DIFFERENCES IN ACETYLCHOLINE CONTENT, BINDING AND AFFINITY PARAMETERSOF MUSCARINIC RECEPTORS IN THE PREOPTIC-ANTERIOR HYPOTHALAMIC AREA DURING THE ESTROUS-CYCLE OF THE RAT

The cholinergic system of the preoptic anterior hypothalamic area (POA -AHA) has been shown to modulate the secretion of gonadotropins and ov ulation in a circadian and asymmetric way. We have now measured the ac etylcholine (ACh) content and binding parameters of the muscarinic ago nist (H-3)-N-methyl-scopolamine during the oestrous cycle of the rat i n both sides of the POA-AHA. ACh content was maximum on dioestrus day 1 and minimum on dioestrus day 2. ACh content was asymmetrical on dioe strus day 1 and on the day of pro-oestrus: the higher ACh content occu rred on the right side of POA-AHA. Asymmetrical ACh content was symmet rical on dioestrus day 2 and on the day of oestrus. The maximal bindin g capacity (B-max), was higher on the left side of the POA-AHA on the day of pro-oestrus. The dissociation constant (K-d) was higher on the left side at pro-oestrus, oestrus and on dioestrus day 1. On dioestrus day 2 the values of the binding parameters were opposite to that on o ther days of the oestrous cycle. The results support the existence of an intrinsic and bilaterial asymmetry activity in the afferent choline rgic system of the POA-AHA, which changes during the oestrous cycle.