Motivated lateralized behaviour in the rat: Role of the ventral hippocampus

Abstract

Lateralization of the brain in mammals has made animals more competitive during interaction with the environment in evolution. This property, first described in the 19th century in man, refers to the differentially modulation and control of some neuronal circuits of brain hemispheres on determined behavioural functions. In spite that lateralization has been described in several different animal species, still there are aspects not fully understood related to behavioural functions or identification of specific brain circuits involved. In the rat, coping behaviour is quite important for successful surviving; proper behavioural responses and careful analysis of spatial clues of the environment are needed. However, if lateralization mechanisms in the brain participate in these processes is still not known. In this work, exploratory lateralized responses and the possible role of the hippocampus as a probable lateralized structure were investigated. Intact and rats implanted with microinjection guide cannulae into the hippocampus were tested in three lateralized devices, the T labyrinth (TL), the multiple compartment labyrinth (MCL), and the double lateral hole-board labyrinth (DHBL). Decisions making to select left or right responses for seeking shelter (the TL), passing through left or right doors in a compartments in series (the MCL), and exploring left or right walls in a corridor (the DHBL) were investigated in these two groups of rats. Results show that intact rats presented lateralized exploratory behaviour with a left-bias in the DHBL but random responses in the other devices. This left preference observed in the DHBL was manifested in spending more time exploring the left wall of the DHBL than the right one. Hippocampus implanted rats retained the left-bias exploration in this device. Blocking the neural activity of left, right or both hippocampi with lidocaine in the implanted rats, the spontaneous left-bias exploration was nullified only when lidocaine was microinjected into the left hippocampus. Results suggest that the hippocampal structure is functionally lateralized for modulating exploration in novel environments emphasizing the hippocampus role on coping behaviour in the rat.