Effects of peripubertal pharmacological blockade of GnRH action on neuronal function and architecture.

It has long been recognised that hormones have a profound effect on how we think and behave. Modern imaging studies have shown that there are hormone dependent effects on both the structure and functioning of the brain, which might explain these effects of hormones on behaviour in both humans and animals. While some of these hormone induced differences may start very early in life, including prior to birth, it has also been suggested that the changes in reproductive hormones at puberty may lead to alterations in the structure of the brain and its cells that could be responsible for differences in social behaviour and the way we process information as adults. Consequently, any changes in the pattern of hormones experienced at puberty (either naturally or as a result of medical interventions or exposure to chemicals in our environment) may affect normal brain development. In this regard, it is worthy of note that there are known changes in behaviour as humans and animals go through the pubertal transition, such as increased risk taking and there are a variety of clinical conditions associated with altered brain function such as schizophrenia, eating- and obsessive compulsive-disorders, which often become apparent at puberty. Using the sheep as an animal model, this project will tease apart the effects of changes in reproductive hormones on male brain development and whether the peripubertal period represents a critical period of normal brain development. This will be done by blocking the pubertal transition in male sheep using a drug treatment currently used to block puberty in human patients for a variety of medical conditions including growth retardation and early onset gender identity disorder. We will do this by either delaying puberty or differentiating the effects of GnRH (a hormone produced in the brain that drives activity within the reproductive system) and gonadal steroids, by replacing testosterone in animals in which activity within the reproductive axis was stopped by blocking the effects of GnRH. This work is of significance as the medical blockade of puberty is widely used in the treatment of a variety of conditions in human medicine, including growth deficiency and gender dysphoria. If the pubertal changes in reproductive hormones indeed play a crucial role in the maturation of the adolescent brain, the cognitive and/or reproductive functions of patients receiving this treatment may be permanently affected. This work also has the potential to inform us about changes in cognitive function that occur as we age and may contribute to the risk of developing conditions such as Alzheimer's disease, as these changes also occur when the levels of reproductive hormones in the body change as reproductive function declines. This project will contribute to a fundamental understanding of the mechanisms that underlie the interaction between endocrine factors and the neural changes that occur in association with activation and senescence within the reproductive system. Achieving these objectives may direct intervention strategies that can be used in the treatment of neurocognitive conditions, the incidence/risk of which increases at puberty, such as obsessive compulsive disorder and schizophrenia and with ageing e.g. Alzheimer's disease.

It has long been recognised that behaviour and cognitive function are influenced by reproductive state and differ between the sexes as a consequence of differential steroid exposure. Recent advances in neuroimaging methods have allowed identification of differences in brain structures that may underlie such sexual dimorphisms. Recently, GnRH receptor expression has been documented in extra-hypothalamic areas (e.g. the hippocampus), providing a possible link between puberty and sex differences in behaviour and cognition. Classically, sexual differentiation of the brain is thought to occur following prenatal exposure to gonadal steroids. However, profound neuronal development also occurs during adolescence. While puberty is characterised by marked hormonal changes, little is known about the influence of pubertal hormones on the organisation of neural networks, behaviour and cognitive ability. This study will temporally delay puberty using a GnRH agonist treated ovine model and examine effects of dissociation of pubertal hormone changes and developmental age, on behaviour, cognitive function, neuroendocrine systems and neuronal architecture in the hypothalamus and non-endocrine brain regions. Real-time rtPCR, in-situ hybridisation and immunohistochemical methods will be used to investigate steroid receptor expression and neurotransmitter systems in the pituitary gland and hypothalamus. As steroids (including locally produced neural oestrogen) can have a profound influence on neuronal plasticity, synaptic density and dendritic spine morphology will be investigated in the hippocampus and amygdala using immunohistological, biochemical and electron microscopy techniques. The study will elucidate long-term effects of pharmacological blocking, or significantly delaying, puberty and will inform us relative to endocrine causes of neuropathological conditions seen upon reaching adulthood and following reproductive senescence.

1) Who will benefit from the research? The research that is proposed in this grant application aims to understand the consequences and fundamental mechanisms by which peripubertal exposure to a GnRH agonist alters brain function and impacts on cognition and behaviour. Those who will benefit are patients who are currently treated in the medium or long term with such agonists, including patients with steroid stimulated benign or malignant tumours, those with growth deficiency and gender identity disorder. As GnRH receptors are also found in non reproduction controlling areas of the brain and in other peripheral tissues the research has potential to impact on other conditions which manifest themselves at times of change in GnRH secretion; at puberty and as reproductive function declines. These conditions include, seriously debilitating and potentially life limiting neurocognitive illnesses like schizophrenia, obsessive compulsive disorder, anorexia nervosa and dementias. In addition health professionals will benefit from a better understanding of the consequences of giving GnRH agonists to their clients. Specialised drug companies may better understand the pharmacological effects of their products, be able to better target drug their development programmes for increased safety profiles and wealth creation. Policy makers will be better informed to make key financial and strategic decisions. The general public will be made more aware of the impact of substances in their environment that can affect their health and wellbeing in later life. This may impact on lifestyle choices for the benefit of the individual and dependents. Students and researchers will gain from training in the area of neuroscience and reproductive and behavioural science and the University will gain from employment for technical and administrative staff.
2) How will they benefit? The patients will benefit from a better informed health, pharmaceutical and health policy sectors and their treatment can be better tailored to their needs. This will have knock on effects for family and carers and increase the general wellbeing of subsections of society. Scientists, especially those researching brain function and how is may be altered during key developmental windows, will expand these areas of research and train and employ others in their endeavours. Other benefits have been outlined in the previous section.