Neural systems for early independent ingestion: Regional metabolic changes during ingestive responding and dehydration.

Abstract

The ingestive behavior of young rodents, studied independently of the mother and suckling, provides a system for the developmental analysis of the neurobiology of feeding and drinking. In these experiments regional neural metabolic activity, as assessed by semiquantitative deoxyglucose (DG) autoradiography, was related to dehydration and ingestive behavior in 6-day-old rat pups. During simple ingestive responding, changes in relative DG uptake, representative of changes in neural metabolic activity, occurred primarily in hindbrain sensory and motor nuclei. Producing cellular dehydration resulted in activity changes primarily in the basal forebrain. When pups were dehydrated and allowed to ingest during the DG-uptake period, activity changes were seen in both the hindbrain and forebrain areas that responded to ingestion or dehydration alone as well as in regions that were not affected by either manipulation alone. These latter changes, which result from an interaction of behavioral and physiological stimuli, call attention to areas that may subserve motivational aspects of behavior. Extracellular dehydration was found to produce fewer and different forebrain responses in neural metabolic activity. During ingestion, the only effects of extracellular dehydration that overlapped with those of cellular dehydration appeared in circumventricular hypothalamic regions and brain stem motor nuclei. Thus, there appeared to be only a limited final common pathway for these two types of dehydration-induced drinking. Taken together, these findings in infant rats depict distributed neural systems subserving ingestion and responding to state change. They provide a starting point early in ontogeny for the developmental analysis of neural substrates of ingestive systems.

The trajectory of sensory pathways from the lamina terminalis to the insular and cingulate cortex: a neuroanatomical framework for the generation of thirst

“…The dorsal midline of the thalamus in particular has been implicated in viscerosensory awareness, whereas the lateral portion of the dorsal midline has been implicated in cognitive awareness. Both of these thalamic regions have previously been shown to be involved in osmotic signaling (18,22,25). The present study further characterizes these regions by identifying the paraventricular and medial part of the mediodorsal thalamic nuclei as potentially both relaying osmotic signals to the insular and cingulate cortex, albeit the significance was not reached for both nuclei (see Fig.…”

“…Two cortical regions implicated in the emotional aspects of thirst, the activity of which is altered by hyperosmotic stimulation or dehydration, are the insular and cingulate cortex (17,20,21,48,54). These two cortical regions receive direct projections from multiple thalamic nuclei (24,28,29,43,53,68); however, only the paraventricular and mediodorsal thalamic nuclei have been implicated in osmotic signaling (17,22,25), albeit inconsistently (21,60). The paraventricular and mediodorsal thalamic nuclei receive direct projections from the preoptic region of the brain containing the lamina terminalis (11,50,71); however, no studies have addressed the issue directly.…”

The first suckling episode in the rat: The role of endogenous activity at mu and kappa opioid receptors

“…Experimental data indicating that opiate antagonists suppress food intake, while opioid agonist drugs enhance it, support the hypothesis that opioid systems are involved in the regulation of adult feeding behavior (Bodnar, 1996;Olson, Olson, Vaccarino, & Kastin, 1998). Nevertheless, the role of opioid systems in the control of suckling is still unclear, inasmuch as suckling is regulated by different behavioral and physiological control mechanisms, and cannot be viewed as equivalent to adult feeding Hall, 1989Hall, , 1990.…”

Ontogeny of hypothalamic-hindbrain feeding control circuits

“…Studies of independent ingestion in neonatal rats indicate that most direct controls of meal size (i.e., olfactory, orosensory, and viscerosensory) are operational as early as postnatal Day 1, with later additional sensory refinement (Ackerman, Albert, Shindledecker, Gayle, & Smith, 1992;Hall, 1979;Hall & Bryan, 1980, 1981Hall, 1989;Hudson & Distel, 1999). Thus, the basic neural circuits through which these direct controls affect ingestive behavior already are functional in neonatal rats.…”