Nervous System in Medaka Larvae

Abstract

AbstractThis chapter provides an overview of the nervous system of the medaka larvae, which can perform various complex behaviors, except for those involved in reproduction. A brain atlas of the medaka larvae, which is an ordered set of histological sections taken from a single individual, is shown in the final section. A newly hatched larva (stage 39) has a tiny (the maximum width of 0.4–0.5 mm) brain in which the fiber system is well developed. The nerves of the peripheral nervous system (PNS) are divided into two main groups: the cranial nerves and spinal nerves. Teleosts have two unique pairs of cranial nerves, the anterior and posterior lateral line nerves, because aquatic vertebrates have a sensory organ called the lateral line organ that senses water flow. In addition, teleosts lack two pairs of cranial nerves that are found in mammals (accessory and hypoglossal nerves). Thus, the medaka larva has 12 pairs of cranial nerves. The larva has 34 pairs of spinal nerves, including two rostralmost pairs of the spino-occipital nerves. Each spinal nerve splits into three major branches (dorsal ramus, ventral ramus, and lateral branch of the dorsal ramus) in the segmental muscle, and these branches are distributed to the skin and skeletal muscles of the trunk, tail, and fins. In the brain atlas, larval CNS and PNS are shown in detail with sagittal, frontal, and horizontal Nissl-stained sections.KeywordsBrain atlasCentral nervous systemCranial nerveLateral line nerveLarvaNervous systemPeripheral nervous systemSpinal nerveSpino-occipital nerve