The exploratory behaviour of rats in the hole-board apparatus: is head-dipping a valid measure of neophilia?

Abstract

The exploratory behaviour of laboratory rodents is of interest within a number of areas of behavioural pharmacology. However, how best to measure exploratory behaviour in rodents remains a contentious issue. Many unconditioned tests, such as the open field, potentially confound general locomotor activity with exploration. The hole-board apparatus appears to avoid this confound, as head-dipping into holes in the floor is assumed to be a valid measure of the subject's attraction towards novelty (neophilia). This study aimed to investigate whether head-dipping should be considered a valid measure of neophilia by comparing performance of adult male and female Lister hooded rats on the hole-board task (a) over repeated sessions and (b) when novel objects were absent or present underneath the holes. The results show that head-dipping initially decreased across repeated exposures, while time spent in the aversive central area increased. No change in head-dipping was seen in response to objects being placed underneath the holes. Rather than being a measure of neophilia, these results support the hypothesis that head-dipping represents an escape response, which declines as the subject becomes less fearful. These results are compared with previous studies of repeated exposure to other novel environments.

Fig. 1

(a) Percentage of entries into the central area across five trials without objects (white bars) and five trials with objects (black bars) (means and S.E.M.; N = 16). Post hoc analyses: *p < 0.01; a–d represent pairs of trials that differ at p < 0.01; (b) percentage of time spent in the central area across five trials without objects (white bars) and five trials with objects (black bars) (means and S.E.M.; N = 16). Post hoc analyses: *p < 0.01; a–d represent pairs of trials that differ at p < 0.01.

Fig. 2

Frequency of head-dipping during five trials without objects (white bars) and five trials with objects (black bars) (means and S.E.M.; N = 16). Post hoc analyses: *p < 0.01; a–c represent pairs of trials that differ at p < 0.01.

Fig. 3

Frequency of rearing during five trials without objects (white bars) and five trials with objects (black bars) (means and S.E.M.; N = 16).