The pharmaco-ontogeny of the perifornical lateral hypothalamic beta 2-adrenergic and dopaminergic receptor systems mediating epinephrine- and dopamine-induced suppression of feeding in the rat.

The functional ontogeny of beta 2-adrenergic and dopaminergic receptors in the perifornical lateral hypothalamus (PLH) that mediate adrenergic and dopaminergic suppression of feeding in rats was investigated. Rat pups, ranging in age from 2 to 15 days, were removed from their mothers and implanted with a brain cannula directed unilaterally at the PLH or a more rostral site lateral to the anterior nucleus of the hypothalamus. On the next day, following a 22-h period of food and water deprivation, each pup was implanted with an intra-oral cannula for oral infusion of milk that could be swallowed or rejected. Subsequently, each pup received an intracerebral injection of saline, or a single dose of epinephrine (EPI, 0.1-30.0 nmol), the beta 2-adrenergic receptor agonist salbutamol (1.0-30.0 nmol) or the dopaminergic receptor agonist apomorphine (1.0-30.0 nmol). Milk intake was then assessed following a 1-h period of infusion. The results showed significant dose-dependent suppression of milk intake in pups as young as 2 days of age in response to PLH injection of EPI, salbutamol and apomorphine. In contrast to its effectiveness in the PLH at 2 days of age, EPI failed to suppress milk intake at this age following injection into a more rostral site lateral to the anterior nucleus of the hypothalamus. Together, these findings suggest that both beta 2-adrenergic and dopaminergic receptors, mediating adrenergic and dopaminergic suppression of feeding, are functionally mature very early in the postnatal development of the rat. Moreover, consistent with evidence in adult rats, these catecholaminergic receptors in young pups appear to be located in the region of the PLH.     

Clonidine-induced feeding: Analysis of central sites of action and fiber projections mediating this response

Clonidine (CLON), an alpha-adrenergic agonist, was used in conjunction with norepinephrine (NE) to elicit feeding in satiated rats that had sustained hypothalamic electrolytic lesions, or coronal knife cuts at the hypothalamic, midbrain or pontine level of the brainstem. Electrolytic lesions of the paraventricular nucleus (PVN) of the hypothalamus significantly attenuated feeding normally stimulated by intraperitoneal injection of CLON. This contrasts with lesions in the dorsomedial or perifornical hypothalamic regions which had no effect on CLON-elicited eating. Knife cuts placed in the posterior hypothalamus and throughout the midbrain tegmentum also left intact the CLON eating response, in contrast to specific cuts in the dorsal pontine tegmentum which disrupted feeding elicited by PVN injections of NE and CLON, as well as by peripheral administration of CLON. Analyzed together, these results with effective and ineffective cuts relative to CLON and NE feeding provide evidence for an alpha-adrenergic feeding circuit which originates in the PVN and descends from this nucleus, via a dorsal periventricular course, through the diencephalon and midbrain. Further caudally, these fibers mediating NE and CLON feeding then appear to traverse ventrolaterally into the dorsolateral pontine tegmentum on their way to the dorsal medulla.     

Relationship of adrenergic and electrical brain stimulation induced feeding responses

Electrical and adrenergic brain stimulation can induce eating in satiated animals. This report explores the interrelationship of brain feeding systems mediating eating in response to norepinephrine and electrical stimulation of the hypothalamus in rats. It was found that simultaneous adrenergic and electrical brain stimulation resulted in a significant increase in food intake as compared to each stimulation condition alone. Furthermore, pharmacological blockade of the alpha-adrenergic receptors in the hypothalamus attenuated feeding in response to adrenergic, but not electrical brain stimulation. Results are interpreted to suggest that these feeding systems are independent at the level of the diencephalon. The role of the vagus nerve as an efferent link through which these brain systems may influence feeding behavior is discussed.     

Synthesis and assembly of adenovirus type 2 polypeptides. II. Reversible inhibition of hexon assembly at 42 degrees

Hexon polypeptides (monomers) synthesized at 42° do not assemble into capsomeres (trimers) until temperature stepdown to 37°. Structural studies of monomer and trimer show them to be identical in molecular weight and tryptic peptide patterns. Cyanide and mercaptoethanol, both of which can interact with sulfhydryl groups, inhibit hexon assembly. Therefore, the oxidation state of each sulfhydryl group of cysteine was examined, but was found to be the same for free polypeptides and capsomeres. These observations suggest that factors other than the primary structure of the polypeptides are important for in vivo assembly.     

Clonidine hyperphagia: Neuroanatomic substrates and specific function

Recent studies have indicated that hhe ₂-noradrenergic agonist clonidine (CLON), when peripherally and centrally administered, potentiates feeding is satiated rats in a manner similar to the observed following injection of norepinephrine (NE) into the hypothalamic paraventricular nucleus (PVN). The present experiments examines the effects of CLON on meal patterns and macronutrient selection and compared these findings to earlier NE-stimulated feeding studies. Administration of CLON (25 nmoles), directly into the PVN (n = 5), similar to PVN injected NE, produced an increase in meal size (190%) and freeding duration (164%), with no change in meal frequency. Additional tests were conducted in rats with PVN electrolytic or 6-hydroxydopamine lesions. In Sham rats (n = 16) peripheral CLON (0.05 mg/kg), like NE, produced an increase in food intake and particularly potentiated carbohydrate ingestion. Discrete electrolytic lesions of the PVN (n = 5) abolished this CLON-induced feeding and carbohydrate preference, suggesting that the PVN may be a primary site for CLON-stimulated hyperphagia. Neurotoxin lesions of the PVN (n = 17), which reduced PVN NE levels by 75%, failed to alter peripheral CLON-induced feeding. This and other evidence indicates that this agonist may be acting via postsynaptic ₂ receptors in the PVN to potentiate carbohydrate intake, rather than via presynaptic release of NE from nerve endings in the PVN.     

L-Tryptophan's effects on mouse killing, feeding, drinking, locomotion, and brain serotonin

Injections of the serotonin precursor l-tryptophan (25, 50, and 100 mg/kg IP), inhibited mouse killing behavior in rats, as indicated by a dose dependent increase in latencies to attack and kill mice. Tests in 24 hr food deprived rats revealed that feeding behavior was also significantly decreased by about 30% by tryptophan injections (50--100 mg/kg IP). Concomitant with the behavioral changes were increased levels of brain serotonin and its metabolite 5-hydroxyindoleacetic acid. Drinking, latencies to sniff mice, and ability to locomote on a rotating rod were not affected by l-tryptophan injections, although spontaneous activity in an open field was reliably reduced by 33% with a dose of 100 mg/kg. Thus, while the degree of selectivity for tryptophan's effects on behavior remains open to question, these findings are consistent with hypotheses of an inhibitory role for central serotonergic systems, particularly in mouse killing and feeding behaviors.     

Distribution of α-adrenergic, β-adrenergic and dopaminergic receptors in discrete hypothalamic areas of rat

Catecholamine receptor binding sites were measured in discrete hypothalamic nuclei or regions as well as in certain extrahypothalamic areas of the adult male rat. For each assay, discrete areas were microdissected from frozen tissue sections and pooled from several animals. Specific high affinity binding sites were assessed at fixed ligand concentrations for [³H]p-aminoclonidine (PAC) and [³H](2-C 2′,6′-(CH₃O)₂ phenoxyethylamino)-methylbenzodioxan (WB-4101) for α-adrenergic receptor sites, for [³H]dihydroalprenolol (DHA) for β-adrenergic receptor sites, and for [³H]2-amino-6, 7-dihydroxy-1,2,3,4-tetrahydronaphtalene (ADTN) and [³H]spiroperidol in the presence of cinanserin for dopaminergic receptor sites.Regional variations in [³H]WB-4101 binding were relatively small in magnitude, with most hypothalamic and extrahypothalamic areas possessing between 60 and 90% of the binding in frontal cortex. [³H]PAC binding showed a wider range of binding density across brain areas than did [³H]WB-4101, but, in general, variations in [³H]PAC binding paralleled those in [³H]WB-4101 binding. In hypothalamus, binding was characterized as being predominantly to α₁-receptors in the of [³H]WB-4101 and to α₂-receptors in the case of [³H]PAC. The medial hypothalamic areas exhibited a somewhat higher density of these α-adrenergic sites than did the lateral hypothalamus (perifornical hypothalamus and medial forebrain bundle). Also, the ratio of [³H]PAC to [³H]WB-4101 binding differed in different hypothalamic areas, ranging from 1.5:1 to 4:1. The median eminence was exceptional in that it contained appreciable [³H]PAC but no significant [³H]WB-4101 binding sites at the radioligand concentrations tested. Binding of [³H]DHA to β-adrenergic receptors varied over approximately a 3-fold range in the different hypothalamic areas, with binding highest in the medial forebrain bundle and the medial preoptic area, and lowest in the periventricular, dorsomedial and posterior hypothalamic nuclei, the median eminence and the zona incerta. The ratio of β-adrenergic to α-adrenergic binding sites was generally lower in the medial than in the lateral hypothalamic areas and higher in the extrahypothalamic areas examined than in the hypothalamus. With regard to [³H]spiroperidol and [³H]ADTN binding to dopaminergic sites, the striatum, nucleus accumbens and olfactory tubercle showed a greater density of [³H]spiroperidol than of [³H]ADTN sites, in contrast to the hypothalamus where [³H]ADTN binding was more predominant. Within the hypothalamus, [³H]ADTN binding was relatively uniform, while [³H]spiroperidol binding was quite high in four hypothalamic areas (lateral perifornical area, medial forebrain bundle, paraventricular and dorsomedial nuclei), intermediate in the median eminence and arcuate nucleus, and low or not detectable in all other hypothalamic areas.