CREB deficient mice show inhibition and low activity in novel environments without changes in stress reactivity

The ability to respond to unexpected or novel stimuli is critical for survival. Determining that a stimulus is indeed novel requires memory to ascertain its lack of familiarity. As the long-term synaptic changes involved in memory formation require the cAMP response element binding protein (CREB), we examined the extent to which CREB is involved in responses to novel environments. These environments typically trigger an endocrine stress response. Thus, we measured behavioural and stress hormone responses to three novel and one familiar environment in mice with a targeted disruption of the alpha and delta isoforms of the CREB gene (CREB(alphadelta-) deficient mice). We found CREB(alphadelta-) deficient mice to be less active and more inhibited in the elevated plus maze, open field, and light/dark box, without showing differences in anxiety-like behaviour. This inhibition is unique to novel environments because these mice display a normal phenotype in the home cage, a familiar environment. Although CREB(alphadelta-) deficient mice exhibit altered behaviour in novel environments, they show normal reactivity to mild and moderate stress as both basal and stress levels of corticosterone are similar to those of wild-type controls. This is the first report of CREB(alphadelta-) deficient mice to: (i) show altered behaviour, not related to learning and memory-associated behaviours, upon initial exposure to environments and (ii) serve as an animal model that can dissociate locomotor activity from anxiety-like behaviour in novel environments.     

Fos expression after mating in noradrenergic cells of the A1 and A2 areas of the medulla is altered by adrenalectomy

In the female rat, the integrity of the ventral noradrenergic bundle (VNAB) is necessary to carry stimuli from the uterine cervix and vagina to brain areas involved in mating-induced pseudopregnancy. Because adrenal hormones are known to alter noradrenergic function, we examined whether adrenalectomy altered mating-induced Fos expression in the A1 and A2 noradrenergic cell groups that project through the VNAB. Ovariectomized females were adrenalectomized (ADX) or sham-operated (Sham) and, 2 weeks after surgery, were given oestrogen and progesterone and mated. They received 15 intromissions, five intromissions or 15 mounts-without-intromission (mounts-only) from a male. Two hours after mating, rats were perfused and brains were collected; controls were perfused after being taken directly from their home cage. After immunocytochemical staining, Fos-immunoreactive (Fos-IR) and dopamine-beta-hydroxylase-immunoreactive (DBH-IR) cells and the percentage of DBH cells that were labelled with Fos (% DBH/Fos) were counted. In the A1 area, Fos-IR and percentage DBH/Fos were not affected by adrenalectomy. Although an overall effect of mating treatment was found for both measures, no specific mating treatment increased labelled cells above home cage levels. In the caudal, middle and rostral A2, 15 intromissions induced a significant increase in Fos-IR in Sham females above all other groups and a higher percentage of DBH/Fos in the middle and rostral A2 areas. ADX females showed no rise in either Fos-IR or percentage DBH/Fos after 15 intromissions. However, in the middle and rostral A2, ADX females showed significantly increased Fos-IR and percentage DBH/Fos after mounts-only treatment above Sham mounts-only females and all other ADX groups. These results demonstrate that adrenal hormones suppress activation of A2 cells to mounts-only stimuli but contribute to A2 activation in response to intromissions from males. The latter effect may result from stress associated with receipt of vaginocervical stimulation during mating.     

Effects of dietary PCB exposure on adrenocortical function in captive American kestrels (Falco sparverius)

We experimentally examined the effects of dietary exposure to polychlorinated biphenyls (PCBs) on adrenocortical function in American kestrels (Falco sparverius). Nine captive male American kestrels previously exposed to a PCB mixture (Aroclor1248:1254:1260; 1:1:1) in their diet were subjected to a standardized capture, handling and restraint protocol designed to produce an increase in circulating corticosterone. A similar protocol has been applied to a wide range of avian species and was used here to evaluate the response of PCB-exposed and control kestrels to a defined physical stressor. Both baseline and stress-induced corticosterone levels were significantly lower in PCB-exposed birds when compared with control birds of the same age. PCB-exposed birds exhibited significantly lower corticosterone levels during the corticosterone response when compared with control birds, independent of body condition. Furthermore, baseline corticosterone concentrations exhibited a hormetic response characterized by an inverted U-shaped dose response in relation to total PCB liver burden. These results support several recent studies which report decreased levels of circulating corticosterone in PCB-exposed wild birds. The results presented here provide the first evidence that exposure to an environmentally relevant level of PCBs (approximately 10 mg/kg body weight) can impair the corticosterone stress response in kestrels, potentially increasing the susceptibility of birds to environmental stressors such as severe weather and predatory and human disturbance.     

增液汤抑制幼鼠胸腺细胞凋亡作用的机制探讨

目的 :观察预防性应用增液汤注射剂对幼鼠胸腺细胞凋亡及其相关基因的影响。方法 :给 4～ 5周龄Wistar大鼠腹腔注射增液汤注射剂和地塞米松 ,采用原位末端标记 (TUNEL)法分析不同处理组的凋亡细胞 ,同时采用免疫组化方法检测幼鼠胸腺细胞bcl 2和bax基因蛋白表达情况。结果 :用TUNEL法标记凋亡细胞 ,荧光显微镜下 ,地塞米松组可见致密浓染的黄绿色荧光 ,呈局灶状分布 ;而增液汤组只有散在的荧光。光镜观察地塞米松组TUNEL阳性细胞数目较多 ,其凋亡指数为 0 4 1± 0 0 1;增液汤组TUNEL阳性细胞数目较少 ,凋亡指数为 0 0 7± 0 0 0 4 ,与地塞米松组比较 ,差异有显著性 (P <0 0 1)。免疫组织化学结果表明 ,地塞米松组bcl 2基因蛋白呈低表达 ,其蛋白阳性率为 (0 196 0± 0 0 0 6 0 ) % ,bax蛋白过度表达 ,蛋白阳性率为 (0 4 315± 0 0 16 5 ) % ,bcl 2 /bax <1;相反增液汤组细胞bcl 2基因蛋白呈高表达 ,bax基因蛋白仅有少量表达 ,其蛋白阳性率为 (0 5 0 10± 0 0 170 ) %和 (0 185 4± 0 0 0 9) % ,bcl 2 /bax >1。两组比较 ,差异有显著性 (P <0 0 1)。结论 :通过调控凋亡基因bcl 2 /bax表达 ,增强胸腺细胞对地塞米松的抵抗 ,进而抑制细胞凋亡 ,可能是增液汤抑制幼鼠胸腺细胞凋亡的重要作用环     

Gene expression of neuropeptide Y in the nucleus of the solitary tract is activated in rats under restricted daily feeding but not under 48-h food deprivation

The two neuropeptide Y (NPY) systems innervating the hypothalamic paraventrivular nucleus were examined regarding their roles in the prefeeding corticosterone peak developed under restricted daily feeding (RF). Protein and mRNA levels of NPY were measured in the arcuate nucleus (ARC) and the nucleus of the solitary tract (NST) in rats under 48-h food deprivation (48-hFD), RF, and 72-h food deprivation imposed after RF (post-RF 72-hFD) with 7 days of ad libitum feeding in between. NPY protein and mRNA levels in the ARC significantly increased with 48-hFD and decreased with re-feeding, whereas those in the NST were not changed by 48-hFD. When rats had RF imposed with free access to food from 10.00 to 12.00 h (lights on from 06.00 to 18.00 h) for 3 weeks, NPY concentrations in the ARC increased at 10.00 h, just prior to the daily meal, but those in the NST did not change significantly throughout the period examined. On the other hand, NPY mRNA levels in both the ARC and NST increased before the meal supply and remained high for 4 h after feeding. Under post-RF 72-hFD, the prefeeding peak of NPY mRNA was detected in the NST, but NPY mRNA levels in the ARC were continuously high throughout the 24-h period. These findings indicate that the NPY neurons from the NST are specifically activated by RF, whereas those from the ARC are generally stimulated by an increased food demand.     

Interleukin 1 beta enhances conditioned fear memory in rats: possible involvement of glucocorticoids

Central administration of 15 ng interleukin (IL)-1beta in the rat significantly enhanced conditioned fear memory assessed by a passive avoidance task, when retested at 24 and 48 h post-training. Pain threshold was unaffected by 15 ng IL-1beta administration. IL-1beta treatment also increased serum corticosterone. This increase in serum corticosterone was further enhanced in rats given both IL-1beta and footshock. Furthermore, the glucocorticoid receptor antagonist mifepristone blocked IL-1beta-induced elevation in corticosterone and also attenuated the enhanced conditioned fear memory. Central administration of IL-1beta significantly increased prostaglandin E2 and decreased the anti-inflammatory cytokine IL-10 release from whole blood cultures; therefore this treatment appears to be effective in inducing an inflammatory response in both the periphery and the brain. The present study confirms that IL-1beta can enhance conditioned fear memory, an effect which is correlated with changes in glucocorticoid function. This facilitation of defensive behaviour could reflect adaptive responses which may enhance survival during sickness.     

An antagonist of estrogen receptors blocks the induction of adult neurogenesis by insulin-like growth factor-I in the dentate gyrus of adult female rat

Interdependence between estradiol and insulin-like growth factor-I has been documented for different neural events, including neuronal differentiation, synaptic plasticity, neuroendocrine regulation and neuroprotection. In the present study we have assessed whether both factors interact in the regulation of neurogenesis in the adult rat dentate gyrus. Wistar albino female rats were bilaterally ovariectomized and treated with estradiol, insulin-like growth factor-I and/or the estrogen receptor antagonist ICI 182,780. Estradiol was administered in a subcutaneous silastic capsule. Insulin-like growth factor-I and ICI 182,780 were delivered in the lateral cerebral ventricle. Animals received six daily injections of 5-bromo-2-deoxyuridine and were killed 24 h after the last injection. The total number of 5-bromo-2-deoxyuridine-positive neurons was significantly increased in animals treated with insulin-like growth factor-I, compared with rats treated with vehicles, while rats treated with both insulin-like growth factor-I and estradiol showed a higher number of 5-bromo-2-deoxyuridine-positive neurons than rats treated with insulin-like growth factor-I or estradiol alone. The antiestrogen ICI 182,780 blocked the effect of insulin-like growth factor-I on the number of 5-bromo-2-deoxyuridine neurons with independence of whether the animals were treated or not with estradiol. These findings suggest that estrogen receptors are involved in the induction of adult neurogenesis by insulin-like growth factor-I in the dentate gyrus, and that estradiol and insulin-like growth factor-I have a cooperative interaction to promote neurogenesis. The interaction between insulin-like growth factor-I and estradiol may participate in changes in the rate of neurogenesis during different endocrine and physiological conditions, and may be related to the decline in neurogenesis with ageing.     

Gender specific effect of neonatal handling on stress reactivity of adolescent rats

Early neonatal handling of rat pups produces dampened hypothalamic-pituitary-adrenal axis reactivity to stress in adult male offspring. However, less is known about whether there is a similar effect for females. Although, most studies of neonatal handling have examined subsequent effects during adulthood, adolescence is an important developmental stage for stress responsivity. To address these issues, the effect of neonatal handling on the endocrine stress response and brain activity of male and female rats was determined in response to acute restraint stress during adolescence. Consistent with previous findings in adult males, neonatal handling reduced restraint stress-induced hormone levels in adolescent males. However, in contrast, we found elevated plasma hormone concentrations in handled females. A gender-specific handling effect on brain activity was also evident, with significantly increased stress-induced activation of the posterior cingulate cortex of handled females, as measured by c-fos mRNA expression. The striking gender difference in the effect of early neonatal handling provides evidence that this must be considered as an important variable in subsequent stress responsivity induced by early manipulations.