The ontogeny of feeding and drinking: Effects of early brain damage

Electrophysiological analysis of circuits controlling energy homeostasis

Since the discovery of leptin and the central melanocortin circuit, electrophysiological studies have played a major role in elucidating mechanisms underlying energy homeostasis. This review highlights the contribution of findings made by electrophysiological measurements to the current understanding of hypothalamic neuronal networks involved in energy homeostasis with a specific focus on the arcuate-paraventricular nucleus circuit.

The lateral hypothalamic area revisited: ingestive behavior

This article discusses the role of the lateral hypothalamic area (LHA) in feeding and drinking and draws on data obtained from lesion and stimulation studies and neurochemical and electrophysiological manipulations of the area. The LHA is involved in catecholaminergic and serotonergic feeding systems and plays a role in circadian feeding, sex differences in feeding and spontaneous activity. This article discusses the LHA regarding dietary self-selection, responses to high-protein diets, amino acid imbalances, liquid and cafeteria diets, placentophagia, "stress eating," finickiness, diet texture, consistency and taste, aversion learning, olfaction and the effects of post-operative period manipulations by hormonal and other means. Glucose-sensitive neurons have been identified in the LHA and their manipulation by insulin and 2-deoxy-D-glucose is discussed. The effects on feeding of numerous transmitters, hormones and appetite depressants are described, as is the role of the LHA in salivation, lacrimation, gastric motility and secretion, and sensorimotor deficits. The LHA is also illuminated as regards temperature and feeding, circumventricular organs and thirst and electrolyte dynamics. A discussion of its role in the ischymetric hypothesis as an integrative Gestalt concept concludes the review.

Modulation of lateral hypothalamic activity by olfactory bulb and sciatic stimulation

Lateral hypothalamic area (LHA) single unit activity (extracellular) was studied in response to electrical stimulation of the olfactory bulb (OB) or sciatic nerve in adult albino rats (n = 39) anesthetized with dialurethane. Olfactory stimulation resulted in a greater proportion of LHA units showing inhibitory rather than excitatory responses, while sciatic nerve stimulation resulted in similar proportions of units showing inhibitory and excitatory responses. Of the 76 LHA units tested with both OB and sciatic nerve stimulation, 36% responded to both stimulation sites, 18% responded only to OB stimulation, 26% responded only to sciatic nerve stimulation, and 20% were unresponsive to either stimulation. The locations of responsive units were diffuse throughout the LHA sampled. The response characteristics of LHA neurons to external sensory stimulation are consistent with the anatomy and putative integrative functions of this brain region.

Influence of litter size on the RNA content of VMH and LHA in preweaning rats

The nutritional status in the early postnatal period may significantly influence the development and functional activity of food intake regulating mechanisms. Therefore we investigated the weight gains and total RNA content of the ventromedial (VMH) and lateral (LHA) hypothalamic cells of rat pups in normal litters (8 pups/nest) and in reduced litters (2 pups/nest) reared permanently (from birth to weaning) or temporarily (from 1st to 5th day) in reduced nests. A significant decrease of weight gains was found in pups reared in reduced litters during the first 5 days which resulted in significant differences of body weight between the pups from normal and reduced litters on 5th day of life. On the 15th and 30th days, there were no significant differences in body weight between these animals, but the RNA content in VMH cells of pups reared in reduced litters was significantly increased on the 15th and 30th days. The RNA content in the LHA cells was unchanged. The results show that reducing a rat litter to 2 pups caused short-term undernutrition leading to permanent changes of the RNA content in the VMH neurons. The possible consequences of the permanently changed RNA content of this hypothalamic structure are discussed.

Ontogeny of phenylalanine (endogenous cholecystokinin) induced modulation of food intake in normal and undernourished rats

1. The development of endogenous cholecystokinin (CCK) effects on food intake was studied in normal and undernourished growing rats of postnatal day 1-22. 2. Food intake was estimated by recording the gain in body weight before weaning. 3. l-phenylalanine, a potent stimulant of endogenous CCK release, suppressed 30 min food intake in normally nourished pups of day 7-15 or more but not of day 1-6 rats. 4. However, l-phenylalanine did not affect 24 hr gain in body weight day 1-6 or more, rat pups. 5. l-phenylalanine neither suppressed 30 min food intake nor affected 24 hr body weight in day 16-19 or 20-22 undernourished rat pups. 6. The study suggests that the endogenous CCK satiety effects appear early in the second week of postnatal life in normally nourished rats, whereas in undernourished rat pups it does not appear till day 20-22.

Postnatal development of sensory influences on neurons in the ventromedial hypothalamic nucleus of the rat

Extracellular unitary records were obtained from neurons in the ventromedial hypothalamic nucleus (VMH) of very young (1-25 days of postnatal age) and adult rats. Spontaneous unitary activity and evoked responses to both external (somatic, gustatory, and olfactory) and internal sensory (systemic administration of hypertonic saline and glucose solutions) stimulation were determined in order to assess the functional development of VMH neurons and their afferents. The basic electrophysiological characteristics of VMH neurons were established prenatally. From the date of birth, many VMH neurons had: spontaneous action potential generation; evoked responses to external or internal sensory stimulation; and convergent sensory inputs. In contrast, the major developmental change in the neurophysiological properties of VMH neurons was the diminution with increasing age of the convergence of external and internal sensory influences. This developmental 'fine-tuning' of a complex functional feature of VMH neurons is important because the maturation of convergence coincides with a 'critical period' of VMH ontogenesis demonstrated in behavioral and experimental brain damage reports.

Effects of serotonergic and cholinergic antagonists on suckling behavior of neonatal, infant, and weanling rat pups

In Experiment 1, Sprague-Dawley rat pups at postnatal days 3-4, 7-8, 10-11, 15-16, and 23-24 were tested for suckling behavior on their anesthesized multiparous dams following administration of metergoline or scopolamine. The serotonergic antagonist, metergoline, inhibited suckling in 3- to 4- and 7- to 8-day-old rat pups, but was not found to influence suckling in older pups. Scopolamine, a cholinergic antagonist, reduced suckling primarily in 3- to 4-day-old pups. In Experiment 2, parity of the maternal female was manipulated to assess whether this variable would influence suckling behavior and the effects of metergoline on suckling of weanlings. Baseline levels of suckling were reduced in 23- to 24-day-old pups of primiparous dams when compared with multiparous-derived offspring. Administration of metergoline increased the amount of time that these primiparous-derived pups spent attached to nipples, but did not influence suckling of offspring of multiparous dams, perhaps as a result of a ceiling effect on suckling behavior in these animals.

Postnatal development of sensory influences on lateral hypothalamic neurons of the rat

Extracellular unitary records were obtained from neurons in the lateral hypothalamic area (LHA) of very young (1-25 days of postnatal age) and adult rats. Spontaneous unitary activity and evoked responses to external sensory (somatosensory, gustatory and olfactory) and internal sensory (administration of hypertonic saline and glucose solutions) stimulation were determined in these neurons in order to assess their functional development. The basic electrophysiological characteristics of LHA neurons were established prenatally. From the day of birth, many LHA neurons had: (1) spontaneous spike generation; (2) evoked responses to external and internal sensory stimulation; and (3) convergent sensory inputs. However, each of these neurophysiological properties was modified considerably during postnatal ontogenesis: (4) spontaneous activity of LHA neurons with evoked responses to sensory stimulation increased with age; (5) internal sensory influences tended to diminish while evoked response magnitude and complexity were augmented developmentally; and (6) convergence of sensory influences decreased in older rats. This developmental 'fine tuning' of the functional features of LHA neurons is important because their maturation coincides with certain 'critical periods' of LHA ontogenesis demonstrated in behavioral, morphological, pharmacological and experimental brain damage reports.

A method for stereotaxic implantation in neonatal rats

Presented are methods of implanting chronically indwelling electrodes or cannulas into brain infant rats. Anesthesized pups are restrained in a flexible alginate mold that is place in the stereotaxic instrument. Details of electrode implant are given. We routinely use these methods to accurately place electrodes into subcortical structures of 3- to 15-day-old pups with less than 2% loss of the implant.

Septal destruction in infant rats and the ontogeny of drinking behaviors

Male and female albino rat pups sustained septal destruction at 10 days of age and body weight and water intakes were measured daily throughout development until 200 days of age. During development the septal and control rats received a battery of drinking tests (e.g., cellular dehydration, hypovolemia, renin). Septal rats (males and females) were hyperdipsic for daily water intakes as early as 31 days of age and the daily hyperdipsia persisted through 200 days of age. On the battery of drinking tests, septal rats consumed water at control volumes on all tests except water deprivation (following which females were hyperdipsic) and food deprivation (during which both males and females were hyperdipsic). Urine output-water intake relationships were determined, and a series of food deprivation tests were conducted during development to determine the etiology of the developmental septal hyperdipsia. All results suggest that hyperdipsia associated with septal destruction during the preweaning period is a primary condition and not secondary to altered output mechanisms, abnormal feeding-drinking patterns, or displacement behavior.