The morphology of motoneurons and dorsal root fibers in the frog's spinal cord

Morphology of brachial segments in mudpuppy (Necturus maculosus) spinal cord studied with confocal and electron microscopy

“…4A, arrowhead). We did not find clear separation between ventromedial (axial) and ventrolateral (limb) MN groups that have been described for the frog (Silver, 1942;Kennard, 1959;Stensaas and Stensaas, 1971;Szekely, 1976). However, the largest MN somata (30 -50 m) tended to occur more laterally than somewhat smaller cells (20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35)Figs.…”

“…With the exception of work on axial motoneurons (Fetcho, 1986) and marginal neurons (Schroeder and Egar, 1990), the available information is scarce and pertains mostly to the early stages of development in related species, including Ambystoma (Coghill, 1913;Herrick, 1948), Salamandra (van Gehuchten, 1897; see also Cajal, 1995, for other references), and Triturus (Blight, 1978;Harper and Roberts, 1993). In contrast to a relatively extensive literature on spinal cord anatomy in anurans (Silver, 1942;Kennard, 1959;Stensaas and Stensaas, 1971;Llinas and Precht, 1976;Szekely, 1976;Szekely and Czeh, 1976;Schotland and Tresch, 1997), there is less information in classical anatomical studies of tailed amphibians (Urodele). Herrick's monumental work on Ambystoma (1948) and Necturus (see Herrick, 1948, for references) omits this region, and to date detailed morphological features of the brachial spinal cord in adult Necturus have not been described.…”

Mechanisms of post‐synaptic excitation in amphibian motoneurones.

“…It should be noted in this connexion that although it was believed for a long time that in the frog the dorsal root fibres may establish synaptic articulations exclusively with distal dendrites of motoneurones (Chambers, Sprague & Liu, 1960; recent anatomical evidence shows that collaterals of dorsal root fibres make synaptic contacts on the proximal dendrites and on the somata of frog motoneurones (Szekely, 1976).…”

Effects of some divalent cations on synaptic transmission in frog spinal neurones.

“…This region corresponds to the Substantia gelatinosa, where according to anatomical (Liu & Chambers, 1957;Szekely, 1976) and electrophysiological (Brookhart & Fadiga, 1960) evidence, the bulk of the dorsal root afferent fibres end or pass through.…”

“…This value probably represents an over-estimate of the 'genuine' synaptic delay, as defined for the frog neuromuscular junction (Katz & Miledi, 1965c), and includes time lags arising from conduction of impulses to the terminals and delays introduced by electrotonic propagation of the e.p.s.p.s (Rall, 1967). These appear to be generated mainly at distal dendritic branches (Liu & Chambers, 1957;Szekely, 1976) and thus the start of local current through the dendritic post-synaptic membrane, probably precedes the onset of the e.p.s.p. intracellularly recorded at the motoneurone soma.…”