Interaction of hunger and thirst in the motivational arousal underlying hoarding behavior in the rat.

Rats were studied in which hoarding of food could be elicited by a 16-hr food deprivation schedule. It was found that (a) prolonged water restriction, with food ad lib, failed to induced hoarding in spite of a spontaneous reduction in food intake and a fall in body weight to below levels normally critical for the onset of hoarding. Thus, different physiological deficits are not necessarily equivalent or additive in the elicitation of food hoarding, and water lack may suppress it. (b) Hoarding behavior was released in water-deprived animals by a brief drink of water. A 30-min delay to allow absorption of the ingested water significantly enhanced the release of hoarding. Air drinking by water-deprived rats did not release hoarding. Thus, the absence of hoarding during water lack may be caused by an active inhibitory process that can itself be inhibited or canceled by postingestional effects of drinking but not by oropharyngeal stimulation mimicking water signals. (c) Although water lack prevented hoarding in response to concomitant self-imposed fasting, hoarding ensued at maximal rates when a further mild degree of food deprivation was superimposed. Thus, the inhibition of hoarding by dehydration operates subtractively, not multiplicatively, and, with free access to food, the inhibition of hoarding by thirst tends to be balanced, exactly, by the facilitatory effect of concomitant fasting; thus superadded food deprivation can take full effect. It is concluded that in states of motivational arousal, specific inhibitory mechanisms may inhibit, subtractively, certain activities biologically irrelevant to prevailing physiological needs.