Increased synaptic activity in magnocellular neurons of supraoptic nucleus and plasma vasopressin levels due to acute administration of morphine in male rats

The magnocellular neurons (MCNs) of the supraoptic nucleus (SON) play a crucial role in control of physiological and pathophysiologiccal condition due to two peptides that they synthesize, i.e. Oxytocin (OXT) and Vasopressin (AVP). The activity of MCNs is regulated by a variety of excitatory and inhibitory inputs. Opioid receptors are one of the important receptors in SON synapses. The aim of the present study is to evaluate the effect of acute morphine application on SON synapses and AVP release in rats. In this study, whole cell patch clamp recording of neurons in rat (70-100 g, 3–4 weeks old) brain slice preparations consisting of SON was used to investigate the effect acute of lowest effective dose of morphine (25μM) administration on spontaneous inhibitory and excitatory post synaptic currents (sIPSCs and sEPSCs) in MCNs. Also, AVP levels were measured in blood samples of rats using ELISA technique after the Morphine injection (30 mg/kg, ip). Bath application of morphine produced an increase in sEPSCs and a decrease in sIPSCs frequencies. Measurement of plasma AVP revealed an increase in hormone levels 45 min after systemic administration of morphine. P-values of less than 0.05 were considered statistically significant. It is suggested that acute administration of morphine stimulates the MCNs and AVP secretion.