The long-term goals of our research program are to determine how gestational cocaine exposure changes the course of development of neural circuits that mediate cognitive, emotional and reward systems. Intravenous, low dose cocaine administration to pregnant rabbits results in enhanced dendritic growth by cortical projection neurons and increased expression of a Ca++-binding protein by interneurons. There is a striking reduction in DA D1 receptor coupling to its respective G-protein, resulting in a permanent loss of D1 receptor-mediated responses. Defects occur predominantly in regions of dense dopamine (DA) innervation, such as anterior cingulate cortex (ACC) and striatum. The onset of changes occurs embryonically and persists in the adult, in many ways mimicking receptor loss. Our preliminary studies in the D1 receptor knockout mouse reveal similar abnormalities in ACC neuron development. The data suggest that changes in D1 receptor signaling initiate a cascade of alterations that results in abnormal development of forebrain circuits. Thus, the prenatal drug exposure and genetic models each provide unique opportunities for understanding the impact of substance abuse on forebrain development. Studies will probe mechanisms underlying the cellular and molecular adaptations. In addition, we will test how these adaptations alter future CNS responsiveness to cocaine and specific stressors, such as glutamate excitotoxicity. Experiments in three specific aims will use biochemical. neuroanatomical and molecular approaches to address the hypotheses.
In Aim 1, we will investigate changes in cell signaling through which in utero cocaine exposure alters dendritic growth. We will analyze alterations in the phosphorylation state of proteins comprising the converging DA and glutamate signaling systems. D1 receptor uncoupling could be caused by changes in receptor trafficking. Experiments will examine aberrant cytoplasmic sequestration of DA receptors. To more specifically link DA receptor dysfunction to developmental abnormalities changes will be examined in the D1 -I- mouse and in rabbits treated gestationally with a direct D1 agonist.
In Aim 2 experiments will investigate the mechanisms through which in utero cocaine exposure disrupts the development of interneurons. Neuroanatomical analysis will establish whether D1 receptor co-expression by specific subpopulations of interneurons defines the cells most susceptible to gestational cocaine. Intracellular dye labeling of interneurons will be used to analyze dendritic development under circumstances of DA receptor dysfunction.
In Aim 3, two experimental approaches will be used to investigate how the CNS, first exposed to cocaine prenatally, responds to later cocaine exposure or excitotoxic insults. First, using gene microarrays, we will determine differences in transcriptional responses that are induced by cocaine challenges in normal and experimental rabbits. Second, the excitotoxic responsiveness o isolated neurons from normal and cocaine-exposed animals will be investigated in cell-based assays. The interdisciplinary approaches will define alterations in brain structure and molecular adaptations due to prenatal cocaine exposure, with a goal ultimately to design interventions that may ameliorate the long-term behavioral consequences o drug exposure.
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