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 corticotropinreleasing 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.The c-fos gene (1, 2) is expressed in many tissues in response to growth factor stimulation (3-9). It has been suggested that induction of protooncogenes such as c-fos may be important in the establishment of prolonged functional changes in neurons (10). It has been demonstrated by immunohistochemical methods that various types of stimulation induce a c-Fos protein-like immunoreactivity in specific neuron populations in various brain regions (11)(12)(13). Thus, immunohistochemical analysis of expression of c-Fos protein in nervous tissue may represent a new tool in neurobiology for metabolic mapping at the cellular level (14). In fact, numerous papers based on this methodology have appeared during the last 2 years.In the present study we have used immunohistochemistry to analyze to what extent various stressors may induce expression of c-Fos-like immunoreactivity in certain brain regions. In addition, antisera to neuropeptides and transmitter-synthesizing enzymes were used to further characterize c-Fos-activated neurons. Of particular interest to us has been the question whether or not intracerebroventricular (i.c.v.) injections of the mitosis inhibitor colchicine (15) may affect stress-related systems. Ever since colchicine was shown to inhibit axonal transport (16,17) and to cause marked accumulation of amine storage granules in cell bodies (18), this drug has been used to improve histochemical visualization of transmitters, peptides, and related substances in neuronal cell bodies (19,20). Our results demonstrate that several stress-inducing procedures as well as i.c.v. colchicine treatment, including the i.c.v. injection procedure per se, cause expression of c-Fos protein in restricted neuronal cell populations both in the hypothalamus, including the corticotropin-releasing factor (CRF)-positive neurons in the paraventricular nucleus (PVN), and in the lower brainstem, particularly in catecholamine neurons. MATERIALS AND METHODSMale Sprague-Dawley rats (250...

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By using immunnohistochenstry and in situ hybridization, we have demonstrated that the nitric oxide (NO)-synthesizing enzyme NO synthase is present in gonadotrophs and in folliculo-steilate cells of the anterior pituitary gland of male and female rats. A marked increase in levels of NO synthase protein and mRNA was observed after gonadectomy. In vitro studies on dispersed anterior pituitary cells suggest that NO inhibits gonadotropin-releasing-hormonestimulated luteinizing hormone release. An inhibitory effect of NO has also been shown on growth-hormone-releasinghormone-stimulated release of growth hormone [Kato, M. (1992) Endoerinology 131, 2133-2138J. Thus these findings support a dual mechanism for NO in the control of anterior pituitary hormone secretion, an autocrine mediation of luteinizing hormone release on gonadotrophs, and a paracrine effect on growth hormone secretion involving folliculo-steilate cells cloely related to somatotrophs. We speculate that NO may participate in producing the pulsatfle secretion patterns ofthese two pituitary hormones.It is now well established that nitric oxide (NO), a free radical gas, is not only an endothelium-derived relaxing factor but also an inter-and intracellular messenger in many other biological systems (1)(2)(3)(4)(5). NO is formed from L-arginine by the enzyme NO synthase (NOS). This enzyme has been purified from rat brain (6,22), and the gene for rat brain NOS has been cloned (7). Thus, by using immunohistochemistry and in situ hybridization, it has been possible to map the distribution of NOS in various tissues including the nervous system (refs. 8, 9, 23 and 24; see also ref. 10). Little is known about the cellular localization of NOS in the endocrine system, but there is information on possible functional roles for NO in hormonal regulation. For example, the cytokine interleukin 1 increases production of NO in insulin-producing cells (11,12). At the pituitary level Kato (13) has shown that NO inhibits growthhormone (GH)-releasing-hormone (GHRH)-stimulated GH secretion. With regard to localization of NOS in the pituitary gland, this enzyme has so far been demonstrated only in the posterior lobe, presumably representing nerve endings originating from the magnocellular hypothalamic neurosecretory neurons, which also contain NOS (8,10).In the present study, we have used in situ hybridization and immunohistochemistry utilizing light and electron microscopy to find evidence for NO synthesis in the anterior pituitary. In addition we have evaluated a role for NO in the release of luteinizing hormone (LH)

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