Effects of osmotic pressure, glucose, and temperature on neurons in preoptic tissue slices

The preoptic area contains thermosensitive, osmosensitive, and glucosensitive neurons, which have been implicated in thermal, osmotic, and metabolite regulations, respectively. In this study, rat preoptic tissue slices are used to examine the specificity of these neurons by determining their individual firing rate responses to thermal, osmotic, and glucose stimuli. Of the neurons classified according to thermosensitivity, 35% were warm sensitive, 10% were cold sensitive, and 55% were temperature insensitive. Of these, 107 neurons were also tested for their responses to tissue slice perfusions of low-glucose and/or hyperosmotic media. These experimental perfusions affected one-third of the temperature-insensitive neurons and nearly half of the thermosensitive neurons and generally excited warm-sensitive neurons and inhibited cold-sensitive neurons. A lack of specificity was also observed between the groups of osmosensitive and glucosensitive neurons, since most of the responsive neurons were affected by both hyperosmotic and low-glucose media. Although these findings do not suggest a strong functional specificity for preoptic neurons, they do support previous studies that emphasize interactions between regulatory systems.