Association between increase in cyclic AMP and subsequent induction of tyrosine hydroxylase in rat adrenal medulla. Experiments with swimming stress

Neuropeptide y gates a stress-induced, long-lasting plasticity in the sympathetic nervous system

Acute stress evokes the fight-or-flight reflex, which via release of the catecholamine hormones affects the function of every major organ. Although the reflex is transient, it has lasting consequences that produce an exaggerated response when stress is reexperienced. How this change is encoded is not known. We investigated whether the reflex affects the adrenal component of the sympathetic nervous system, a major branch of the stress response. Mice were briefly exposed to the cold-water forced swim test (FST) which evoked an increase in circulating catecholamines. Although this hormonal response was transient, the FST led to a long-lasting increase in the catecholamine secretory capacity measured amperometrically from chromaffin cells and in the expression of tyrosine hydroxylase. A variety of approaches indicate that these changes are regulated postsynaptically by neuropeptide Y (NPY), an adrenal cotransmitter. Using immunohistochemistry, RT-PCR, and NPY(GFP) BAC mice, we find that NPY is synthesized by all chromaffin cells. Stress failed to increase secretory capacity in NPY knock-out mice. Genetic or pharmacological interference with NPY and Y1 (but not Y2 or Y5) receptor signaling attenuated the stress-induced change in tyrosine hydroxylase expression. These results indicate that, under basal conditions, adrenal signaling is tonically inhibited by NPY, but stress overrides this autocrine negative feedback loop. Because acute stress leads to a lasting increase in secretory capacity in vivo but does not alter sympathetic tone, these postsynaptic changes appear to be an adaptive response. We conclude that the sympathetic limb of the stress response exhibits an activity-dependent form of long-lasting plasticity.

Both synaptic and antidromic stimulation of neurons in the rat superior cervical ganglion acutely increase tyrosine hydroxylase activity

Electrical stimulation of the preganglionic cervical sympathetic trunk produces an acute increase in the rate of DOPA synthesis in the rat superior cervical ganglion. The present study was designed to test the possibility that this acute transsynaptic stimulation of catechol biosynthesis could be, at least in part, a consequence of an increase in the firing rate of the postganglionic sympathetic neurons. For this purpose, the effect of stimulation in vitro of the preganglionic cervical sympathetic trunk was compared to that of stimulation of the predominantly postganglionic internal and external carotid nerves. Stimulation of the cervical sympathetic trunk at 10 Hz for 30 min produced a 4.6-fold increase in DOPA synthesis, while simultaneous stimulation of the two postganglionic trunks produced a 3.1-fold increase. The internal carotid nerve is known to contain a small population of preganglionic fibers that synapse on principal neurons in the ganglion before entering this nerve trunk. To eliminate the possibility that the effect of stimulation of the internal carotid nerve is mediated by synaptic stimulation via these preganglionic "through fibers", the effect of stimulation of previously decentralized ganglia was examined. While decentralization reduced the magnitude of the effect of stimulation of the internal and external carotid nerves, a 2.0-fold increase in DOPA synthesis was still seen. In addition, when these nerve trunks were stimulated in control ganglia that had been maintained in organ culture for 48 h to allow time for the degeneration of afferent nerve terminals, DOPA synthesis increased 4.1-fold.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of carbachol and 56 mm-potassium chloride on the cyclic AMP-mediated induction of tyrosine hydroxylase in neuroblastoma cells in culture

Tyrosine hydroxylase (TH) activity is increased two- to threefold in neuroblastoma cell line NBP2 maintained in culture for 48 h in the presence of either the inhibitor of cyclic AMP-phosphodiesterase (PDE), 4-(3-butoxy-4-methoxybenzyl)-2-imidazolidinone (RO 20-1724), or the activator of adenylate cyclase, prostaglandin E1 (PGE1). Cyclic AMP levels are elevated 70-80% and 30-40% throughout the 48-h treatment with RO 20-1724 and PGE1, respectively. Carbachol does not affect either basal TH activity or cyclic AMP levels in the cells. However, the cholinergic agonist delays the induction of TH elicited by either RO 20-1724 or PGE1. This delay is prevented by atropine. The elevation in cyclic AMP levels elicited by either RO 20-1724 or PGE1 is blocked for 1 h or 15 min, respectively, after treatment with carbachol. Cyclic AMP levels then begin to rise until they reach those levels observed in the presence of RO 20-1724 or PGE1 alone by 12 h or 1 h of treatment, respectively. Time course studies demonstrate that this transient inhibition of the elevation of cyclic AMP is associated with a 48-h delay in the induction of TH elicited by either RO 20-1724 or PGE1. In contrast, the induction elicited by 8-bromo cyclic AMP is unaffected by carbachol. A depolarizing concentration (56 mM) of KCl produces a 24-h delay in the induction of TH elicited by RO 20-1724, without affecting the concomitant elevation of cyclic AMP produced by the PDE inhibitor. Furthermore, 56 mM-KCl inhibits the induction of TH elicited by 8-bromo cyclic AMP. It thus appears that carbachol delays the induction of TH by transiently inhibiting the elevation of cyclic AMP, whereas potassium depolarization delays the induction of TH by inhibiting a process with a site of action that is distal to the elevation of cyclic AMP.