Neurodevelopmental disorders (NDDs) are a widespread and growing public health challenge, affecting as many as 17% of children in the United States. Recent epidemiological studies have implicated ambient exposure to pyrethroid pesticides during pregnancy in the risk for NDDs in the unborn child. Using a litter-based, independent discovery–replication cohort design, we exposed mouse dams orally during pregnancy and lactation to the Environmental Protection Agency's reference pyrethroid, deltamethrin, at 3 mg/kg, a concentration well below the benchmark dose used for regulatory guidance. The resulting offspring were tested using behavioral and molecular methods targeting behavioral phenotypes relevant to autism and NDD, as well as changes to the striatal dopamine system. Low-dose developmental exposure to the pyrethroid deltamethrin (DPE) decreased pup vocalizations, increased repetitive behaviors, and impaired both fear conditioning and operant conditioning. Compared with control mice, DPE mice had greater total striatal dopamine, dopamine metabolites, and stimulated dopamine release, but no difference in vesicular dopamine capacity or protein markers of dopamine vesicles. Dopamine transporter protein levels were increased in DPE mice, but not temporal dopamine reuptake. Striatal medium spiny neurons showed changes in electrophysiological properties consistent with a compensatory decrease in neuronal excitability. Combined with previous findings, these results implicate DPE as a direct cause of an NDD-relevant behavioral phenotype and striatal dopamine dysfunction in mice and implicate the cytosolic compartment as the location of excess striatal dopamine.

The dopamine D 3 receptor (D 3 R) has emerged as a promising pharmacotherapeutic target for the treatment of several diseases including schizophrenia, Parkinson's disease, and substance use disorders. However, studies investigating the D 3 R's precise role in dopamine neurotransmission or how it may be exploited to modulate responses to drugs of abuse have produced contrasting results, in part because most D 3 R-targeted compounds often also interact with D 2 receptors (D 2 R). To resolve this issue, we set out to systematically characterize and compare the consequences of selective D 2 R or D 3 R antagonists on the behavioral-stimulant properties of cocaine in mice, and to identify putative neurobiological mechanisms underlying their behavior-modifying effects. Pretreatment with the selective D 2 R antagonist L-741,626 attenuated, while pretreatment with the selective D 3 R antagonist PG01037 enhanced, the locomotor-activating effects of both acute cocaine administration as well as sensitization following repeated cocaine dosing. While both antagonists potentiated cocaine-induced increases in presynaptic dopamine release, we report for the first time that D 3 R blockade uniquely facilitated dopamine-mediated excitation of D 1-expressing medium spiny neurons in the nucleus accumbens. Collectively, our results demonstrate that selective D 3 R antagonism potentiates the behavioralstimulant effects of cocaine in mice, an effect that is in direct opposition to that produced by selective D 2 R antagonism or nonselective D 2-like receptor antagonists, and is likely mediated by facilitating D 1-mediated excitation in the nucleus accumbens. These findings provide novel insights into the neuropharmacological actions of D 3 R antagonists on mesolimbic dopamine neurotransmission and their potential utility as pharmacotherapeutics.

Background:The D3 receptor (D3R) has emerged as a promising pharmacotherapeutic target for the treatment of several diseases including schizophrenia, Parkinson's disease, and substance use disorders. However, studies investigating the modulatory impact of D3R antagonism on dopamine neurotransmission or the effects drugs of abuse have produced mixed results, in part because D3R-targeted compounds often also interact with D2 receptors (D2R). The purpose of this study was to compare the consequences of selective D2R or D3R antagonism on the behavioral effects of cocaine in mice, and to identify the neurobiological mechanisms underlying their modulatory effects. Methods: We characterized the effects of selective D2R or D3R antagonism in mice on 1) basal and cocaine-induced locomotor activity, 2) presynaptic dopamine release and clearance in the nucleus accumbens using ex vivo fast scan cyclic voltammetry, and 3) dopamine-mediated signaling in D1-expressing and D2-expressing medium spiny neurons using ex vivo electrophysiology. Results: Pretreatment with the selective D2R antagonist L-741,626 attenuated, while pretreatment with the selective D3R antagonist PG01037 enhanced, the locomotor-activating effects of acute and repeated cocaine administration. While both antagonists potentiated cocaine-induced increases in presynaptic DA release, D3R blockade uniquely facilitated DAmediated excitation of D1-expressing medium spiny neurons in the nucleus accumbens. Conclusions: Selective D3R antagonism potentiates the behavioral-stimulant effects of cocaine in mice, an effect that is in direct opposition to that produced by selective D2R antagonism or nonselective D2-like receptor antagonists, likely by facilitating D1-mediated excitation in the nucleus accumbens. These findings provide important insights into the neuropharmacological actions of D3R antagonists on mesolimbic dopamine neurotransmission.