Recording of mouse ventral tegmental area dopamine-containing neurons

Abstract We examined the electrophysiologic and pharmacologic properties of dopamine-containing ventral tegmental area neurons in the mouse using extracellular singleunit recording techniques in both chloral hydrate-anesthetized mice and in vitro mouse midbrain slices. In vivo the ventral tegmental area neurons had long-duration action potentials (2 to 5 ms) and discharged at 1 to 9 spikes/s with either a decremental burst pattern or a regular pattern. Systemic administration of the dopamine agonist, apomorphine, decreased their firing rate, and the dopamine receptor blocker, haloperidol, reversed this effect. Similarly, systemic administration of the dopamine-releasing agent, d -amphetamine, suppressed their discharge rate, an effect blocked by pretreatment of the animals with α-methyl- p -tyrosine. When recorded in vitro from midbrain slices, ventral tegmental area neurons showed electrophysiologic properties similar to those found in vivo ; however, the neurons recorded in vitro fired at a significantly faster rate and their firing pattern tended to be more pacemaker-like, especially when recordings were made in an incubation medium that blocked synaptic transmission (i.e., low calcium/high magnesium). The activity of most of these neurons was suppressed by addition of apomorphine to the incubation medium, an effect reversed by haloperidol. Pretreatment with α-methyl- p -tyrosine produced no significant change in the discharge pattern or rate for cells recorded in vitro . These data indicate that mouse ventral tegmental area dopamine neurons in vivo exhibit the same electrophysiologic and pharmacologic properties as do rat and cat dopamine-containing neurons and that in vitro they fire with pacemaker regularity in a low-calcium/high-magnesium medium. The in vitro preparation offers an approach to examining the fundamental properties of ventral tegmental area dopamine-containing neurons in the absence of afferent inputs.