Sensitization of enteric neurons to morphine by HIV-1 Tat protein.

BACKGROUND: Gastrointestinal (GI) dysfunction is a major cause of morbidity in acquired immunodeficiency syndrome (AIDS). HIV-1-induced neuropathogenesis is significantly enhanced by opiate abuse, which increases proinflammatory chemokine/cytokine release, the production of reactive species, glial reactivity, and neuronal injury in the central nervous system. Despite marked interactions in the gut, little is known about the effects of HIV-1 in combination with opiate use on the enteric nervous system. METHODS: To explore HIV-opiate interactions in myenteric neurons, the effects of Tat ± morphine (0.03, 0.3, and 3 µM) were examined in isolated neurons from doxycycline- (DOX-) inducible HIV-1 Tat(1-86) transgenic mice or following in vitro Tat 100 nM exposure (>6 h). KEY RESULTS: Current clamp recordings demonstrated increased neuronal excitability in neurons of inducible Tat(+) mice (Tat+/DOX) compared to control Tat-/DOX mice. In neurons from Tat+/DOX, but not from Tat-/DOX mice, 0.03 µM morphine significantly reduced neuronal excitability, fast transient and late long-lasting sodium currents. There was a significant leftward shift in V(0.5) of inactivation following exposure to 0.03 µM morphine, with a 50% decrease in availability of sodium channels at -100 mV. Similar effects were noted with in vitro Tat exposure in the presence of 0.3 µM morphine. Additionally, GI motility was significantly more sensitive to morphine in Tat(+) mice than Tat(-) mice. CONCLUSIONS & INFERENCES: Overall, these data suggest that the sensitivity of enteric neurons to morphine is enhanced in the presence of Tat. Opiates and HIV-1 may uniquely interact to exacerbate the deleterious effects of HIV-1-infection and opiate exposure on GI function.

Intra-accumbal Tat1-72 alters acute and sensitized responses to cocaine.

The effects of Tat, an HIV-1 protein, on intravenous cocaine-induced locomotor activity were examined in ovariectomized rats. Animals were habituated to activity chambers, administered an i.v. baseline/saline injection, and 24 h later, received bilateral, intra-accumbal microinjections of Tat1-72 (15 microg/microl) or vehicle. Twenty four hours later, rats received the first of 14 daily i.v. cocaine injections (3.0 mg/kg/inj, 1 /day) or saline. Locomotor activity was measured in automated chambers for 30 min following baseline and after the 1st and 14th cocaine injections. Observational time sampling following cocaine was also performed. Following acute cocaine/saline, Tat significantly increased cocaine-induced total activity over the 30-min session, with no significant effects for activity in the central compartment. Repeated cocaine injections produced behavioral sensitization with approximately 2-fold higher levels of total activity, approximately 3-fold higher levels of centrally directed activity, and increased locomotor scores via direct observations. Following repeated cocaine/saline, Tat altered the development of cocaine-induced behavioral sensitization for total activity with prior Tat exposure attenuating the development of cocaine-induced sensitization. Collectively, these data show that bilateral microinjection of Tat into the N Acc alters i.v. cocaine-induced behavior, suggesting that Tat produces behavioral changes by disrupting the mesocorticolimbic pathway.