摘要:

AbstractThe electric communication system includes both special muscle‐derived cells orelectrocytesthat produce species‐typical electric signals, orelectric organ discharges(EODs), and specialized sensory receptors, orelectroreceptors, that encode the electric fields set up by EODs. Steroid hormones can influence the characteristic properties of both EODs and electroreceptors. Steroids appear to directly effect the anatomy and physiology of the electrocytes that generate an EOD. In contrast, the steroid effect on electroreceptors may be predominantly via an indirect mechanism whereby changes in the spectral characteristics of the EOD appear to induce changes in the spectral sensitivity of electroreceptors. Continued studies of electrosensory and electromotor systems will offer insights into the cellular bases for the development and evolution of steroid‐sensitive pathways in the vertebrate nervous s

ISSN:0022-3034    

DOI:10.1002/neu.480170303

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1986

数据来源: WILEY

摘要:

AbstractThe striated bulbocavernosus (BC) muscles of the rodent perineum are innervated by motoneurons in the spinal nucleus of the bulbocavernosus (SNB). In adulthood, the BC muscles are present in males only. However, newborn female rats have BC muscles, and SNB cells have made both anatomical and functional contact with them. Nevertheless, both motoneurons and muscles will degenerate unless androgens are administered perinatally. Such androgen treatment appears to be acting primarily on the BC muscles themselves, since the muscles are spared by androgen even after the loss of supraspinal neural afferents or even the entire lumbosacral spinal cord. Furthermore, androgen can spare SNB motoneurons that are themselves androgen insensitive. Perinatal steroid treatments can also alter the final spinal location of SNB cells as determined by retrograde tracing studies. Androgen continues to modify the morphology of the SNB system in adulthood, altering the size of both motoneurons and targets, which may be important for the reproductive function of BC muscles. Finally, the sexually dimorphic character of motoneuronal groups innervating perineal muscles seems to be common in mammals, since the homologue of the SNB, Onuf's nucleus, has more cells in males than in females in both dogs and humans.

ISSN:0022-3034    

DOI:10.1002/neu.480170304

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1986

数据来源: WILEY

摘要:

AbstractFollowing the pioneering work of Nottebohm, the brain regions involved in song production in songbirds have become a focus of extensive research in several laboratories. As both singing behavior and the neuroanatomy of song control regions are strongly affected by sex steroids in many songbird species, this system has become regarded as an ideal model system in which one can potentially determine how steroids affect neuronal anatomy, how altered anatomy leads to altered physiology, and how the altered physiology causes changes in singing. In the initial part of this review, I shall focus on canaries and zebra finches as most of our knowledge of the song system has been obtained from these two species. I shall describe singing behavior, the constituents of the song system, what is known of how these nuclei contribute to song, and how each is affected by steroid fluctuations. I shall then speculate on new ways of posing questions on hormone—anatomy interaction in this system (which I will illustrate with preliminary data from my own lab). This review will be brief as several reviews of aspects of the song system have recently been published (Arnold, 1982; Nottebohm, 1984; Arnold and Gorski, 1984; DeVoogd, 1984; Konishi, 1985

ISSN:0022-3034    

DOI:10.1002/neu.480170305

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1986

数据来源: WILEY

摘要:

AbstractThe ipsilateral retinothalamic projection of the frogXenopus laevisis formed by the axons of a subset of retinal ganglion cells which are found throughout peripheral and non‐nasodorsal retina. Unlike the crossed retinotectal and retinothalamic projections, which begin to form during early embryonic stages, the ipsilateral projection does not begin to develop until late in tadpole life, at stages when thyroxine first becomes detectable in the circulation. Blocking the production of thyroid hormone in tadpoles prevents the development of the ipsilateral projection, in a reversible manner. Intraocular injection of thyroxine can “rescue” the development of the projection in tadpoles which otherwise remain premetamorphic. In addition, the projection from one eye of a metamorphically‐blocked tadpole can be induced to form by an intraocular injection of thyroxine at a dose which has no detectable effect on retinal development in the other, untreated eye. These results indicate that the development of the ipsilateral retinothalamic projection is dependent upon thyroxine, and strongly suggest that the hormone acts at the level of the eye, rather than at the optic chiasm or thalamic target, to bring about the development of a new pathway. A number of ways in which thyroxine might act in the system are di

ISSN:0022-3034    

DOI:10.1002/neu.480170306

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1986

数据来源: WILEY

摘要:

AbstractSouth African clawed frogs use sex‐specific vocalizations during courtship. In the male, vocalizations are under the control of gonadal androgen. Though females have moderate levels of circulating androgen, they do not give male‐typical mate calls. Both muscles of the vocal organ and neurons of the central nervous system (CNS) vocal pathway are sexually dimorphic and androgen‐sensitive. Recent studies suggest that the failure of androgen to masculinize adult females results from a male‐specific, androgen‐regulated developmental program. At metamorphosis the larynx is sexually monomorphic and feminine in morphology, muscle fiber number and androgen receptor content. During the next six months, under the influence of increasing androgen titers and high receptor levels, myoblasts proliferate in the male and muscle fibers increase at an average rate of 100/day. Females have much lower hormone levels, receptor values decline and they display no net addition of fibers. At metamorphosis, both males and females have approximately 4000 muscle fibers. By adulthood, males have eight times the female fiber number. In the CNS, adult laryngeal motor neurons are more numerous with larger somata and dendritic trees in males than in females. Certain connections of neurons in the vocal pathway are also less robust in females. Unlike the periphery, motor neuron number does not appear to be established by androgen‐induced proliferation. Our current hypothesis is that androgen acts at the level of laryngeal muscle to produce more muscle fibers and thus provide more target for motor neurons in the male. This process could regulate cell number by ontogenetic cell death. In the CNS, androgen‐target neurons become capable of accumulating hormone shortly before metamorphosis. Androgen receptor in larygeal motor neurons may permit the dendritic growth characteristic of males by increasing sensitivity to afferent stimuli. Such a process could account for the observed differences in CNS vocal “circuitry” inX. laevisand thus behavioral differences

ISSN:0022-3034    

DOI:10.1002/neu.480170307

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1986

数据来源: WILEY

摘要:

AbstractInsect metamorphosis is controlled by a small ensemble of developmental hormones including a class of steroids—the ecdysteroids. In the tobacco hornworm,Manduca sexta, the progession from the larval to pupal to adult stages is controlled by the relative blood titers of ecdysteroids and juvenile hormone (JH). The cellular events in the nervous and muscular systems which accompany metamorphosis resemble those of embryonic development, but they occur in an animal which is larger and experimentally more tractable than an embryo. In this paper we review the role of ecdysteroids in directing the metamorphosis of the nervous and muscular systems inManduca, and how JH modifies the cellular responses to the steroids. In particular, we describe how these hormones control muscle degeneration, changes in the structure and function of identified neurons, and programmed neuron death. One general finding is that interactions between cells (e.g., neurons and their target muscles) are not involved in their hormonal responses, but rather the hormones act independently and in parallel at the different sites. Another key finding is that the critical periods and hormonal requirements for the commitment to a particular differentiative pathway, and the phenotypic expression of that pathway, can differ, and are therefore experimentally separable. Finally, we find that the significance of a hormonal signal (e.g., a rise in blood ecdysteroids) is interpreted differently depending upon the previous history of hormone exposure of a neuron or muscle. This progressive change in the interpretation of hormonal signals is a major mechanism by which a limited number of hormones can orchestrate a complicated phenomenon such as metamorphosi

ISSN:0022-3034    

DOI:10.1002/neu.480170308

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1986

数据来源: WILEY

ISSN:0022-3034    

DOI:10.1002/neu.480170302

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1986

数据来源: WILEY