Expression of c-Fos immunoreactivity in transmitter-characterized neurons after stress

The effect of intracerebroventricular injection of the mitosis inhibitor colchicine and of immobilization stress, subcutaneous injection of capsaicin, and intraperitoneal injection of hypertonic salt solution on expression of c-Fos-like immunoreactivity was studied in the rat brain with immunohistochemistry. All the procedures induced c-Fos immunoreactivity in parvocellular neurons of the paraventricular nucleus, and many of these neurons also contained corticotropin-releasing factor immunoreactivity. c-Fos immunoreactivity was also observed, for example, in subpopulations of neurons in the locus coeruleus, the ventrolateral medulla oblongata, and the nucleus tractus solitarii. Many of these cells also expressed catecholamine-synthesizing enzymes. The results suggest that intraventricular injection of colchicine is a stressful stimulus and support the view that several catecholamine cell groups in the lower brainstem are part of the brain circuitry mediating stress reactions, as are the hypothalamic neurons that contain corticotropin-releasing factor.