Actions and Interactions of Alcohol and Transforming Growth Factor b1 on Prepubertal Hypothalamic Gonadotropin- Releasing Hormone

BackgroundAlcohol (ALC) diminishes gonadotropin-releasing hormone (GnRH) secretion and delays puberty. Glial transforming growth factor 1 (TGF1) plays a role in glial-neuronal communications facilitating prepubertal GnRH secretion. We assessed the effects of acute ALC administration on TGF1-induced GnRH gene expression in the brain preoptic area (POA) and release of the peptide from the medial basal hypothalamus (MBH). Furthermore, we assessed actions and interactions of TGF1 and ALC on an adhesion/signaling gene family involved in glial-neuronal communications. MethodsPrepubertal female rats were administered ALC or water via gastric gavage at 7:30am. At 9:00am, saline or TGF1 (100ng/3l) was administered into the third ventricle. At 3:00pm, the POA was removed and frozen for gene expression analysis and repeated for protein assessments. In another experiment, the MBH was removed from ALC-free rats. After equilibration, tissues were incubated in Locke's medium only or medium containing TGF1 with or without 50mM ALC for measurement of GnRH peptide released in vitro. ResultsTGF1 induced GnRH gene expression in the POA, and this effect was blocked by ALC. We also described the presence and responsiveness of the TGF1 receptor in the POA and showed that acute ALC exposure not only altered the TGF1-induced increase in TGF-R1 protein expression but also the activation of receptor-associated proteins, Smad2 and Smad3, key downstream components of the TGF1 signaling pathway. Assessment of an adhesion/signaling family consisting of glial receptor protein tyrosine phosphatase beta and neuronal contactin-associated protein-1 (Caspr1) and contactin showed that the neuronal components were induced by TGF1 and that ALC blocked these effects. Finally, TGF1 was shown to induce release of the GnRH peptide in vitro, an action that was blocked by ALC. ConclusionsWe have demonstrated glial-derived TGF1 induces GnRH gene expression in the POA and stimulates release of the peptide from the MBH, actions necessary for driving the pubertal process. Importantly, ALC acted at both brain regions to block stimulatory effects of TGF1. Furthermore, ALC altered neuronal components of an adhesion/signaling family previously shown to be expressed on GnRH neurons and implicated in glial-GnRH neuronal communications. These results further demonstrate detrimental effects of ALC at puberty.