Selective Vulnerability of Striatal D2 versus D1 Dopamine Receptor-Expressing Medium Spiny Neurons in HIV-1 Tat Transgenic Male Mice

• Published in: The Journal of neuroscience 2017-06, Vol.37 (23), p.5758-5769
• Main Authors: Schier, Christina J, Marks, William D, Paris, Jason J, Barbour, Aaron J, McLane, Virginia D, Maragos, William F, McQuiston, A Rory, Knapp, Pamela E, Hauser, Kurt F
• Format: Article
• Language: English
• Subjects: Animals; Anxiety; Behavior, Animal - physiology; Breeding; Caudate-putamen; Central nervous system; Chronic infection; Circuits; Corpus Striatum - metabolism; Dendritic spines; Dendritic Spines - physiology; Dopamine; Dopamine D1 receptors; Dopamine D2 receptors; Excitability; Exploration; HIV; Human immunodeficiency virus; Locomotion - physiology; Male; Mice; Mice, Inbred C57BL; Mice, Transgenic; Neostriatum; Neural networks; Neurons; Neuropathogenesis; Open-field behavior; Organ Specificity; Receptors, Dopamine D1 - metabolism; Receptors, Dopamine D2; Rodents; Spiny neurons; tat Gene Products, Human Immunodeficiency Virus - genetics; tat Gene Products, Human Immunodeficiency Virus - metabolism; Tat protein; Tissue Distribution; Transcription; Transgenic mice
• ISSN: 0270-6474; 1529-2401
• DOI: 10.1523/JNEUROSCI.0622-17.2017

Despite marked regional differences in HIV susceptibility within the CNS, there has been surprisingly little exploration into the differential vulnerability among neuron types and the circuits they underlie. The dorsal striatum is especially susceptible, harboring high viral loads and displaying marked neuropathology, with motor impairment a frequent manifestation of chronic infection. However, little is known about the response of individual striatal neuron types to HIV or how this disrupts function. Therefore, we investigated the morphological and electrophysiological effects of HIV-1 -activator of transcription (Tat) in dopamine subtype 1 (D1) and dopamine subtype 2 (D2) receptor-expressing striatal medium spiny neurons (MSNs) by breeding transgenic Tat-expressing mice to -tdTomato- or -eGFP-reporter mice. An additional goal was to examine neuronal vulnerability early during the degenerative process to gain insight into key events underlying the neuropathogenesis. In D2 MSNs, exposure to HIV-1 Tat reduced dendritic spine density significantly, increased dendritic damage (characterized by swellings/varicosities), and dysregulated neuronal excitability (decreased firing at 200-300 pA and increased firing rates at 450 pA), whereas insignificant morphologic and electrophysiological consequences were observed in Tat-exposed D1 MSNs. These changes were concomitant with an increased anxiety-like behavioral profile (lower latencies to enter a dark chamber in a light-dark transition task, a greater frequency of light-dark transitions, and reduced rearing time in an open field), whereas locomotor behavior was unaffected by 2 weeks of Tat induction. Our findings suggest that D2 MSNs and a specific subset of neural circuits within the dorsal striatum are preferentially vulnerable to HIV-1. Despite combination antiretroviral therapy (cART), neurocognitive disorders afflict 30-50% of HIV-infected individuals and synaptodendritic injury remains evident in specific brain regions such as the dorsal striatum. A possible explanation for the sustained neuronal injury is that the neurotoxic HIV-1 regulatory protein -activator of transcription (Tat) continues to be expressed in virally suppressed patients on cART. Using inducible Tat-expressing transgenic mice, we found that dopamine subtype 2 (D2) receptor-expressing medium spiny neurons (MSNs) are selectively vulnerable to Tat exposure compared with D1 receptor-expressing MSNs. This includes Tat-induced reductions in D2 MS