HIGH LICK RATE IS MAINTAINED THROUGHOUT SPONTANEOUS LIQUID MEALS IN FREELY FEEDING RATS

To investigate the microstructure of spontaneous meals in freely feedi ng rats, 16 adult male Sprague Dawley rats were housed individually in custom-designed lickometer cages and maintained on a milk diet. Licks were recorded over 23 h at millisecond accuracy via a computer-contro led lickometer. Analysis of lick data revealed an average of about 12 discrete meals/day occurring mainly during the dark phase. The most st riking feature of both dark and light meals was the maintenance of a h igh initial rate of licking until an abrupt decline at the end of the meal. This pattern of licking is very different from the exponential d ecay of lick rate reported in scheduled test meals of palatable soluti ons. Thus, the microstructure of licking for meals is affected in an a pparently fundamental way by whether a meal is scheduled or spontaneou s, suggesting a basic difference in the underlying physiologic control s. (C) 1997 Elsevier Science Inc.