Subpopulations of corticotropin-releasing hormone neurosecretory cells distinguished by presence or absence of vasopressin: confirmation with multiple corticotropin-releasing hormone antisera

Parvocellular corticotropin-releasing hormone neurosecretory cells in the hypothalamic paraventricular nucleus project axons to the portal capillary plexus in the external zone of the median eminence. Immunocytochemical studies have identified two approximately equal subpopulations of these corticotropin-releasing hormone neurons in normal rats, distinguished by the presence or absence of co-existent vasopressin, and different responses to stress. However, it was recently proposed that the vasopressin deficient cells do not contain corticotropin-releasing hormone, but have been misidentified due to cross-reactivity of the corticotropin-releasing hormone antiserum to peptide histidine-isoleucineamide. It is shown here that the same set of corticotropin-releasing hormone neurons (including both vasopressin expressing and vasopressin deficient subtypes) was labeled with multiple corticotropin-releasing hormone antisera. These included two antisera that did not cross-react with peptide histidine-isoleucineamide: one against ovine corticotropin-releasing hormone, and one rat corticotropin-releasing hormone antiserum absorbed with peptide histidine-isoleucineamide. The results provide further support for the hypothesis of functionally distinct compartments of the corticotropin-releasing hormone neurosecretory system that can modulate the ratio of vasopressin to corticotropin-releasing hormone in portal blood.