In vivo electrophysiological analysis of mechanisms of monoaminergic pain inhibitory systems
These approaches have both advantages and disadvantages. For instance, an extracellular recording can be made from peripheral and central neurons, measuring the change in excitability of a nerve or neuron by the number of action potentials (Fig. 1).22–24 However, it is usually impossible to analyze synaptic responses, with a few exceptions. In contrast, an intracellular recording can analyze changes in excitability or synaptic responses of peripheral and central neurons, but this method is limited to relatively large cells.9,10,36 Patch-clamp recordings can be adapted to in vitro studies12,14,16,26,30,33,35,38,42,43 and in vivo studies of small to large CNS cells.12,14,16,18,20,21,27–29,33,35,39,47,48 With an infrared differential interference contrast (IR-DIC) microscope that enables us to visualize individual neurons, we can easily make recordings from any neurons in voltage-clamp preparations,51 although this method is not applicable for analyzing CNS neurons in vivo. Nevertheless, blind patch-clamp recordings without the IR-DIC microscope system may be a useful way to obtain recordings from neurons located near the surface of the brain in vivo.5
This review provides a brief history of electrophysiological recording methods and describes the physiological mechanisms of descending pain inhibitory systems using data from in vivo patch-clamp recordings18,25,46,50 combined with in vitro slice studies.