Prenatal alcohol exposure (PAE) is a common risk factor that predisposes subjects to an array of mental disorders, particularly drug addiction. Due to elusive understanding of PAE-elicited neuroadaptations, available options to prevent and treat PAE-induced disorders are limited. In this proposed research, a three-part hypothesis regarding the synaptic mechanisms by which PAE affects risk for addictions in later life will be evaluated. The first part of this hypothesis stipulates that a major glutamatergic pathway, originating in the medial prefrontal cortex (mPFC) and directly influencing the principal neuronal population in the nucleus accumbens (NAc), the medium-sized spiny neurons (MSNs), is targeted by PAE to promote addiction development. Additionally, sub-regions of the mPFC target distinct compartments of the NAc, with the infralimbic mPFC (IL) preferentially projecting to the NAc shell and the prelimbic mPFC (PrL) to the NAc core; a second feature of our hypothesis is the idea that PAE-induced synaptic alterations are pathway/projection-specific. The third component of our hypothesis postulates that PAE leads to aberrant synaptic development in the NAc by accelerating the pruning/maturation of silent synapses (SSs), thought to be immature glutamatergic synapses containing stable NMDA receptors (NMDARs) but lacking stable AMPA receptors (AMPARs), and that this abnormal maturational process results from the recruitment of atypical Ca2+-permeable (CP)-AMPARs in the MSNs. Based upon our preliminary data, we predict that (1) Maturation/pruning of SSs is accelerated in the IL- shell projections but not PrL-core from rats subjected to PAE, compared to control animals (prenatal control exposure, PCE), (2) PAE affects the maturation/pruning of SSs via the recruitment of atypical CP-AMPARs, rather than the typical Ca2+-impermeable (CI)-AMPARs into excitatory synapses on MSNs in the NAc, and (3) PAE predisposes animals to heightened drug-seeking, an effect that can be reversed by manipulating PAE- induced SS-based synaptic alterations in the specific excitatory innervation to the NAc. These hypotheses will be tested employing state-of-the-art techniques including whole-cell patch clamp, intravenous self-administration, optogenetics, single-cell staining and spine labeling. The outcome of this work will provide a novel and precise approach to understanding the neural mechanisms underlying PAE-induced mental disorders such as substance abuse, and to discovering novel biological targets for treatment.
The concept of silent synapses will be introduced for the first time to alcohol studies. T hese immature and modifiable synapses are targeted by p renatal alcohol exposure (PAE) and atypical glutamate AMPA receptors are involved in the maturation of these silent synapses after PAE. We will disable these atypical AMPA receptors to reverse PAE-induced abnormal synapses and reduce their vulnerability to drugs of abuse, through which we hope to improve the understanding of neural mechanisms and provide a precise target for reversing the high risk of drug addiction in PAE individuals.
