AJP - Regulatory, Integrative and Comparative Physiology, Vol 240, Issue 1 16-R22, Copyright © 1981 by American Physiological Society
Amino acid incorporation in medial hypothalamic nuclei: circadian, perikarya, and neuropil variations
A. N. Van den Pol
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.
