Effects of microiontophoretically applied chemicals on hypothalamic neural activity

Seven barrel electrodes were utilized to record simultaneously from and apply chemicals to single neurons in the hypothalamus of anesthesized male hooded rats. When a stable baseline discharge frequency was established for lateral preoptic area (LPA) or lateral hypothalamic (LH) neurons, glutamate, norepinephrine, acetylcholine, glucose and sodium were administered microiontophoretically. In addition, the effects of microiontophoretically administered chemicals and LPA or LH electrical stimulation on hypothalamic neural activity were in some cases determined for the same neuron. Recordings from 53 hypothalamic neurons indicate that the direct application of these chemicals affect LPA and LH neural activity at relatively low ejection currents in a dose related manner. In the LPA, glutamate which has a nonspecific effect and increased the discharge frequency in 96% of the cells tested, was used to establish the reliability of the techniques and baseline. Norepinephrine decreased (73%), acetylcholine increased (28%) and decreased (12%), glucose increased (12%), and sodium increased (4%) discharge frequency. In the LH, glutamate increased (91%), norepinephrine decreased (33%), acetylcholine increased (50%) and decreased (14%), glucose increased (12%) and decreased (6%), and sodium increased (20%) discharge frequency. Also, significant relations between chemical and electrical stimulation suggest that norepinephrine and possibly acetylcholine might be involved in the interactions between the LPA and LH neurons. Results are discussed in terms of the neurochemical modulation of ingestive behavior.