ULTRASTRUCTURAL-LOCALIZATION AND AFFERENT SOURCES OF CORTICOTROPIN-RELEASING FACTOR IN THE RAT ROSTRAL VENTROLATERAL MEDULLA - IMPLICATIONSFOR CENTRAL CARDIOVASCULAR REGULATION

We investigated the ultrastructural localization, afferent sources, an d arterial pressure effects of corticotropin-releasing factor (CRF) in the nucleus reticularis rostroventrolateralis (RVL), a region of the ventrolateral medulla containing C1 adrenergic neurons and sympatho-ex citatory reticulospinal afferents to sympathetic preganglionic neurons . A polyclonal antibody to CRF was localized in acrolein-fixed section s through the rat RVL by the peroxidase-antiperoxidase (PAP) method. L ight microscopy showed that 1-7 perikarya/30 mum section and numerous varicose processes contained CRF-like immunoreactivity (CRF-LI). By el ectron microscopy, CRF-LI was most intensely localized to large (80-10 0 nm) dense-core vesicles within numerous terminals and a few perikary a and large dendrites. Approximately half of the terminals containing CRF-LI were in direct contact with unlabeled perikarya or dendrites; t he remainder were in apposition to either unlabeled terminals or astro cytes. Most synaptic specializations were asymmetric synapses on small , unlabeled dendrites. To examine potential extrinsic sources of CRF-c ontaining terminals in the C1 area of the RVL, PAP immunocytochemical localization of CRF was combined with retrograde transport of wheat ge rm agglutinin-conjugated horseradish peroxidase (WGA-HRP). In all case s examined, a number of dually labeled neurons were found in the parav entricular nucleus (PVN) of the hypothalamus and a few dually labeled neurons were observed in the nuclei of the solitary tract; these label ed neurons were ipsilateral to the unilateral injection of WGA-HRP int o the C1 area. Fewer dually labeled perikarya were detected in the lat eral hypothalamic area and the lateral parabrachial nuclei, ipsilatera l to the WGA-HRP injection. Additional physiological studies showed th at bilateral microinjections of CRF into the C1 area of the RVL of ure thane-anesthetized rats elicited a dose-related increase in arterial p ressure. The results suggest that within the C1 area of the RVL, CRF r eleased from terminals, arising predominantly from the PVN of the hypo thalamus and probably from local neurons as well, may excite sympathoe xcitatory reticulospinal neurons.