Abstract
To study the mechanisms and consequences of dendritic peptide release in vivo, we have combined microdialysis with single cell recording. A purpose-designed small microdialysis loop is placed on the exposed ventral surface of the supraoptic nucleus (SON) in anaesthetised rats to allow sampling of extracellular fluid which enables the in vivo measurement of dendritic peptide release and the direct application of substances via the dialysate to influence dendritic activity. Through the centre of the loop we insert a microelectrode into the SON to monitor the electrical activity of identified magnocellular neurons, classified as oxytocin and vasopressin cells by their firing patterns and physiological responses. By placing an additional stimulating electrode in a brain area of interest we can electrically-stimulate afferent inputs to the SON (e.g. organum vasculosum of the lamina terminalis, nucleus tractus solitarius, olfactory bulb). Post-stimulus histograms reveal the effects of transmitters released from these inputs. We can thus monitor physiological regulation of dendritic release in vivo during pharmacological control of dendritic mechanisms, and with concurrent monitoring of somatic action potential activity. We have used this approach to determine the actions of neuroactive substances such classical transmitters, endogenous opioids, adenosine, nitric oxide, steroids, and glial-derived factors, which affects both neuronal activity and dendritic peptide release. These studies provided insights in many local neuronal autoregulatory mechanisms. [J Physiol Sci. 2008;58 Suppl:S21]
