Effects of neonatal stimulation on later cognitive function and hippocampal nerve growth factor

Behavioral insensitivity to restraint stress, absent fear suppression of behavior and impaired spatial learning in transgenic rats with hippocampal neuropeptide Y overexpression

Exogenous neuropeptide Y (NPY) reduces experimental anxiety in a wide range of animal models. The generation of an NPY-transgenic rat has provided a unique model to examine the role of endogenous NPY in control of stress and anxiety-related behaviors using paradigms previously used by pharmacological studies. Locomotor activity and baseline behavior on the elevated plus maze were normal in transgenic subjects. Two robust phenotypic traits were observed. (i) Transgenic subjects showed a markedly attenuated sensitivity to behavioral consequences of stress, in that they were insensitive to the normal anxiogenic-like effect of restraint stress on the elevated plus maze and displayed absent fear suppression of behavior in a punished drinking test. (ii) A selective impairment of spatial memory acquisition was found in the Morris water maze. Control experiments suggest these traits to be independent. These phenotypic traits were accompanied by an overexpression of prepro-NPY mRNA and NPY peptide and decreased NPY-Y1 binding within the hippocampus, a brain structure implicated both in memory processing and stress responses. Data obtained using this unique model support and extend a previously postulated anti-stress action of NPY and provide novel evidence for a role of NPY in learning and memory.

Use of osmotic minipumps for sustained drug delivery in rat pups: effects on physical and neurobehavioural development

Osmotic minipumps are often used as an alternative to repetitive injections for prolonged drug delivery in adult rats. The appropriateness of using this technology for sustained drug delivery in newborn rats, however, has not been validated. Our objective was to determine if implantation of osmotic minipumps, and the associated surgical stress, during a critical developmental period, affects early development and subsequent behaviour. SD rat pups were assigned to control, minipump, or sham surgery treatment conditions (n=12/group). On P8, pups were briefly anaesthetised with isoflurane in oxygen, and Alzet 1007D osmotic minipumps, loaded with normal saline, were aseptically implanted (removed on P17). Sham-treated rats received identical treatment (with the exception of pump placement), while control pups were left undisturbed. Development was examined daily using a standard test battery (P9-P21), and learning and memory in pups was assessed in a T-maze (P15, P17 and P19). Weight (P27 and P72), open-field (P25, P26 and P27) and novel water maze performance (P60-P72) were examined in the resulting adult. With the exception of a transient decrease in weight gain, pump-treated animals did not differ from either sham or control rats, on any pre- or postweaning assessment. Based on these results we conclude that the use of osmotic minipumps in rat pups is a viable alternative to repeated injections for sustained drug delivery.

Environmental stimulation increases survival in mice transgenic for exon 1 of the Huntington's disease gene

Mice transgenic for the first exon of the human Huntington's disease (HD) gene carrying an expanded CAG repeat expansion (R6/2 line) develop a progressive neurologic phenotype with symptoms resembling those seen in HD. The overt symptoms of R6/2 mice worsen with age, resulting in a rapid decline in health and premature death between 13 and 18 weeks of age. In this study, we characterized the onset and progression of the overt phenotype in R6/2 mice and examined factors that affect the phenotype and life expectancy of these mice. In particular, the effects of altering home cage environment, through changing feeding regimes and providing environmental stimulation, were investigated. We show that changes in feeding regimes significantly improved the general well-being and life expectancy of R6/2 mice. Furthermore, we find that various forms of environmental stimulation, including regular behavioral testing, significantly improved the survival of R6/2 mice over and above that resulting from the enhanced feeding regime. The fact that environmental stimulation improves the health and life expectancy in R6/2 mice not only enables the mice to serve as more useful research tools, but also suggests that environmental stimulation may have a beneficial impact on the progression of HD in patients.

Effects of multisensory environmental stimulation on contextual conditioning in the developing rat

The effect of increased exposure to multisensory stimulation during development on conditioned freezing to contextual cues in preweanling Sprague-Dawley rats was examined. Rats given increased environmental stimulation exhibited long-term contextual conditioning at a younger age than rats that did not receive such stimulation when there was either low or moderate levels of conditioning (Experiments 1 and 2). These differences in contextual conditioning were not a result of the stimulated rats reacting differently to shock (Experiment 4) or merely freezing more than the nonstimulated rats in all situations (Experiment 3). The role of the glucocorticoid system in the enhanced contextual learning of stimulated preweanling rats and the advantages of the contextual conditioning procedure for studying the effects of environmental stimulation are discussed.

Long-term environmental enrichment leads to regional increases in neurotrophin levels in rat brain

A number of studies have demonstrated that both morphological and biochemical indices in the brain undergo alterations in response to environmental influences. In previous work we have shown that rats raised in an enriched environmental condition (EC) perform better on a spatial memory task than rats raised in isolated conditions (IC). We have also found that EC rats have a higher density of immunoreactivity than IC rats for both low and high affinity nerve growth factor (NGF) receptors in the basal forebrain. In order to determine if these alterations were coupled with altered levels of neurotrophins in other brain regions as well, we measured neurotrophin levels in rats that were raised in EC or IC conditions. Rats were placed in the different environments at 2 months of age and 12 months later brain regions were dissected and analyzed for NGF, brain-derived neurotrophic factor (BDNF), and neurotrophin-3 (NT-3) levels using Promega ELISA kits. We found that NGF and BDNF levels were increased in the cerebral cortex, hippocampal formation, basal forebrain, and hindbrain in EC animals compared to age-matched IC animals. NT-3 was found to be increased in the basal forebrain and cerebral cortex of EC animals as well. These findings demonstrate significant alterations in NGF, BDNF, and NT-3 protein levels in several brain regions as a result of an enriched versus an isolated environment and thus provide a possible biochemical basis for behavioral and morphological alterations that have been found to occur with a shifting environmental stimulus.

The importance of neurobiological research to the prevention of psychopathology

There is both a biological and environmental component to the neural substrates for various forms of psychopathology. Brain dysfunction itself not only constitutes a formidable liability to psychopathology, but also has an impact on environmental and social responses to the individual, compounding the risk for an adverse outcome. Environmental conditions, such as social and physical stimulus deprivation, poverty, traumatic stress, and prenatal drug exposure, can further compromise brain function in the context of existing liabilities. The relationship between genetic and environmental processes is interactive, fluid, and cumulative in their ability to influence an individual's developmental trajectory and alter subsequent behavioral outcomes. Given the codependent relationship between these processes, brain function is now believed to be malleable via manipulations of the environment in ways that may decrease liability for psychopathology. Research that explores these relationships and ways in which interventions can redirect this developmental track may substantially advance both the science and practice of prevention. Studies attempting to isolate the neurobiological effects of socioenvironmental factors are reviewed, implications for intervention strategies are discussed, and a future research agenda is proposed to provide greater insight into specific brain-environment relationships. Armed with this knowledge, prevention scientists may eventually design programs that directly target these effects to reverse or attenuate negative outcomes.

A unifying hypothesis of Alzheimer's disease. III. Risk factors

Normal ageing and Alzheimer's disease (AD) have many features in common and, in many respects, both conditions only differ by quantitative criteria. A variety of genetic, medical and environmental factors modulate the ageing-related processes leading the brain into the devastation of AD. In accordance with the concept that AD is a metabolic disease, these risk factors deteriorate the homeostasis of the Ca(2+)-energy-redox triangle and disrupt the cerebral reserve capacity under metabolic stress. The major genetic risk factors (APP and presenilin mutations, Down's syndrome, apolipoprotein E4) are associated with a compromise of the homeostatic triangle. The pathophysiological processes leading to this vulnerability remain elusive at present, while mitochondrial mutations can be plausibly integrated into the metabolic scenario. The metabolic leitmotif is particularly evident with medical risk factors which are associated with an impaired cerebral perfusion, such as cerebrovascular diseases including stroke, cardiovascular diseases, hypo- and hypertension. Traumatic brain injury represents another example due to the persistent metabolic stress following the acute event. Thyroid diseases have detrimental sequela for cerebral metabolism as well. Furthermore, major depression and presumably chronic stress endanger susceptible brain areas mediated by a host of hormonal imbalances, particularly the HPA-axis dysregulation. Sociocultural and lifestyle factors like education, physical activity, diet and smoking may also modulate the individual risk affecting both reserve capacity and vulnerability. The pathophysiological relevance of trace metals, including aluminum and iron, is highly controversial; at any rate, they may adversely affect cellular defences, antioxidant competence in particular. The relative contribution of these factors, however, is as individual as the pattern of the factors. In familial AD, the genetic factors clearly drive the sequence of events. A strong interaction of fat metabolism and apoE polymorphism is suggested by intercultural epidemiological findings. In cultures, less plagued by the 'blessings' of the 'cafeteria diet-sedentary' Western lifestyle, apoE4 appears to be not a risk factor for AD. This intriguing evidence suggests that, analogous to cardiovascular diseases, apoE4 requires a hyperlipidaemic lifestyle to manifest as AD risk factor. Overall, the etiology of AD is a key paradigm for a gene-environment interaction. Copyright 2000 John Wiley & Sons, Ltd.

Effects of environmental enrichment on cognitive function and hippocampal NGF in the non-handled rats

In this study we examine whether exposure to differential housing after weaning would counteract the effects of postnatal handling (H) or nonhandling (NH) treatment by affecting learning and memory processes in young rats. In addition, we seek to determine if experience in enriched environment would alter hippocampal nerve growth factor (NGF) levels which is one of the factors known to be involved in the regulation of the survival and differentiation of developing basal forebrain neurones. Rats were either exposed to handling treatment, or left undisturbed starting day 1 after birth through day 21. After weaning on day 22, we exposed half of the H rats and half of the NH rats to environmental enrichment for 60 days. The other respective half of the rats was housed in isolated environmental condition (IC). Behavioural measures were taken in open field test, and spatial water maze test. Exposure to enriched environment following postnatal handling and nonhandling increased hippocampal NGF levels, and improved cognitive function in the both groups, with NH rats being more responsive to the effects of enrichment. Our results suggest that environmental enrichment has the potential to prevent or reduce the cognitive and neurochemical deficits in the adult animals associated with nonhandling.