Katharine V. Northcutt

Social contact elicits immediate-early gene expression in dopaminergic cells of the male prairie vole extended olfactory amygdala

Male prairie voles (Microtus ochrogaster) are a valuable model in which to study the neurobiology of sociality because, unlike most mammals, they pair bond after mating and display paternal behaviors. Research on the regulation of these social behaviors has highlighted dopamine (DA) neurotransmission in both pair bonding and parenting. We recently described large numbers of dopaminergic cells in the male prairie vole principal nucleus of the bed nucleus of the stria terminalis (pBST) and posterodorsal medial amygdala (MeApd), but such cells were very few in number or absent in the non-monogamous species we examined, including meadow voles. This suggests that DA cells in these sites may be important for sociosexual behaviors in male prairie voles. To gain some insight into the function of these DAergic neurons in male prairie voles, we examined expression of the immediate-early genes (IEGs) Fos and Egr-1 in tyrosine hydroxylase (TH)-immunoreactive (TH-ir) cells of the pBST and MeApd after males interacted or not with one of several social stimuli. We found that IEGs were constitutively expressed in some TH-ir neurons under any social condition, but that IEG expression in these cells decreased after a 3.5-h social isolation. Thirty-minute mating bouts (but not 6- or 24-h bouts) that included ejaculation elicited greater IEG expression in TH-ir cells than did non-ejaculatory mating, interactions with a familiar female sibling, or interactions with pups. Furthermore, Fos expression in TH-ir cells was positively correlated with the display of copulatory, but not parental, behaviors. These effects of mating were not found in other DA-rich sites of the forebrain (including the anteroventral periventricular preoptic area, periventricular anterior hypothalamus, zona incerta, and arcuate nucleus). Thus, activity in DAergic cells of the male prairie vole pBST and MeApd is influenced by their social environment, and may be particularly involved in mating and its consequences, including pair bonding.

Sex and species differences in tyrosine hydroxylase-synthesizing cells of the rodent olfactory extended amygdala

The bed nucleus of the stria terminalis (BST) and the medial amygdala (MeA) are anatomically connected sites necessary for chemosensory regulation of social behaviors in rodents. Prairie voles (Microtus ochrogaster) are a valuable model for studying the neural regulation of social behaviors because, unlike many other rodents, they are gregarious, pair bond after copulating, and are biparental. We herein describe sex and species differences in immunoreactivity for tyrosine hydroxylase (TH), the rate‐limiting enzyme for catecholamine synthesis, in the BST and MeA. Virgin male prairie voles had a large number of TH‐immunoreactive cells in areas analogous to the rat principal nucleus of the BST (pBST) and the posterodorsal medial amygdala (MeAPd). Virgin female prairie voles had far fewer TH‐immunoreactive cells in these sites (∼17% of the number of cells as males in the pBST, ∼35% of the number of cells in the MeAPd). A few TH‐immunoreactive cells were found in the BST of male and female hamsters and meadow voles, but not in rats. The MeApd also contained a few TH‐immunoreactive cells in male and female hamsters and male meadow voles, but not rats. Castration greatly reduced the number of TH‐immunoreactive cells in the male prairie vole pBST and MeAPd, an effect that could be reversed with testosterone. Furthermore, treating ovariectomized females with testosterone substantially increased TH‐immunoreactive cells in both sites. Therefore, a species‐specific sex difference in TH expression is found in a chemosensory pathway in prairie voles. Expression of TH in these sites is influenced by circulating gonadal hormones in adults, which may be related to changes in their display of social behaviors across the reproductive cycle. J. Comp. Neurol. 500:103–115, 2007.

Sexual dimorphism and steroid responsiveness of the posterodorsal medial amygdala in adult mice

The posterodorsal aspect of the medial amygdala (MePD) is sexually dimorphic in regional volume, rostrocaudal extent, and neuronal soma size in rats. These dimorphisms are maintained by circulating gonadal hormones, as castration of adult male rats reduces MePD measures, while testosterone treatment of females increases them. We now report that the MePD is also sexually dimorphic in volume, rostrocaudal extent, and somal area in BALB/c mice. Four weeks after castration of adult male mice, MePD regional volume and soma size are reduced, but rostrocaudal extent is not, compared to sham-castrated males. Treatment of adult ovariectomized females with an aromatized metabolite of testosterone, estradiol, for 8 weeks increased MePD volume and soma size, but not rostrocaudal extent. To probe the possible role of afferents in the steroid-induced plasticity of the MePD, we examined the effect of removing the olfactory bulbs in gonadally intact males and in estrogen-treated females. Bulbectomy had no effect on MePD morphology with one exception: among gonadally intact males, neuronal soma size was slightly smaller in the right MePD of bulbectomized males compared to males with intact bulbs. These results indicate that the sexual dimorphism and hormone responsiveness of the MePD that has been extensively studied in rats is also present in mice, which offers genetic tools for future research. We detected little or no evidence that olfactory bulb afferents play a role in maintaining MePD morphology in adult mice.

Progesterone and medroxyprogesterone acetate differentially regulate α4 subunit expression of GABAA receptors in the CA1 hippocampus of female rats.

The Womens Health Initiative trials - in which more extreme adverse outcomes were observed in the medroxyprogesterone acetate (MPA) + conjugated equine estrogen (CEE) arm, as compared to the CEE only arm - suggest that the addition of MPA to estrogen treatment has undesirable consequences. An important question raised by these results is whether the adverse outcomes observed in the progestin arm can be attributed to effects that are unique to MPA or are common to all progestins. In this study we explored the potential for MPA and progesterone (P4) to differentially impact neuroendocrine function by comparing their effects on mRNA expression for the alpha4 subunit of GABA(a) receptors in the CA1 hippocampus of female rats. Prior research has shown that P4, acting through its reduced metabolite allopregnanolone (AP), can mediate alpha4 subunit expression, thereby altering GABA(A) receptor gated currents. By contrast, MPA competitively inhibits the enzymes necessary for the synthesis of AP. In this study, ovariectomized females were primed with estradiol benzoate and then treated with P4, MPA, or vehicle. Subjects were sacrificed 12 h or 24 h later and in situ hybridization was used to measure alpha4 mRNA in the CA1 hippocampus. At 12 h but not 24 h, alpha4 mRNA was reduced in the P4 group as compared to the MPA group, and as compared to the vehicle group. These results suggest that MPA, while progestational in terms of its effects in the uterus, is not a simple substitute for P4 in other systems. The relative impact of these two progestins on neuroendocrine function must be carefully explored.

Neuroanatomical Projections of the Species-Specific Tyrosine Hydroxylase-Immunoreactive Cells of the Male Prairie Vole Bed Nucleus of the Stria Terminalis and Medial Amygdala

The principal nucleus of the bed nucleus of the stria terminalis (BSTpr) and posterodorsal part of the medial amygdalar nucleus (MEApd) are densely interconnected sites transmitting olfactory information to brain areas mediating sociosexual behaviors. In male prairie voles (Microtus ochrogaster), the BSTpr and MEApd contain hundreds of cells densely immunoreactive for tyrosine hydroxylase (TH). Such tremendous numbers of TH-immunoreactive (TH-ir) cells do not exist in other rodents examined, and studies from our laboratory suggest these cells may be part of a unique chemical network necessary for monogamous behaviors in prairie voles. To obtain information about how these TH-ir cells communicate with other sites involved in social behaviors, we first used biotinylated dextran amine (BDA) to determine sites that receive BSTpr efferents and also contain TH-ir fibers. Only in the medial preoptic area (MPO) and MEApd did we find considerable comingling of BDA-containing and TH-ir fibers. To examine if these sites receive input specifically from BSTpr TH-ir cells, the retrograde tracer Fluorogold was infused into the MPO or MEApd. Almost 80% of TH-ir projections to the MPO originated from the BSTpr or MEApd, involving about 40% of all TH-ir cells in these sites. In contrast, the MEApd received almost no input from TH-ir cells in the BSTpr, and received it primarily from the ventral tegmental area. Retrograde tracing from the BSTpr itself revealed substantial input from MEApd TH-ir cells. Thus, the male prairie vole brain contains a species-specific TH-ir network involving the BSTpr, MEApd, and MPO. By connecting brain sites involved in olfaction, sociality and motivation, this network may be essential for monogamous behaviors in this species.

l-Amino acid decarboxylase- and tyrosine hydroxylase-immunoreactive cells in the extended olfactory amygdala and elsewhere in the adult prairie vole brain

Neurons synthesizing dopamine (DA) are widely distributed in the brain and implicated in a tremendous number of physiological and behavioral functions, including socioreproductive behaviors in rodents. We have recently been investigating the possible involvement of sex- and species-specific TH-immunoreactive (TH-ir) cells in the male prairie vole (Microtus ochrogaster) principal bed nucleus of the stria terminalis (pBST) and posterodorsal medial amygdala (MeApd) in the chemosensory control of their monogamous pairbonding and parenting behaviors. These TH-ir cells are not immunoreactive for dopamine-beta-hydroxylase (DBH), suggesting they are not noradrenergic but possibly DAergic. A DAergic phenotype would require them to contain aromatic L-amino acid decarboxylase (AADC) and here we examined the existence of cells immunoreactive for both TH and AADC in the pBST and MeApd of adult virgin male and female prairie voles. We also investigated the presence of TH/AADC cells in the anteroventral periventricular nucleus (AVPV), medial preoptic area (MPO), arcuate nucleus (ARH), zona incerta (ZI), substantia nigra (SN) and ventral tegmental area (VTA). Among our findings were: (1) the pBST and MeApd each contained completely non-overlapping distributions of TH-ir and AADC-ir cells, (2) the AVPV contained surprisingly few AADC-ir cells and almost no TH-ir cells contained AADC-ir, (3) approximately 60% of the TH-ir cells in the MPO, ARH, and ZI also contained AADC-ir, (4) unexpectedly, only about half of TH-ir cells in the SN and VTA contained AADC-ir, and (5) notable populations of AADC-ir cells were found outside traditional monoamine-synthesizing regions, including some sites that do not contain AADC-ir cells in adult laboratory rats or cats (medial septum and cerebral cortex). In the absence of the chemical requirements to produce DA, monoenzymatic TH-ir cells in the virgin adult prairie vole pBST, MeApd, and elsewhere in their brain may instead produce L-DOPA as an end product and use it as a neurotransmitter or neuromodulator, similar to what has been observed for monoenzymatic TH-synthesizing cells in the laboratory rat brain.

Plasticity in the Cerebellum and Primary Somatosensory Cortex Relating to Habitual and Continuous Slender Branch Climbing in Laboratory Mice (Mus musculus)

The origin of the mammalian order Primates is nested within a Euarchontan ancestry that was probably exploiting the fine branch arboreal niche in a facultative way. A putative transition into this habitat may have begun with a more generalized small‐bodied mammal that lacked climbing specializations for grasping hands and feet. Here, we investigate whether mice exhibit central nervous system (CNS) plasticity associated with learning to grasp/climb proficiently. House mice were used to study phenotypic plasticity within the cerebellum and primary somatosensory cortex associated with the fine branch niche. This experimental treatment has previously been shown to influence skeletal plasticity in part because climb‐training encourages tail use and facultative pedal grasping. The CNS necessary to coordinate and control these locomotor behaviors was investigated in a standard mouse model (N = 10 male CD‐1/ICR mice), and plasticity was detected by histomorphometric and immunohistologic changes within the cerebellum and cerebrum. The climbing group had a significantly smaller relative granule cell layer in cerebellar lobule 1–3 than the control group (P < 0.10), but increased nerve growth factor immunoreactivity in white matter tracts of these lobules (P < 0.05). Qualitative observations in the primary somatosensory cortex revealed greater pyramidal/stellate cell counts in climbers. We suggest that coordinated tail and hindlimb learning within the arboreal milieu is facilitated by increased growth factor expression and neuronal alterations in the CNS. These findings suggest that mammals with a generalized Euarchontogliran body plan were capable of facultative pedal grasping and tail use so as to exploit the terminal branch niche. Anat Rec, 296:822–833, 2013.

Perinatal hypothyroidism increases play behaviors in juvenile rats

ABSTRACT Thyroid hormones play an instrumental role in the development of the central nervous system. During early development, the fetus is dependent on maternal thyroid hormone production due to the dysfunction of its own thyroid gland. Thus, maternal thyroid dysfunction has been shown to elicit significant abnormalities in neural development, neurochemistry, and behavior in offspring. Previous reports have suggested that human maternal hypothyroidism may increase the chances of having children with autism spectrum disorder and attention‐deficit/hyperactivity disorder. However, very few studies have evaluated social behaviors in animal models of perinatal hypothyroidism. To evaluate the possibility that hypothyroidism during development influences the expression one of the most commonly observed non‐reproductive social behaviors, juvenile play, we used the validated rat model of perinatal hypothyroidism by methimazole administration (MMI; 0.025% in drinking water) from GD12‐PD23. Control animals had regular drinking water. During adolescence (PD33–35), we tested subjects for juvenile play behavior by introducing them to a same‐sex, unfamiliar (since weaning) littermate for 30 min. Play behaviors and other behaviors (sleep, social contact, locomotion) were then scored. MMI‐treated subjects played more than twice as much as control animals, and the increase in some behaviors was particularly dramatic in males. Locomotor and other affiliative social behaviors were unaffected. These data suggest that perinatal hypothyroidism may alter the organization of the neural networks regulating play behaviors, but not other social behaviors. Moreover, this implicates perinatal hypothyroidism as a potential etiological factor in the development of neurobehavioral disorders, particularly those characterized by heightened social interactions and impulsivity. HIGHLIGHTSPerinatal hypothyroidism dramatically increased juvenile play behavior.Perinatal hypothyroidism did not alter other social behaviors in juveniles.Increases in play may reflect an increase in motivation or impulsivity.

Student-Designed Service-Learning Projects in an Undergraduate Neurobiology Course.

One of the challenges in teaching a service-learning course is obtaining student buy-in from all students in the course. To circumvent this problem, I have let students in my undergraduate Neurobiology course design their own service-learning projects at the beginning of the semester. Although this can be chaotic because it requires last-minute planning, I have made it successful through facilitating student communication in the classroom, requiring thorough project proposals, meeting with students regularly, and monitoring group progress through written reflection papers. Most of my students have strong opinions about the types of projects that they want to carry out, and many students have used connections that they have already made with local organizations. Almost all projects that students have designed to this point involve teaching basic concepts of neurobiology to children of various ages while simultaneously sparking their interest in science. Through taking ownership of the project and designing it such that it works well with their strengths, interests, and weekly schedule, students have become more engaged in service learning and view it as a valuable experience. Despite some class time being shifted away from more traditional assignments, students have performed equally well in the course, and they are more eager to talk with others about course concepts. Furthermore, the feedback that I have received from community partners has been excellent, and some students have maintained their work with the organizations.