Postnatal changes in motoneurone electrotonic coupling studied in the in vitro rat lumbar spinal cord.

Abstract

SUMMARY1. Electrotonic coupling between motoneurones innervating ankle flexor and extensor muscles, as well as between unidentified lumbar motoneurones, was studied using intracellular recordings in an in vitro spinal cord-hindlimb preparation isolated from rats between birth (PO) and 13 days (P13).2. Graded ventral root stimulation could elicit graded, short latency depolarizations (SLD) which preceded, coincided with, or followed the antidromic action potential. These SLDs were identified as electrotonic junctional potentials by their latency, relative insensitivity to changes in membrane potential and their resistance to one or more of the following: (1) high-frequency stimulation, (2) collision with a somatofugal action potential, (3) removal of Ca2+ from the bathing solution.3. SLDs were studied in 162 neurones and were identified in 77-2 % of the cells in preparations from P0 to P3 rats (n = 57), but only in 30-8 % at P8 to P13 (n = 39).4. SLDs were largest in the youngest animals (P0 to P3), decreasing from a mean of 1-31 mV (±0-17, n = 34) to 0-56 mV (±010, n = 7) at P8 to P13. The SLDs comprised two to eight (4-3+0±36) all-or-none components as determined from twenty collision experiments.5. Electrotonic coupling between motoneurones was specific. SLDs could be elicited in given motoneurones by stimulation of their homonymous but never of their antagonistic muscle nerves.6. These results indicate that electrotonic coupling between lumbar motoneurones in neonatal animals exhibits a high degree of specificity and that its significance, as judged by the amplitude and frequency of occurrence of SLDs, decreases postnatally at a rate that can be correlated with the functional maturity of the motoneurones and the muscular system.

Connexin36 vs. connexin32, “miniature” neuronal gap junctions, and limited electrotonic coupling in rodent suprachiasmatic nucleus

“…In contrast, two of the three plaque gap junctions found in a single replica of P14 SCN were larger than 100 connexons (Fig. 5), consistent with previous reports of relatively stronger coupling of immature neurons (Fulton et al, 1980;Walton and Navarette, 1991).…”

“…In contrast, two of the three plaque gap junctions found in a single replica of P14 SCN were larger than 100 connexons (Fig. 5), consistent with previous reports of relatively stronger coupling of immature neurons (Fulton et al, 1980;Walton and Navarette, 1991).As a separate verification of Cx36 in neuronal gap junctions, one sample was double-labeled using both monoclonal and polyclonal antibodies to Cx36. Two sizes of gold beads for monoclonal anti-Cx36 (6-nm and 12-nm gold) and one size (18-nm gold beads) for polyclonal anti-Cx36 (Fig.…”

Restoration of frequency-dependent depression of the H-reflex by passive exercise in spinal rats

“…40,41 Gap junctions allow synchronous activation by electrical coupling of spinal motoneurons, but their expression ceases after 7-14 days postnatally. 42 Tx thus may lead to an increase in neuronal (specifically Connexin 36) gap junction protein expression. In addition, MBET for 30 days in Tx rats was found to normalize low frequency depression of the H-reflex and to lead to a decrease in Connexin 36 expression.…”

Dopaminergic modulation of dye coupling between neurons in the core and shell regions of the nucleus accumbens

“…However, there was also anatomical and physiological evidence of its presence in lower vertebrates (Bennett, 1963;Yamada and Ishikawa, 1965;Kaneko, 197 l), and in 197 1 Baker and Llinas demonstrated that electrical transmission takes place between rat mesencephalic neurons (Baker and Llinas,197 1). Following this first report in the mammalian brain, physiological evidence for electrical coupling was found in several brain regions, including the inferior olive (Llinas et al, 1974) retina (Piccolino et al, 1982(Piccolino et al, , 1984Lasater and Dowling, 1985a,b), substantia nigra (Grace and Bunney, 1983) hippocampus (MacVicar and Dudek, 198 1;Taylor and Dudek, 1982;Dudek and Snow, 1985;Ntiiiez et al, 1990), striatum spinal cord motoneurons (Gogan et al, 1977;Walton and Navarrete, 1991) and lateral vestibular nucleus (Wylie, 1973). Electrotonic transmission is a mode of communication between sets of two or more cells in which apposed membranes are connected by gap junctions.…”