Development of the equine brain motor system.

The purpose of the present study was to demonstrate the structural maturation of the horse brain in the critical period of development emergence of coordinated locomotion. Equine brains from 14 days before expected birth to adulthood were fixed in formaldehyde and embedded in paraffin. After taking the outer parameters of the brains, full series of large-area coronal sections were prepared on a special microtome and stained with Nissl's cresyl violet and Haidenhain's iron-haematoxylin. Microscopic images of sections were digitized and were subjected to computer-aided image analysis. The gross morphology of the brains and the image analysis of histological preparations suggest that in the perinatal period studied there is no substantial increase in brain size and mass, while the amount of Nissl substance and myelin grows rapidly till postnatal day 45. Then a relative decrease of both is observed till adulthood accompanied by a doubling of brain size and mass. It is concluded that during the maturation of the equine brain, decisive changes of the motor system such as up-regulation of protein sysnthesis and full myelination of motor tracts takes place during the critical period of onset of coordinated locomotion.