Over the past two decades, obtaining a better understanding of the physiological significance of co- localization of neuropeptide and classical neurotransmitters such as norepinephrine (NE) in the brain has been an important yet elusive goal in neuroscientific research. NE modulates a variety of processes involved in the response to stress. However, several observations have suggested that NE interacts in important ways with other modulatory neurotransmitters with which it may be co-localized, for the full manifestation of this modulatory influence. In this project, we propose using a multidisciplinary strategy of pharmacological, physiological, behavioral, neurochemical and anatomical approaches to investigate the functional interaction of NE and galanin (GAL), a neuropeptide with which it is prominently co-localized. It is thought that NE acts in limbic forebrain regions, such as central amygdala (CeA) and lateral bed nucleus of the stria terminalis (BSTL), to facilitate neuroendocrine and behavioral components of the stress response. We hypothesize that under conditions of intense activation of the noradrenergic system, GAL is released along with NE in the CeA and BSTL, and acts to buffer the modulatory effects of NE on these affective and hormonal components of the stress response. These hypotheses will be tested by exposing rats to acute immobilization stress, and selectively amplifying the stress-induced activation of the noradrenergic system by pretreatment with yohimbine. The first two aims are pharmacological investigations.
In Aim 1, a GAL antagonist will be microinjected, alone or with an adrenergic antagonist, directly into CeA or BSTL of rats to test the hypothesis that GAL attenuates the facilitatory effect of NE on stress-induced ACTH secretion when stress-induced activation of the NE system is amplified by yohimbine. Similarly, Aim 2 tests the hypothesis that GAL attenuates the facilitatory influence of NE on stress-induced anxiety, as measured on the social interaction test and the elevated plus maze test. The last two aims are to investigate the neural mechanisms and substrates underlying these interactions.
Aim 3 addresses the neurochemical substrates underlying these interactions by measuring GAL release in CeA and BSTL using microdialysis. Finally, in Aim 4, immunocytochemistry and in situ hybridization will be used io reveal the anatomical substrates for these interactions, by identifying cells in CeA and BSTL that are activated by stress and also express post-synaptic receptors for NE and GAL. In sum, the experiments outlined in this proposal represent a multidisciplinary investigation of the interaction of the neuropeptide GAL with the classic monoaminergic neurotransmitter NE, in modulating hormonal and affective components of the stress response in CeA and BSTL. By providing a basic neurobiological context within which to better understand the functional and regulatory interactions between monoamines and neuropeptides, these results may guide the future development of novel or more effective therapeutic strategies for the treatment of stress- related psychiatric disorders such as depression, anxiety or PTSD.
