Impaired Maturation of Pre-Synaptic Cholinergic Nerve Terminals in the Superior Cervical Ganglia After Administration of Guanethidine and Dexamethasone

Abstract

It has been suggested that the normal development of the post-synaptic cells is critical for the normal maturation of the presynaptic cholinergic nerve terminals in the peripheral sympathetic nervous system. Thus the surgical, immunological or pharmacological mani pulations (1, 2) for destruction of sympathetic ganglion cells block the normal development of choline acetyltransferase (ChAc), the enzyme restricted to the cholinergic nerve terminals (3).In this study, guanethidine and dexamethasone were employed to investigate further the role of the post-synaptic cells in the maturation of pre-synaptic nerve terminals.Prolonged administration of guanethidine to newborn or adult rats produces irreversible destruction of peripheral adrenergic cell bodies (4, 5). Dexamethasone retards the normal growth of these neurons (6) with possible concomitant proliferation of adrenaline-containing neurons (7,8). This drug was found herein to have an additional growth retarding effect on the adrenal chromaffin cells, a property not shared with guanethidine (9). This agent may, therefore, provide a tool for studying the possible retrograde trans-synaptic control mechanism in chrornaffin cells.Part of this work was presented in Sendai, Japan, June 1976 at the annual meeting of the Physiological Society of Japan. MATERIALS AND METHODSGuanethidine dissolved in physiological saline was injected daily s.c. at a dose of 15 50 pg/g of body weight into newborn Wistar rats of both sexes and 25 mg/kg to adult male rats. Dexamethasone was injected daily s.c. at a dose of 0.1 /Ig/g into newborn rats and 0.2 ng/g to rats of various ages. The animals were sacrificed by exposure to ether. Su perior cervical ganglion (SCG) pairs and duodenum (approx. I cm length) were homogenized in 0.2-0.4 ml of 10 mM tris buffer, pH 7.4 containing 0.2% triton X-100 using a small glass to-glass homogenizer. Adrenal pairs were homogenized in 0.2-2.0 ml of the same solution using a teflon pestle glass homogenizer and the supernatant was used for the assay of enzymes after centrifugation at 10,000 g for 10 mnin (conventional refrigerated centrifuge).The activity of tyrosine hydroxylase (TH) was determined by the 14CO2 trapping method developed by Waymire et al (10) with a 73 /tM tyrosine and a 2 mM 5,6-dimethyltetrahy dropterine concentration. The activity of dopamine-a-hydroxylase (DBH) was assayed by the phenylethanolamine N-methyltransferase (PNMT) coupled method of Molinoff et al (11) employing an optimal copper concentration. The ChAc and the PNMT activities were measured by the methods of Fonnum (12) and Saavedra et al (13) with slight modifications (14), respectively. The protein was assayed by the method of Lowry et al (15) employing bovine serum albumin as a standard. Reagent blanks included the same concentrations of triton X-100 as those in samples. RESULTSEffects of guanethidine on the activities of some enzymes in the SCG and adrenals Daily injection of guanethidine to newborn rats for 13 days impaired little the normal developmental increase of body ...

Prenatal Dexamethasone Exposure Causes Loss of Neonatal Hypoxia Tolerance: Cellular Mechanisms

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Nutritional Influences on Adrenal Chromaffin Cell Development: Comparison with Central Neurons

“…An important question is if these adrenomedullary deficits might be epiphenomena associated with glucocorticoid responses to overcrowding or other nonspecific stress. The ontogeny of both tyrosine hydroxylase and phenylethanolamine N-methyltransferase, as well as catecholamine levels themselves, are profoundly affected by corticosteroids (8,14). However, the current results indicate no significant change in circulating corticosterone levels in the animals reared in large litters.…”