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.

Sex differences in dendritic morphology of a song control nucleus in the canary: a quantitative Golgi study.

Singing in the canary is a learned male behavior controlled predominantly by nuclei in the left hemisphere (Nottebohm and Nottebohm, '76; Nottebohm et al., '76; Nottebohm, '77). These nuclei are several times larger in males than in females (Nottebohm and Arnold, '76). One of the telencephalic song control nuclei, robustus archistriatalis (RA), was examined in Golgi-stained tissue sections from the left and right hemispheres of male and female canaries. At least four cell classes were present in each sex. One of these cell classes was further studied with a variety of quantitative techniques. No hemispheric differences were seen in either sex. However, dendrites from male cells tend to branch and end further from the cell body than do dendrites from female cells. This difference is seen most clearly when serial sections are used to reconstruct the entire dendritic tree.

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.

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.

Developmental changes in the distribution of NADPH-diaphorase-containing neurons in telencephalic nuclei of the zebra finch song system.

Extensive recent research has focused on the potential role of nitric oxide (NO) in synaptic plasticity. Could the capacity to synthesize NO be associated with neural and behavioral plasticity in the song system? The timing of song learning and of major developmental changes in song system anatomy are known. We searched for an association between NO and these developmental events by observing the distribution of neurons staining for NADPH-diaphorase, an enzyme used in the synthesis of NO, in the brains of zebra finches. Both male and female brains were taken at different developmental ages from day 21 to adulthood. We found that the incidence of stained neurons in the song system nuclei is lower than in surrounding areas. The incidence of staining decreases with development, with most of the decrease occurring prior to the auditory learning phase of song learning. The developmental changes were quantified for area X and found to be highly significant, with a 56% decrease in staining frequency from day 21 to adulthood in males and a 23% decrease in females for the equivalent region. We also found a sexual dimorphism in the song system of adult birds, consisting of a reduced incidence of stained neurons in song system nuclei area X, high vocal center (HVC), and nucleus robustus (RA) archistrialis in males compared with females. These findings suggest that NO is less involved in the plasticity underlying song acquisition than in the earlier formation of the song system.

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.

Relations between song repertoire size and the volume of brain nuclei related to song: comparative evolutionary analyses amongst oscine birds.

Song and brain structure are compared amongst 41 species of oscine birds by using the method of independent evolutionary contrasts. We find a significant correlation between the relative volume of the song control centre, the high vocal centre (HVC), and the number of song types typically found in the repertoire. Relative HVC volume is not correlated with the number of different syllable types per song bout. The relative volume of a second song nucleus, area X, is not significantly correlated with either measure. Relative HVC volume is uncorrelated with relative volume of the hippocampus, a brain area involved in other forms of memory. This is the first evidence for repeated independent evolution of an association between complexity of learned song and the relative volume of one of the song control nuclei though to be involved in song learning.

Variation in the volume of zebra finch song control nuclei is heritable: developmental and evolutionary implications.

In many songbird species, females prefer males that sing a larger repertoire of syllables. Males with more elaborate songs have a larger high vocal centre (HVC) nucleus, the highest structure in the song production pathway. HVC size is thus a potential target of sexual selection. Here we provide evidence that the size of the HVC and other song production nuclei are heritable across individual males within a species. In contrast, we find that heritabilities of other nuclei in a song-learning pathway are lower, suggesting that variation in the sizes of these structures is more closely tied to developmental and environmental differences between individuals. We find that evolvability, a statistical measure that predicts response to selection, is higher for the HVC and its target for song production, the robustus archistriatalis (RA), than for all other brain volumes measured. This suggests that selection based on the functions of these two structures would result in rapid major shifts in their anatomy. We also show that the size of each song control nucleus is significantly correlated with the song related nuclei to which it is monosynaptically connected. Finally, we find that the volume of the telencephalon is larger in males than in females. These findings begin to join theoretical analyses of the role of female choice in the evolution of bird song to neurobiological mechanisms by which the evolutionary changes in behaviour are expressed.

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.

Sexual dimorphism and species differences in HVC volumes of cowbirds.

Cowbirds exhibit extensive variation in their social, territorial, and reproductive behaviors. Nissl-stained brain sections of specimens from a previous study (J. C. Reboreda, N. S. Clayton, & A. Kacelnik, 1996) were used to study the gross anatomy of a song control nucleus in 3 South American cowbirds (bay-winged, Molothrus badius; shiny, M. bonariensis; and screaming, M. rufoaxillaris). Cowbird high vocal center (HVC) volumes were consistently higher in males than in females in all 3 species. The largest HVC size of females found in bay-winged cowbirds is consistent with observations that females of this species, but not of the other 2 species, occasionally sing. The extent of the sexual dimorphism of relative HVC size was highest for the sexually dichromatic and promiscuous shiny cowbirds and smaller for the monochromatic and monogamous bay-winged and screaming cowbirds, suggesting that selection pressures associated with morphological traits and social systems are reflected in brain architecture.

Greater song complexity is associated with augmented song system anatomy in zebra finches.

We revisited the relationship between brain anatomy and song behavior in zebra finches. Consistent with previous studies in other songbirds, we find that differences in volume of the telencephalic song control nucleus HVc is predictive of differences in repertoire size and phrase duration in zebra finches. We extend the study of brain and behavior correlations in song birds by showing that repertoire size in zebra finches can be predicted by variance in several brain nuclei, providing the first demonstration that volumetric differences across multiple components of a neural network are predictive of song behavior.

Greater song complexity is associated with augmented song system anatomy in zebra finches.

We revisited the relationship between brain anatomy and song behavior in zebra finches. Consistent with previous studies in other songbirds, we find that differences in volume of the telencephalic song control nucleus HVc is predictive of differences in repertoire size and phrase duration in zebra finches. We extend the study of brain and behavior correlations in song birds by showing that repertoire size in zebra finches can be predicted by variance in several brain nuclei, providing the first demonstration that volumetric differences across multiple components of a neural network are predictive of song behavior.

Distortions induced in neuronal quantification by camera lucida analysis: comparisons using a semi-automated data acquisition system.

Quantitative analysis of dendritic structure is widely used in assessing neural relationships in Golgi-stained tissue. Quantitative techniques are tedious and time-consuming. A computer-microscope system is described which speeds data acquisition and analysis. Three neuronal samples are analyzed both by this computerized system and by camera lucida techniques. We demonstrate that the computerized techniques result in far fewer errors in data transcription and analysis than the camera lucida procedure. In addition, we show that the amount of distortion in camera lucida drawings caused by collapsing 3 dimensions into 2 varies both with cell class and cell dendrite type. This prevents the use of any simple statistical procedures for deriving 3-dimensional information from 2-dimensional data.

Non invasive in vivo anatomical studies of the oscine brain by high resolution MRI microscopy.

We describe in this paper an in vivo Magnetic Resonance Imaging (MRI) procedure that allows one to obtain three-dimensional high quality images of the entire brain of small passerine birds such as the canary with a slice thickness of 58 micron and an image resolution of 78 microns. This imaging procedure was completed in 70 min on anaesthetised birds that later recovered uneventfully and could be reused for subsequent additional imaging. To illustrate the high resolution and anatomical detail that can be achieved, examples of coronal images through the entire hypothalamus are provided in the same sectioning plane as the previously published canary brain atlas. The data set can be used to create sections in any desired plane and the entire data set can be viewed from any point of view in a volume rendered image. This provides a useful tool in understanding the three-dimensional organisation of the brain. Similar procedures can also be applied on fixed brains and might allow an even better anatomical resolution of images because time constrains no longer limit the duration of image acquisition. The non-invasive MRI technique enables to study neuroanatomical features with a high resolution and without killing the animal subjects so that measures can be obtained in a same individual both before and after an experimental treatment.

Expression of immediate early genes in the hippocampal formation of the black-capped chickadee (Poecile atricapillus) during a food-hoarding task.

Black-capped chickadees store food in many different locations in their home range and are able to accurately remember these locations. We measured the number of cells immunopositive for three different Immediate Early Gene products (Fra-1, c-Fos and ZENK) to map neuronal activity in the chickadee Hippocampal Formation (HF) during food storing and retrieval. Fra-1-like immunoreactivity is downregulated in the dorsal HF of both storing and retrieving chickadees compared to controls. In retrieving birds, the number of Fos-like immunoreactive neurons relates to the number of items remembered, while the number of ZENK-like immunoreactive neurons in the HF may be related to the accuracy of cache retrieval. These results imply that the brain might process complex information by recruiting more neurons into the network of active neurons. Thus, our results could help explain why food-hoarding birds have more HF neurons than non-hoarders, and why this number increases in autumn when large numbers of food items are cached.

Anterior forebrain pathway is needed for stable song expression in adult male white-crowned sparrows (Zonotrichia leucophrys).

The anterior forebrain pathway of the avian song system is involved in juvenile song learning, but its function in adult song behavior is not known. This report uses lesions to study the role of a particular forebrain nucleus, IMAN, in the seasonal regeneration of song in adult white-crowned sparrows (Zonotrichia leucophrys oriantha). White-crowned sparrows, even when acoustically isolated as juveniles, crystallize a single song which they maintain throughout adulthood. The lateral portion of the magnocellular nucleus of the anterior neostriatum (1MAN) was lesioned bilaterally in adult males maintained on short days (8 h of light). Daylength was increased to 16 h following the surgeries, and all birds were recorded in the post-lesion singing season. Lesioned birds showed a large decrease in song note frequency following the lesions, significantly larger than did intact, age-matched controls. Further changes were seen in the post-lesion songs of seven of 11 successfully lesioned males. These changes included variability in song pattern, loss of frequency control and addition of new notes, some of which had been practiced during juvenile song development. These changes seemed especially large in birds that had either been acoustically isolated or had not fully copied a tape-tutor song during juvenile song development. These results are the first to indicate that the motor memories for song elements that had been practiced and discarded early in life are retained, and they suggest that 1MAN affects seasonal song expression by selectively reinforcing a particular song pattern.

Synaptogenesis and changes in synaptic morphology related to acquisition of a new behavior.

Systemic testosterone treatment induces adult female canaries to develop male-like song. This same treatment induces a doubling in size of the forebrain nucleus robustus archistriatalis (RA), known to be involved in song control, and a 51% increase in the number of synapses formed on RA neurons. In central RA, the number of synaptic vesicles per synapse increases as do several measures of synaptic size. Housing in spring-like conditions is also associated with larger synapses and more vesicles per synapse than housing in fall-like conditions. We suggest that formation of new synapses on existing neurons leading to or associated with modifications in synaptic morphology is important for acquisition of a new behavior. We also suggest that maximal behavioral and anatomical effects are associated with testosterone given under spring-like conditions.

Lucifer Yellow filling of area X-projecting neurons in the high vocal center of female canaries.

The avian high vocal center (HVC) is a complex forebrain nucleus that coordinates the sensorimotor integration necessary for song learning and production. It receives auditory and potentially somatosensory input, and sends major projections to vocal motor and anterior forebrain nuclei. The HVC has at least four morphological classes of neurons for which the connectivity remains uncertain. Previous studies have alluded to the functional identity of the cell classes, but none have provided the definitive evidence necessary for subsequent identification of behaviorally relevant changes within known neuronal populations. The cell filling technique we have adapted for use in the song system provides a method by which hodologically identified classes can be described with precision, and song related changes in their morphology can be readily identified. Neurons in female canaries (Serinus canarius) that project to Area X of the anterior forebrain pathway were retrogradely labeled, selectively filled with Lucifer Yellow in a fixed slice preparation, and converted to a Golgi-like stain through an immunocytochemical reaction. We have identified Area X-projecting neurons as belonging to the thick dendrite class of Nixdorf et al. [B.E. Nixdorf, S.S. Davis, T.J. DeVoogd, Morphology of golgi-impregnated neurons in hyperstriatum ventralis, pars caudalis in adult male and female canaries, J. Comp. Neurol. 284 (1989) 337-349] and have shown definitively that they are among the HVC neurons that can receive direct auditory input, as this cell class has short dendrites that extend into the shelf region ventral to HVC that is known to receive auditory inputs. Well-filled axons had collaterals that ramified and terminated within the nucleus, demonstrating a network through which Area X-projecting cells can contribute to intrinsic HVC communication.

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.

The distribution of substance P and neuropeptide Y in four songbird species: a comparison of food-storing and non-storing birds.

The distributions of the neuropeptides substance P (SP) and neuropeptide Y (NPY) were investigated in four songbird species that differ in their food-storing behavior. The food-storing black-capped chickadee (Parus atricapillus) was compared to the non-storing blue tit (Parus caeruleus) and great tit (Parus major) within the avian family Paridae, as well as to the non-storing dark-eyed junco (Junco hyemalis). All four species showed a similar distribution of SP throughout the brain with the exception of two areas, the hippocampal complex (including hippocampus (Hp) and parahippocampus (APH)) and the Wulst (including the hyperstriatum accessorium (HA)). SP-like immunoreactivity was found in cells of the Hp in juncos, but not in the three parid species. Two areas within the APH and HA showed SP-like immunoreactivity in all four species. The more medial of these (designated SPm) is a distinctive field of fibers and terminals found throughout the APH and extending into the HA. A positive relationship between SPm and Hp volume was found for all four species with the chickadee having a significantly larger SPm area relative to telencephalon than the other species. The distribution of SP in this region may be related to differences in food-storing behavior. In contrast to substance P, NPY distribution throughout the brain was similar in all four species. Further, NPY-immunoreactive cells were found in the Hp of all four species and no species differences in the number of NPY cells was observed.