The effects on feeding of galanin and M40 when injected into the nucleus of the solitary tract, the lateral parabrachial nucleus, and the third ventricle.

Several reports indicate that central injection of galanin stimulates feeding, and that there is macronutrient specificity in this response. In addition, the galanin receptor antagonist, M40, reduces food intake when injected centrally. The nucleus of the solitary tract (NTS) and the lateral parabrachial nucleus (PBN) contain galanin receptors, and are involved in the control of food intake. Hence, we sought to compare the feeding response to galanin injection into these areas with that of third ventricle (3V) galanin injection. The feeding response to injection of galanin was greatest for the 3V. Hindbrain injection of galanin stimulated food intake only at the beginning of the dark period. NTS injection of M40 inhibited intake of a macronutrient diet in food-deprived rats, but was ineffective at reducing dark-onset feeding or deprivation-induced chow intake. 3V injection of M40 did not reduce deprivation-induced intake. PBN injection of galanin at dark onset had no effect in a group of fat-preferring rats. These results suggest that hindbrain galanin may contribute to feeding by inhibiting satiety, and that hypothalamic galanin receptors are involved with stimulation of intake. Furthermore, the absence of a consistent pattern of the stimulation of macronutrient intake suggests that galanin may not be a significant effector of macronutrient selection during individual meals.