Synaptic Dysfunction Underlies Alterations in the Initiation of Goal-Directed Behaviors: Implications for Hiv-1 Associated Apathy

Abstract

Individuals living with human immunodeficiency virus type 1 (HIV-1) exhibit an increased prevalence of neuropsychiatric comorbities (e.g., apathy) relative to their seronegative counterparts. Given the profound functional consequences associated with apathy, conceptualizing the multidimensional neuropsychiatric syndrome, and associated neural mechanisms, following chronic HIV-1 viral protein exposure remains a critical need. HIV-1 associated apathy was examined by quantifying goal-directed behaviors, indexed using voluntary wheel running, during the diurnal and nocturnal cycle. Apathetic behaviors in the HIV-1 Tg rat were characterized by a profound decrease in the number of running bouts during both the diurnal and nocturnal cycle, supporting a prominent deficit in the self-initiation of spontaneous behaviors. Additionally, HIV-1 Tg animals exhibited a decreased reinforcing efficacy of voluntary wheel running during the nocturnal cycle. Following the completion of voluntary wheel running, synaptic dysfunction in medium spiny neurons (MSNs) of the nucleus accumbens (NAc) was examined as a potential neural mechanism underlying HIV-1 associated apathy. HIV-1 Tg animals displayed prominent synaptic dysfunction in MSNs of the NAc, characterized by decreased synaptic connectivity and a population shift towards an immature dendritic spine phenotype relative to control animals. Synaptic dysfunction accounted for 42.0% to 68.5% of the variance in the number of running bouts affording a key neural mechanism underlying the self-initiation of spontaneous behaviors. The establishment of a fundamental neural mechanism underlying apathy affords a key target for the development of novel therapeutics and cure strategies for affective alterations associated with HIV-1.