Influences of ethanol and temperature on sucrose-evoked response of gustatory neurons in the hamster solitary nucleus

Abstract

Taste-responsive neurons in the nucleus of the solitary tract (NST), the first gustatory nucleus, often respond to thermal or mechanical stimulation. Alcohol, not a typical taste modality, is a rewarding stimulus. In this study, we aimed to investigate the effects of ethanol (EtOH) and/or temperature as stimuli to the tongue on the activity of taste-responsive neurons in hamster NST. In the first set of experiments, we recorded the activity of 113 gustatory NST neurons in urethane-anesthetized hamsters and evaluated responses to four basic taste stimuli, 25% EtOH, and 40°C and 4°C distilled water (dH 2 O). Sixty cells responded to 25% EtOH, with most of them also being sucrose sensitive. The response to 25% EtOH was significantly correlated with the sucrose-evoked response. A significant correlation was also observed between sucrose-and 40°C dH 2 O-and between 25% EtOH-and 40°C dH 2 O-evoked firings. In a subset of the cells, we evaluated neuronal activities in response to a series of EtOH concentrations, alone and in combination with 32 mM sucrose (EtOH/Suc) at room temperature (RT, 22°C-23°C), 40°C, and 4°C. Neuronal responses to EtOH at RT and 40°C increased as the concentrations increased. The firing rates to EtOH/Suc were greater than those to EtOH or sucrose alone. The responses were enhanced when solutions were applied at 40°C but diminished at 4°C. In summary, EtOH activates most sucrose-responsive NST gustatory cells, and the concomitant presence of sucrose or warm temperatures enhance this response. Our findings may contribute to elucidate the neural mechanisms underlying appetitive alcohol consumption.

Massive perturbation of sound representations by anesthesia in the auditory brainstem

“…However, this shift of experimental practice is mostly focused on processing higher stages including cortex (8)(9)(10), thalamus (11)(12)(13) and colliculus (14,15). For early sensory areas, located deep in the brainstem, most of our knowledge still relies on recordings performed under anesthesia based on the assumption that this has a minimal impact on sensory processing at this stage (16)(17)(18)(19)(20)(21). Recent progress of extracellular recording and even imaging (22) techniques now give access to the brainstem in awake conditions, including pioneering recordings in the cochlear nucleus, the first relay of the auditory system (22)(23)(24).…”