William Grisham

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.

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.

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.

Prenatal flutamide 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.

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.

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.

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

Abstract One model of the sexual differentiation of the zebra finch song system holds that both major metabolites of testosterone, dihydrotestosterone (DHT) and estradiol (E 2 ), act together to masculinize the song system. To test this model, we administered a putative inhibitor of 5 α -reductase (MK-434) to decrease the synthesis of DHT from testosterone (T) in hatchling zebra finches. We tested MK-434s inhibition of 5 α -reductase, 5 β -reductase, and aromatase in vivo and in vitro. In vivo, MK-434 significantly inhibited 5 α -reductase activity but also reduced the activities of 5 β -reductase and aromatase. In vitro, MK-434 was extremely effective in inhibiting 5 α -reductase in the rat prostate but only slightly inhibited 5 α -reductase in the zebra finch telencephalon, where it also reduced aromatase and 5 β -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 lMAN, HVC, and RA; and the number of neurons in HVC and lMAN. 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.

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 systems morphology. Co-administering flutamide, an androgen receptor blocker, with estrogen impedes estrogens 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.

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. Anat Rec, 2013.

Teaching Bioinformatics and Neuroinformatics by Using Free Web-based Tools

This completely computer-based modules purpose is to introduce students to bioinformatics resources. We present an easy-to-adopt module that weaves together several important bioinformatic tools so students can grasp how these tools are used in answering research questions. Students integrate information gathered from websites dealing with anatomy (Mouse Brain Library), quantitative trait locus analysis (WebQTL from GeneNetwork), bioinformatics and gene expression analyses (University of California, Santa Cruz Genome Browser, National Center for Biotechnology Informations Entrez Gene, and the Allen Brain Atlas), and information resources (PubMed). Instructors can use these various websites in concert to teach genetics from the phenotypic level to the molecular level, aspects of neuroanatomy and histology, statistics, quantitative trait locus analysis, and molecular biology (including in situ hybridization and microarray analysis), and to introduce bioinformatic resources. Students use these resources to discover 1) the region(s) of chromosome(s) influencing the phenotypic trait, 2) a list of candidate genes—narrowed by expression data, 3) the in situ pattern of a given gene in the region of interest, 4) the nucleotide sequence of the candidate gene, and 5) articles describing the gene. Teaching materials such as a detailed student/instructors manual, PowerPoints, sample exams, and links to free Web resources can be found at http://mdcune.psych.ucla.edu/modules/bioinformatics.