Electrophysiological properties of neonatal rat motoneurones studied in vitro.

Abstract

SUMMARY1. The electroresponsive properties of neonatal lumbar spinal motoneurones were studied using isolated, hemisected spinal cords from neonatal rats aged [3][4][5][6][7][8][9][10][11][12] days. The extracellular and intracellular responses to electrical stimulation of the ventral and dorsal root were studied as well as. the intracellular response to current injection.2. Field potentials recorded in the lateral motor area following electrical stimulation of lumbar ventral roots had a triphasic positive-negative-positive wave form. The negative component did not return to the base line smoothly but exhibited a ' shoulder' where the negativity increased in duration. Following electrical stimulation of the dorsal root, presynaptic field potentials were recorded upon activation of the afferent axons as well as following synaptic activation of interneurones and motoneurones.3. The input resistances of neonatal motoneurones determined from the slope of current-voltage plots were high compared with the adult. The resistance decreased with age with a mean of 18-1 MC for animals 3-5 days old, 8-8 M0 for animals 6-8 days old and 5-4 MC for animals 9-11 days old. Values for the membrane time constant were similar to those in the adult with a mean of 4-5 ms.4. Action potentials elicited by ventral or dorsal root stimulation or by intracellular current injection were marked by a pronounced after-depolarization (a.d.p.) and an after-hyperpolarization (a.h.p.). The amplitude of the a.h.p. varied with that of the a.d.p.5. The amplitude of excitatory post-synaptic potentials (e.p.s.p.s) elicited by electrical stimulation ofthe dorsal root was affected by intracellular current injection. Two types of e.p.s.p.s were distinguished: those with a biphasic reversal (early phase first) and those in which the early phase was unaffected by inward current injection while the later phase was reversed. Unlike in the adult, the reversals could be achieved with low current levels and the amplitude of both types of e.p.s.p. was increased by inward current injection. (b) there is a low maximum firing frequency (near 30 Hz) and (c) the slope of the firing frequency-injected current (f-I) plot has a high gain.8. These results are discussed with respect to previous findings in adult rat and cat and with reference to the properties of the developing nervous and muscular systems.

Activation of 5-HT2A receptors upregulates the function of the neuronal K-Cl cotransporter KCC2

“…3A). The earliest component representing the monosynaptic excitation of motoneurons (25,26) was not affected by TCB-2 (0.1-0.15 μM; Fig. 3 A and B).…”

The electrical geometry, electrical properties and synaptic connections onto rat V motoneurones in vitro.

“…The AHP duration in motoneurones is known to be closely correlated with the mechanical properties of the muscle innervated (for review see Kernell, 1983 (Fulton & Walton, 1986) and, with the exception of the changes in AHP duration, similar to those reported for immature and mature hypoglossal motoneurones (Haddad et al 1990 of transmission are not an inherent feature of transmission at synapses onto trigeminal motoneurones but rather may be the result of active inhibition of synapses, and (2) variations in the incidence of failures can produce significant alterations in the efficacy of transmission at synapses of single presynaptic neurones onto single motoneurones.…”

“…spinal motoneurones: Fulton & Walton, 1986;Smith, Liu & Feldman, 1988;Takahashi, 1990; (Appenteng & Girdlestone, 1987;Appenteng, Conyers & Moore, 1989;Grimwood et al 1992). Second was the observation that the dendrites of trigeminal motoneurones are predominately orientated longitudinally and do not extend more than 400 jtm in the mediolateral direction …”

Lamina VII neurons are rhythmically active during locomotor-like activity in the neonatal rat spinal cord

“…sõl' Chen et al, 1992) for neonatal rats, therefore it is difficult to attribute specific afferents to the stimulation and difficult to discuss latencies (Kudo and Yamada, 1985;Kiehn et al, 1994a (Kiet et al, 1992 Orlovsþ, 1975), RCs (McCrea et al, 1980) and ventral midlumbar group II interneurons (Shefchyk et al, 1990) Fulton and Walton (1986 There is evidence for a CPG for locomotion in humans (Clancie et al, 1994 …”