BEHAVIORAL AND NEUROENDOCRINE RESPONSES TO LIGHT MEDIATED BY SEPARATE VISUAL PATHWAYS IN RAT

Vision plays an important role in the behavioral adaptation of animals and in the control of neuroendocrine responses to light such as that of the pineal melatonin-forming enzyme, hydroxyindole-O-methyltransferase (HIOMT). Previous experiments have suggested that there is a separation of function between primary and accessory components of the visual pathways in the mediation of behavioral responses and the pineal HIOMT response to light. The present experiments were performed to test this further. Rats were trained to make a simple visual discrimination (light-on vs. light-off). Lesions were placed which either: (1) transected the inferior accessory optic tracts bilaterally sparing one primary optic tract or (2) transected both primary optic tracts sparing the inferior accessory optic tracts. Following accessory optic tract lesions, the pineal HIOMT response to light was lost but the visual discrimination habit was retained. In contrast to this primary optic tract lesions resulted in loss of the visual discrimination but preservation of the pineal HIOMT response. These data support the view that there is a separation of function among the central visual pathways. © 1969.