Role of the septal area in feeding behavior elicited by electrical stimulation of the lateral hypothalamus of the rat.

1. The present study was undertaken to investigate the influence of the septal area on neural mechanisms involved in feeding behavior elicited by electrical stimulation of the lateral hypothalamic area of the rat. 2. Electrolytic damage to medial and lateral septal nuclei induced a significant increase (18.29 +/- 1.69 to 25.05 +/- 2.31 g, P less than 0.05, N = 14) in food intake elicited by hypothalamic stimulation. The threshold current for stimulus-induced eating decreased by 20% after septal lesion. 3. A significant decrease in food ingestion was observed after electrical stimulation of the septal nuclei, either preceding (27.47 +/- 1.57 to 19.30 +/- 2.06 g, P less than 0.05, N = 13) or simultaneous (26.20 +/- 1.60 to 12.10 +/- 2.40 g, P less than 0.05, N = 11) with hypothalamic stimulation. 4. The results indicate an inhibitory effect of the septum on the lateral hypothalamic area and also suggest that the functional state of the lateral hypothalamus, which is responsible for the feeding behavior, depends on the activity pattern of the septal area.

Role of the septal area in feeding behavior elicited by electrical stimulation of the lateral hipothalamus of the rat

The present study was undertaken to investigate the influence of the septal area on neural mechanisms involved in feeding behavior elicited by electrical stimulation of the lateral hypothalamic area of the rat. Electrolytic damage to medial and lateral septal nuclei induced a significant increase (18.29 + or - 1.69 to 25.05 + or - 2.31 g, P<0.05, N = 14) in food intake elicited by hypothalamic stimulation. The threshold current for stimulus-induced eating decreased by 20% after septal lesion. A significant decrease in food ingestion was observed after electrical stimulation of the septal nuclei, either preceding (27.47 + or - 1.57 to 19.30 + or - 2.06 g P <0.05, N = 13) or simultaneous (26.20 + or - 1.60 to 12.10 + or - 2.40 g, P<0.05, N = 11) with hypothalamic stimulation. The results indicate an inhibitory effect of the septum on the lateral hypothalamic area and also suggest that the functional state of the lateral hypothalamus, which is responsible for the feeding behavior, depends on the activity pattern of the septal area

Intraseptal microinjections of carbachol and angiotensin II in rats: effects on taste preferences.

The present study examined the effects of carbachol and angiotensin II injected into the medial and lateral septal areas (MSA and LSA) on the ingestion of primary taste solutions in a free-choice situation. The injection of carbachol or angiotensin II into MSA and LSA of water sated rats evoked a preference for the sweet tasting saccharin solution and water. The lateral septal rats also preferred acetic acid solution. Only the total fluid intake differed significantly among the four groups. In the water deprived rats injection of chemical to the respective groups induced the ingestion of NaCl solution. The MSA rats on injection of carbachol also preferred saccharin apart from NaCl. There was a significant difference in the NaCl intake among the four groups. The quinine solution was not consumed by all the groups. These results indicate that both the carbachol and angiotensin II induce the ingestion of saccharin, NaCl and water. The MSA might be more sensitive in inducing NaCl intake as compared with LSA during deprivation schedule and cholinergic stimulation. The LSA also evokes a preference for the sour tasting acetic acid. Furthermore, the data also suggest that the neurons sensitive to angiotensin are more potent than cholinergic neurons of LSA in producing salt preference.

Taste preferences in a free-choice situation following electrical stimulation and lesion of septal area in rats.

In the present study, electrical stimulation of medical or laternal septal areas and total or restricted lesions of these were conducted to observe the effect on ingestion of primary taste solutions in a free-choice situation. Stimulation induced a specific decrease in the intake of NaCl solution and had no effect on saccharin, acetic acid and quinine solutions and water. Total septal lesion or restricted lesions of medial or lateral septal areas induced hyperdipsia in rats. The lesioned rats, in a free-choice situation preferred NaCl, saccharin, as well as acetic acid solutions. This increase in acetic acid intake after lesion suggests that sour taste is also affected. Furthermore, there was no consumption of quinine solution before and after the lesion. This might be due to the presence of sweet tasting saccharin solution in this free-choice situation. These results indicate that the septal area causes aversion to NaCl intake, probably by inhibiting lateral hypothalamic neurons responsible for NaCl ingestion. The consumption of large quantities of saccharin, NaCl and acetic acid after the septal lesion suggests that the rats become overresponsive to taste factors in a free-choice situation.

Feeding behavior elicited by electrical stimulation of the lateral hypothalamic area in the rat: role of the adrenergic pathways and receptors.

To study the role played by neurotransmitters and their receptor mechanisms in the control of feeding behavior elicited by electrical stimulation, drugs that affect neurotransmission were injected via cannula electrodes into the lateral hypothalamic area. Pretreatment with noradrenaline (0.5 and 1.0 nmol) significantly increased the effect of hypothalamic stimulation on feeding, whereas injection of 1.0, 2.0 and 4.0 nmol of adrenaline or dopamine was ineffective. Phentolamine (40.0, 80.0 and 100.0 nmol) and propranolol (40.0, 80.0 and 120.0 nmol) induced a decrease in food intake, suggesting the involvement of both alpha and beta receptors in this mechanism. However, isoprenaline (20.0 nmol) also reduced food intake. Reduction of food intake by propranolol was probably related to the action of the local anesthetic. Alphamethyl-p-tyrosine (203.0 nmol), reserpine (32.8 nmol) and 6-hydroxydopamine (200.0 nmol) inhibited the feeding behavior elicited by electrical stimulation of the lateral hypothalamic area. These results suggest that electrical stimulation of the lateral hypothalamic area elicits feeding behavior by releasing noradrenaline. Alpha-adrenergic receptors seem to play a facilitatory role in feeding behavior.

Effect of electrical and chemical stimulation of the lateral hypothalamus on taste preferences.

Bipolar stainless steel electrodes or stainless steel cannulas were implanted stereotaxically into the lateral hypothalamus of rats. Drinking was elicited by electrical or chemical (carbachol or angiotensin II) stimulation of animals, which were offered water and solutions of sodium chloride, saccharin, acetic acid and quinine. During electrical stimulation, ingestion of water and of all the solutions increased significantly. The same rats ingested significantly more sodium chloride and saccharin solution after 23 h water deprivation and electrical stimulation of the lateral hypothalamus. Carbachol administered into the lateral hypothalamus induced ingestion of saccharin solution and water but not of sodium chloride. Angiotensin II injected into the lateral hypothalamus did not induce drinking in most of the rats and those which drank preferred sodium chloride, saccharin and water. Several of the rats which did not respond to angiotensin II injection into the lateral hypothalamus, 72 h after angiotensin II responded to injection of carbachol by drinking the saccharin solution. The results of electrical stimulation suggest that the lateral hypothalamus consists of neurons involved in the ingestion of primary taste solutions. Depending on the functional state of the organism, lateral hypothalamic stimulation modifies ingestion of other taste substances but not of salt, as indicated by water deprivation. Chemical stimulation indicates that the neurotransmitter responsible for salt intake is not cholinergic and that the cholinergic neurons evoke preference for sweet taste and water. It appears that angiotensin II is involved in salt intake, as well as in producing preference for sweet taste and water.

Effects of catecholamines injected into the septal area of the rat brain on natriuresis, kaliuresis and diuresis.

Urinary output of Na+ and K+, and volume of urine have been studied in conscious, unrestrained, water-loaded male rats following the intraseptal injection of catecholamines. Natriuresis and kaliuresis increased after injecting noradrenaline (NA), the intensity being dose related. The dose-response curve suggests that a monomolecular interacting takes place between NA and pharmacological receptors present in the septal area. No change was observed in diuresis. Systematic mapping of the septal area yielded about the same results for all sites except a zone located in the lateral nucleus that was more sensitive. An alpha blocker (dibenamine), injected intraseptally before NA, showed an inhibitory effect while a beta blocker (propranolol) yielded a potentiation effect. These same effects of the blocking agents were observed when adrenaline was used instead of NA. Lidocaine, which inhibits the re-uptake of NA, showed an enhancement of the natriuretic and kaliuretic effect of NA, and the same effect was observed when the enzymatic destruction of NA was prevented by nialamide, an inhibitor of monoaminoxidase. Dopamine showed a natriuretic effect, but no effect was observed on K+ and urine output. Serotonin had no action on natriuresis, kaliuresis and diuresis.

Natriuresis, kaliuresis and diuresis in the rat following microinjections of carbachol into the septal area.

The effects of intraseptal injection of carbachol on natriuresis, kaliuresis and diuresis has been studied in conscious, unrestrained water-loaded male rats. Urinary sodium and potassium excretion increased following injections into the septal area. The intensity of the natriuresis and kaliuresis was dose-related. An antidiuretic effect was also observed. The Na+/K/ ratio increased with increasing doses of carbachol, indicating that the rise in urinary sodium exceeded that of potassium. Systematic mapping of the septal area yielded about the same results for all sites, excepting a zone located in the anterior-dorsal part of the medial nucleus which appeared more sensitive. The natriuretic effect of intraseptal carbachol in adrenalectomized rats demonstrated the secondary role played by the adrenals. Contrariwise the decrease of the natriuretic effect observed either in hypophysectomized rats or in rats bearing a median eminence lesion receiving intraseptal carbachol showed the important participation of these structures in urinary Na+ excretion. Adrenalectomy or median eminence lesions did not modify the kaliuretic response while hypophysectomy produced a transitory diminution. This fact favours the hypothesis of different mechanisms involved in Na+ and K+ excretion following intraseptal carbachol. These results leave open the question as to mechanism of action but suggest a possible role of the pituitary in mediating the responses. Also, the possibility of a role played by hemodynamic shifts is suggested.