Changes in the ventral dendrite of Mauthner neurons in goldfish after optokinetic stimulation

Recent studies have established that following an optomotor drum rotating in the direction contralateral to that spontaneously preferred by goldfish fry inverts their motor asymmetry. Studies of the structure of Mauthner neurons (MN) using the histological technique of three-dimensional reconstruction along with measurement of the volumes of the right and left MN in these fish showed that the ipsilateral MN underwent a three-fold reduction in the volume of the ventral dendrite (VD), which was in inverse proportion to the functional activity of the MN. The total volume of the contralateral MN was 25% larger than the volume of the ipsilateral MN, the situation typical of intact fish. It is suggested that the decreases in the size of the VD receiving afferentation from the contralateral eye, which follows the moving band of the optomotor drum, results from the specific contralateral visual stimulation, and is the first evidence of the possible natural stimulation of the MN via the VD.