Activity-based anorexia is associated with reduced hippocampal cell proliferation in adolescent female rats.

Activity-based anorexia (ABA) is an animal model of anorexia nervosa that mimics core features of the clinical psychiatric disorder, including severe food restriction, weight loss, and hyperactivity. The ABA model is currently being used to study starvation-induced changes in the brain. Here, we examined hippocampal cell proliferation in animals with ABA (or the appropriate control conditions). Adolescent female Sprague-Dawley rats were assigned to 4 groups: control (24h/day food access), food-restricted (1h/day food access), exercise (24h/day food and wheel access), and ABA (1h/day food access, 24h/day wheel access). After 3 days of ABA, 5-bromo-2'-deoxyuridine (BrdU; 200mg/kg, i.p.) was injected and the rats were perfused 2h later. Brains were removed and subsequently processed for BrdU and Ki67 immunohistochemistry. The acute induction of ABA reduced cell proliferation in the dentate gyrus. This effect was significant in the hilus region of the dentate gyrus, but not in the subgranular zone, where adult neurogenesis occurs. Marked decreases in cell proliferation were also observed in the surrounding dorsal hippocampus and in the corpus callosum. These results indicate a primary effect on gliogenesis rather than neurogenesis following 3 days of ABA. For each brain region studied (except SGZ), there was a strong positive correlation between the level of cell proliferation and body weight/food intake. Future studies should examine whether these changes are maintained following long-term weight restoration and whether alterations in neurogenesis occur following longer exposures to ABA.

Effects of the hypnotic drug zolpidem on cell proliferation and survival in the dentate gyrus of young and old rats.

Sleep loss/disruption has been shown to suppress adult hippocampal neurogenesis. Whether the administration of hypnotic drugs, by promoting sleep, especially in older subjects, who typically exhibit poor sleep, has a beneficial effect on neurogenesis parameters is unknown. We examined the effects of zolpidem, a widely prescribed nonbenzodiazepine hypnotic, on cell proliferation and survival in the dentate gyrus of young ( approximately 2 1/2 months) and old ( approximately 13 months) male Sprague-Dawley rats. Zolpidem (5, 10 or 20 mg/kg, i.p.) or vehicle was administered twice daily, at the beginning and middle of the sleep period, for either 2 days (acute study) or 21 days (chronic study). Proliferation and cell survival were measured by staining for Ki67 or 5-bromo-2'-deoxyurdine (BrdU), respectively. Acute administration of zolpidem produced a suppression of cell proliferation, which attained statistical significance only in the aged animals. The magnitude of the suppressive effect was larger in the hilus than in the subgranular zone (SGZ). In contrast, chronic administration of zolpidem produced little or no effect on proliferation in either age group, despite marked differences in basal proliferation levels between the two age groups. Similarly, there was little change in cell survival following chronic zolpidem administration in young versus old animals. A slight reduction of cell survival in the granular cell layer (GCL)/SGZ was observed in young animals and a slight augmentation in aged animals. To the extent that zolpidem improves sleep, these data suggest little or no benefit of hypnotic drug treatment on neurogenesis parameters in young or old rats.

Age-dependent decline in hippocampal neurogenesis is not altered by chronic treatment with fluoxetine.

There has been ongoing controversy as to whether selective serotonin reuptake inhibitors (SSRIs) exhibit the same antidepressant efficacy and risk profile within different age groups. Although the etiology of such potential differences is currently not clear, age-dependent differences in the rate of hippocampal neurogenesis offer one possibility. In the current studies we have therefore examined whether fluoxetine, the prototypical selective serotonin reuptake inhibitor, differentially modulates neurogenesis in adolescent, young adult, and aged rats. Proliferation in the dentate gyrus was measured by assaying expression of the endogenous proliferative marker, Ki67. Survival of proliferating cells was assayed by staining with BrdU. We confirmed previous reports that the rate of neurogenesis, as well as the survival of proliferating cells, decreases significantly with age. Moderate decreases were found in young adult rats relative to adolescent rats, and profound decreases were found in aged rats. We additionally found that age did not alter the response to 25 days of treatment with fluoxetine. In fact, we did not observe enhancement of hippocampal neurogenesis, nor enhancement of proliferating cell survival, in any of the three age groups despite using doses of fluoxetine which have been reported to be effective. In addition to finding no age-dependent effects, our data question the general reproducibility of previously reported fluoxetine effects in animals.

Repeated brief social defeat episodes in mice: effects on cell proliferation in the dentate gyrus.

Stressful experiences can affect hippocampal structure and function and can suppress new cell birth in the adult hippocampus in several species. Here we examine how repeated intermittent social defeat affects cell proliferation in the dentate gyrus (DG) in mice. Adult male CFW mice were subjected to 10 daily social defeat episodes, 3 defeat episodes within one day or a single defeat episode. Intruder mice were injected with 5-bromo-2'-deoxyuridine (BrdU, 200mg/kg, i.p.) 1h after the last fight, and incorporation of BrdU into proliferating cells in the DG was quantified. In a third experiment, aggressive resident mice were allowed to fight with an intruder mouse every day for 10 days, and these residents were injected with BrdU 1h after the last aggressive encounter. There was a significant decrease in cell proliferation in mice that received 10 social defeats, confirming and extending earlier results. This decrease is correlated with the intensity of the defeat experiences, as quantified by frequency of attack bites. Cell proliferation was slightly inhibited after a single defeat, although this effect was not significant. Three defeats within a 5-h period had no effect on levels of proliferation. Offensive aggressive stress in the residents did not result in any changes in hippocampal cell proliferation. These data indicate that repeated intermittent social defeat experienced over multiple days suppresses proliferation in the DG, and this may have important implications for our understanding of hippocampal changes related to stress psychopathologies.

Effect of number of tailshocks on learned helplessness and activation of serotonergic and noradrenergic neurons in the rat.

Adult male albino rats were exposed to varying numbers of tailshocks (0, 10, 50 or 100). The following day, their escape latencies in a shuttlebox were measured in order to estimate the degree of learned helplessness (LH) produced by the varying number of shocks. Only the groups exposed to 50 or 100 shocks displayed evidence of LH. In a parallel experiment, c-fos activation was used to determine the degree of activation of raphe serotonergic neurons (FosIR+5-HT) and locus coeruleus (LC) noradrenergic neurons (FosIR+TH) produced by the same shock conditions. Compared to unhandled cage controls, all shock groups (0 shocks was a restrained group) significantly activated both raphe and LC neurons. The 50 and 100 shock groups had significantly higher degrees of activation of serotonergic neurons in the rostral raphe groups and the LC than the 0 and 10 shock groups. These data are consistent with the hypothesis that activation of rostral raphe serotonergic neurons and LC noradrenergic neurons beyond a certain threshold may be critical for the development of LH. The relevance of these results for elucidating the neural bases of psychopathology is discussed.

Inescapable shock activates serotonergic neurons in all raphe nuclei of rat.

Animal studies examining the effects of stress upon brain serotonergic neurons have not presented a clearcut and consistent picture. One stressor that has been shown to exert a consistently strong effect on serotonin release and c-fos activation in the dorsal raphe nucleus of rats is a series of inescapable electrical shocks. Using immunohistochemical double labeling for c-fos activation and serotonin, we examined the effects of delivering 100 inescapable tailshocks to rats on serotonergic neuronal activation throughout the brainstem raphe system. This stimulus exerted a consistent and strong activation of the entire midline brain stem system of serotonergic neurons. The implications of these findings for animal models of human psychopathology are discussed.