Genetically expressed HIV-1 viral proteins attenuate nicotine-induced behavioral sensitization and alter mesocorticolimbic ERK and CREB signaling in rats

Abstract

The prevalence of tobacco smoking in HIV-1 positive individuals is 3-fold greater than that in the HIV-1 negative population; however, whether HIV-1 viral proteins and nicotine together produce molecular changes in mesolimbic structures that mediate psychomotor behavior has not been studied. This study determined whether HIV-1 viral proteins changed nicotine-induced behavioral sensitization in HIV-1 transgenic (HIV-1Tg) rats. Further, we examined cAMP response element binding protein (CREB) and extracellular regulated kinase (ERK1/2) signaling in the prefrontal cortex (PFC), nucleus accumbens (NAc) and ventral tegmental area (VTA). HIV-1Tg rats exhibited a transient decrease of activity during habituation, but showed attenuated nicotine (0.35mg/kg, s.c.)-induced behavioral sensitization compared to Fisher 344 (F344) rats. The basal levels of phosphorylated CREB and ERK2 were lower in the PFC of HIV-1Tg rats, but not in the NAc and VTA, relative to the controls. In the nicotine-treated groups, the levels of phosphorylated CREB and ERK2 in the PFC were increased in HIV-1Tg rats, but decreased in F344 animals. Moreover, repeated nicotine administration reduced phosphorylated ERK2 in the VTA of HIV-1Tg rats and in the NAc of F344 rats, but had no effect on phosphorylated CREB, indicating a region-specific change of intracellular signaling. These results demonstrate that HIV-1 viral proteins produce differences in basal and nicotine-induced alterations in CREB and ERK signaling that may contribute to the alteration in psychomotor sensitization. Thus, HIV-1 positive smokers are possibly more vulnerable to alterations in CREB and ERK signaling and this has implications for motivated behavior, including tobacco smoking, in HIV-1 positive individuals who self-administer nicotine.

Figure 1

Body weight of HIV-1Tg and F344 rats during the nicotine or saline treatment period. Beginning at 12 weeks of age, rats were injected subcutaneously with nicotine or saline prior to locomotor measurement. Data are presented as the mean ± S.E.M. n=8 rats per group.

Figure 2

The time-course data during the habituation and the saline baseline sessions. Panels A and B show the total horizontal activity (mean ± S.E.M.) during the first 30 min of the habituation period. Panel C shows the total horizontal activity (mean ± S.E.M.) across the first 30 min of the session following saline injection. * p < 0.05, difference between HIV-1Tg and F344 rats at the corresponding time interval. n=8 rats per group.

Figure 3

The time-course data during the behavioral sensitization phase. HIV-1Tg and F344 rats were administered nicotine (Nic; 0.35 mg/kg; s.c.) or saline (Sal) on Days 1–19. Panel A shows the total horizontal activity (mean ± S.E.M.) during the 30 min pre-injection habituation period. Panel B shows the total horizontal activity (mean ± S.E.M.) during the 60 min following nicotine or saline injection. n=8 rats per group.

Figure 4

The time-course data for total horizontal activity during day 1 and day 19 of the behavioral sensitization phase. Panels A and B show the total horizontal activity (mean ± S.E.M.) across the 60-min session. Panels C and D show the time course of the total horizontal activity (mean ± S.E.M.) during each 5-min time interval. * p < 0.05 difference between HIV-1Tg and F344 rats. # p < 0.05 difference between nicotine- and saline-treatment group. n=8 rats per group.

Figure 5

Levels of ERK, CREB and TH proteins in the PFC in HIV-1Tg and F344 rats. (A) Representative western blots showing the protein density of CREB, pCREB, ERK1/2, pERK1/2, TH and β-tubulin in nicotine or saline treated HIV-1Tg (HIV-1Tg-Nic, HIV-1Tg-Sal) and F344 rats (F344-Nic, F344-Sal). (B) Total and phosphorylated protein levels of ERK1, ERK2 and CREB along with levels of TH after chronic nicotine or saline injection. Ratios are presented as the mean percentage of β-tubulin ± S.E.M. * p < 0.05 difference between HIV-1Tg and F344 rats. # p < 0.05 difference between the nicotine- and saline-treatment groups. n=8 rats per group.

Figure 6

Levels of ERK, CREB and TH proteins in the NAc in HIV-1Tg and F344 rats. (A) Representative western blots showing the protein density of CREB, pCREB, ERK1/2, pERK1/2, TH and β-tubulin in the nicotine or saline treated HIV-1Tg (HIV-1Tg-Nic, HIV-1Tg-Sal) and F344 rats (F344-Nic, F344-Sal). (B) Total and phosphorylated protein levels of ERK1, ERK2 and CREB along with levels of TH after chronic nicotine or saline injection. Ratios are presented as the mean percentage of β-tubulin ± S.E.M. # p < 0.05 difference between the nicotine- and saline-treatment groups. n=8 rats per group.

Figure 7

Levels of ERK, CREB and TH proteins in the VTA in HIV-1Tg and F344 rats (A) Representative western blots showing the protein density of CREB, pCREB, ERK1/2, pERK1/2, TH and β-tubulin in the nicotine or saline treated HIV-1Tg (HIV-1Tg-Nic, HIV-1Tg-Sal) and F344 rats (F344-Nic, F344-Sal). (B) Total and phosphorylated protein levels of ERK1, ERK2 and CREB along with levels of TH after chronic nicotine or saline injection. Ratios are expressed as the mean percentage of β-tubulin ± S.E.M. # p < 0.05 difference between the nicotine- and saline-treatment group. n=8 rats per group.