The compulsive-like aspect of the head dipping emission in rats with chronic electrolytic lesion in the area of the median raphe nucleus.
Head dipping (HD) is a behavioral pattern considered to have a risk assessment or an exploratory role and is used as a complementary parameter to evaluate anxiety in experimental animals. Since rats with electrolytic lesion in the area of the median raphe nucleus displayed high frequencies of HD in a previous study, the present investigation was undertaken to confirm this observation and to determine its anxiety-related origin. HD episodes were counted in adult male Wistar rats (270-350 g) with electrolytic lesion (N = 11) and sham-lesioned controls (N = 12). When HD was measured for 60 min on an elevated open platform, lesioned rats emitted 13 times more HD than controls (264.7 +/- 93.3 vs 20.3 +/- 7.6 episodes), with the difference being statistically significant (P < 0.05). HD counts during 10-min sessions held 7, 14, 21, 27, and 63 days after lesion showed significantly higher means (range: 28.14 +/- 5.38 to 62.85 +/- 9.48) compared to sham-lesioned controls (range: 7.37 +/- 1.13 to 8.5 +/- 1.45). Normal rats stepped down into their home cages when the vertical distance between them and the cage was short (16 cm), and the step-down latencies increased with increasing depths (36.7 +/- 7.92 to 185.87 +/- 35.44 s). Lesioned rats showed a similar behavior when facing the shortest depth, but had a significantly increased number (23.28 +/- 2.35 episodes) and latency (300 +/- 0.00 s) of HD compared to normal rats (9.25 +/- 1.37 episodes and 185.87 +/- 35.44 s) when facing the greatest depth (30 cm). This suggests that HD may be a depth-measuring behavior related to risk assessment.
Hoshino
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K
Departamento de Ciências Biológicas, Faculdade de Ciências, Universidade Estadual Paulista, Av. Luis Edmundo Carrijo Coube, s/n 17033-360 Bauru, SP, Brazil. hoshino@fc.unesp.br
Uga
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DA
de Paula
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HM
D000818:Animals; D001007:Anxiety / Q000503:physiopathology*; D001522:Behavior, Animal / Q000502:physiology*; D004556:Electric Injuries; D005106:Exploratory Behavior / Q000502:physiology*; D006257:Head; D008297:Male; D011903:Raphe Nuclei / Q000293:injuries*; D051381:Rats; D017208:Rats, Wistar