Investigation into the Specificity of Angiotensin II-induced Behavioral Desensitization

Angiotensin II (AngII) plays a key role in maintaining body fluid homeostasis. The physiological and behavioral effects of central AngII include increased blood pressure and fluid intake. In vitro experiments demonstrate that repeated exposure to AngII reduces the efficacy of subsequent AngII, and behavioral studies indicate that prior icv AngII administration reduces the dipsogenic response to AngII administered later. Specifically, rats given a treatment regimen of three icv injections of a large dose of AngII, each separated by 20 min, drink less water in response to a test injection of AngII than do vehicle-treated controls given the same test injection. The present studies were designed to test three potential explanations for the reduced dipsogenic potency of AngII after repeated administration. To this end, we tested for motor impairment caused by repeated injections of AngII, for a possible role of visceral distress or illness, and for differences in the pressor response to the final test injection of AngII.We found that repeated injections of AngII neither affected drinking stimulated by carbachol nor did they produce a conditioned flavor avoidance. Furthermore, we found no evidence that differences in the pressor response to the final test injection of AngII accounted for the difference in intake. In light of these findings, we are able to reject these three explanations for the observed behavioral desensitization, and, we suggest instead that the mechanism for this phenomenon may be at the level of the receptor.

Applied Developmental Psychology as an Implementation of the Life-Span View of Human Development

Application of knowledge about psychological development should, ideally, be theory based. As such, these applications represent “natural ontogenetic experiments”; the results of the evaluation of such interventions feed back to the theory, helping to support, falsify, or refine the ideas from the theory which led to the particular application. Such applied developmental intervention research is central within a currently popular perspective of life-span human development. Thus, applied developmental intervention research provides critical tests of such key concepts within this life-span perspective as: plasticity; multidirectionality; the synthesis of continuous and discontinuous processes across ontogeny; contextual embeddedness; and the role of individuals as agents in their own development. This paper elucidates some of the major features of the dynamic linkage between applied developmental psychology and this view of life-span human development. Key elements of this life-span perspective and the facts of developmental intervention, as seen from this perspective, are specified. Finally, the doctoral training program at the authors' institution is presented as one example of how this link may be institutionalized in the form of graduate education.

Rats Acquire Stronger Preference for Flavors Consumed Towards the End of a High-fat Meal

Rats learn to prefer flavors associated with postingestive effects of nutrients. The physiological signals underlying this postingestive reward are unknown. We have previously shown that rats readily learn to prefer a flavor that was consumed early in a multi-flavored meal when glucose is infused intragastrically (IG), suggesting rapid postingestive reward onset. The present experiments investigate the timing of postingestive fat reward, by providing distinctive flavors in the first and second halves of meals accompanied by IG fat infusion. Learning stronger preference for the earlier or later flavor would indicate when the rewarding postingestive effects are sensed. Rats consumed sweetened, calorically-dilute flavored solutions accompanied by IG high-fat infusion (+ sessions) or water (− sessions). Each session included an “Early” flavor for 8 min followed by a “Late” flavor for 8 min. Learned preferences were then assessed in two-bottle tests (no IG infusion) between Early(+) vs. Early(−), Late(+) vs. Late(−), Early(+) vs. Late(+), and Early(−) vs. Late(−). Rats only preferred Late(+), not Early(+), relative to their respective (−) flavors. In a second experiment rats trained with a higher fat concentration learned to prefer Early(+) but more strongly preferred Late(+). Learned preferences were evident when rats were tested deprived or recently satiated. Unlike with glucose, ingested fat appears to produce a slower-onset rewarding signal, detected later in a meal or after its termination, becoming more strongly associated with flavors towards the end of the meal. This potentially contributes to enhanced liking for dessert foods, which persists even when satiated.

Rats Acquire Stronger Preference for Flavors Consumed Towards the End of a High-fat Meal

Rats learn to prefer flavors associated with postingestive effects of nutrients. The physiological signals underlying this postingestive reward are unknown. We have previously shown that rats readily learn to prefer a flavor that was consumed early in a multi-flavored meal when glucose is infused intragastrically (IG), suggesting rapid postingestive reward onset. The present experiments investigate the timing of postingestive fat reward, by providing distinctive flavors in the first and second halves of meals accompanied by IG fat infusion. Learning stronger preference for the earlier or later flavor would indicate when the rewarding postingestive effects are sensed. Rats consumed sweetened, calorically-dilute flavored solutions accompanied by IG high-fat infusion (+ sessions) or water (- sessions). Each session included an "Early" flavor for 8min followed by a "Late" flavor for 8min. Learned preferences were then assessed in two-bottle tests (no IG infusion) between Early(+) vs. Early(-), Late(+) vs. Late(-), Early(+) vs. Late(+), and Early(-) vs. Late(-). Rats only preferred Late(+), not Early(+), relative to their respective (-) flavors. In a second experiment rats trained with a higher fat concentration learned to prefer Early(+) but more strongly preferred Late(+). Learned preferences were evident when rats were tested deprived or recently satiated. Unlike with glucose, ingested fat appears to produce a slower-onset rewarding signal, detected later in a meal or after its termination, becoming more strongly associated with flavors towards the end of the meal. This potentially contributes to enhanced liking for dessert foods, which persists even when satiated.