after lesion production. Several of these changes may be due to the reduced food intake, others appear to be due to a "true" lesion effect.

The nutrient balance hypothesis: peptides, sympathetic activity, and food intake

Food intake can be increased or decreased after either central or peripheral administration of peptides. Galanin, neuropeptide Y, opioid peptides, growth hormone releasing hormone and desacetyl-MSH increase food intake whereas insulin, glucagon, cholecystokinin, anorectin, corticotropin releasing hormone, neurotensin, bombesin, enterostatin, cyclo-his-pro and thyrotropin-releasing hormone reduce food intake. A number of these peptides also affect the activity of the sympathetic nervous system. The peptides which have been tested have a reciprocal effect on food intake and sympathetic activity. Opioids, NPY and GHRH, which increase food intake, decrease sympathetic activity. Conversely, peptides which reduce food intake, increase sympathetic activity, with glucagon, cholecystokinin, corticotropin releasing hormone, calcitonin, neurotensin and bombesin being examples, Several of these peptides also affect the intake of specific nutrients. Insulin reduces food intake in animals fed a high carbohydrate diet, but not when fed a high fat diet. Neuropeptide Y increases carbohydrate intake. Galanin and opioid peptides increase fat intake. Enterostatin and cyclo-His-Pro, on the other hand reduce fat intake. Glucagon decreases protein intake. The effect of peptides on the intake of specific nutrients suggests that peptides may work in part by modulating basic feeding mechanisms to lead to the selection of specific nutrients from the diet. This hypothesis might be called a nutrient specific model of peptide-induced food intake.

Food intake, sympathetic activity, and adrenal steroids

Food Intake is reciprocally related to the activity of sympathetic nerves to brown adipose tissue. This reciprocal or feedback relation is shown for hypothalamic lesions, drugs, and many peptides. These peptides also modulate intake of specific nutrients. Galanin and opioids increase fat intake, whereas enterostatin decreases fat intake. NPY increases carbohydrate intake and growth hormone releasing hormone decreases protein intake. The activity of the sympathetic nervous system is low in obesity and adrenalectomy reverses this decrease in sympathetic activity and reverses or stops the progression of obesity. One mechanism for this effect of adrenal steroids is through a transacting substance which is involved in steroid actions and the production of obesity.

Effects of cholecystokinin on sympathetic activity to interscapular brown adipose tissue

The effects of injecting cholecystokinin (CCK) into the third ventricle or into selected hypothalamic sites on electrical firing rate of sympathetic nerves to interscapular brown fat (IBAT) has been investigated in anesthetized rats. The hypothesis for these experiments was that there was a reciprocal relationship between sympathetic activity and food intake. Since CCK reduces food intake we predicted that CCK would stimulate sympathetic activity to IBAT. Following the injection of CCK into the third ventricle there was an increase in firing rate of sympathetic nerves to IBAT. When the peptide was injected into either the ventromedial hypothalamic nucleus (VMH) or lateral hypothalamic area (LHA), there was likewise an increase in sympathetic firing rate. The injection of CCK into the paraventricular nucleus produced a small decrease in sympathetic firing rate. In contrast, no effect was seen following injection of CCK into the preoptic area or dorsomedial hypothalamic nucleus. Thus, the VMH or LHA appear to be the principal hypothalamic areas mediating the stimulation of sympathetic activity to IBAT which is observed following the third ventricular injection of CCK. These studies support the hypothesis of a reciprocal relationship between the effects of CCK on the thermogenic component of the sympathetic nervous system and food intake and identify the VMH and LHA as the primary sites for this effect.

Reciprocal relation between the sympathetic nervous system and food intake

The present studies have examined the hypothesis that food intake and sympathetic activity are inversely related. Following lateral hypothalamic lesions, food intake decreases and sympathetic activity rises. When pair-gained animals are used, the sympathetic activity of the LH-lesioned animals is above that of ad lib fed controls, and the sympathetic activity of the pair-gained animals is below that of the controls. With VMH-lesions, food intake rises and sympathetic activity falls. Several drugs, including 2-deoxy-D-glucose, fenfluramine, corticotropin releasing hormone, and neuropeptide Y, all show this reciprocal relationship. Three exceptions to this rule, the rat with a PVN lesion, cold exposure and animals eating a highly palatable diet, are discussed. Under the usual circumstances, the sympathetic activity appears to play a tonic role in regulating the onset of a meal, and the acute changes in sympathetic activity after eating may play a role in the onset of satiety.

Relationship between uptake of norepinephrine by hypothalamic homogenates and the activity of brown adipose tissue

It has previously been established that norepinephrine (NE) in the central nervous system is involved in feeding and the development of obesity. The present experiments were carried out to investigate the relationship between the uptake of NE by a crude hypothalamic homogenate and NE-mediated sympathetic activity in interscapular brown adipose tissue (IBAT). Sympathetic nervous system activity was assessed by measuring the binding of the purine nucleotide guanosine-5'-diphosphate (GDP) to mitochondria isolated from IBAT. Four situations known to alter food intake and sympathetic activity, namely, corticotropin releasing factor infusion, adrenalectomy, fenfluramine treatment and obesity due to genetic transmission were studied. In each case, [3H]NE uptake by the hypothalamic preparation and GDP binding to IBAT mitochondria were measured. A highly significant negative correlation between the uptake of NE by hypothalamic homogenates and the binding of GDP to IBAT mitochondria was obtained in both lean and obese animals. These findings are discussed with regard to the regulation of food intake and sympathetic nervous system mediated thermogenesis.

Effect of corticotropin releasing hormone and neuropeptide Y on electrophysiological activity of sympathetic nerves to interscapular brown adipose tissue

It has been proposed that there is a reciprocal relationship between food intake and sympathetic activity. To test this hypothesis corticotropin releasing hormone, which suppresses feeding behavior, and neuropeptide Y, which stimulates it, were injected intracerebroventricularly and sympathetic nerve activity to interscapular brown adipose tissue measured in anesthetized rats. Multi-unit discharges of sympathetic nerves to interscapular brown adipose tissue were recorded electrophysiologically. The intracerebroventricular injection of corticotropin releasing hormone (250 and 500 pmol) increased sympathetic nerve activity and the intracerebroventricular injection of neuropeptide Y (250-500 pmol) suppressed sympathetic nerve activity in a dose-dependent manner. The intracerebroventricular injection of vehicle did not affect sympathetic nerve activity. The result is consistent with the hypothesis that these brain peptides are neuromodulators of the sympathetic nervous system which may control energy expenditure in interscapular brown adipose tissue. The effects of these two brain peptides on sympathetic nerve activity are opposite to their effects on feeding behavior suggesting that sympathetic activity and food intake may be reciprocally related.

Glutamate injection into the suprachiasmatic nucleus stimulates brown fat thermogenesis in the rat

Injection of glutamate (100 mM to 1 M, in 0.25 micrograms saline) into the hypothalamic suprachiasmatic nucleus (SCN) dose-dependently increased interscapular brown adipose tissue (IBAT) and core temperatures in the urethane-anaesthetized rat. This effect was more pronounced in rats tested during the light-off period than in animals tested during the light-on period. Prior injection of the local anaesthetic, procaine (5% in 0.5 microliter saline), into the ipsilateral ventromedial hypothalamic nucleus (VMH) attenuated the increases in IBAT and core temperatures induced by intra-SCN glutamate. The VMH has previously been implicated in the central regulation of BAT thermogenesis; the present results suggest the pathway arising in the SCN exerts an excitatory influence on VMH neurons involved in the control of BAT function.

Effect of norepinephrine, serotonin and tryptophan on the firing rate of sympathetic nerves

The firing rate of sympathetic nerves innervating interscapular brown adipose tissue (IBAT) has been recorded following microinjection of monoamines into the ventromedial (VMN) and paraventricular nuclei (PVN). Microinjection of norepinephrine (10 nmol) into the paraventricular nucleus produced a biphasic pattern in the firing rate of the sympathetic efferent nerves to IBAT. There was an initial dose-related 20% inhibition of firing rate followed 2 min later by 10% increase above control. When 10 times as much norepinephrine was injected into the ventromedial hypothalamus, there was a small 5% decrease in firing rate and a later significant dose-related increase in firing rate. These effects of norepinephrine were blocked by phentolamine, an alpha-adrenergic blocking drug, but not by propranolol, a beta-adrenergic blocking drug. Injection of serotonin into the paraventricular nucleus produced a short-lived but significant increase in firing rate of sympathetic nerves to brown adipose tissue. Comparable amounts of serotonin injected into the ventromedial nucleus produced a similar magnitude of increase in firing rate which lasted longer. There was a clear dose-response effect of serotonin injected into the PVN, but a much less impressive response when serotonin was injected into the VMN. The response to injections of tryptophan in both the VMN and PVN was similar to those seen with serotonin. When serotonin or tryptophan were injected into the PVN and VMN simultaneously, there was a synergistic increase in sympathetic firing rate. These data are consistent with the hypothesis that both norepinephrine and serotonin can modulate sympathetic firing rate through interaction with neurons in either the VMN or PVN.

Effects of corticotropin releasing factor on genetically obese (fatty) rats

Corticotropin releasing factor (CRF) has been administered into the third ventricle of lean and genetically obese Zucker fatty rats in both acute and chronic experiments. Following a single injection of CRF (5 micrograms or approximately 1 nmole) there was an acute reduction of food intake in both the lean and obese animals, but the effect was greater in the obese. This effect persisted for the first three hours but was no longer detectable in either lean or genetically obese animals at 6 hours. Binding of GDP to mitochondria from interscapular brown adipose tissue in 21-hour deprived animals was lower in the fatty rats than in the lean controls. The injection of CRF significantly increased GDP binding in both the lean and fatty rats. During chronic infusion of CRF into the third ventricle of fatty rats, there was a significant decrease in food intake in the obese rats and fall of body weight in both groups. The basal levels of GDP binding were significantly lower in the saline-infused fatty rats than in the saline-infused lean controls. The chronic infusion of CRF increased GDP binding in the fatty rats but not in the lean animals. The CRF-treated values for GDP binding in fatty rats however, remained significantly below the baseline values in the control animals. Chronic CRF infusion also significantly lowered glucose levels in the fatty rat. These studies are consistent with the hypothesis that CRF may be involved in the decreased food intake and increased sympathetic activity observed in genetically obese fatty rats following adrenalectomy.

Interaction of adrenalectomy and fenfluramine treatment on body weight, food intake and brown adipose tissue

Three experiments have examined the interaction of adrenalectomy and fenfluramine on food intake, body weight and the binding of guanosine-5'-diphosphate (GDP) to interscapular brown adipose tissue (IBAT). In the first experiment, GDP-binding by IBAT mitochondria from adrenalectomized or sham-operated animals was measured for 3 hr after one of 3 doses of fenfluramine. Fenfluramine stimulated GDP-binding at lower doses in the adrenalectomized animals than in the controls. In the first chronic experiment, adrenalectomy prevented the restoration of normal food intake observed 8-10 days after the beginning of fenfluramine treatment. Adrenalectomy also increased weight loss and enhanced GDP binding to mitochondria from IBAT in rats treated with fenfluramine. In the second chronic experiment, the combination of fenfluramine and adrenalectomy led to a progressive weight loss, continuing hypophagia and stimulation of GDP-binding by IBAT, whereas rats treated with fenfluramine alone showed a recovery of food intake at a stabilized but lower body weight. These data are consistent with the hypothesis that adrenalectomy and fenfluramine disable two separate components of the food intake system and that when combined, produce a profound and persisting disturbance in energy or nutrient balance.

Nutrient balance and obesity: an approach to control of food intake in humans

This article has examined the regulated systems that control nutrient balance. From this analysis, the following conclusions may be suggested: 1. Each nutrient is regulated separately in a feedback system. 2. The control of glucose is regulated by the size of the glycogen stores; the size of the fat depots, by the rate of hepatic fatty acid oxidation; and protein, by the size of the protein depots. 3. Obesity can occur as a result of hyperphagia or from repartitioning the deposition of nutrients. In either case, there is a relative or absolute reduction in the activity of the sympathetic nervous system, requiring adequate levels of circulating corticosteroids.

Lateral and medial hypothalamic lesions do not acutely affect brown adipose tissue thermogenesis

The acute effect of lateral (LH) and medial (MH) hypothalamic lesions on mitochondrial GDP binding in brown adipose tissue (BAT) (an index of thermogenic state) was studied one and two days postlesion. Groups of rats were lesioned, sham-lesioned, or unoperated and were all fasting. An additional group of unoperated rats had access to food throughout the study. The objective was to determine whether the hypermetabolic state and rapid weight loss known to be induced by LH lesions were attributable to the activation of BAT thermogenesis, and, if so, whether these effects were specific for LH lesions. No effect of either lesion on BAT thermogenic state could be detected at either time studied. Despite that fact, LH-lesioned rats, but not MH-lesioned rats, were hyperthermic at both times. We conclude that the prolonged hyperthermia which occurs shortly after LH lesions is not due to an activation of BAT thermogenesis. Instead, it can be likened to the febrile state in which an initial and brief activation of both nonshivering thermogenesis in BAT and shivering thermogenesis in muscles occurs only during the rising phase of the fever and is suppressed as soon as a stable hyperthermic state is reached. It thus appears unlikely that substantial and prolonged activation of BAT thermogenesis is a major mechanism that promotes exaggerated short-term weight loss in the LH-lesioned rat.

Effect of fenfluramine on sympathetic firing rate

The effects of acute and chronic treatment with fenfluramine have been explored in two experiments. Three and twenty-four hours following the injection of fenfluramine 20 mg/kg the firing rate of sympathetic efferent nerves to brown adipose tissue was significantly increased compared to sham injected controls. Body weight loss following acute treatment with fenfluramine was significantly greater at three and twenty-four hours than in the vehicle-treated controls. In the chronic experiment animals were treated once daily for 12 days with 20 mg/kg of fenfluramine. There were two control groups. One control group ate ad lib and a second control group was pair fed to maintain body weight comparable to that of the fenfluramine-treated animals. By the twelfth day food intake in the fenfluramine-treated animals had returned to control levels. Sympathetic firing rate after three days of treatment with fenfluramine was significantly higher in the treated animals than in ad lib fed controls. The ad lib fed controls were likewise significantly higher than the vehicle-treated, pair-gained controls. After 12 days of treatment fenfluramine treated animals had sympathetic firing rates which were still slightly but significantly higher than those of the vehicle-treated controls whereas the vehicle-treated, pair-gained animals had a small but significantly reduced firing rate. These data support the hypothesis that fenfluramine can increase peripheral sympathetic activity.