Olfactory bulbectomy induces rapid and stable changes in basal and stress-induced locomotor activity, heart rate and body temperature responses in the home cage.

Background: Olfactory bulbectomy (OBX) in rats causes several behavioral and neurochemical changes. However, the extent and onset of physiological and behavioral changes induced after bulbectomy have been little examined.
Methods: Male Sprague-Dawley rats received telemetric implants. Before and immediately after OBX surgery, basal and stress-induced heart rate, body temperature, and locomotor activity were measured in the home cage in sham (n=9) and OBX animals (n=11). Stress was induced using novel cage stress or witness stress.
Results: Bulbectomized animals differed physiologically and behaviorally from shams. Nocturnally, OBX animals were significantly more active compared with shams, had a higher core body temperature and displayed a decreased heart rate variability. During the light period, OBX animals had a significantly lower basal heart rate and a reduced heart rate variability. These effects became apparent 2-3 days after OBX surgery, and were stable over time. After witness stress, OBX animals showed smaller autonomic (body temperature and heart rate) responses compared with shams, but showed no difference in locomotor responses. In contrast, novel cage stress led to increased locomotor responses in OBX rats compared with sham rats, while no differences were found in autonomic responses.
Conclusion: Removal of the olfactory bulbs results in rapid, stable and persistent changes in basal locomotor activity, body temperature, heart rate and heart rate variability. Although the sleep-wake cycle of these parameters is not altered, increases in circadian amplitude are apparent within 3 days after surgery. This indicates that physiological changes in the OBX rat are the immediate result of olfactory bulb removal. Further, stress responsivity in OBX rats depends on stressor intensity. Bulbectomized rats display smaller temperature and heart rate responses to less intense witness stress compared with sham rats. Increased locomotor responses to more intense novel cage stress are present in the home cage as well as the open field. The present study shows that olfactory bulbectomy has rapid and persistent influence on basal and stress-induced physiological parameters.