Potentiation of pressor and behavioral responses to brain stimulation following bilateral olfactory bulbectomy in freely moving rats

The effects of bilateral olfactory bulb (OB) ablation on pressor and behavioral responses to stimulation of the posterior hypothalamic area (PHA) and midbrain reticular formation (MRF) were investigated in unanesthetized and unrestrained rats with chronic electrodes and arterial cannula implants. Bilateral olfactory bulbectomy induced a marked increase in emotional responses to given stimuli. A high incidence of muricide was also observed after olfactory bulbectomy. The threshold for inducing behavioral arousal and pressor response to PHA and MRF stimulation significantly decreased at 5 and 10 days after olfactory bulbectomy. The pressor responses to either PHA or MRF stimulation were markedly enhanced. The enhancement in pressor response to MRF stimulation occurred immediately after olfactory bulbectomy and persisted throughout the experiment, while that to PHA stimulation appeared gradually and reached maximum at 10 days after olfactory bulbectomy. These results suggested that olfactory bulbectomy has a great influence not only on emotionality but also on the central neural mechanisms of autonomic regulation.