The distribution of angiotensin II (AII)-immunoreactive cells and fibers was examined
in adult male Sprague-Dawley rats with and without colchicine pretreatment. As seems
to be the case for a number of other neuropeptides, AII is preferentially found in
brain stem, hypothalamic, and limbic structures involved in the control of homeostatic
functions. AII-stained cell bodies were most prominent in magnocellular parts of the
paraventricular and supraoptic nuclei, and cells were also found in parvocellular
parts of the former. Other hypothalamic nuclei containing cell bodies include the
suprachiasmatic nucleus, the medial preoptic area, and perifornical parts of the lateral
hypothalamic area. Of considerable interest was robust staining in several of the
circumventricular organs, in particular the subfornical organ, where both cells and
fibers were found. The results of water deprivation and nephrectomy suggest that this
staining does not represent uptake of circulating peptide, but instead, represents
AII-containing neural connections. In the thalamus, AII-stained cells were found in
the paraventricular nucleus, the central medial nucleus, the nucleus reuniens, and
rostral parts of the zona incerta. Two cell groups in the basal telencephalon, in
the dorsal part of the bed nucleus of the stria teminalis and in the medial nucleus
of the amygdala, lay at either end of an AII-stained pathway coursing through the
stria terminalis. In the midbrain, immunoreactive cells were found in the interpeduncular
and peripeduncular nuclei, and one pontine cell group was detected in the most lateral
part of the lateral parabrachial nucleus. The only AII-stained cells in the medulla
were in the nucleus of the solitary tract, near the margin of the area postrema. Fibers
were found at all levels of the central nervous system, from the olfactory bulbs to
the spinal cord, where terminal fields were observed in the substantia gelatinosa
and in the intermediolateral cell column. Longitudinally oriented fibers were present
throughout the periventricular fiber system and in the medial forebrain bundle, including
its caudal extension in ventrolateral parts of the brain stem. It is suggested that,
at many different levels, AIIserves as both a hormone and neurotransmitter for fluid
balance.