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

Farel, Paul B.; Wray, Sibyl; Meeker, Marianne L.

doi:10.1016/0165-3806(93)90169-b

“…Our findings are reminiscent of reports in bullfrogs, where the late differentiation of so-called 'Type-L' cells is thought to augment motoneuron number in the lumbar spinal cord as the animal grows (Farel, 1987;Farel et al, 1993). Type L cells do not meet the normal criteria for motoneurons, but express motoneuron-specific markers (Farel et al, 1993), and are similar in appearance to the small cells in Onuf's nucleus [Fig. 2,present report and Fig.…”

Section: Increased Motoneuron Cell Counts: Late Differentiation Of Mosupporting

confidence: 69%

Breeding status affects motoneuron number and muscle size in naked mole‐rats: Recruitment of perineal motoneurons?

Seney

¹

,

Goldman

²

,

Forger

³

2006

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Naked mole-rats live in large colonies and exhibit a strict reproductive hierarchy. Each colony has one breeding female and one to three breeding males; all other individuals are nonreproductive subordinates. Subordinates show a remarkable lack of sex differences in behavior and anatomy, but can become reproductive if removed from the colony. We recently reported that the striated perineal muscles and their innervating motoneurons, which are sexually dimorphic in all other mammals examined to date, are not dimorphic in subordinate naked mole-rats. Here we asked whether sexual differentiation of this neuromuscular system occurs when a subordinate becomes a breeder. The size and number of cells within Onuf's nucleus (homologue of the rat spinal nucleus of the bulbocavernosus) as well as perineal muscle volume were examined in subordinate and breeding naked mole-rats of both sexes. Sex differences in perineal motoneurons were not observed, regardless of social status. To our surprise, however, counts of motoneurons in Onuf's nucleus were increased approximately 30% in breeders of both sexes. This was accompanied by a reciprocal decrease in cells in Onuf's nucleus that were characterized by small soma size, and lacked a clear nucleus or nucleolus. Although not exhibiting typical motoneuron morphology, some of these small cells were positive for the motoneuron marker, SMI-32. The neuronal changes correlate with increased perineal muscle volumes in breeders. We propose that small, relatively undifferentiated cells are recruited to the pool of large Onuf's nucleus motoneurons when subordinate naked mole-rats become breeders.

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“…These type-L (less-differentiated) neurons lack the cytological characteristics typical of sensory neurons, yet respond positively to a neuron-specific immunological probe (Meeker et al, 1995; see also Farel et al, 1993;St. In contrast, there is evidence for late maturation of incompletely differentiated neurons in the frog.…”

Section: Sensory Neuron Addition In Postnatal Ratsmentioning

confidence: 99%

Sensory neuron number in neonatal and adult rats estimated by means of stereologic and profile‐based methods

Popken¹,

Farel²

1997

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Postnatal neuron addition, if it occurred, would have profound implications both for the conceptualization of developmental processes and for efforts directed at replacing neurons that were lost to injury or disease. Although dorsal root ganglia (DRGs) offer the advantages of clear boundaries and functional homogeneity, studies comparing neuron number in the DRGs of animals of different ages or sizes have yielded conflicting results. In the present study, neuron number in DRGs L3-L6 was compared in neonatal (approximately 11 days old, mean weight of 24.5 g, mean volume of 25 cm3) and adult (approximately 80 days old, mean weight of 373.5 g, mean volume of 346 cm3) male Sprague-Dawley rats. Estimates of neuron number were derived by using both stereological (physical disector) and profile-counting (one or more nucleoli within a nucleus) methods. The reliability and validity of the two methods were evaluated by comparing estimates of neuron number with those derived from three-dimensional reconstruction of a subset of neurons. The recommended protocol for using the physical disector was found to give accurate estimates of neuron number, but the heterogeneous distribution of neurons in the ganglion led to sampling errors of up to 50%. Reliability was improved by increasing the number of disector pairs examined. Counts of nuclear/nucleolar profiles were more reliable, but introduced a bias that worked against the experimental hypothesis in that estimates of neuron number in neonates exceeded actual values. Nonetheless, both methods indicated that adult rats had more DRG neurons than did neonates. Profile counts were 19% higher in adults (P < .01, two-tailed t-test); and data obtained by using the physical disector showed that adult rats had 28% more neurons than did neonates (P < .05). The difference in neuron number between adults and neonates could be due either to neuron proliferation or to late differentiation of neurons that do not assume a typical appearance until adulthood.

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“…A population of cells has been identified in the DRG that cannot be labeled with HRP from either the periphery or the ventral root. These type-L (less-differentiated) neurons lack the cytological characteristics typical of sensory neurons, yet respond positively to a neuron-specific immunological probe (Meeker et al, 1995; see also Farel et al, 1993;St. Wecker et al, 1995).…”

Section: Sensory Neuron Addition In Postnatal Ratsmentioning

confidence: 99%

Sensory neuron number in neonatal and adult rats estimated by means of stereologic and profile-based methods

Popken

¹

,

Farel

²

1997

Self Cite

View full text Add to dashboard Cite

Postnatal neuron addition, if it occurred, would have profound implications both for the conceptualization of developmental processes and for efforts directed at replacing neurons that were lost to injury or disease. Although dorsal root ganglia (DRGs) offer the advantages of clear boundaries and functional homogeneity, studies comparing neuron number in the DRGs of animals of different ages or sizes have yielded conflicting results. In the present study, neuron number in DRGs L3-L6 was compared in neonatal (approximately 11 days old, mean weight of 24.5 g, mean volume of 25 cm3) and adult (approximately 80 days old, mean weight of 373.5 g, mean volume of 346 cm3) male Sprague-Dawley rats. Estimates of neuron number were derived by using both stereological (physical disector) and profile-counting (one or more nucleoli within a nucleus) methods. The reliability and validity of the two methods were evaluated by comparing estimates of neuron number with those derived from three-dimensional reconstruction of a subset of neurons. The recommended protocol for using the physical disector was found to give accurate estimates of neuron number, but the heterogeneous distribution of neurons in the ganglion led to sampling errors of up to 50%. Reliability was improved by increasing the number of disector pairs examined. Counts of nuclear/nucleolar profiles were more reliable, but introduced a bias that worked against the experimental hypothesis in that estimates of neuron number in neonates exceeded actual values. Nonetheless, both methods indicated that adult rats had more DRG neurons than did neonates. Profile counts were 19% higher in adults (P < .01, two-tailed t-test); and data obtained by using the physical disector showed that adult rats had 28% more neurons than did neonates (P < .05). The difference in neuron number between adults and neonates could be due either to neuron proliferation or to late differentiation of neurons that do not assume a typical appearance until adulthood.

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

Cited by 24 publications

References 40 publications

Breeding status affects motoneuron number and muscle size in naked mole‐rats: Recruitment of perineal motoneurons?

Breeding status affects motoneuron number and muscle size in naked mole‐rats: Recruitment of perineal motoneurons?

Sensory neuron number in neonatal and adult rats estimated by means of stereologic and profile‐based methods

Sensory neuron number in neonatal and adult rats estimated by means of stereologic and profile-based methods

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