Chloral Hydrate versus Isofluorane anesthesia and their differential impact on the midbrain system

Isoflurane (ISO) has become one of the most commonly used anesthetics for animal surgery, has largely replaced chloral hydrate (CH). Despite this shift, the physiological consequences of these anesthetics on dopamine neuron (DA) function have not been directly compared. This is particularly relevant for DA neurons in the ventral tegmental area (VTA), a critical network involved in reward and motivation.

In this study, we compared the electrophysiological properties of VTA DA neurons under CH and ISO anesthesia in male and female rats. Extracellular recordings were used to assess population activity, mean firing rate, and phasic burst firing across medial, central, and lateral VTA regions. Relative frequency distributions of firing rate and spikes per burst were also assessed.

Measures of population activity, mean firing rate using extracellular recordings of the population, and relative frequency distributions of firing rate, as well as spikes per burst, were assessed. With either anesthetic, active neurons and firing rate distributions were comparable. The percentage of spikes fired in bursts was also similar between ISO and CH. In addition, the relative frequency of both spikes in bursts and firing rate was the same. Furthermore, the population activity and VTA subregion differences in both groups were the same.

The electrophysiological profiles of VTA dopamine neurons obtained under ISO anesthesia closely matched those recorded under CH.

These findings demonstrate that CH and ISO exert comparable effects on the baseline electrophysiological properties of VTA DA in vivo.