Learning disabilities are the most common behavioral deficit observed in patients with Fetal Alcohol Spectrum Disorder (FASD). Currently, there are no established clinically effective pharmacotherapeutic interventions for these behavioral problems. Using a well-established rat model of FASD, we have reported that the histamine H3 receptor inverse agonist / antagonist ABT-239 ameliorates prenatal alcohol exposure (PAE)-induced deficits in synaptic plasticity and learning. We have also observed increased H3 receptor-effector coupling and a heightened H3 receptor-mediated inhibition of the probability of glutamate release in dentate gyrus of PAE rats. Collectively, these results suggest that PAE increases H3 receptor-mediated inhibition of glutamate release and that ABT-239 reduces this heightened inhibitory influence. One parsimonious explanation for why PAE rats are more sensitive to H3 receptor agents is a PAE-induced increase in the expression of the rH3A isoform of histamine H3 receptors relative to the rH3C isoform. This putative shift would confer greater sensitivity to the inhibitory effects of histamine H3 receptor agonists in PAE rats. The principal objectives of this NMARC research component application are to: 1) Examine whether PAE increases the expression of rH3A relative to rH3C in entorhinal cortical neurons projecting to the dentate gyrus. 2) More thoroughly establish the consequences of a PAE-induced elevation in H3 receptor-effector coupling and the effects of second H3 receptor inverse agonist / antagonist namely, SAR152954, on H3 receptor-mediated inhibition of glutamatergic neurotransmission in dentate gyrus.
In Specific Aim 1 A, we will employ in situ hybridization and qRT-PCR approaches to first confirm whether PAE increases the rH3A/rH3C mRNA expression ratio.
In Aim 1 B, we will use a [35S]-GTP?S binding assay in histological sections to conduct a more detailed examination of the effects of PAE on H3 receptor- effector coupling and assess the differential sensitivity of PAE rats to SAR152954 relative to controls.
In Specific Aim 2 A, we will conduct in vitro slice physiology studies to examine: 1) The impact of PAE on the effects of the H3 receptor agonist methimepip on fEPSP responses and pair-pulse plasticity in dentate gyrus, under baseline and after theta burst stimulation conditions. 2) The effects of SAR152954 alone and in the presence of methimepip on paired-pulse ratio and long-term potentiation.
In Aim 2 B, we will examine the impact of PAE on fEPSP and PPR before and after high frequency stimulations in awake freely moving rats. We predict that SAR152954 will ameliorate the heightened H3 receptor mediated inhibition of synaptic plasticity in PAE rats at concentrations/doses that do not impair synaptic transmission in control rats. These studies address two of the three strategic objectives of NMARC, namely advancing our understanding of the neurobiological consequences of PAE, as well as working towards establishing the mechanistic basis for novel interventions to treat of PAE- induced deficits in synaptic plasticity and memory. These studies could provide additional preclinical rational for considering drugs such as SAR152954 for clinical trials in patients with FASD. 1
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