Brian E. Derrick - US grants

The objective of the proposed activity of the CNRC will be to organize a year-round Seminar in the Neurosciences. Eminent National and International neuroscientists will be invited to UTSA, and allowed to interact with CNRC participants on a bi-weekly basis. Speakers chosen will include members of the External Advisory Board and Mentors for the subprojects proposed by individual investigators. This interaction will include two primary events: (1) Presentation of the visiting scientists's most recent findings to faculty and students *in a Symposium format; (2) One-on-one interaction with individual CNRC members and other faculty with related interests to allow sharing of new techniques and knowledge among those with similar interests. Each participant will spend approximately two to three days at the center to provide the presenters time to participate in each of these activities. Invited participants are requested by members of the center, and will include renowned scientists in the fields of neuroanatomy, neurocomputation, molecular neuroscience, cellular physiology, neurophysiology, developmental neuroscience, and behavioral neuroscience. Speakers also will include those whose research is of clinical relevance, addressing neurological disorders and findings with clinical relevance.

DESCRIPTION: (Adapted From The Applicant's Abstract): The overall goal of this project is to evaluate the contribution of opioid and NMDA receptors in the induction of associative long term potentiation (LTP) in the major afferent systems of the CA3 region of the hippocampus. The CA3 region receives afferents displaying two forms of LTP induction: NMDA receptor and opioid receptor- dependent. Opioid receptor-dependent LTP is observed in medial perforant path and commissural projections to area CA3. Out initial studies show that mossy fiber projections to area CA3 display associative LTP, but associative mossy fiber LTP induction requires repetitive synaptic activity, which is necessary for the activation of opioid receptors. However, associative mossy fiber LTP also is blocked by NMDA receptor antagonists. Likewise, the induction of NMDA receptor-dependent LTP at medial perforant path-CA3 synapses is blocked by opioid receptor antagonists when it is induced by coactivation of opioidergic afferents. Our primary hypothesis is that both opioid and NMDA receptors contribute to associative LTP induction between synapses utilizing these different induction processes. The studies in specific aim 1 will determine if opioid and/or NMDA receptor antagonists alter associative LTP induction between the opioid receptor-dependent LTP at lateral perforant path-CA3 synapses and NMDA receptor-dependent medial perforant path-CA3 synapses using each projection as either the weakly stimulated (associated) or the strongly stimulated (conditioning) pathway. The studies in specific aim 2 will determine if associative LTP in opioidergic afferents is frequency-dependent by virtue of frequency-dependent opioid peptide release, and if associative LTP in afferents displaying opioid receptor-dependent LTP confer frequency-dependent constraints on LTP induction at non- opioidergic synapses. This will be determined by using a single- pulse associative paradigm, in which low frequency stimulation of one pathway is paired with high-frequency stimulation of another pathway in the presence of oioid receptor selective antagonists. The studies in specific aim 3 will determine if the optimal temporal parameters of associative interaction among CA3 afferents corresponds to the normal sequence of activation by CA3 afferents, and if opioid peptides contribute to this effect. These data will have implication regarding conditions in which associative information storage may normally occur among the afferent systems of the CA3 region. Because each pathway displays distinct requirements for associative LTP inductions, endogenous opioid peptides may confer both temporal and frequency-dependent constraints on the associative induction of LTP. This would suggest that the order of afferent activity and opioid peptide release may regulate virtually all associative information storage occurring among projections to the CA3 region of the hippocampus.

neurosciences; meeting /conference /symposium; minority institution research support; biomedical facility;

granule cell; long term potentiation; neurogenesis; synapses; cell proliferation; evoked potentials; cooperative study; dentate gyrus; cell differentiation; stimulus /response; neural plasticity; mossy fiber; apoptosis; electrophysiology; laboratory rat;

long term potentiation; neurotransmitters; neural plasticity; gene expression; neural information processing; hippocampus; neural facilitation; neurotransmitter antagonist; developmental genetics; neuropharmacology; cholinergic receptors; adrenergic receptor; memory; behavior test; controlled environment; electrophysiology; electrodes; electroencephalography; laboratory rat;

DESCRIPTION (provided by applicant): New neurons are continually added to the granule cell (GC) layer of the dentate gyrus during adulthood. Within 2 weeks, over 50% of these granule cells die, with most surviving GCs incorporating into the dentate circuit. Although the functional significance of dentate neurogenesis is unclear, treatments that reduce GC neurogenesis impair associative memory, and associative learning tasks increase the survival of new GCs. Thus the regulation of GC survival appears important for associative learning. Our preliminary studies show low-frequency stimulation of the perforant pathway, the principal glutamatergic projection to the dentate gyrus, confers complete survival of immature GC neurons 8 days of age. Furthermore, subsequent activation of the same perforant path fibers 1 week later induces the immediate-early gene (IEG) Zif268 in immature neurons. Our primary hypothesis is afferent activity promotes GC survival, most likely via GABAa receptor activation. This, in turn, initiates rapid development of immature GCs into functional, mature GCs that display NMDA receptors and synaptic plasticity as reflected in the activity-dependent expression of the IEG Zif268. To test these hypotheses, we will use adult rats with permanently implanted electrodes in the perforant pathway and dentate gyrus. The effects of perforant path stimulation on GC neurogenesis is assessed by administering bromodeoxyuridine (BrdU), a thymidine analog incorporated only in dividing cells, in conjunction with unbiased stereology and fluorescent immuno-cytochemistry to quantify BrdU-positive cells, IEG protein expression and markers of GC development (progenitor, immature and mature). In the studies of Specific Aim 1, we will determine the `critical period'after mitosis during which perforant path stimulation can confer survival of newly- generated GC neurons. We also will explore the factor(s) that are provided by afferent activity that confer GC survival, and determine whether local or systemic administration of GABAa, AMPA, or NMDA receptor antagonists block GC survival mediated by perforant path stimulation. In Specific Aim 2, we will determine if conferring survival of 8 day old GCs also accelerates their functional development This will be assessed by determining the earliest time point when NR2B NMDAR subunits and Zif268, an IEG protein implicated in synaptic plasticity, can be expressed following afferent-induced GC survival when compared with unstimulated GCs of the same age. We also will explore possible factors provided by afferent activity that are crucial for Zif268 expression, and determine if GABAa, AMPA, or NMDA receptor antagonists block Zif268 expression in surviving GCs. In Specific Aim 3, we will determine if increasing or depleting the population of 8-day old, survival-competent GCs facilitates or impairs performance in spatial or episodic memory tasks. These studies will contribute to understanding stem cell survival, crucial for treating neurological disorders, and will facilitate the PI's development goal of obtaining mainstream funding to maintain a viable research/teaching laboratory environment at a minority institution. Public Health Relevance: An understanding of neurogenesis in the adult dentate gyrus will provide information regarding how the functional development of immature granule cells is regulated by synaptic activity in vivo. The factors necessary for neuronal survival and appropriate targeting of neurons generated from adult stem cells remain unknown, limiting the ability of transplanted cells to be used as a treatment for various diseases- such as Alzheimer's disease, Parkinson's disease, ischemia, and brain trauma - that involve a loss of neurons. As regulating neuronal stem cell survival is essential to achieve the goal of treatment with stem cells, these studies will provide crucial information on how neuronal stem cells survive and incorporate into extant neural circuits, and address a major caveat in stem cell therapy.