Changes in emotional behavior of mice in the hole-board test after olfactory bulbectomy

The most consistent behavioral change caused by olfactory bulbectomy (OBX) is a hyperemotional response to novel environmental stimuli. The aim of this study was to characterize the emotional behavior of OBX mice using the hole-board test. After the olfactory bulbs were lesioned, sham and OBX mice were housed in single cages for 14 days. The number of head-dips in the hole-board test in single-housed OBX mice was significantly greater than that in single-housed sham mice. The head-dipping behaviors in single-housed sham and OBX mice were reversed by treatment with diazepam, a typical benzodiazepine anxiolytic. (±)-8-Hydroxy-2-(di-n-propylamino) tetraline hydrobromide (8-OH-DPAT), a selective 5-HT_1A-receptor agonist that has a non-benzodiazepine anxiolytic-like effect, and (+)-4-[(aR)-a-((2S,5R)-4-allyl-2, 5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N-diethyl benzamide (SNC80), a δ-opioid-receptor agonist, also significantly reversed the number of head-dips in single-housed sham and OBX mice. In conclusion, we suggest that the single-housed OBX mice showed heightened emotional behavior (e.g., increase in head-dipping behavior) in the hole-board test. In addition, we suggest that the hyperemotional behavior characterized by head-dipping behavior in OBX mice was selectively reversed by benzodiazepine and non-benzodiazepine anxiolytics.