Biomedical subjects

S E Wray

Publications and source records attributed to S E Wray.

4 recordsLinked to original sources

PubMed1993

Size-related increase in motoneuron number: evidence for late differentiation.

The number of motoneurons in the lumbar lateral motor column (LMC) was compared in bullfrogs (Rana catesbeiana) ranging in body length from 2.5 to 19 cm. Large frogs had 36% more motoneurons than small frogs; however, within the caudal third of the LMC, large frogs had over 70% more motoneurons than small frogs. Injection of small frogs with [3H]thymidine every third day for 20-22 weeks gave no evidence of motoneuron birth. Instead, a pool of small, incompletely differentiated (type L) motoneurons appears to be converted into mature (type M) motoneurons as the animal grows. This hypothesis is supported by several lines of evidence: (1) the number of type-M motoneurons varies directly with body size while the number of type-L cells varies inversely; (2) the increase in type-M motoneurons and the decrease in type-L cells are restricted to the same regions of the LMC; and (3) type-L cells exhibited both immunoreactivity to neurofilament antibodies and histochemical evidence of acetylcholinesterase activity, a marker for spinal motoneurons.

Acetylcholinesterase↗

PubMed1992

Neuromuscular specificity following cross-stage hindlimb transplantation.

In order to determine whether spinal motoneurons can regenerate to their proper targets at stages beyond those when such specificity is typically expressed, autologous and homologous (same- and cross-stage) hindlimb transplantations were performed using bullfrog tadpoles (Rana catesbeiana). Neuromuscular specificity was assessed by applying horseradish peroxidase to the ventral thigh of the transplanted hindlimb and mapping the locations of retrogradely labeled motoneurons. Previously, we found that the hindlimb was reinnervated normally in young tadpoles whose motor nerves were transected. However, motor axons in older animals showed no evidence of target specificity when reinnervating the tadpole's own limb. In the present study, innervation was normal in young tadpoles whose hindlimb was removed and replaced in its original position. Axons of older hosts innervating hindlimbs transplanted from young tadpoles distinguished flexor from extensor limb regions, but failed to distinguish thigh from shank, demonstrating that axons in older animals can respond to at least some guidance cues. The lack of specificity along the proximal-distal axis appears to be a consequence of homologous transplantation since limbs transplanted from one young tadpole to another showed the same loss of proximal-distal specificity. One possibility is that the shank degenerates when the hindlimb is transplanted to a different host. Shank motoneurons, lacking their proper target, may then innervate the thigh. However, shank motoneurons did not innervate the thigh when motor nerve transection was combined with amputation of the hindlimb just above the presumptive knee.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Neuron addition in the postmetamorphic frog.

Neuron number among somatic motoneurons, sensory neurons, and sympathetic postganglionic neurons that innervate the hindlimb was correlated with body length in the bullfrog, Rana catesbeiana. Two to three times more dorsal root and sympathetic ganglion neurons are found in the largest than the smallest specimens. Hindlimb motoneurons show a 20% increase in number, but this increase is restricted to the caudal third of the motor pool. Within this region, 60% more motoneurons are found among the largest frogs. Cell division does not appear to be the mechanism of neuron addition. Instead, we propose that a pool of undifferentiated neurons mature to maintain functional capabilities as the animal increases in size.

Animals↗

PubMed1989

Regenerative specificity of motor axons when reinnervation is partially suppressed.

We asked whether regenerating hindlimb motor axons would innervate inappropriate hindlimb regions if competition from appropriate innervation were prevented. The three ventral roots that innervate the hindlimb in the bullfrog (Rana catesbeiana) tadpole were transected, and the two more rostral roots were ligated to prevent regeneration. The most caudal root, which primarily supplies more distal limb musculature in unoperated tadpoles, was left free to regenerate. The specificity of regeneration was assessed by retrogradely labeling spinal motoneurons with HRP placed in the ventral thigh, a region that receives most of its innervation from the ligated roots. Despite the lack of competition from appropriate innervation, the regenerating root did not provide substantial innervation to proximal limb musculature. The same result was obtained in tadpoles operated upon at stages when regeneration of motor axons is specific and in tadpoles at stages when regenerating motor axons do not reinnervate their appropriate targets (Farel and Bemelmans, 1986), although the mechanisms in each case are likely different.

Animals↗