Characteristics of stimulation-induced feeding sites in the sulcal prefrontal cortex

Neural substrates for the processing of cognitive and affective aspects of taste in the brain

Taste is unique among the sensory systems in that, besides its recognition of quality, it is innately associated with hedonic aspects of reward and aversion. This review of the literature will show how taste information is conveyed through the central gustatory pathways to the cortical gustatory area and is processed in terms of qualitative and quantitative aspects. Taste information is also sent to the reward system and feeding center via several brain sites including the prefrontal cortex, insular cortex, and amygdala. The reward system contains the ventral tegmental area, nucleus accumbens, and ventral pallidum; it finally sends information to the lateral hypothalamic area, the feeding center. The dopamine system originating from the ventral tegmental area mediates the motivation to consume palatable food. The actual ingestive behavior is promoted by the orexigenic neuropeptides from the hypothalamus. In the last section, the neural substrate of learning and memory of taste is introduced and the biological mechanisms are elucidated.

Control of motor seizures by brotizolam with maintenance of stable refractory periods for self-stimulation

In recent years, we have been pursuing our mapping investigations of the substrate for brain-stimulation reward in regions of the anterior hypothalamic and lateral preoptic areas. However, one problem is that stimulation of these sites often generates overt seizures so that their suppression via a pharmacological means would be very useful. The sedative-hypnotic benzodiazepine, brotizolam, is reportedly a long-lasting anticonvulsant. Hence, its effects on motor seizures elicited from stimulation of the lateral preoptic area were evaluated in the first experiment. Both tested doses (5.0 and 7.5 mg/kg) of the drug were shown to significantly decrease the number, and marginally, the severity of stimulation-induced seizures; furthermore, this effect was relatively long lasting, up to about 3 h. The higher dose of brotizolam did not alter the single-pulse thresholds for self-stimulation, a requirement for evaluations of poststimulation excitability, the purpose of the second experiment. Here, our interest was in documenting whether the membrane properties of the stimulated neurons, as assessed by refractory periods, were altered by brotizolam. No differences in the time course of recovery were observed; refractoriness began between 0.4 and 0.8 ms, and reached 50% recovery by 2.0 ms, which is consistent with the pattern of poststimulation excitability typically measured at these sites. Thus, in addition to its long-lasting suppression of motor seizures in rats, brotizolam does not alter the time course of recovery from refractoriness of the neurons that mediate brain-stimulation reward in the lateral preoptic area.

Changes in medial prefrontal cortical dopamine levels associated with response-contingent food reward: an electrochemical study in rat

Voltammetry was used to monitor in rats changes in medial prefrontal cortex (PFC) dopamine (DA) levels associated with response-contingent presentation of a condensed milk reward. During two initial training sessions, minor DA signal fluctuations were seen when animals consumed a standard 30 sec (0.2 ml) meal earned on a continuous reinforcement schedule. There was no evidence of experience-dependent changes in these fluctuations. Under delayed reinforcement conditions, lever-presses were followed by DA signal increases that were time-locked to the delay duration, and these were followed by signal decreases when animals eventually received the reward. Such decreases became more pronounced when the standard rate of milk delivery was tripled, but were attenuated when milk delivery was reduced to half the usual rate. Withholding earned milk resulted in signal increases. In contrast, DA signal increases were observed during milk consumption when the standard meal duration was unexpectedly shortened to 15 sec or lengthened to 60 or 90 sec. Orderly changes in DA signal were also observed under partial reinforcement conditions. Unreinforced responses were associated with DA signal decreases, whereas transient increases were seen during the 30 sec meal that followed reinforced responses. These findings indicate that response-contingent reward presentation elicits synchronous changes in PFC DA transmission. They also suggest that the DA input to PFC is activated when rewards are presented under conditions that deviate from those that the animals had come to expect, particularly so when the temporal structure of learned associations is altered.