Hypothalamic and hindbrain NPY, AGRP and NE increase consummatory feeding responses

Abstract

Feeding behavior is comprised of both appetitive and consummatory responses to food. Appetitive responses include the motivated acquisition of food. Consummatory responses, including swallowing, are those that move the food from the mouth to the stomach. Intraoral delivery of liquid food bypasses the requirement for appetitive responses and has been used to examine consummatory responses directly in intact rats. In the present study, we administered neuropeptide Y (NPY), agouti-related protein (AGRP) and norepinephrine (NE), into the paraventricular nucleus of the hypothalamus (PVN) or into the fourth cerebral ventricle to examine their effects on the consummatory component of feeding behavior in the rat. To measure consummatory responses, milk (40% lactose free cow's milk diluted with water) was infused intraorally through a chronic cheek fistula (1 ml/min), using an alternating 5 min on -1 min off schedule, until rejection occurred. We found that both hypothalamic and fourth ventricle injections of NPY, AGRP and NE significantly increased consumption of the intraorally-delivered milk. Our results indicate that the circuitry for modulation of consummatory ingestive responses includes NE, NPY and AGRP receptors operating in both hypothalamic and hindbrain sites.

Fig. 1

Consummatory intake of 40% lactose free milk solution infused through an intraoral fistula following PVH injection of 0.9% saline (SAL, 200 nl), neuropeptide Y (NPY, 78 pmol/200 nl), agouti-related protein (AGRP, 200pmol/200 nl), or norepinephrine (NE, 40 nmol/200 nl). Milk intake after NPY, AGRP and NE was significantly increased, compared to intake following PVH saline injections. Data are expressed as mean intraoral intake in ml ± SEM. (*P ≤ 0.01 vs intake after saline).

Fig. 2

Consummatory intake of 40% lactose free milk solution infused through an intraoral fistula following 4^th ventricular (4V) injection of 0.9% saline (SAL, 200 nl), neuropeptide Y (NPY, 78 pmol/200 nl), agouti-related protein (AGRP, 200 pmol/200 nl), or norepinephrine (NE, 40 nmol/200 nl). NPY, AGRP and NE injections all significantly increased milk consumption, compared to intake following 4V saline injections. Data are expressed as mean intraoral intake in ml ± SEM. (*P < 0.001 vs intake after saline).

Fig. 3

Consummatory intake of a 0.1M sucrose solution infused through an intraoral fistula after injection of 0.9% saline (SAL, 200 nl) and neuropeptide Y (NPY, 78 pmol/200 nl) into the PVH. Data are expressed as mean intraoral intake in ml ± SEM. NPY injection significantly increased intake of the sucrose solution in comparison to the intake after PVH saline injection (*P < 0.001).

Fig. 4

Effects of lateral ventricular (LV) injection of NPY (1.2 nmol in 3 μl) or saline (0.9% in 3 μl) on consummatory intake of three test solutions (40% cow’s milk, 0.1M sucrose solution and 1M sucrose solution) infused through an intraoral fistula. Data are expressed as mean intraoral intake in ml ± SEM. Lateral ventricular NPY injections significantly increased consumption of both milk and sucrose solutions, compared to the intake of these diets after LV saline (*P ≤ 0.02).