DISTRIBUTION OF TARGET-CELLS FOR 1,25-DIHYDROXYVITAMIN-D(3) IN THE BRAIN OF THE YELLOW-BELLIED TURTLE TRACHEMYS-SCRIPTA

Five h after injection of tritiated 1,25-dihydroxyvitamin D3 into Trac hemys scripta, neurons with nuclear concentrations of radioactivity we re identified in distinct regions within the central nervous system. C oinjection of a 100-fold excess of non-labeled 1,25-dihyroxyvitamin D3 abolished or reduced the specific nuclear binding of tracer. Target n eurons were present in ventral periventricular brain regions including tuberculum olfactorium, nucleus accumbens, cortex piriformis, primord ium hippocampi, nucleus striae terminalis, dorsal ventricular ridge, a mygdala, nucleus infundibularis and tectum opticum. With the exception of the nucleus infundibularis and the tectum opticum, target neurons can be continuously followed from the ventrolateral nucleus accumbens throughout the nucleus striae terminalis into the amygdala. The genera l distribution of target neurons is similar to that described for rode nts but more restricted to the above regions. The results show that ta rget neurons for vitamin D are located in brain regions including seve ral components of the limbic and thalamic systems in which gonadal ste roids as well as aminergic and peptidergic messengers exert their acti ons. Vitamin D, the heliogenic steroid hormone, may therefore be invol ved in the orchestration of season-specific processes such as reproduc tion and related behaviors.