Habituation of the startle response in adrenalectomized rats

In a series of three experiments adrenalectomized, sham-operated and non-operated rats (N = 15) were presented with 27 tones at each of three intensities on two successive days or 60 tones at a 60 sec interstimulus interval with each tone being followed by another tone either 2, 4, 8 or 16 sec later, or 50 tones at a 30 sec interstimulus interval on each of five successive days. All groups had equivalent initial startle amplitudes and showed equivalent rates of response decrement at each test intensity and each interstimulus interval as well as over successive days of exposure. The results indicate that the adrenal glands are not crucial for habituation of the acoustic startle response and suggest that those aspects of stress adaptation that require an intact adrenal-pituitary system are not important for habituation of the startle.