A Partial Blockade of Catecholaminergic Neurotransmission with 6-Hydroxydopamine Decreases mRNA Level of Gonadotropin Releasing Hormone in the Male Rat Hypothalamus

Abstract

Central catecholamines (CA) are known to be involved in the regulation of synthesis and secretion of gonadotropin releasing hormone (GnRH) from the hypothalamus. However, no attempt has been yet made to determine whether CA affects GnRH gene expression. To this end, the effect of 6-hydroxydopamine (6-OHDA), a catecholaminergic neurotoxin, on GnRH mRNA level was examined. Hypothalamic tissues obtained from adult male rats were incubated with medium containing 6-OHDA. To ensure the effect of 6-OHDA on CA depleting action, CA levels in media and in postincubation tissues were determined. Increasing concentrations of 6-OHDA resulted in decrease in norepinephrine (NE) and dopamine (DA) contents in a dose dependent manner. Treatment with 6-OHDA (5 × 10^–4 M) produced a time-dependent decrease in NE but not DA, when CA levels in media were determined at 30 min intervals during the incubation period. To determine changes in GnRH mRNA level in response to 6-OHDA treatment in vitro, for 2.5 h total cytoplasmic RNA fractions were isolated from postincubation hypothalamic tissues and used for RNA-blot hybridization with ³²P-labeled GnRH riboprobe. A blockade of CA neurotransmission with 6-OHDA (5 × 10^–4 M) significantly reduced GnRH mRNA level by half over its control and internal control (actin mRNA) groups. Northern blot analysis revealed that addition of NE (1 × 10^–6 M) reversed the decreased GnRH mRNA level by 6-OHDA. These studies clearly demonstrated that GnRH mRNA level was modified by the combination of 6-OHDA and/or NE in rat hypothalamic tissues incubated in vitro, indicating that CA neurotransmission influences GnRH gene expression.