title: Amino acid incorporation in medial hypothalamic nuclei: circadian, perikarya, and neuropil variations.
abstract: Amino acid, [3H]lysine, incorporation was examined with autoradiographic techniques in four nuclei of the medial hypothalamus during four consecutive 6-h periods. Rats which had previously been maintained under 12:12 light-dark conditions were kept in constant darkness during the day of [3H]lysine administration to prevent any direct influence of light on hypothalamic activity. Forty-five minutes after intraperitoneal injection of the tritiated amino acid, animals were killed. After autoradiography processing, grain counting revealed that the suprachiasmatic and magnocellular paraventricular nuclei showed a statistically significant circadian variation in the number of grains over neural perikarya. A time-of-day effect was also found in the grain count over neuropil of the arcuate, ventromedial, and paraventricular nuclei. A corresponding behavioral study found that feeding continued to occur primarily during the 12 h of night, even with lights out for 24 h. These data suggest an endogenous circadian variation in one or more factors that influence amino acid uptake and protein synthesis in some hypothalamic neurons. When [3H]lysine uptake was analyzed in terms of grains/100 micrometer 2 of cell area, the arcuate and paraventricular nuclei showed a significantly greater (double) uptake of [3H]lysine than did the suprachiasmatic or ventromedial nuclei. Four times more grains were counted over somata than over an equal area of cell-free neuropil.
mesh_terms: D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D001345:Autoradiography; D002940:Circadian Rhythm; D007031:Hypothalamus / Q000378:metabolism*; D007033:Hypothalamus, Middle / Q000378:metabolism*; D008297:Male; D009419:Nerve Tissue Proteins / Q000096:biosynthesis; D009474:Neurons / Q000378:metabolism; D010286:Paraventricular Hypothalamic Nucleus / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D013495:Supraoptic Nucleus / Q000378:metabolism
chemical_list: D000596:Amino Acids; D009419:Nerve Tissue Proteins