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Digitized by the Internet Archive 2015 in https://archive.org/details/oralhabituationcOOmulv ORAL HABITUATION AND THE CONTROL OF INGESTIVE BEHAVIORS IN RATS by Susan Swithers Mulvey Department of Experimental Psychology Duke University Dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Experimental Psychology in the Graduate School of Duke University ABSTRACT (Psychology - Biological) ORAL HABITUATION AND THE CONTROL OF INGESTIVE BEHAVIORS IN RATS by Susan Swithers Mulvey Department of Experimental Psychology Duke University An abstract of a dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Experimental Psychology in the Graduate School of Duke University 1991 ABSTRACT Previous studies of ingestion in rats documented changes in ingestive behavior attributed to consequences of associative learning, but little attention has been focused on the influences of ongoing experience within an ingestive episode. In the studies reported here, oral experience was provided to rat pups in a series of brief intra-oral infusions and steady decreases in the level of oral responsivity were observed. This habituation of mouthing responses resulted in long-lasting suppression of actual intake that was specific to the diet experienced orally. When intervals between diet stimulus infusions were relatively long (circa 1 min), suppression was evident even 3 hrs after habituation experience. A short-lasting decremental process modulated oral activity when inter-stimulus intervals were short, but the effect was brief (lasting less than 30 minutes). During the course of this oral habituation, patterns of electromyographic activity in masticatory and tongue muscles, changed dramatically within and across trials and after oral habituation had developed, activity in 2 of the muscles was greatly reduced or abolished. The effects of ongoing oral experience were also found to be modulated by other ingestion-related physiological signals. Oral responsiveness in 6-hr deprived pups was modulated by gastric fill; gastric fill enhanced the expression of oral habituation. In contrast, gastric fill failed to affect habituation of mouthing responses in 24-hr deprived pups. Examination of the neural substrates of oral habituation in decerebrate pups revealed that the expression of oral habituation can be accomplished by the hindbrain. Further, decerebrate pups showed the capacity to integrate gastric fill and oral signals, but unlike neurologically intact pups, decerebrate pups demonstrated a response to gastric loads even after 24 hrs deprivation. Thus, while oral habituation and gastric fill modulation of habituation are subserved by the brainstem, the modulatory effects of deprivation on the integration of oral experience with gastric fill arise from the forebrain. The low level of neural representation of oral habituation -iii-