Suprachiasmatic Nucleus Vasopressin Messenger RNA: Circadian Variation in Normal and Brattleboro Rats

In situ hybridization of an oligonucleotide probe complementary to vasopressin messenger RNA (mRNA) in sections from normal or Brattleboro rat hypothalami revealed hybridization densities in each of three vasopressin-rich nuclei: the supraoptic, paraventricular, and suprachiasmatic. When entrained to a daily light-dark cycle, each rat strain displayed diurnal variation in hybridizable mRNA in the suprachiasmatic, but not in the supraoptic or paraventricular nuclei. The higher values for suprachiasmatic mRNA in the morning correlate well with previously elucidated morning increases in vasopressin immunoreactivity in the cerebrospinal fluid. These results (i) support the utility of in situ hybridization techniques for elucidating physiological influences on regional peptidergic function, (ii) are consistent with a prominent role for vasopressinergic suprachiasmatic neurons in generating the cerebrospinal fluid vasopressin rhythm, and (iii) suggest that regulation of this mRNA rhythm is not dependent on release of intact peptide.