Motoneurons innervating guinea pig perineal muscles are sexually dimorphic in size but not number

Freeman, Louise M.; Breedlove, S. Marc

doi:10.1016/0006-8993(95)00442-s

Cited by 14 publications

(13 citation statements)

References 32 publications

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“…This confirms our previous observations in subordinates (Peroulakis et al, 2002) and stands in contrast to other mammals examined to date, where the size and/or number of motoneurons innervating perineal muscles are greater in males (Breedlove and Arnold, 1980;Ueyama et al, 1985; and Breedlove, 1986;Wagner and Clemens, 1989;Freeman and Breedlove, 1995;Ulibarri et al, 1995;Forger et al, 1996).…”

Section: Relative Absence Of Neural Sex Differencessupporting

confidence: 91%

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

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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Section: Relative Absence Of Neural Sex Differencessupporting

confidence: 91%

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

2006

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“…While most rodents segregate BC and IC motoneurons into separate nuclei (Freeman and Breedlove, 1995; Jordan et al, 1982; Tobin and Payne, 1991) musk shrews resemble carnivores in the organization of most BC and IC motoneurons into a single laterally placed cluster, usually called Onuf’s nucleus (Forger and Breedlove, 1986; Forger et al, 1996). Interestingly, Onuf’s nucleus in humans is found in a more ventromedial position, similar to the shrew MN, which also contained a few BC and IC-innervating motoneurons (Fig.…”

Section: Discussionmentioning

confidence: 99%

Sex difference in Onuf's nucleus homologue in the Asian musk shrew

Polak¹,

Freeman²

2010

Brain Research

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Perineal muscles essential for copulatory functioning are innvervated by Onuf’s nucleus in humans and the spinal nucleus of the bulbocavernosus (SNB) and dorsolateral nucleus (DLN) in rats. These structures sexually differentiate as a result of developmental androgen exposure in most species examined. The homologous structure in the Asian musk shrew (Suncus murinus) is a single cluster in the lateral DLN/Onuf’s position in the ventral horn of the spinal cord; these motoneurons innervate both the bulbocavernosus and ischiocavernosus muscles of the musk shrew. We found the expected sex difference in motoneuron number in the shrew DLN, but not in two neighboring motoneuron clusters, the retrodorsolateral nucleus (RDLN) and ventrolateral nucleus (VLN). Male musk shrews also have significantly larger soma areas in the VLN and DLN than females, and male DLN motoneurons have significantly larger nuclei than female. The sex difference in DLN motoneuron number was evident both in raw counts and after accounting for split nuclei error.

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“…3,4,6,18,19,38,39,55 Furthermore, the motoneurons innervating the ischiocavernosus muscle are located in the dorsolateral (DL) region, and those innervating the bulbocavernosus and levator ani muscles are located in the dorsomedial (DM) region of the ventral horn. 17 Therefore, the relative location of motoneurons in specific motor pools can be identified within a specific area in the ventral horn of the spinal cord as well as within the rostral to caudal direction at specific segmental level(s) of the spinal cord. 41,46,48 Although there is some overlap, alpha motoneurons are relatively large and innervate extrafusal muscle fibers, and gamma motoneurons are relatively small and innervate the intrafusal muscle fibers of muscle spindles.…”

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confidence: 99%

Comparison of the response of motoneurons innervating perineal and hind limb muscles to spaceflight and recovery

et al. 2000

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Motoneurons innervating guinea pig perineal muscles are sexually dimorphic in size but not number

Cited by 14 publications

References 32 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?

Sex difference in Onuf's nucleus homologue in the Asian musk shrew

Comparison of the response of motoneurons innervating perineal and hind limb muscles to spaceflight and recovery

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