Progressive Degeneration and Adaptive Excitability in Dopamine D1 and D2 Receptor-Expressing Striatal Neurons Exposed...

Area of Science:

• Neuroscience
• Virology
• Neuropharmacology

Background:

• The striatum is vulnerable to HIV-1 infection, leading to medium spiny neuron (MSN) damage.
• Opioid use disorder can worsen HIV-1-induced MSN damage.
• The effects of sustained HIV-1 exposure and acute opioid use on dopamine D1 and D2 receptor-expressing MSNs are not well understood.

Purpose of the Study:

• To investigate the functional and structural consequences of progressive HIV-1 Tat exposure and acute morphine on D1 and D2 MSNs.
• To determine if MSNs adapt to combined HIV-1 Tat and opioid insults.

Main Methods:

• Used Drd1-tdTomato or Drd2-eGFP reporter mice crossed with conditional HIV-1 Tat transgenic mice.
• Assessed MSNs in ex vivo brain slices using whole-cell patch-clamp electrophysiology and biocytin filling.
• Examined effects of varying durations of Tat exposure (48h, 2 weeks, 1 month, 2 months) combined with acute morphine.

Main Results:

• Both D1 and D2 MSNs showed increased excitability after 48h of Tat exposure.
• D1 MSNs initially decreased firing rates with prolonged Tat exposure but returned to control levels after 2 months.
• D2 MSNs showed sustained Tat-dependent excitability increases at 2 weeks, also returning to control levels by 2 months.
• Acute morphine increased D1 MSN excitability regardless of Tat duration.
• Despite significant synaptodendritic degeneration and phospho-tau accumulation after 2 months of Tat, MSN excitability returned to baseline levels.

Conclusions:

• D1 and D2 MSNs demonstrate remarkable adaptation to sustained HIV-1 Tat exposure and acute morphine.
• Functional recovery of MSN excitability occurs despite substantial morphologic damage.
• These findings highlight unique adaptive mechanisms in striatal neurons under combined neuropathogenic insults.