Corticotropin-releasing factor (CRF) is localized in fibers in the noradrenergic nucleus locus ceruleus (LC) and alters LC discharge characteristics when administered centrally. To determine whether CRF functions as a neurotransmitter in the LC during stress, the effects of hemodynamic stress on LC discharge were compared to those of CRF. Hemodynamic stress elicited by intravenous nitroprusside infusion produced identical effects on LC spontaneous and sensory-evoked discharge as those reported for centrally administered CRF. Thus, nitroprusside increased LC spontaneous discharge rates, and disrupted LC discharge evoked by sensory stimuli such that the stimuli were less effective in producing phasic increases in LC discharge. The neuronal effects of nitroprusside were completely blocked by central administration of the CRF receptor antagonist, α helical CRF9–41, but not by pretreatment with dexamethasone which blocks stress-elicited hypophyseal CRF release. The present results confirm other reports of LC activation by stressors, and extend these studies by demonstrating that, in certain circumstances, this activation is dependent on endogenous CRF. This study supports the concept that CRF functions as a neurotransmitter in the LC in the initiation of stress responses.

OP-1, also known as BMP-7, is a member of the TGF-P superfamily of proteins and was originally identified on the basis of its ability to induce new bone formation in vivo. OP-1 mRNA is found in the developing kidney and adrenal gland as well as in some brain regions (Ozkaynak et al. [1991] Biochem. Biophys. Res. Commun. 179116123). We have tested the effect of recombinant human OP-1 on quail trunk neural crest cultures. The number of catecholamine-positive cells which developed after 7 days in vitro in the presence of OP-1 was increased in a dose-dependent manner, with a greater than 100-fold maximal stimulation observed. The increase in the number of catecholamine-positive cells in the presence of OP-1 was paralleled by an increase in the number of tyrosine hydroxylase (TH)-positive cells. In contrast, total and melanocyte cell number were unaffected by the presence of OP-1. The number of Islet-1-immunoreactive cells was also increased by OP-1, but to only about half the value seen for TH. Double label experiments revealed these Islet-1-positive cells were a subset of the TH-positive cells. Inhibitors of DNA synthesis prevented the OP-1-mediated increase in adrenergic cell number, indicating that OP-1 does not act on a postmitotic cell population. However, labeling studies with bromodeoxyuridine indicated that OP-1 did not increase the proportion of the cell population engaged in DNA synthesis. Thus, the OP-1-mediated increase in adrenergic cell number most likely occurs as a result of the enhanced survival of a subpopulation of adrenergic precursors or an increase in their probability of adrenergic differentiation, but not by increasing the mitotic rate of adrenergic precursors or adrenergic cells themselves. In contrast to OP-1, TGF-PI decreased adrenergic cell number. When OP-1 and TGF-P1 were added simultaneously, TGF-P1 antagonized the OP-1-mediated increase in adrenergic cell number in a dose-dependent manner. 0 1995 Wiley-Liss, Inc.

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We had previously shown NADPH diaphorase activity in fixed tissue slices of the insular cortex of the Syrian golden hamster (Mesocricetus auratus). The objective of this work was to determine the chemical identity of agents responsible for the observed NADPH diaphorase activities. Three different enzymatic NADPH diaphorase activities were distinguished in the insular cortex. (a) The activity seen in endothelial cells was not characterized histochemically, but it co-localized with eNOS-like immunoreactivity. (b) The neuronal Type I activity showed little sensitivity to 10(-5) M dicoumarol, could use either alpha- or beta-NADPH with almost equal facility, and co-localized with nNOS-like immunoreactivity. This activity was primarily attributable to nNOS. (c) The neuronal Type II activity was greatly attenuated by 10(-5) M dicoumarol, had a strong preference for beta-NADPH (rather than alpha-NADPH), and did not co-localize with any NOS-like immunoreactivity. These characteristics also apply to the NADPH diaphorase activity observed in the diffuse blue band in Layers II and III of agranular and dysgranular insular cortex and in the meshwork of cortical fibers. This staining was due primarily to a dicoumarol-sensitive dehydrogenase(s), either an isozyme of DT diaphorase (EC 1.6.99.2), or NADPH dehydrogenase (quinone) (EC 1.6. 99.6), or to a novel dicoumarol-sensitive NADPH dehydrogenase.

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