A "Four Core Genotypes" rat model to distinguish mechanisms underlying sex-biased phenotypes and diseases

Background

We have generated a rat model similar to the Four Core Genotypes mouse model, allowing comparison of XX and XY rats with the same type of gonad. The model detects novel sex chromosome effects (XX vs. XY) that contribute to sex differences in any rat phenotype.

Methods

XY rats were produced with an autosomal transgene of Sry , the testis-determining factor gene, which were fathers of XX and XY progeny with testes. In other rats, CRISPR-Cas9 technology was used to remove Y chromosome factors that initiate testis differentiation, producing fertile XY gonadal females that have XX and XY progeny with ovaries. These groups can be compared to detect sex differences caused by sex chromosome complement (XX vs. XY) and/or by gonadal hormones (rats with testes vs. ovaries).

Results

We have measured numerous phenotypes to characterize this model, including gonadal histology, breeding performance, anogenital distance, levels of reproductive hormones, body and organ weights, and central nervous system sexual dimorphisms. Serum testosterone levels were comparable in adult XX and XY gonadal males. Numerous phenotypes previously found to be sexually differentiated by the action of gonadal hormones were found to be similar in XX and XY rats with the same type of gonad, suggesting that XX and XY rats with the same type of gonad have comparable levels of gonadal hormones at various stages of development.

Conclusion

The results establish a powerful new model to discriminate sex chromosome and gonadal hormone effects that cause sexual differences in rat physiology and disease.

Teaching Neuroscience: Reviving Neuroanatomy, Notes on the 2022 Society for Neuroscience Professional Development Workshop on Teaching

Students often find neuroanatomy a daunting exercise of rote memorization in a dead language. This workshop was designed to enliven the teaching of neuroanatomy. We recast the topic by extending it to the cellular and sub-cellular levels, animating it by learning to build a brain, and infusing the topic with the lively arts. Due to COVID's interference with the usual schedule of Society for Neuroscience (SfN) events, the 2021 Professional Development Workshop on Teaching was held as a webinar on April 12, 2022 with a follow-up question and answer session on June 7. In this workshop, not only were innovative teaching methods presented, but also the very definition of neuroanatomy was pushed to the limits-even reaching into the molecular and subcellular level. The presenters provided means of engaging students that were no cost, low cost, or well within the reach of most academic institutions. Judging by the attendance, this webinar was quite successful in its goals. Our speakers presented exciting and varied approaches to teaching neuroanatomy. Kaitlyn Casimo presented how the vast resources of the Allen Institute could be employed. Marc Nahmani described how open data resources could be utilized in creating a Course-Based Undergraduate Research Experience (CURE) on neural microanatomy. Erika Fanselow presented novel ways to overcome one of students' big hurdles in grasping neuroanatomy: understanding 3-D relationships. Len White described a creative approach in teaching neuroanatomy by incorporating the humanities, particularly art and literature. This article presents synopses of the presentations, which are written by the four presenters. Additionally, prompted by questions from the viewers, we have constructed a table of our favorite resources. A video of the original presentations as well as links to the subsequent Q & A sessions is available at https://neuronline.sfn.org/training/teaching-neuroscience-reviving-neuroanatomy/.

PROJECT DiViNe: DIVERSE VOICES IN NEUROSCIENCE: Profiles of Rita Levi-Montalcini, Ricardo Miledi, Simon LeVay, Erich Jarvis, and Steve Ramirez

In this paper we share the first five of what we hope will be many profiles of neuroscientists from historically underrepresented or marginalized groups. This initial collection of profiles, meant to stake out the general territory for future offerings, takes as its subjects a fairly broad range of individuals from Nobel laureates to early career scientists and educators. The goal of this project is to facilitate the dissemination of materials neuroscience educators can use to highlight the scientific contributions and personal stories of scientists from historically marginalized groups, and has been developed more extensively in the Editorial that accompanies this collection (Frenzel and Harrington, 2021). We believe that by sharing these stories, and highlighting the diversity of those who have and will continue to contribute to the field of neuroscience, we can help to foster a more inclusive discipline for our undergraduate students. Each of these profiles is a testament to the respect these contributors hold for their subjects. We hope that others might see this new feature as an opportunity to share the admiration they have for those who have impacted them as colleagues, mentors, and role models.

FraidyRat: A Virtual Module Examining the Neural Circuitry Underlying Fear Conditioning

FraidyRat is a teaching tool that allows students to investigate the neural basis of fear conditioning and extinction using a virtual rat with a virtual brain. FraidyRat models well-known phenomena at both a behavioral and neural level. Students use virtual versions of tract tracing, systemic and intracerebrally infused drugs, neural recording, and electrical stimulation to understand the neural substrates underlying the observed behavior. This module helps students develop critical thinking skills in order to deduce immediate cause and effect as well as inductive reasoning to grasp the broader scheme. This module utilizes scaffolded instruction and formative assessment to shape the thinking of students as they unfold and discover the neural mechanisms responsible for fear conditioning and extinction in FraidyRat, which largely reflect what is found in real rats. Experience with this three-week module resulted in students showing significant gains in content knowledge as well as a trend toward gains in critical thinking. An attitudinal questionnaire showed that students had an overall positive experience. This module can be replicated at any institution with just a computer. All materials are available at: https://mdcune.psych.ucla.edu/modules/fraidy-rat.

Teaching Computation in Neuroscience: Notes on the 2019 Society for Neuroscience Professional Development Workshop on Teaching

The 2019 Society for Neuroscience Professional Development Workshop on Teaching reviewed current tools, approaches, and examples for teaching computation in neuroscience. Robert Kass described the statistical foundations that students need to properly analyze data. Pascal Wallisch compared MATLAB and Python as programming languages for teaching students. Adrienne Fairhall discussed computational methods, training opportunities, and curricular considerations. Walt Babiec provided a view from the trenches on practical aspects of teaching computational neuroscience. Mathew Abrams concluded the session with an overview of resources for teaching and learning computational modeling in neuroscience.

Brain Volume Fractions in Mammals in Relation to Behavior in Carnivores, Primates, Ungulates, and Rodents

The volume fraction (VF) of a given brain region, or the proper mass, ought to reflect the importance of that region in the life of a given species. This study sought to examine the VF of various brain regions across 61 different species of mammals to discern if there were regularities or differences among mammalian orders. We examined the brains of carnivores (n = 17), ungulates (n = 8), rodents (n = 7), primates (n = 11), and other mammals (n = 18) from the online collections at the National Museum of Health and Medicine. We measured and obtained the VF of several brain regions: the striatum, thalamus, neocortex, cerebellum, hippocampus, and piriform area. We refined our analyses by using phylogenetic size correction, yielding the corrected (c)VF. Our groups showed marked differences in gross brain architecture. Primates and carnivores were divergent in some measures, particularly the cVF of the striatum, even though their overall brain size range was roughly the same. Rodents predictably had relatively large cVFs of subcortical structures due to the fact that their neocortical cVF was smaller, particularly when compared to primates. Not so predictably, rodents had the largest cerebellar cVF, and there were marked discrepancies in cerebellar data across groups. Ungulates had a larger piriform area than primates, perhaps due to their olfactory processing abilities. We provide interpretations of our results in the light of the comparative behavioral and neuroanatomical literature.

Using Online Images to Teach Quantitative Skills via Comparative Neuroanatomy: Applying the Directives of Vision and Change

Vision and Change calls for increasing the quantitative skills of biology majors, which includes neuroscience majors. Accordingly, we have devised a module to give students practice at regression analyses, covariance, and ANOVA. This module consists of a quantitative comparative neuroanatomy lab in which students explore the size of the hippocampus relative to the brain in 62 different mammalian species-from an anteater to a zebu. We utilize a digital image library (with appropriate metadata) allowing students to quantify the size of the hippocampus as well as obtain an index of the size of the brain in these various species. Students then answer the following questions: (1) Do brains scale with body size? (2) Does the hippocampus scale with brain size? (3) If we control for body size, does the hippocampus still scale with brain size? (4) How does the hippocampus change as a proportion of brain size? (5) Is the proportional scaling of the hippocampus different among primates, carnivores, and other mammals? (6) Do the data provide evidence for mosaic or concerted evolution? Measures of the pedagogical efficacy showed clear and significant gains on a PreTest vs PostTest assessment of material related to the module. An open ended qualitative measure revealed students' perception of the purposes of the module, which were consistent with the learning goals. This module utilizes open access digital resources and can be performed at any institution. All the materials or links to online resources can be found at https://mdcune.psych.ucla.edu/modules/cna.

Teaching with Big Data: Report from the 2016 Society for Neuroscience Teaching Workshop

As part of a series of workshops on teaching neuroscience at the Society for Neuroscience annual meetings, William Grisham and Richard Olivo organized the 2016 workshop on "Teaching Neuroscience with Big Data." This article presents a summary of that workshop. Speakers provided overviews of open datasets that could be used in teaching undergraduate courses. These included resources that already appear in educational settings, including the Allen Brain Atlas (presented by Joshua Brumberg and Terri Gilbert), and the Mouse Brain Library and GeneNetwork (presented by Robert Williams). Other resources, such as NeuroData (presented by William R. Gray Roncal), and OpenFMRI, NeuroVault, and Neurosynth (presented by Russell Poldrack) have not been broadly utilized by the neuroscience education community but offer obvious potential. Finally, William Grisham discussed the iNeuro Project, an NSF-sponsored effort to develop the necessary curriculum for preparing students to handle Big Data. Linda Lanyon further elaborated on the current state and challenges in educating students to deal with Big Data and described some training resources provided by the International Neuroinformatics Coordinating Facility. Neuroinformatics is a subfield of neuroscience that deals with data utilizing analytical tools and computational models. The feasibility of offering neuroinformatics programs at primarily undergraduate institutions was also discussed.

Proposed Training to Meet Challenges of Large-Scale Data in Neuroscience

The scale of data being produced in neuroscience at present and in the future creates new and unheralded challenges, outstripping conventional ways of handling, considering, and analyzing data. As neuroinformatics enters into this big data era, a need for a highly trained and perhaps unique workforce is emerging. To determine the staffing needs created by the impending era of big data, a workshop (iNeuro Project) was convened November 13–14, 2014. Participants included data resource providers, bioinformatics/analytics trainers, computer scientists, library scientists, and neuroscience educators. These individuals provided perspectives on the challenges of big data, the preparation of a workforce to meet these challenges, and the present state of training programs. Participants discussed whether suitable training programs will need to be constructed from scratch or if existing programs can serve as models. Currently, most programs at the undergraduate and graduate levels are located in Europe—participants knew of none in the United States. The skill sets that training programs would need to provide as well as the curriculum necessary to teach them were also discussed. Consistent with Vision and Change in Undergraduate Biology Education: A Call to Action¹, proposed curricula included authentic, hands-on research experiences. Further discussions revolved around the logistics and barriers to creating such programs. The full white paper, iNeuro Project Workshop Report, is available from iNeuro Project².

Undergraduate Neuroscience Education in the U.S.: Quantitative Comparisons of Programs and Graduates in the Broader Context of Undergraduate Life Sciences Education

The impact of undergraduate neuroscience programs on the broader landscape of life sciences education has not been described. Using data from the National Center for Education Statistics, we found that the number of undergraduate neuroscience programs in the U.S. continues to grow. Within any given institution, neuroscience programs exist alongside a small number of other life sciences undergraduate programs, suggesting that neuroscience is one of few major options from which students can choose from at many institutions. Neuroscience majors constitute a substantial proportion of all life sciences graduates at many institutions, and in several cases, neuroscience majors were the majority of life sciences graduates. Thus, neuroscience programs contribute substantially to life sciences education, and neuroscience is a highly attractive major among undergraduate students where these programs are available. These data have implications for institutions with existing neuroscience programs as well as for institutions seeking to establish a new program.

An Instructor's Guide to (Some of) the Most Amazing Papers in Neuroscience

Although textbooks are still assigned in many undergraduate science courses, it is now not uncommon, even in some of the earliest courses in the curriculum, to supplement texts with primary source readings from the scientific literature. Not only does reading these articles help students develop an understanding of specific course content, it also helps foster an ability to engage with the discipline the way its practitioners do. One challenge with this approach, however, is that it can be difficult for instructors to select appropriate readings on topics outside of their areas of expertise as would be required in a survey course, for example. Here we present a subset of the papers that were offered in response to a request for the "most amazing papers in neuroscience" that appeared on the listserv of the Faculty for Undergraduate Neuroscience (FUN). Each contributor was subsequently asked to describe briefly the content of their recommended papers, their pedagogical value, and the audiences for which these papers are best suited. Our goal is to provide readers with sufficient information to decide whether such articles might be useful in their own classes. It is not our intention that any article within this collection will provide the final word on an area of investigation, nor that this collection will provide the final word for the discipline as a whole. Rather, this article is a collection of papers that have proven themselves valuable in the hands of these particular educators. Indeed, it is our hope that this collection represents the inaugural offering of what will become a regular feature in this journal, so that we can continue to benefit from the diverse expertise of the FUN community.

Gel Scramble: An E-Tool for Teaching Molecular Neuroscience

In this completely digital teaching module, students interpret the results of two separate procedures: a restriction endonuclease digestion, and a polymerase chain reaction (PCR). The first consists of matching restriction endonuclease digest protocols with images obtained from stained agarose gels. Students are given the sequence of six plasmid cDNAs, characteristics of the plasmid vector, and the endonuclease digest protocols, which specify the enzyme(s) used. Students calculate the expected lengths of digestion products using this information and free tools available on the web. Students learn how to read gels and then match their predicted fragment lengths to the digital images obtained from the gel electrophoresis of the cDNA digest. In the PCR experiment, students are given six cDNA sequences and six sets of primers. By querying NCBI BLAST, students can match the PCR fragments to the lengths of the predicted in silico PCR products. The ruse posed to students is that the gels were inadvertently mislabeled during processing. Although students know the experimental details, they do not know which gel goes with a given restriction endonuclease digest or PCR-they must deduce the answers. Because the gel images are from actual students' experiments, the data sometimes result from mishandling/mislabeling or faulty protocol execution. The most challenging part of the exercise is to explain these errors. This latter aspect requires students to use critical thinking skills to explain aberrant outcomes. This entire exercise is available in a digital format and downloadable for free at http://mdcune.psych.ucla.edu/modules/gel.

Quantitative examination of the bottlenose dolphin cerebellum

Neuroanatomical research into the brain of the bottlenose dolphin (Tursiops truncatus) has revealed striking similarities with the human brain in terms of size and complexity. However, the dolphin brain also contains unique allometric relationships. When compared to the human brain, the dolphin cerebellum is noticeably larger. Upon closer examination, the lobule composition of the cerebellum is distinct between the two species. In this study, we used magnetic resonance imaging to analyze cerebellar anatomy in the bottlenose dolphin and measure the volume of the separate cerebellar lobules in the bottlenose dolphin and human. Lobule identification was assisted by three-dimensional modeling. We find that lobules VI, VIIb, VIII, and IX are the largest lobules of the bottlenose dolphin cerebellum, while the anterior lobe (I-V), crus I, crus II, and the flocculonodular lobe are smaller. Different lobule sizes may have functional implications. Auditory-associated lobules VIIb, VIII, IX are likely large in the bottlenose dolphin due to echolocation abilities. Our study provides quantitative information on cerebellar anatomy that substantiates previous reports based on gross observation and subjective analysis. This study is part of a continuing effort toward providing explicit descriptions of cetacean neuroanatomy to support the interpretation of behavioral studies on cetacean cognition.

Teaching neuroinformatics with an emphasis on quantitative locus analysis

Although powerful bioinformatics tools are available for free on the web and are used by neuroscience professionals on a daily basis, neuroscience students are largely ignorant of them. This Neuroinformatics module weaves together several bioinformatics tools to make a comprehensive unit. This unit encompasses quantifying a phenotype through a Quantitative Trait Locus (QTL) analysis, which links phenotype to loci on chromosomes that likely had an impact on the phenotype. Students then are able to sift through a list of genes in the region(s) of the chromosome identified by the QTL analysis and find a candidate gene that has relatively high expression in the brain region of interest. Once such a candidate gene is identified, students can find out more information about the gene, including the cells/layers in which it is expressed, the sequence of the gene, and an article about the gene. All of the resources employed are available at no cost via the internet. Didactic elements of this instructional module include genetics, neuroanatomy, Quantitative Trait Locus analysis, molecular techniques in neuroscience, and statistics-including multiple regression, ANOVA, and a bootstrap technique. This module was presented at the Faculty for Undergraduate Neuroscience (FUN) 2011 Workshop at Pomona College and can be accessed at http://mdcune.psych.ucla.edu/modules/bioinformatics.

Using digital images of the zebra finch song system as a tool to teach organizational effects of steroid hormones: a free downloadable module

Zebra finch song behavior is sexually dimorphic: males sing and females do not. The neural system underlying this behavior is sexually dimorphic, and this sex difference is easy to quantify. During development, the zebra finch song system can be altered by steroid hormones, specifically estradiol, which actually masculinizes it. Because of the ease of quantification and experimental manipulation, the zebra finch song system has great potential for use in undergraduate labs. Unfortunately, the underlying costs prohibit use of this system in undergraduate labs. Further, the time required to perform a developmental study renders such undertakings unrealistic within a single academic term. We have overcome these barriers by creating digital tools, including an image library of song nuclei from zebra finch brains. Students using this library replicate and extend a published experiment examining the dose of estradiol required to masculinize the female zebra finch brain. We have used this library for several terms, and students not only obtain significant experimental results but also make gains in understanding content, experimental controls, and inferential statistics (analysis of variance and post hoc tests). We have provided free access to these digital tools at the following website: http://mdcune.psych.ucla.edu/modules/birdsong.

Call for JUNE Editorial Board Members and Reviewers

JUNE’s Editorial Board plans to expand the offerings and visibility of the journal by publishing more frequently and getting its content indexed on services such as PUBMED and ERIC. Because JUNE is produced by a team of volunteer editors and reviewers, additional volunteers are needed to help plan, structure, and achieve these goals. We are hereby inviting individuals to apply to become a JUNE Editorial Board member and/or reviewer. If you or a colleague you can recommend are interesting in lending your strengths in planning, leadership, communication and/or editorial skills, we need you to help improve and advance JUNE. Please send a letter of interest or nomination and CV to Bill Grisham, Associate Editor (grisham@lifesci.ucla.edu).

The journal of undergraduate neuroscience education: history, challenges, and future developments

The 'JUNE and You' sessions presented at the July 2008 Undergraduate Neuroscience Education workshop, sponsored jointly by Faculty for Undergraduate Neuroscience (FUN) and Project Kaleidoscope (PKAL), featured background information about the history and mission of the Journal of Undergraduate Neuroscience Education (JUNE), followed by an informative discussion about the challenges facing JUNE, including new ideas for future developments. This article will highlight some of the information and ideas generated and shared at this conference. Critical discussion points included the need to keep members of FUN actively engaged in submitting and reviewing articles for JUNE. Ways in which authors, reviewers, and interested faculty members could best help in promoting the mission and vision of JUNE were discussed. Concerns about recent hackings into the JUNE website were also raised, and possible solutions and measures that can be taken to minimize this in the future were discussed. In addition, ideas for expanding the role of JUNE to provide a forum to evaluate new and emerging website information that is pertinent to undergraduate neuroscience education was discussed. Ideas for future developments of JUNE included revolving postings of articles as they are accepted, providing links to several related websites, and allowing updates for articles that have been previously published in JUNE. Finally, ideas for maintaining and expanding JUNE's stature as the resource for undergraduate neuroscience education included ensuring that JUNE is listed on important search vehicles, such as PubMed.

Modular Digital Course in Undergraduate Neuroscience Education (MDCUNE): A Website Offering Free Digital Tools for Neuroscience Educators

We are providing free digital resources for teaching neuroscience labs at http://mdcune.psych.ucla.edu/. These resources will ultimately include materials for teaching laboratories in electrophysiology of neuronal circuits (SWIMMY), a Neuroinformatics/Bioinformatics module, and two modules for investigating the effects of hormones on early CNS development-one focusing on the development of the song system and one focusing on sex differences in spinal cord motor neurons. All of these modules are inquiry based-students gain from genuine experiences in doing actual studies rather than just simulations. These materials should provide instructors the ability to provide good quality laboratory experiences regardless of resource limitations. Currently, modules on sex differences in the spinal cord and virtual neural circuits (SWIMMY) are available on our website. More will be available in summer 2009 and 2010. SWIMMY was demonstrated at the Faculty for Undergraduate Neuroscience (FUN) Workshop-The Undergraduate Neuroscience Education: Interactions, interdisciplines, and curricular best practices at Macalester College in July 2008.

X chromosome number causes sex differences in gene expression in adult mouse striatum

Previous research suggests that sex differences in the nigrostriatal system are created by direct effects of the sex chromosomes (XX vs. XY), independent of the action of gonadal hormones. Here we tested for sex chromosome effects on expression of three mRNAs in the striatum and nucleus accumbens of adult mice of the four core genotypes model (XX and XY gonadal males, XX and XY gonadal females). Mice were gonadectomized (GDX) at 47-51 days old to eliminate group differences in the levels of gonadal steroids. Three weeks later, mice were killed and brains collected for in situ hybridization of the striatum, or the striatum was dissected out for quantitative reverse transcriptase-polymerase chain reaction (RT-PCR). Expression in XX and XY mice was measured by in situ hybridization using riboprobes encoding the dynorphin precursor Pdyn (prodynorphin), the substance P precursor Tac1 (preprotachykinin) or dopamine D2 receptor. XX mice had higher expression, relative to XY mice of the same gonadal sex, of Pdyn and Tac1 mRNA in specific striatal regions. Quantitative PCR confirmed that GDX XX mice have higher Pdyn expression in striatum than XY mice, regardless of their gonadal sex. XX had higher Pdyn expression than XY or XO mice, indicating that the sex chromosome effect is the result of XX vs. XY differences in the number of X chromosomes, probably because of sex differences in the expression of X gene(s) that escape inactivation. We detected no sex chromosome effect on D2 receptor mRNA.

A dose-response study of estradiol's effects on the developing zebra finch song system

To gauge the sensitivity of the female zebra finch song system to estradiol (E2), we used subcutaneous implants to administer various doses of E2 to hatchling female zebra finches. Four different doses of E2 were administered: 50, 15, 5 and 0-microg via subcutaneous silicon "ropes" at hatching, and the brains were examined in adulthood. Further, we examined whether masculinization was all-or-none once a threshold was reached or if the morphology of the song system would show a graded response to the various doses of E2. Finally, we asked if the various dependent measures - volume of song nuclei, neuron size, and neuron number - would show differential sensitivity to E2. Fifteen micrograms was sufficient to masculinize many aspects of the song system and was often as effective as 50-microg, causing a dramatic difference relative to the 0-microg group. Different aspects of the song system seemed differentially sensitive to the effects of E2: volumes of song control nuclei, the size of RA neurons, and the number of HVC neurons were significantly masculinized by 15-microg E2, but the number of RA neurons and HVC and lMAN soma sizes required 50-microg. The results suggest that several developmental processes are influenced by E2, possibly because of multiple sites of action or multiple processes that respond to E2.

IFEL TOUR: A Description of the Introduction to FUN Electrophysiology Labs Workshop at Bowdoin College, July 27-30, and the Resultant Faculty Learning Community

The workshop "Introduction to FUN Electrophysiology Labs" was organized by Patsy Dickinson (Bowdoin College), Steve Hauptman (Bowdoin College), Bruce Johnson (Cornell University), and Carol Ann Paul (Wellesley College). It took place July 27-30 2006 at Bowdoin College. There were fifteen participants, most of whom were junior faculty at college and universities around the country. This article describes the workshop content, the incorporation of lab exercises at home institutions, and the faculty learning community that has resulted from the workshop.

Effects of long-term flutamide treatment during development in zebra finches

The molecular mechanisms responsible for the sexual differentiation of the zebra finch song system remain mysterious. Androgen receptors are expressed in a sexually dimorphic fashion in the zebra finch song system: males have more cells expressing androgen receptors, and this sex difference appears very early in development (day 9 posthatch). Estrogen administration to hatchling females up-regulates androgen receptor expression in their song system and profoundly masculinizes their song system's morphology. Co-administering flutamide, an androgen receptor blocker, with estrogen impedes estrogen's masculinizing effects on the song system, suggesting that androgens are required for masculine development. Accordingly, to investigate further the role of androgens in the sexual differentiation of the zebra finch song system, we sought to block androgen activity in males by administering large, sustained doses of flutamide from just before androgen receptors are expressed in the song system (day 7) through to the day of sacrifice (days 61-63). Flutamide profoundly reduced the size of the testes, demonstrating that this drug and mode of administration could have a large impact on tissues. In contrast, flutamide had only a minor impact on the song system: the number of RA neurons was slightly reduced, and the corrected HVC volume showed a trend toward demasculinization. Other brain measures (uncorrected HVC, and corrected and uncorrected volumes of Area X, lMAN, RA, and Rotundus; neuron size in lMAN, HVC, and RA; and number of HVC and LMAN neurons) were not significantly affected. The present results do not support an important role for androgen in masculinizing the song circuit after posthatch day 7.

Minireview: Sex chromosomes and brain sexual differentiation

The brains of males and females differ, not only in regions specialized for reproduction, but also in other regions (controlling cognition, for example) where sex differences are not necessarily expected. Moreover, males and females are differentially susceptible to neurological and psychiatric disease. What are the origins of these sex differences? Two major sources of sexually dimorphic information could lead to sex differences in brain function. Male and female brain cells carry a different complement of sex chromosome genes and are influenced throughout life by a different mix of gonadal hormones. Until recently all sex differences in the brain have been attributed to the differential action of gonadal hormones. Recent findings, however, suggest that brain cells that differ in their genetic sex are not equivalent, and that difference may contribute to sex differences in brain function. Here we discuss evidence for sex chromosome effects on both neural and nonneural systems, which together provide support for the idea that XX and XY cells differentiate even before they are influenced by gonadal hormones, and even if they are exposed to similar levels of gonadal steroids. Fortunately, new model systems for studying sex chromosome effects have recently been developed, and they should help in testing further the role of sex chromosome genes.

Sex differences and organizational effects of androgen in spinal cord motor nuclei

This article describes a laboratory module taught at UCLA and offers digitized microscope images that will allow instructors to recreate this module at their home institutions with only a computer required. This module allows for 1) an exploration of the effects of hormones on neural development, 2) the demonstration of sex differences in the nervous system, 3) the production of robust and statistically significant data by novice undergraduates, 4) the discussion of sophisticated statistical analyses (ANOVAs with significant main effects and an interaction), and 5) the understanding of at least some of the neuroanatomy of the spinal cord. Specifically, this module both replicates and extends a previously published experiment on sexually dimorphic neurons in the spinal cord of rats (Grisham et al., 1992), which examined the effect of antiandrogen exposure (Flutamide) in utero on sexually dimorphic spinal motoneurons in male and female rats.

Neural, not gonadal, origin of brain sex differences in a gynandromorphic finch

In mammals and birds, sex differences in brain function and disease are thought to derive exclusively from sex differences in gonadal hormone secretions. For example, testosterone in male mammals acts during fetal and neonatal life to cause masculine neural development. However, male and female brain cells also differ in genetic sex; thus, sex chromosome genes acting within cells could contribute to sex differences in cell function. We analyzed the sexual phenotype of the brain of a rare gynandromorphic finch in which the right half of the brain was genetically male and the left half genetically female. The neural song circuit on the right had a more masculine phenotype than that on the left. Because both halves of the brain were exposed to a common gonadal hormone environment, the lateral differences indicate that the genetic sex of brain cells contributes to the process of sexual differentiation. Because both sides of the song circuit were more masculine than that of females, diffusible factors such as hormones of gonadal or neural origin also likely played a role in sexual differentiation.

Antiandrogen blocks estrogen-induced masculinization of the song system in female zebra finches

Song behavior and the neural song system that serves it are sexually dimorphic in zebra finches. In this species, males sing and females normally do not. The sex differences in the song system include sex differences in the proportion of neurons that express androgen receptors, which is higher in specific brain regions of males. Estradiol (E2) administered in early development profoundly masculinizes the song system of females, including the proportion of neurons expressing androgen receptors. We examined whether or not the expression of these androgen receptors was causally related to the E2-induced masculinization of this system by co-administering Flutamide, which blocks androgen action at the receptor, along with E2 at hatching. E2 alone had its usual masculinizing effect on the female song system, measured in adulthood: increasing the size of song nuclei, the size of neurons in HVC, RA, and 1MAN, and the number of neurons in HVC. E2's masculinizing action, however, was significantly diminished on all measures by co-administering Flutamide. Indeed, females receiving both E2 and Flutamide were never significantly more masculine than controls on any measure. Flutamide alone had no effect. Our results strongly suggest that the activation of androgen receptors is necessary for the E2-induced masculinization of the song system in females.

Androgen synthesis in a songbird: a study of cyp17 (17alpha-hydroxylase/C17,20-lyase) activity in the zebra finch

Androgens and estrogens influence the maturation and function of numerous tissues in both male and female birds, especially the brains of the oscine songbirds. Although there exist a very large number of studies that have investigated circulating sex steroids in many species of wild and captive-held songbirds, there remain a significant number of questions about the sites of synthesis of the active steroids that act on the songbird brain. Estrogens are derived from androgen. Thus, the synthesis of androgen itself is critical for both androgen- and estrogen-dependent actions in both male and female songbirds. Therefore, we have undertaken studies of the enzyme 17alpha-hydroxylase/C17,20-lyase (Cyp17), the enzyme responsible for the synthesis of androgens from their progestin or pregnane precursors via their 17alpha-hydroxy intermediates. Here we have characterized optimal conditions for measuring Cyp17 in gonads of adult zebra finches via the conversion of tritiated [3H]progesterone into 17alpha-hydroxy P (17alpha-hydroxylase activity) and androstenedione and testosterone (C17,20-lyase) activity. Cyp17 activity is abundant in testis, with lesser amounts in ovary. Low levels of Cyp17 activity were also detected in male adrenals, but not in any other tissue, including brain. Testicular Cyp17 activity is readily inhibited in vitro by ketoconazole, a specific Cyp17 inhibitor. Ketoconazole works less well in vivo. In males castrated and/or treated with fadrozole, an inhibitor of aromatase, we detected no extragonadal sites of Cyp17 activity, although fadrozole appeared to increase circulating androgens in both castrated and intact males. Thus, we still do not know the site of androgen synthesis in these males. Further studies of Cyp17 will be useful in understanding more about the mechanisms of androgen delivery to neural circuits in adult and developing songbirds.

A putative 5 alpha-reductase inhibitor demasculinizes portions of the zebra finch song system

One model of the sexual differentiation of the zebra finch song system holds that both major metabolites of testosterone, dihydrotestosterone (DHT) and estradiol (E2), act together to masculinize the song system. To test this model, we administered a putative inhibitor of 5 alpha-reductase (MK-434) to decrease the synthesis of DHT from testosterone (T) in hatchling zebra finches. We tested MK-434's inhibition of 5 alpha-reductase, 5 beta-reductase, and aromatase in vivo and in vitro. In vivo, MK-434 significantly inhibited 5 alpha-reductase activity but also reduced the activities of 5 beta-reductase and aromatase. In vitro, MK-434 was extremely effective in inhibiting 5 alpha-reductase in the rat prostate but only slightly inhibited 5 alpha-reductase in the zebra finch telencephalon, where it also reduced aromatase and 5 beta-reductase activities. These results suggest that MK-434 might differentially influence the availability of androgenic and estrogenic substrates, depending on the relative abundance of these enzymes in brain. MK-434 demasculinized (decreased) the number and decreased the density of RA neurons but did not significantly affect any other sexually dimorphic aspect of the song system, including the volumes of RA, HVC, and Area X; the size of neural somata in IMAN, HVC, and RA; and the number of neurons in HVC and IMAN. The differential influence of MK-434 on sexually dimorphic characteristics suggests that the various sexually dimorphic characteristics of the song system (1) are sensitive to different hormones, depending on the characteristic; or (2) have different sensitivities to hormone levels, some being easily affected by slightly reduced hormone levels whereas others are not; or (3) have markedly different critical periods depending on the characteristic. Regardless of the reason(s) for differential effects on the sexually dimorphic characteristics of the song system, the data clearly suggest that steroid hormones play a role in the normal masculine development of the song system.

Sexual differentiation of the brain in songbirds

The brain regions that control song in zebra finches are much larger in males, who sing, than in females, who do not. Two major theories have been proposed to explain sexual differentiation of the neural song circuit. The 'mammalian' theory suggests that sex steroid secretions of the tests cause masculine development in males. The 'avian' theory suggests that ovarian secretions induce feminine patterns of development in females. Although experimental evidence provides some support for the mammalian theory, neither theory comfortably predicts the outcomes of experiments that bear on the mechanisms of sexual differentiation. In particular, it has been relatively difficult to block sex steroid synthesis and action in genetic males in a way that prevents masculine neural differentiation. Moreover, genetic females that possess large amounts of testicular tissue can have a feminine neural song circuit, suggesting that testicular secretions are not solely responsible for the masculine patterns of differentiation. The results indicate that new theories are needed to explain sexual differentiation of the song system.

Lack of a synergistic effect between estradiol and dihydrotestosterone in the masculinization of the zebra finch song system

Previous studies have suggested that both major active metabolites of testosterone, estradiol (E2) and dihydrotestosterone (DHT), are needed for complete masculinization of the brain regions that control song in passerine birds. However, DHT treatment of hatchling female zebra finches has only small masculinizing effects on the song system. To assess whether E2 and DHT have a synergistic effect on the masculinization of the zebra finch song system, female zebra finches were given Silastic implants of E2 on the day of hatching (day 1) either without any additional hormone treatment or in combination with DHT on days 1, 14, or 70. At 105 to 110 days of age, we measured the volumes of Area X, higher vocal center (HVC), robust nucleus of the archistriatum (RA), soma sizes in HVC, RA, and the lateral magnocellular nucleus of the neostriatum (IMAN), and neuron density and number in RA. E2 masculinized all of the measures in the song system with the exception of the number of neurons in RA. DHT did not synergize with E2 to produce any additional masculinization of the attributes measured. These data demonstrate that the combination of E2 and DHT did not result in the complete masculinization of the song control nuclei and argue against the importance of androgen in sexual differentiation of the song system.

A direct comparison of the masculinizing effects of testosterone, androstenedione, estrogen, and progesterone on the development of the zebra finch song system

To assess which hormones are capable of masculinizing the neural song system of zebra finch hatchlings, we implanted female hatchlings with estrogen (estradiol [E2], 75 micrograms, n = 9), testosterone (T, 75-88 micrograms, n = 13), androstenedione (AE, 75 micrograms, n = 7), progesterone (P, 117 micrograms, n = 10), or nothing (Blanks, n = 10) and compared these to unimplanted males (n = 7). Implants, consisting of a hormone and Silastic mixture encased in polyethylene tubing, were placed under the skin of the breast on the day of hatching. Birds were killed when they were sub-adult (58 to 68 days old). We measured volumes of area X, the higher vocal center (HVC), and the robust nucleus of the archistriatum (RA); measured soma sizes in the lateral magnocellular nucleus of the neostriatum (lMAN), HVC, and RA; and counted RA neurons. E2 masculinized all measures in the song system and nearly sex-reversed the size of RA neurons. T masculinized volumes of nuclei and soma sizes but not the number or spacing of RA neurons. E2 was always at least as effective as T in masculinizing measures of the song system and was usually more effective. AE and P did not significantly masculinize any measure. These data suggest that E2 is more potent than aromatizable androgens or P in masculinizing the female song system in development and that the action of E2 alone may be sufficient to masculinize the volume of song control nuclei and the size and number of neurons.

Distribution of GABA-like immunoreactivity in the song system of the zebra finch

GABA-like immunoreactivity (GABA-LIR) was mapped in the male and female zebra finch song system using a polyclonal antibody to GABA. GABA-LIR was found throughout the song system in neurons and neuropil of the robust nucleus of the archistriatum (RA), the higher vocal center (HVC), Area X, the magnocellular nucleus of the neostriatum (MAN), and the dorsomedial portion of the nucleus intercollicularis (DM of ICo). Puncta present in the lateral division of MAN (lMAN) may be local interneurons since the only known afferents of lMAN are from the dorsolateral nucleus of the anterior thalamus (DLM), which did not appear to have any cell bodies with GABA-LIR. Distinct and dense puncta with GABA-LIR were present in DLM, and may be projections from Area X/lobus parolfactorius (LPO). Dramatic sex differences in GABA-LIR distribution were found. Females did not appear to have any GABA-LIR above background in either RA or HVC. Females also did not appear to have a distinct Area X, although they did have many small, lightly staining cell bodies in the corresponding LPO. The distribution of GABA-LIR and sex differences in its distribution suggests that GABAergic neurons may play a role in the acquisition and/or production of song in the zebra finch.

Local intracerebral implants of estrogen masculinize some aspects of the zebra finch song system

The song system of zebra finches is sexually dimorphic: the volumes of the song control nuclei and the neurons within these nuclei are larger in males. The song system of hatchling female zebra finches is masculinized by systemic treatment with estrogen. We investigated the locus of this estrogen action by using microimplants of estradiol benzoate (EB). We implanted female zebra finch nestlings 10-13 days old with Silastic pellets containing approximately 2 micrograms EB at one of several sites: near the higher vocal center (HVC), in the brain distant from HVC, or in the periphery either under the skin of the breast or in the peritoneal cavity. Controls were either unimplanted or implanted near HVC with Silastic pellets without hormone. The brains were fixed by perfusion at 60 days, and the volumes of the song control regions as well as the sizes of individual neurons were measured. Neurons in HVC were larger (more masculine) in the HVC-implanted group than in the other groups, which did not differ among themselves. The size of neurons in the robust nucleus of the archistriatum (RA) and the lateral magnocellular nucleus of the neostriatum (lMAN) were inversely correlated with the distance of the EB pellet to HVC; neurons in RA and lMAN were larger when the EB pellets were closer to HVC. This result suggests that implants near HVC were at or near a site of estrogen action. To our knowledge, this is the first demonstration that localized brain implants of estrogen cause morphological masculinization in any species.

Prenatal beta-endorphin can modulate some aspects of sexual differentiation in rats

Sexually dimorphic traits were studied in offspring of rats injected with 33 micrograms rat beta-endorphin (beta-END) three times daily from Day 14 to Day 21 of pregnancy. beta-END males had shorter neonatal anogenital distances than did controls and were more likely to show the female lordosis pattern as adults, but they did not differ in male copulatory behavior. When given a choice between spending time with an estrous female or a male, beta-END males showed a lower preference for the female than did control males. The number and somal size of neurons in the bulbocavernosus and dorsolateral nucleus of the lumbar spinal cord were unaffected by drug exposure. Elevated beta-END during fetal ontogeny apparently alters the differentiation of some, but not all, sexually dimorphic traits. The data suggest that endogenous opioids may contribute to the etiology of the prenatal stress syndrome.

Prenatal flutamide alters sexually dimorphic nuclei in the spinal cord of male rats

The effects of prenatal exposure to the antiandrogen flutamide on two sexually dimorphic nuclei of the lumbar spinal cord, the dorsolateral nucleus (DLN) and the spinal nucleus of the bulbocavernosus (SNB), were investigated. Rat dams were given daily injections of 5 mg flutamide or vehicle alone from day 11 through 21 of pregnancy. The spinal cords and perineal morphology of their male and female offspring were examined in adulthood. Flutamide reduced the number of SNB and DLN neurons, reduced the somal and nuclear area of SNB neurons, and reduced the weight of the perineal muscles in males. Flutamide produced no effect in females. No sexual dimorphism was found in the mean somal area of DLN neurons, but a sexual dimorphism was found in the distribution of somal areas in our samples; females had proportionately more large neurons than males. Flutamide-treated males also had proportionately more large neurons than control males but fewer than females. A sexual dimorphism was found in the nuclear areas of DLN neurons but flutamide did not influence this trait.

Prenatal !b-endorphin can modulate some aspects of sexual differentiation in rats

Sexually dimorphic traits were studied in offspring of rats injected with 33 micrograms rat beta-endorphin (beta-END) three times daily from Day 14 to Day 21 of pregnancy. beta-END males had shorter neonatal anogenital distances than did controls and were more likely to show the female lordosis pattern as adults, but they did not differ in male copulatory behavior. When given a choice between spending time with an estrous female or a male, beta-END males showed a lower preference for the female than did control males. The number and somal size of neurons in the bulbocavernosus and dorsolateral nucleus of the lumbar spinal cord were unaffected by drug exposure. Elevated beta-END during fetal ontogeny apparently alters the differentiation of some, but not all, sexually dimorphic traits. The data suggest that endogenous opioids may contribute to the etiology of the prenatal stress syndrome.

Prenatal stress alters sexually dimorphic nuclei in the spinal cord of male rats

The spinal nucleus bulbocavernosus (SNB), the dorsolateral nucleus of the spinal cord (DLN), and the bulbocavernosus/levator ani (BC/LA) muscle complex were examined in prenatally stressed and control adult male rats, which had been screened for male copulatory behavior. There was a small but significant decrease in the number of DLN (5%) and SNB (3%) neurons in prenatally stressed males compared to controls. Prenatal stress had no effect on the somal or nuclear area of individual neurons within either nucleus, nor did it affect the weight of the BC/LA muscle complex. There were no differences in any of these measures between males that ejaculated and those did not in either the stressed or the control group. These data suggest that exposure of pregnant rats to transient environmental stressors may result in permanent alterations in androgen-sensitive CNS structures in their male offspring.

Effects of dorsal and medial cortex lesions on reversals in turtles

Two experiments were performed to investigate the effect of cortical lesions on the acquisition and reversal of simultaneous discriminations in turtles. The first experiment examined the effect of cortical lesions on the acquisition and reversal of a spatial discrimination. The results of the first experiment revealed that lesions of the dorsal cortex produced a deficit in spatial learning. The results of the first experiment also revealed that when damage to the dorsal cortex was accompanied by substantial damage to the medial cortex, no deficit was manifest. The second experiment examined the effects of cortical lesions on the acquisition and reversal of a brightness discrimination. The results of the second experiment revealed that damage to neither the dorsal cortex nor the medial cortex produced a deficit. It was suggested that brightness is not represented in the thalamofugal visual pathway but is instead represented in the tectofugal visual pathway in reptiles. It was also suggested that the medial cortex, which is the evolutionary precursor to the mammalian hippocampal formation, functions differently from the mammalian hippocampus.

Function of the dorsal and medial cortex of turtles in learning

The effects of damage to the dorsal and medial cortex of turtles were investigated in two experiments. In the first, damage to the dorsal cortex disrupted acquisition and reversal of a go-no-go discrimination but had no effect on retention of the discrimination if it had been learned preoperatively. Medial cortex damage had no effect. In the second experiment, dorsal cortex damage impaired acquisition, but not extinction or reacquisition, of a discrete-trial keypress. Again, medial cortex damage had no effect. The results suggest that the dorsal cortex is involved in learning in turtles.

Function of the dorsal and medial cortex of turtles in learning

The effects of damage to the dorsal and medial cortex of turtles were investigated in two experiments. In the first, damage to the dorsal cortex disrupted acquisition and reversal of a go-no-go discrimination but had no effect on retention of the discrimination if it had been learned preoperatively. Medial cortex damage had no effect. In the second experiment, dorsal cortex damage impaired acquisition, but not extinction or reacquisition, of a discrete-trial keypress. Again, medial cortex damage had no effect. The results suggest that the dorsal cortex is involved in learning in turtles.