Biomedical subjects

T J DeVoogd

Publications and source records attributed to T J DeVoogd.

13 recordsLinked to original sources

PubMed1992

Effects of sex and androgen treatment on dendritic dimensions of neurons in the sexually dimorphic preoptic/anterior hypothalamic area of male and female ferrets.

A sexually dimorphic group of cells at the dorsal border of the preoptic/anterior hypothalamic area (POA/AH) of ferrets has been previously identified in Nissl-stained tissue. In this study, Golgi-stained tissue was examined in order 1) to determine whether sex differences exist in dendritic dimensions of neurons from this region, and 2) to assess the effects of adult androgen treatment on dendritic morphology in ferrets of both sexes. Brains from adult ferrets given daily injections of testosterone propionate (5 mg/kg body weight) or oil vehicle for 5 weeks after gonadectomy were impregnated by Golgi-Cox procedures. After sectioning at 120 microns, 78 multipolar neurons were selected from the sexually dimorphic POA/AH of 12 ferrets and reconstructed in three dimensions with the aid of a computer-assisted neuron tracing system. Large sex differences were observed in somal area and most aspects of dendritic morphology, including total length, number of branches, and total dendritic surface area. Androgen also appeared to accentuate dendritic arborization in both sexes, but this effect was weaker than the sex effect, more apparent in males than females, and restricted to fewer variables. The most statistically significant effects of adult androgen treatment in males were found for total dendritic surface area and percentage of fourth order dendrites, and in females, average dendritic thickness. These data show that strong sex differences exist in dendritic structure of neurons in the POA/AH, and suggest that alterations in levels of gonadal steroids in adulthood may promote synaptic remodeling in a region of the brain involved in the control of sexually dimorphic behaviors.

Animals↗

PubMed1991

Lateral asymmetries and testosterone-induced changes in the gross morphology of the hypoglossal nucleus in adult canaries.

The caudal portion of the hypoglossal nucleus (tracheosyringeal, nXIIts) contains the motor neurons that innervate the syrinx in songbirds. It receives projections from telencephalic and midbrain nuclei that are necessary for song production. Its neurons concentrate androgens. The present study assesses the gross morphology of the hypoglossal nucleus in canaries. In this species song is more frequent, elaborate, and stereotyped in males than in females. Adult females respond to testosterone by developing a stereotyped song that is sung frequently. Song in male canaries is much more disrupted by damage on the left side of the song system than by damage on the right. We find anatomical correlates for each of these attributes in the nXIIts. This nucleus is 83% larger in males than in females. This is caused primarily by a sex difference in neuropil volume as there is no significant sex difference in the number of neurons in nXIIts. nXIIts grows by 34% in females given testosterone as adults. It is about 8% larger on the left than on the right in males, females, and females treated with testosterone. Sex differences are also found in the rostral (lingualis) portion of nXII, which controls muscles of the tongue, but there is no effect here of adult treatment with testosterone. Comparisons of these data with earlier measures of synaptic density and morphology in nXIIts suggest that the testosterone acts on this nucleus by inducing a modest increase in synapse numbers and by altering the efficacy of synapses in nXIIts. This contrasts with the effects of testosterone on n. robustus archistriatalis, a telencephalic component of the song system in which testosterone induces massive amounts of synaptogenesis.

Animals↗

PubMed1991

Altered daylength affects dendritic structure in a song-related brain region in red-winged blackbirds.

Substantial neural and behavioral plasticity occurs in the avian song system in adulthood. Changes in the volume of one of the song control nuclei, robustus archistriatalis (RA), have been associated with seasonal changes in singing behavior in adult canaries (Serinus canarius) and red-winged blackbirds (Agelaius phoeniceus). The present work assessed the effects of changed daylength on dendritic morphology in RA in adult male red-winged blackbirds. Brains from hand-reared red-winged blackbirds maintained on long days or long days followed by short days were stained with a Golgi-Cox procedure. Dendritic morphology and spine density of type IV neurons from nucleus RA were compared between long and short day birds. Neurons from short day birds have smaller dendritic fields than neurons from long day birds, with the difference greatest for distal dendrites. In addition, the density of dendritic spines is significantly smaller for neurons from short day birds. Together, these changes result in the loss of approximately 40% of the spines on this neuron class. In previous work in adult female canaries, external testosterone administration has been shown to be associated with increases in dendritic field size and synapse number. The similarity of the neuronal changes in RA that are associated with the two sorts of manipulations suggest that some consequences of altered daylength are mediated by changes in the levels of gonadal steroids.

Animals↗

PubMed1991

Endocrine modulation of the development and adult function of the avian song system.

Enough data are now available on the neurobiology of the avian song system and on the development and performance of song that sophisticated questions on the relations between the behavior and the neurobiology can be addressed. This review describes what is known of sex differences and individual differences in the neurobiology of the song system in mature birds. It summarizes data on the role of steroid hormones in the development of the song system and what is known of steroid-related adult plasticity in this system. Finally, it discusses hypotheses on the relations between structure and function in this system and suggests issues that must be addressed in future studies.

Animals↗

PubMed1990

Recent findings on the development of dimorphic anatomy in the avian song system.

Much current research in neuroendocrinology concerns how endocrine information acts on the brain. For example, what processes are used early in life to transduce sex differences in gonadal steroids into structural dimorphisms within the brain? Or, to what extent are the actions of steroids on the developing nervous system unique events and to what extent are they a continuing part of the interplay between the endocrine and the central nervous system? The avian song system has proven to be a very useful model system in which to study these issues. Recent research from my laboratory on the development of sex differences in brain structure and on steroid-related adult plasticity is reviewed below. This review is quite focussed. More general reviews of research on the song system can be found in Arnold ('89), DeVoogd ('86), Konishi ('85), and Nottebohm ('88).

Androgens↗

PubMed1989

Morphology of Golgi-impregnated neurons in hyperstriatum ventralis, pars caudalis in adult male and female canaries.

Golgi-impregnated neurons in the song control nucleus hyperstriatum ventralis, pars caudalis (HVc) in male and female canaries (Serinus canarius) have been divided into classes, primarily on the basis of interneuronal variability in spine density and dendritic branching pattern. At least four neuronal classes are found in HVc: aspinous neurons and three classes of spiny neurons. The "furry" dendrite (FD) cell class consists of neurons with long dendrites that are densely packed with spines. Their cell bodies are between 10 and 15 microns in diameter. Neurons of the thick dendrite (TD) cell class also have long dendrites but only about half as many spines along their dendritic branches. Their cell bodies are between 12 and 18 microns in diameter. Neurons of the short dendrite (SD) cell class are characterized by a low spin density, very thin dendrites, and a small dendritic field. Their cell bodies are between 9 and 13 microns in diameter. The TD class can be divided into two subclasses on the basis of the shape of the dendritic field. Principal component factor analysis and cluster analysis provide objective support for this classification scheme. Neurons of subclass TD2 are sexually dimorphic. Neurons from males have dendritic trees that are about 70% larger and have 40% more dendritic endings than do neurons from females. There may also be small sex differences in dendritic morphology in the SD class and in the remainder of the TD class. There are clearly no sex differences in the dendritic morphology of neurons from the FD class. The direct pathway which is believed responsible for dimorphic song production in canaries is from HVc to nucleus robustus archistriatalis (RA) and then to the motor neurons which control the avian vocal organ. It is surprising that the most striking dimorphism in the present data occurs in neurons which, on morphological grounds, are unlikely to project to RA.

Animals↗

PubMed1989

Synaptic plasticity in the hypoglossal nucleus of female canaries: structural correlates of season, hemisphere, and testosterone treatment.

The caudal portion of the hypoglossal nucleus (nXIIts) contains the motor neurons that control the syrinx in songbirds. In canaries, song occurs seasonally, is principally produced by males, and appears to be produced predominantly by muscles on the left side of the syrinx. The present study measures the effect of seasonal change and manipulation of testosterone levels on synapse number and morphology in nXIIts in adult female canaries. We find that synapse density is lower in testosterone-treated birds than in control birds and lower in fall than in spring. The number of vesicles per presynaptic profile increases in the spring as a result of a general increase in this measure in all synapses. The number of vesicles per presynaptic profile also increases with testosterone treatment, primarily due to an increase in the proportion of synapses associated with unusually high vesicle counts. Together, these changes suggest that large reserves of neurotransmitter may be necessary to sustain singing. Several ultrastructural differences between hemispheres are found. Postsynaptic thickenings are longer, and postsynaptic processes are larger on the left side than on the right side. In the spring, there are more vesicles per synapse on the left than on the right, but this lateralization is reversed in the fall. Thus, lateralization of song production is associated with lateral asymmetries in synapse morphology. These hemispheric differences are relatively small, like those seen at the light microscope level, encouraging further consideration of peripheral as well as CNS sources of functional lateralization. The seasonal and testosterone-induced changes in synapse number and morphology may be components of the periodic reorganization of canary vocalization.

Animals↗

PubMed1989

Genesis and death of vocal control neurons during sexual differentiation in the zebra finch.

Several song-related regions in the adult zebra finch brain have substantially more neurons in males than in females. Such differences appear to arise from sex differences in circulating steroids during early posthatch life. In the present study, developmental mechanisms involved in the production of sex differences are explored by examinations of the normal time course of posthatch neurogenesis and cell death in vocal control circuits. As a first step toward determining whether rates of neuron production may be different in males and females, tritiated thymidine, a marker of cell division, was administered to zebra finches at various times during the first month after hatching. Birds were sacrificed at 60 d. The number of cells formed after hatching and present at 60 d was then evaluated in 3 vocal control regions--HVc (hyperstriatum ventralis pars caudalis) and its 2 principal targets, RA (robust nucleus of the archistriatum) and Area X. Cell death was quantified by counts of normal and pyknotic, degenerating cells made in these nuclei in additional, untreated birds of both sexes at 5 d intervals from 5 to 45 d of age. The combined results of these experiments suggest that differential cell death is a major factor in the development of sex differences in the song control system and provide the first direct evidence for sex differences in cell death in the developing telencephalon. Although developmental time tables differ among the 3 brain areas examined, at specific ages significantly higher numbers of pyknotic cells were observed in HVc, RA, and presumptive Area X in females compared to males. Peak levels of cell death in RA occur 4-6 weeks after hatching. This is about 3 weeks after the onset of sex differences in steroid levels that, in turn, lead to differential organization of song system nuclei. This pattern of results suggests that designation for death and actual cell loss are temporally dissociated in this system. Neuron proliferation for HVc and Area X, but not RA, continues throughout the first 30 d after hatching, and a significant sex difference was found in the number of cells present in HVc at 60 d that were formed after hatching. Comparisons of the timing of cell death and cell incorporation suggest that this difference may be best accounted for by differential survival of neurons formed after hatching rather than differential rates of neuron production. Neither differential neurogenesis nor differential neuron death can fully account for the apparent extreme sexual dimorphism in the number of neurons in Area X.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1988

Small sex differences in song control dendrites are associated with minimal differences in song capacity.

Previous work on canaries and zebra finches has shown that large differences between the sexes exist in the structure of dendrites in n. robustus archistriatalis (RA), one of the principal nuclei involved in the control of song. This sex difference is associated with a general or complete absence of song in females. If dendritic morphology in RA is causally related to capacity for song, large sex differences in structure should not occur in avian species in which both sexes sing. We now report this prediction confirmed for buff-breasted wrens (Thryothorus leucotis), a species in which the members of a breeding pair sing duets with each other. Total dendritic length and number of dendritic branches in RA do not differ in this species. Dendrites from males project about 8 micron further from the cell body than dendrites from females, apparently because of longer dendritic segments near the cell body. We argue that this suggests that differential influences on the structure of RA occurred early in the lives of the wrens.

Animals↗

PubMed1988

Effect of testosterone on input received by an identified neuron type of the canary song system: a Golgi/electron microscopy/degeneration study.

Combinations of the Golgi stain, anterograde degeneration, and electron microscopy are used to further characterize the hormone-sensitive "type IV" neuron of the forebrain nucleus robustus archistriatalis (RA) of adult female canaries. Anterograde degeneration was used to "stain," at the electron-microscopic level, the axon terminals of neurons projecting to RA from hyperstriatum ventralis, pars caudalis (HVc) and from the lateral magnocellular nucleus of the anterior neostriatum (L-MAN). The HVc neurons projecting to RA type IV cells form synapses predominantly on the dendritic spines of those cells, while L-MAN neurons that project to RA type IV cells form a 2.5:1 mixture of shaft and spine synapses. There were about 1000 synapses from HVc neurons (about 30% of all spine synapses) on typical type IV cells and about 50 synapses from L-MAN neurons. Earlier work had shown that in female canaries the dendrites of type IV neurons of the avian song control nucleus RA increase in total length after systemic testosterone treatment, and that this increase in dendritic length was accompanied by the development of malelike song. We now show that testosterone treatment also increases the number of dendritic spines present in type IV neurons. Presumably this is accompanied by an increase in the number of synaptic inputs received by type IV cells. Earlier evidence suggested that the testosterone-induced addition of extra dendritic length to type IV cells occurred at existing dendritic tips. We tested the hypothesis that these added peripheral ends received a special subset of inputs, which might then account for the change in behavior, and found it to be false. Mapping and counts of degenerating synapses resulting from lesion of HVc and L-MAN suggest that under the influence of hormone, new synapses are added throughout the dendritic tree, with no special distribution or change in ratio of inputs occurring at the tip of dendrites. Under the influence of testosterone, each type IV cell may receive only "more of the same" inputs it received before onset of treatment. We speculate on how such changes in circuitry may relate to song stability and learning.

Animals↗

PubMed1986

Steroid interactions with structure and function of avian song control regions.

Following 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).

Aging↗

PubMed1978

Subsynaptic plate perforations: changes with age and experience in the rat.

The relative frequency of appearance of discontinuities in the postsynaptic thickening, or perforations in the subsynaptic plate, increased with age and experience. Rats reared from weaning in complex or social environments had a significantly higher proportion of occipital cortical synapses with perforations than did rats reared in isolation. In addition, the relative frequency of these perforations more than tripled between 10 and 60 days of age. Shifts in the frequency of perforations can occur independently of changes in the size of synpases. This result suggests a new potential mechanism of synaptic plasticity.

Aging↗

PubMed1977

Sex differences in dentritic patterns in hamster preoptic area.

Sexual dimorphism is described in the dentritic field pattern of Golgi-stained neurons from the dorsomedial preoptic area of adult golden hamsters (Mesocricetus auratus). Data were obtained through a mathematical reconstruction of dentritic densities of neurons sampled from this area in males and females. Males tended to have a central concentration, while females showed an irregular dendritic density distribution with concentrations dorsolateral, ventral and medial to the area of highest dentriic density in the males. These results suggest sex differences in the afferent inputs to neurons in the dorsomedial preoptic area which may be related to functional sexual dimorphism in physiology and behavior.

Animals↗