http://hdl.handle.net/1983/99 Fri, 17 May 2013 13:31:07 GMT 2013-05-17T13:31:07Z http://hdl.handle.net/1983/1833 Primitive roles for inhibitory interneurons in developing frog spinal cord Li, W-C; Higashijima, Shin-ich; Parry, DM; Roberts, A; Soffe, SR Understanding the neuronal networks in the mammal spinal cord is hampered by the diversity of neurons and their connections. The simpler networks in developing lower vertebrates may offer insights into basic organization. To investigate the function of spinal inhibitory interneurons in Xenopus tadpoles, paired whole-cell recordings were used.We show directly that one class of interneuron, with distinctive anatomy, produces lycinergic, negative feedback inhibition that can limit firing in motoneurons and interneurons of the central pattern generator during swimming. These same neurons also produce inhibitory gating of sensory pathways during swimming. This discovery raises the possibility that some classes of interneuron, with distinct functions later in development, may differentiate from an earlier class in which these functions are shared. Preliminary evidence suggests that these inhibitory interneurons express the transcription factor engrailed, supporting a probable homology with interneurons in developing zebrafish that also express engrailed and have very similar anatomy and functions. Thu, 01 Jan 2004 00:00:00 GMT http://hdl.handle.net/1983/1833 2004-01-01T00:00:00Z http://hdl.handle.net/1983/103 The spinal interneurons and properties of glutamatergic synapses in a primitive vertebrate cutaneous flexion reflex Li, W-C; Soffe, SR; Roberts, A Unlike the monosynaptic "stretch" reflex, the exact neuronal pathway for a simple cutaneous reflex has not yet been defined in any vertebrate. In young frog tadpoles, we made whole-cell recordings from pairs of spinal neurons. We found direct, excitatory, glutamatergic synapses from touch-sensitive skin-sensory neurons to sensory pathway interneurons, and then from these sensory interneurons to motoneurons and premotor interneurons on the other side of the body. We conclude that the minimal pathway for this primitive reflex, in which stroking the skin on one side leads to flexion on the other side, is disynaptic. This detailed circuit information has allowed us to ask whether the properties of glutamatergic synapses during the first day of CNS development are tuned to their function in the tadpole's responses. Stroking the skin excites a few sensory neurons. These activate primarily AMPA receptors producing short, strong excitation that activates many sensory pathway interneurons but only allows temporal summation of closely synchronous inputs. In contrast, the excitation produced in contralateral neurons by the sensory pathway interneurons is weak and primarily mediated by NMDA receptors. As a result, considerable summation is required for this excitation to lead to postsynaptic neuron firing and a contralateral flexion. We conclude that from their early functioning, synapses from sensory neurons are strong and those from sensory pathway interneurons are weak. The distribution of glutamate receptors at synapses in this developing circuit is tuned so that synapses have properties suited to their roles in the whole animal's reflex responses. Wed, 01 Oct 2003 00:00:00 GMT http://hdl.handle.net/1983/103 2003-10-01T00:00:00Z