Brain region-dependent gene networks associated with selective breeding for increased voluntary wheel-running behavior.

Mouse lines selectively bred for high voluntary wheel-running behavior are helpful models for uncovering gene networks associated with increased motivation for physical activity and other reward-dependent behaviors. The fact that multiple brain regions are hypothesized to contribute to distinct behavior components necessitates the simultaneous study of these regions. The goals of this study were to identify brain-region dependent and independent gene expression patterns, regulators, and networks associated with increased voluntary wheel-running behavior. The cerebellum and striatum from a high voluntary running line and a non-selected control line were compared. Neuropeptide genes annotated to reward-dependent processes including neuropeptide S receptor 1 (Npsr1), neuropeptide Y (Npy), and proprotein convertase subtilisin/kexin type 9 (Pcsk9), and genes implicated in motor coordination including vitamin D receptor (Vdr) and keratin, type I cytoskeletal 25 (Krt25) were among the genes exhibiting activity line-by-region interaction effects. Genes annotated to the Parkinson pathway presented consistent line patterns, albeit at different orders of magnitude between brain regions, suggesting some parallel events in response to selection for high voluntary activity. The comparison of gene networks between brain regions highlighted genes including transcription factor AP-2-delta (Tfap2d), distal-less homeobox 5 gene (Dlx5) and sine oculis homeobox homolog 3 (Six3) that exhibited line differential expression in one brain region and are associated with reward-dependent behaviors. Transcription factors including En2, Stat6 and Eomes predominated among regulators of genes that differed in expression between lines. Results from the simultaneous study of striatum and cerebellum confirm the necessity to study molecular mechanisms associated with voluntary activity and reward-dependent behaviors in consideration of brain region dependencies.

A unique combination of micronutrients rejuvenates cognitive performance in aged mice.

It is widely believed that diet can influence the onset and severity of cognitive aging, but the optimal combination of micronutrients and molecular and cellular mechanisms remain elusive. The purpose of this study was to compare the effects of eight distinct diets, consisting of various concentrations of selected micronutrients, on learning and memory as well as markers of neuronal plasticity, and metabolic and neuro-immune status of the aged hippocampus. Eighteen-month-old male and female C57BL/6J mice were fed the diets for 16 weeks, followed by learning and memory trials on the active avoidance task. Number of immature neurons were measured by immunohistochemical detection of doublecortin (DCX+) in the granule layer of the dentate gyrus. Amount of mitochondrial DNA (mtDNA) and gene expression of molecular markers of mitochondrial biogenesis (Ppargc1α, Sirt1, Tfam), and neuroinflammation (IL-10, Alox15, Ptgs2, IL-1ß, IL-6 and Tnf) were assessed by quantitative real time polymerase chain reaction (qRT-PCR) of hippocampal samples. Tissue levels of selected micronutrients and a number of metabolites were measured by liquid chromatography-mass spectrometry. The diet supplemented with RRR d-alpha tocopheryl acetate, citicholine, 5-methyltetrahydrofolic acid, quercetin and the n-3 fatty acid phosphatidylserine-docosahexaenoic acid, improved performance on the active avoidance learning and memory task compared to all the other less-complex diets. This diet also increased IL-10 expression and attenuated the age-related change in mtDNA content in the hippocampus without affecting metabolite levels. Results suggest cognitive benefits of wholesome diets are partially mediated through combined antioxidant and anti-inflammatory activities of optimized mixtures of micronutrients.

Cerebellum Transcriptome of Mice Bred for High Voluntary Activity Offers Insights into Locomotor Control and Reward-Dependent Behaviors.

The role of the cerebellum in motivation and addictive behaviors is less understood than that in control and coordination of movements. High running can be a self-rewarding behavior exhibiting addictive properties. Changes in the cerebellum transcriptional networks of mice from a line selectively bred for High voluntary running (H) were profiled relative to an unselected Control (C) line. The environmental modulation of these changes was assessed both in activity environments corresponding to 7 days of Free (F) access to running wheel and to Blocked (B) access on day 7. Overall, 457 genes exhibited a significant (FDR-adjusted P-value < 0.05) genotype-by-environment interaction effect, indicating that activity genotype differences in gene expression depend on environmental access to running. Among these genes, network analysis highlighted 6 genes (Nrgn, Drd2, Rxrg, Gda, Adora2a, and Rab40b) connected by their products that displayed opposite expression patterns in the activity genotype contrast within the B and F environments. The comparison of network expression topologies suggests that selection for high voluntary running is linked to a predominant dysregulation of hub genes in the F environment that enables running whereas a dysregulation of ancillary genes is favored in the B environment that blocks running. Genes associated with locomotor regulation, signaling pathways, reward-processing, goal-focused, and reward-dependent behaviors exhibited significant genotype-by-environment interaction (e.g. Pak6, Adora2a, Drd2, and Arhgap8). Neuropeptide genes including Adcyap1, Cck, Sst, Vgf, Npy, Nts, Penk, and Tac2 and related receptor genes also exhibited significant genotype-by-environment interaction. The majority of the 183 differentially expressed genes between activity genotypes (e.g. Drd1) were under-expressed in C relative to H genotypes and were also under-expressed in B relative to F environments. Our findings indicate that the high voluntary running mouse line studied is a helpful model for understanding the molecular mechanisms in the cerebellum that influence locomotor control and reward-dependent behaviors.

Chronically lowering sympathetic activity protects sympathetic nerves in spleens from aging F344 rats.

In the present study, we investigated how increased sympathetic tone during middle-age affects the splenic sympathetic neurotransmission. Fifteen-month-old (M) F344 rats received rilmenidine (0, 0.5 or 1.5mg/kg/day, i.p. for 90 days) to lower sympathetic tone. Controls for age were untreated 3 or 18M rats. We report that rilmenidine (1) reduced plasma and splenic norepinephrine concentrations and splenic norepinephrine turnover, and partially reversed the sympathetic nerve loss; and (2) increased ß-adrenergic receptor (ß-AR) density and ß-AR-stimulated cAMP production. Collectively, these findings suggest a protective effect of lowering sympathetic tone on sympathetic nerve integrity, and enhanced sympathetic neurotransmission in secondary immune organs.

Stimulation of lateral hypothalamic AMPA receptors may induce feeding in rats.

Glutamate or its ionotropic receptor (iGluR) agonists, N-methyl-D-aspartate (NMDA), alpha-amino-3-hydroxy-5-methyl-4-isoxale propionate (AMPA), and kainate (KA) elicit feeding when microinjected into the lateral hypothalamus (LH) of satiated rats. In the present study we investigated the contributions of AMPA and KA receptors (AMPARs and KARs) to feeding initiation. Intense feeding was elicited by LH injection of RS-AMPA (1 and 10 nmol) but not by the isolated, inactive R-AMPA enantiomer (1 and 10 nmol). Further, LH pretreatment with either the non-selective AMPAR/KAR antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 4 nmol) or the selective AMPAR antagonist, GYKI 52466 (10 nmol), suppressed AMPA-elicited food intake and, when combined, blocked AMPA-elicited food intake. These findings suggest that LH AMPARs mediate AMPA injection-elicited feeding with a possible contribution by KARs. In contrast, CNQX or GYKI 52466 injected into the LH at the onset of the nocturnal period or into fasted rats did not suppress the feeding produced by either condition. RS-AMPA injected into the LH of fasted or nocturnal feeding subjects elicited eating in both conditions; however, the magnitude of the increase was greater in fasted rats. These data suggest that selective stimulation of AMPAR in the LH is sufficient to elicit feeding. In contrast, the results did not provide evidence that AMPAR stimulation is necessary for deprivation-induced or nocturnal eating; however, they did suggest that modulatory interactions may exist between these receptors and these forms of naturally occurring eating behavior.

Sympathetic innervation of the spleen in male Brown Norway rats: a longitudinal aging study.

Aging leads to reduced cellular immunity with consequent increased rates of infectious disease, cancer, and autoimmunity in the elderly. The sympathetic nervous system (SNS) modulates innate and adaptive immunity via innervation of lymphoid organs. In aged Fischer 344 (F344) rats, noradrenergic (NA) nerve density in secondary lymphoid organs declines, which may contribute to immunosenescence with aging. These studies suggest there is SNS involvement in age-induced immune dysregulation. The purpose of this study was to longitudinally characterize age-related change in sympathetic innervation of the spleen and sympathetic activity/tone in male Brown Norway (BN) rats, which live longer and have a strikingly different immune profile than F344 rats, the traditional animal model for aging research. Splenic sympathetic neurotransmission was evaluated between 8 and 32 months of age by assessing (1) NA nerve fiber density, (2) splenic norepinephrine (NE) concentration, and (3) circulating catecholamine levels after decapitation. We report a decline in NA nerve density in splenic white pulp (45%) at 15 months of age compared with 8-month-old (M) rats, which is followed by a much slower rate of decline between 24 and 32 months. Lower splenic NE concentrations between 15 and 32 months of age compared with 8M rats were consistent with morphometric findings. Circulating catecholamine levels after decapitation stress generally dropped with increasing age. These findings suggest there is a sympathetic-to-immune system dysregulation beginning at middle age. Given the unique T-helper-2 bias in BN rats, altered sympathetic-immune communication may be important for understanding the age-related rise in asthma and autoimmunity.

Sympathetic nervous system and lymphocyte proliferation in the Fischer 344 rat spleen: a longitudinal study.

UNLABELLED: Aging is associated with reduced cellular immunity, which leads to increased rates of infectious disease, cancer and autoimmunity in the elderly. Previous findings from our laboratory revealed an age-related decline in sympathetic innervation of immune organs that affects immunity. These studies suggested potential sympathetic nervous system involvement in age-induced immune dysregulation. OBJECTIVES: The purpose of this study was to longitudinally characterize the effects of age on sympathetic neurotransmission in the spleen and net sympathetic activity/tone in male Fischer 344 rats. METHODS: Splenic sympathetic neurotransmission was evaluated between 8 and 24 months of age by (1) splenic norepinephrine (NE) concentration and turnover, (2) beta-adrenergic receptor (beta-AR) expression and (3) beta-AR-stimulated splenocyte cAMP production. Measures of sympathetic neurotransmission were correlated with age-related changes in Concanavalin A (Con A)-stimulated splenocyte proliferation. RESULTS: Splenic NE turnover increased during middle age, then subsequently declined by 18 months of age compared with 8-month-old controls (young). Splenic NE concentration increased at 10 months and decreased at 18-24 months, compared with young rats; however, plasma NE levels were not affected by age. Plasma epinephrine levels were decreased at 24 months. NE synthesis blockade increased and decreased the rate of plasma catecholamine depletion in middle and old age, respectively. beta-AR-stimulated cAMP production increased in splenocytes by 15 months. An age-related decrease in Con A-induced splenocyte proliferation was apparent by 10 months and persisted through 24 months. The decline in Con A-induced splenocyte proliferation correlated with the age-related increase in cAMP production. CONCLUSIONS: Aging alters sympathetic nervous system metabolism in the spleen to affect beta-AR signaling to splenocytes, suggesting that altered sympathetic-immune modulation changes are evident by early middle age.

Sympathetic modulation of immunity: relevance to disease.

Optimal host defense against pathogens requires cross-talk between the nervous and immune systems. This paper reviews sympathetic-immune interaction, one major communication pathway, and its importance for health and disease. Sympathetic innervation of primary and secondary immune organs is described, as well as evidence for neurotransmission with cells of the immune system as targets. Most research thus far has focused on neural-immune modulation in secondary lymphoid organs, has revealed complex sympathetic modulation resulting in both potentiation and inhibition of immune functions. SNS-immune interaction may enhance immune readiness during disease- or injury-induced 'fight' responses. Research also indicate that dysregulation of the SNS can significantly affect the progression of immune-mediated diseases. However, a better understanding of neural-immune interactions is needed to develop strategies for treatment of immune-mediated diseases that are designed to return homeostasis and restore normal functioning neural-immune networks.

Dual roles in feeding for AMPA/kainate receptors: receptor activation or inactivation within distinct hypothalamic regions elicits feeding behavior.

We have previously shown that hypothalamic injections of glutamate, or agonists of its ionotropic receptors (iGluRs), elicit intense feeding responses in satiated rats [Brain Res. 613 (1993) 88, Brain Res. 630 (1993) 41]. While attempting to clarify the role of the AMPA and kainate (KA) receptor subtypes in glutamatergic feeding systems, we discovered that lateral hypothalamic (LH) injection of high doses of the competitive AMPA/KA receptor antagonist, NBQX (10 and 30 nmol), elicited a pronounced feeding response. We questioned whether this effect was due to inactivation of AMPA or possibly KA receptors. To determine whether other AMPA/KA antagonists can also elicit feeding, we tested whether injection of CNQX, another AMPA/KA receptor antagonist, also stimulates eating and whether these feeding stimulatory effects were due to antagonists' actions in the LH or in other hypothalamic sites. Here we report that NBQX and CNQX elicit feeding in a dose dependent manner and are most effective when injected into the perifornical hypothalamus (PFH), or into the paraventricular nucleus (PVN) and, to a lesser extent, into the LH of satiated rats. In contrast, AMPA was most effective in stimulating feeding when injected into the LH, confirming previous reports. These data suggest that either activation or inactivation of AMPA/KA receptors in distinct but overlapping hypothalamic sites may be sufficient to induce feeding behavior, indicating a broadened role for glutamate in hypothalamic feeding mechanisms.