Circadian rhythm of tyrosine hydroxylase induction by short-term cold stress: modulatory action of glucocorticoids in newborn and adult rats.

Abstract

The trans-synaptic induction of tyrosine hydroxylase [tyrosine 3-monooxygenase; EC 1.14. were studied in more detail.We wish to report that in adult rats the induction of TH by short-term (1-2 hr) cold stress is subjected to a circadian rhythm both in the adrenal medulla and in the sympathetic ganglia. A causal relationship between the circadian rhythm of TH induction by cold stress and the circadian rhythm of adrenal glucocorticoid synthesis can be deduced from the observation that administration of glucocorticoids to adult animals abolished the circadian rhythm of TH inducibility and that during the postnatal development the circadian rhythm of TH inducibility coincided with the occurrence of the circadian rhythm of plasma corticoids (8). MATERIALS AND METHODS.Male Sprague-Dawley rats (supplied by the Siiddeutsche Versuchstierfarm, Tuttlingen, Germany) weighing 60-70 g were adapted to constant laboratory conditions (temperature kept at 24 i 10 in fully climatized rooms with a 12 hr lightdark cycle changed at 7 a.m. and 7 p.m. respectively) for at least 14 days. They had free access to tap water and food pellets (Nafag AG, Zurzach, Switzerland). After this period of equilibration groups of animals were exposed to a temperature of 40 for 2 hr. Different groups were exposed to the cold starting at 4 hr intervals around the clock and were killed by a blow on the head 48 hr later. Adrenals and superior cervical ganglia were rapidly removed and homogenized in ice-cold 5 mM Tris HCl buffer, pH 7.4, containing 0.1%o Triton X-100. One pair of adrenals was homogenized in 4 ml, one pair of ganglia in 0.5 ml.Neonatal rats were housed in litters of 8 to 10 together with their parents until 25 days of age. Young rats were exposed to 40 for 45-60 min; at the end of the cold exposure the animals were allowed to recover under a heating lamp. They were killed by exposure to ether vapor 48 hr after the beginning of the stress procedure. One pair of adrenals was homogenized in 2 ml of 5 mMil Tris HCl buffer, pH 7.4, containing 0.1% Triton X-100, one pair of superior cervical ganglia in 0.5 ml. The homogenates were centrifuged at 10,000 X g for 20 nin and the supernatant fraction was used for determination of TH activity according to the method of Levitt et al. (9)

Postnatal development of dopaminergic neurons in the rabbit retina

“…Dopamine content and tyrosine hydroxylase activity in the adult retina. In order to minimize any variations in endogenous dopamine levels due to circadian rhythm (Otten and Thoenen, 1975;Thoenen, 1970), rabbits were kept in a stable environment described under "Materials and Methods." They were sacrificed in the light-adapted state at about the same time of the day (2 P.M.).…”

Glucocorticoids and the Development of Neuronal Function: Effects of Prenatal Dexamethasone Exposure on Central Noradrenergic Activity

“…Enhanced development by glucocorticoids has been hypothesized to be prominent for catecholaminergic cells, where morphological and biochemical evidence suggests that exoge nous steroids, administered during the period surrounding the termination of replication and initiation of differentiation, can promote the appearance of enzymes characteristic of the mature phenotype [1,[8][9][10][11][12], However, this view is not without challenge, as expres sion of the genes coding for many of these enzymes is already present in fetal stages prior to the parturitional and postnatal rises in ste roid levels [13], Perhaps more importantly, the direct connection between the morpholog ical and biochemical changes in cell differen tiation and neuronal function has yet to be established. In the current study, we have examined the effects of dexamethasone ad ministered to pregnant rats during late gesta tion on the development of central noradren ergic function, through assessment of trans mitter levels and turnover: the latter is an index of neuronal activity and shows a char acteristic rise associated with the onset of syn aptic function [14][15][16][17], Studies were con ducted across three brain regions with differ ing maturalional profiles [3.…”

“…It should be noted, however, that these findings do not address the separate issue of whether receptor transduction mech anisms are altered by steroid exposure, a con sequence that is likely to occur for at least one pathway, namely P-receptor control of ade nylate cyclase [35], Our results are thus most consistent with the glucocorticoid-induced enhancement of catecholaminergic cell differentiation even when general growth retardation has oc curred. Promotion of noradrenergic cell dif ferentiation by glucocorticoids has been well studied in peripheral tissues [1,8,9,12], and similar events have been postulated to occur in the central nervous system [ 1,10,11 ]. If the underlying mechanism for dexamethasone's effects on transmitter turnover does indeed involve altered cellular development, then it would be expected that regional selectivity would depend primarily upon the maturational profile for cells in each region.…”

A Combined Autoradiographic and Immunocytochemical Study of ³H-Corticosterone Target Neurons and Catecholamine Neurons in Rat and Mouse Lower Brain Stem

“…Neurons in noradrenergic cell groups Ai, As, As, At, and A7 concentrate 'H-estradiol [3,5]. In addition, nuclear accumulation of 3H-estradiol has been demonstrated in cer tain dopamine neurons of the hypothalamus [13]. Catechol amine neurons that are target sites for 3H-dihydrotestosterone are located in pontine noradrenergic cell groups (A4 through A7) but not in the medullary cell groups (Ai and A2) [5].…”

“…Adrenal steroids play a modulatory role in the transsyn aptic induction of TH activity in sympathetic ganglia [13,14], In the rat, a transsynaptic increase in TH activity in the superior cervical ganglia induced by short-term cold stress exhibits a circadian rhythm that is related to endogenous corticosterone secretion [13]. The stress-induced increase in TH activity occurs only when rats are subjected to the cold stress during periods in which endogenous corticosterone secretion is high.…”