Estrogens influence behavioral responses in a kainic acid model of neurotoxicity

Effect of cytosine arabinoside on cerebellar neurofilaments during development: A sexual dimorphism

Previous reports suggest that the resistance of neuronal cytoskeleton to drug toxicity may vary with age and gender. The aim of the present study was to assess the impact of cytosine arabinoside (AraC) treatment on neurofilament (NF) levels and phosphorylation status in the developing cerebellum of male, female and testosterone propionate (1.25 mg/rat)-androgenized female rats. AraC (200 mg/kg bw) was administered from postnatal day (PND) 14–16 and changes in the level and phosphorylation of NFs were detected at PND 16 by Western blot analysis. The drug had no effect in male pups, while it increased the non-phosphorylated NF subunits of medium and low molecular weight in females. Androgenization of females prevented the AraC-induced increase in NF subunits. The levels of estrogen receptor beta (ER-β), known to mediate neuroprotective actions of estrogens in the brain, were significantly higher in the developing female cerebellum, as compared to males and androgenized females.

These data show that the neurofilament cytoskeleton in the developing rat cerebellum exhibits resistance to AraC that appears sexually dimorphic. In young males the resistance is exemplified by a lack of responsiveness, whereas in juvenile females it is presented by an androgenization-sensitive NF upregulation.

Gender differences in susceptibility to kainic acid-induced neurodegeneration in aged C57BL/6 mice

Some epidemiological studies concerning gender differences in Alzheimer's disease (AD) support the higher prevalence and incidence of AD in women, while most studies using animal models of aging have included only male subjects. It is still uncommon for aged males and females to be compared in the same study. In the present study, we investigated how age and gender influence the excitotoxic neurodegeneration by treating C57BL/6 mice (aged females and males as well as adult females and males) with kainic acid (KA) intranasally. Clinical signs, behavioural changes, pathological changes and astrocyte proliferation were tested; and the levels of brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) were measured after KA treatment. The results showed that aged female mice were more sensitive to KA-induced excitotoxicity as demonstrated by severer seizure activity, increased locomotion and rearing in open-field test, prominent hippocampal neuronal damage, enhanced astrocyte proliferation compared with aged males, adult females and adult male mice. In addition, higher BDNF level in hippocampus of aged female mice was observed. These results denote the disparity of aging and gender in KA-induced hippocampal neurodegeneration and aged female mice are more sensitive to the excitotoxicity.

The pharmacology, neuroanatomy and neurogenetics of one-trial object recognition in rodents

Rats and mice are attracted by novel objects. They readily approach novel objects and explore them with their vibrissae, nose and forepaws. It is assumed that such a single explorative episode leaves a lasting and complex memory trace, which includes information about the features of the object explored, as well as where and even when the object was encountered. Indeed, it has been shown that rodents are able to discriminate a novel from a familiar object (one-trial object recognition), can detect a mismatch between the past and present location of a familiar object (one-trial object-place recognition), and can discriminate different objects in terms of their relative recency (temporal order memory), i.e., which one of two objects has been encountered earlier. Since the novelty-preference paradigm is very versatile and has some advantages compared to several other memory tasks, such as the water maze, it has become a powerful tool in current neurophamacological, neuroanatomical and neurogenetical memory research using both rats and mice. This review is intended to provide a comprehensive summary on key findings delineating the brain structures, neurotransmitters, molecular mechanisms and genes involved in encoding, consolidation, storage and retrieval of different forms of one-trial object memory in rats and mice.

Effects of AraC treatment on motor coordination and cerebellar cytoarchitecture in the adult rat

Intact cerebellum cytoarchitecture and cellular communication are indispensable for successful motor coordination and certain forms of memory. Cytosine arabinoside (AraC), often used as an anti-neoplastic agent in humans, can have cerebellum-targeting adverse effects. In order to characterize the nature of AraC-induced cerebellar lesions in an adult rodent model, we have administered AraC (400 mg/kg b.w., i.p.) in adult male Wistar rats for 5 days. The animals' walking pattern, motor coordination, locomotion, spatial navigation and cognition were evaluated, along with neurofilament- and calbindin-like distribution in the cerebellum. AraC-treated rats demonstrated a disturbed walking pattern and a reduced ability of motor learning and coordination, indicative of a mild cerebellar deficit. Although the general locomotion and spatial cognition of AraC-treated rats was not significantly altered, their navigation into the water, in terms of swimming velocity, was irregular, compared to vehicle-treated animals. Neurofilament-like immunostaining was reduced in the molecular cerebellar layer, while calbindin D 28 kDa levels were increased in Purkinje neurons, following AraC treatment. Administration of the antioxidant N-acetylcysteine (NAC) (200 mg/kg b.w., p.o.), for 14 days (prior to and during AraC treatment) largely prevented the AraC-induced behavioral deficits. Our in vivo model of neurotoxicity provides data on the AraC-induced behavioral and cellular alterations concerning the adult rat cerebellum. Furthermore, it provides evidence of a possible neuroprophylactic role of the antioxidant N-acetylcysteine in this model of chemotherapy-induced toxicity.

Estradiol valerate and tibolone: effects on memory

This study investigated the effects of estradiol valerate (EV) and tibolone (TB) treatments on some memory parameters of ovariectomized young (2 months), adult (8 months) and old (20 months) female rats. A Sham-operated group was used as control and the animals were treated daily, by oral gavage, with saline (Sham and placebo NR group), EV (0.3 mg/kg) or TB (0.5 or 1 mg/kg, TB1 and TB2, respectively). In step-down inhibitory avoidance task, the latency of old TB2-treated females in the short-term test was significantly inferior (p<0.05), compared to TB2 adults. In the elevated plus maze, adult NR females spent significantly less time (p<0.05) in the open arms as compared with EV and TB2-treated animals. Additionally, adult TB2-treated females spent significantly less time in the closed arms compared to Sham, NR and TB1 groups. Finally, in the water maze retention test, young TB1-treated animals performed worse when compared to Sham, EV and TB2 females. In the old animals, EV treatment hampered subject performance as compared to all other treatments. Taken together, these results indicate that ovarian hormones differently affect female memory in an age-dependent manner.

Estrogen and brain-derived neurotrophic factor (BDNF) in hippocampus: complexity of steroid hormone-growth factor interactions in the adult CNS

In the CNS, there are widespread and diverse interactions between growth factors and estrogen. Here we examine the interactions of estrogen and brain-derived neurotrophic factor (BDNF), two molecules that have historically been studied separately, despite the fact that they seem to share common targets, effects, and mechanisms of action. The demonstration of an estrogen-sensitive response element on the BDNF gene provided an impetus to explore a direct relationship between estrogen and BDNF, and predicted that the effects of estrogen, at least in part, might be due to the induction of BDNF. This hypothesis is discussed with respect to the hippocampus, where substantial evidence has accumulated in favor of it, but alternate hypotheses are also raised. It is suggested that some of the interactions between estrogen and BDNF, as well as the controversies and implications associated with their respective actions, may be best appreciated in light of the ability of BDNF to induce neuropeptide Y (NPY) synthesis in hippocampal neurons. Taken together, this tri-molecular cascade, estrogen-BDNF-NPY, may be important in understanding the hormonal regulation of hippocampal function. It may also be relevant to other regions of the CNS where estrogen is known to exert profound effects, such as amygdala and hypothalamus; and may provide greater insight into neurological disorders and psychiatric illness, including Alzheimer's disease, depression and epilepsy.

Effects of exposing gonadectomized and intact C57BL/6J mice to a high-frequency augmented acoustic environment: Auditory brainstem response thresholds and cytocochleograms

Gonadectomized and surgically intact adult C57BL/6J (B6) mice of both sexes were exposed for 12h nightly to a high-frequency augmented acoustic environment (AAE): repetitive bursts of a half-octave noise band centered at 20 kHz, 70 dB SPL. The effects of sex, gonadectomy, and AAE treatment on genetic progressive hearing loss (exhibited by B6 mice) were evaluated by obtaining auditory brainstem response thresholds at ages 3-, 6-, and 9-months; hair cell counts (cytocochleograms) were obtained at 9 months. A sex difference in the rate of genetic progressive hearing loss in B6 mice (observed by earlier studies) was confirmed, with females exhibiting a faster rate of threshold elevations and more severe loss of hair cells at age 9 months. Gonadectomy had no consistent effects on the rate or severity of hearing loss in non-exposed mice of either sex. An unexpected finding was that the high-frequency AAE treatment caused additional ABR threshold elevations and hair cell loss. In an earlier study, the same high-frequency AAE treatment on DBA/2J mice ameliorated hearing loss. The most severe AAE-induced losses occurred in surgically intact females, suggesting a potentiating effect of ovarian hormone(s).