Effects And Mechanisms Of Oxytocin On The Electrical Activities Of Hippocampal CA1 Neurons In Rats

The purpose of our present works was to study the electrical activities of the left dorsal hippocampal CAl neurons and the evoked different responses of neurons to electrical stimulation of sciatic nerves in rats. As well, to investigate the effects of different doses of oxytocin on spontaneous and evoked discharge of CAl neurons and the interaction between central oxytocinergic system and adrenergic system, opioidergic system. The experiments were performed on 145 Sprague-Dauley male rats, weighed 180~250grams. Extracellular single-unit discharge recording technique were used to record the spontaneous discharge of CAl neurons. Evoked discharge were induced by electrical stimulation of sciatic nerves. Results demonstrated that: (1) There were bursts in spontaneous discharge of hippocampal CAl neurons. And the total bursts' number and the number of bursts which action potentials were more than three were increased after electrical stimulation of sciatic nerves. Three different responses were found in CAl neurons to electrical stimuli: insignificant response, excitatory response and inhibitory response. The same neuron had different responses to repeated electrical stimuli. (2) Intracerebroventricular injection different doses of OT(lng/5uL,10ng/5uL and 100ng/5μL) could decreased the spontaneous discharge frequency by 60%(9/15),73.3%(11/15) and 75%(9/12) hi hippocampal CAl neurons; In addition, different doses of OT could inhibit the evoked discharge of CAl neurons in a dose-dependent manner. (3) The inhibitory effects of OT(10ng/5μL) on spontaneous and evoked discharge could be blocked by pretreated with OT receptor antagonist, [d(CH2)5-OVT](200ng/2.5μL). (4) Phentolamine- a -adrenoceptor antagonist(10ug/2.5μL), administered intracerebroventricularly before OT could attenuate the inhibitory effects of OT(10ng/5μL) on electrical activities of CAl neurons significantly. (5) Intracerebroventricular injection of naloxone-opioid receptor antagonist could also decrease the inhibitory effect of OT(10ng/5μL). These results suggest that hippocampal CAl neurons have encoding effects to peripheral afferent signals and can modulate many kinds of signals.The responses of CA1 neurons to electrical stimulation of sciatic nerves are plastic. OT can inhibit the electrical activities of CA1 neurons through activating oxytocin receptor in hippocampus. Moreover, adrenergic system and opioidergic system in the central nerves system are involved in the inhibitory effects of OT.