Biomedical subjects

P G St Wecker

Publications and source records attributed to P G St Wecker.

3 recordsLinked to original sources

PubMed1995

Principal neurons of the lumbar sympathetic ganglia increase in number with body size.

Neuron number appears to be matched to body size during early development by the modulation of the processes of proliferation and naturally occurring cell death. However, body size increases rapidly as the juvenile becomes an adult, long after these processes cease to operate. The present study shows that principal neurons of lumbar sympathetic ganglia increase in number four- to fivefold during postmetamorphic life of the bullfrog. Rana catesbeiana. This increase in neuron number cannot be attributed to either counting error or selection bias and was associated with greater innervation of particular hindlimb targets, as demonstrated by retrograde labeling with horseradish peroxidase. Injection of [3H]thymidine (a marker of DNA synthesis) every third day for 20-22 weeks failed to provide evidence of neuron proliferation, although, on the basis of changes in body length during this period, substantial numbers of neurons likely were added. These results combined with previous studies of hindlimb motor and sensory neuron addition are consistent with the hypothesis that the population of sympathetic neurons is augmented by late differentiation of existing precursor cells.

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PubMed1994

Hindlimb sensory neuron number increases with body size.

As an animal grows, its sensory systems face the task of maintaining sensitivity and discrimination in peripheral fields that are continually enlarging. Without the addition of neurons, existing cells would have to innervate a wider skin area, leading to a decrease in the precision with which stimuli are localized. Neurons were counted in the three dorsal root ganglia (DRGs) that innervate the hindlimb of the bullfrog (Rana catesbeiana). Profiles of neuronal nuclei containing the single nucleolus found in these cells were counted in every third section of serially cut ganglia. This means of assessing neuron number was validated by comparing these profile counts with three-dimensional reconstructions of sensory neurons. Large frogs (10-17 cm) had more than twice as many DRG neurons as small frogs (3.3-5 cm). The rate of increase was greatest between 3 and 8 cm, when over 1,300 hindlimb sensory neurons were added for each 1 cm increase in body length. The possibility that selective survival of frogs with many neurons biases estimates of mean neuron number was ruled out by the finding that frogs drawn from the same closed population, half of which were sacrificed immediately and half of which were sacrificed after 1 year's survival, showed expected differences in neuron number. Horseradish peroxidase applied to particular hindlimb nerves retrogradely labeled more neurons in large frogs than small frogs, supporting the hypothesis that added neurons extend their axons to the periphery.(ABSTRACT TRUNCATED AT 250 WORDS)

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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.

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