Effects of mistacial vibrissae removal on the rat exploratory behavior in the elevated plus-maze under two illumination conditions.

Author(s)

Luis Fernando Cardenas Parra

• Document type: Master's Dissertation
• Press: Ribeirão Preto.
• Institution: Universidade de São Paulo (USP). Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto (PCARP/BC)
• Defense date: 1999-09-10

Examining board members

Silvio Morato de Carvalho; Sebastiao de Sousa Almeida; Luiz Eduardo Ribeiro do Valle

• Advisor: Silvio Morato de Carvalho

Abstract

Exploratory behavior in the rat is characterized by a preference for dark environments and by a trend to remain close to vertical surfaces(thigmotaxis). When allowed to freely explore an elevated plus-maze a rat will exhibit a smaller number of entries into the open arms and a smaller time spent in them. This characteristic pattern of behavior can be reverted by the administration of anxiolytic drugs. Although broadly used in the study of fear and anxiety, it still remains unclear what or which are the aversive stimuli that induce the avoidance from the open arms. The present study investigated the role of environmental illumination and thigmotaxis (mediated by mistacial vibrissae) in the exploratory behavior of rats submitted to the elevated plus-maze test. To this end, the vibrissae were removed acutely (5 min before testing) or chronically: days (8, 14 or 25; daily cutting) or in the day of birth and the rats were tested in the plus-maze under two environmental conditions, brightness (150 Lux) or darkness (2 Lux). Results showed that in the darkness rats with vibrissae removed entered more and stayed longer in the open arms than rats with intact vibrissae or rats with removed vibrissae tested under brightness. These results suggest a possible anxiolytic-like effect cause by vibrissa removal added to the absence of light. The increase in exploration of the open arms could be due to the effect of the joint absence of information from both sensorial systems (visual and tactile from the vibrissae) an effect that did not happen when information was lacking from just any one system. Further studies should be performed in order to unravel the neuronal mechanisms involved in the phenomenon. (AU)