RT Journal Article SR Electronic T1 Embryonic development of the leech nervous system: primary axon outgrowth of identified neurons JF The Journal of Neuroscience JO J. Neurosci. FD Society for Neuroscience SP 2098 OP 2111 DO 10.1523/JNEUROSCI.03-10-02098.1983 VO 3 IS 10 A1 JY Kuwada A1 AP Kramer YR 1983 UL http://www.jneurosci.org/content/3/10/2098.abstract AB This paper describes the embryonic development of the leech nervous system and focuses on the differentiation of two identified pressure sensory (P) neurons, the PD and PV neurons. In the adult leech the P neurons have distinctive cell body locations in the central nervous system (CNS), different peripheral axon branching patterns, and different receptive field territories in the skin. The embryonic P neurons also have distinct and reproducible locations in the CNS and have been studied with recording and dye-filled microelectrodes from the time the first growth cones are projected from their somata. The peripheral axons of the P neurons are among the earliest peripheral axons to develop and may play an important role in the formation of peripheral nerves. The first or primary peripheral axons of the P neurons grow directly to their separate target territories. The specificity of the P neurons for their targets is probably not due to temporal differences in the outgrowth of their primary axons. Instead, the PD neuron seems to exhibit a preference early in embryogenesis for the target of its primary axon despite an apparent opportunity to occupy the target of the PV primary axon. It is hypothesized that the primary peripheral axons of the P neurons are among the first axons projected from the CNS and follow environmental cues to reach and innervate their target territories.