Progesterone protects normative anxiety-like responding among ovariectomized female mice that conditionally express the HIV-1 regulatory protein, Tat, in the CNS

Abstract

Increased anxiety is co-morbid with human immunodeficiency virus (HIV) infection. Actions of the neurotoxic HIV-1 regulatory protein, Tat, may contribute to affective dysfunction. We hypothesized that Tat expression would increase anxiety-like behavior of female GT-tg bigenic mice that express HIV-1 Tat protein in the brain in a doxycycline-dependent manner. Furthermore, given reports that HIV-induced anxiety may occur at lower rates among women, and that the neurotoxic effects of Tat are ameliorated by sex steroids in vitro, we hypothesized that 17β-estradiol and/or progesterone would ameliorate Tat-induced anxiety-like effects. Among naturally-cycling proestrous and diestrous mice, Tat-induction via 7days of doxycycline treatment significantly increased anxiety-like responding in an open field, elevated plus maze and a marble-burying task, compared to treatment with saline. Proestrous mice demonstrated less anxiety-like behavior than diestrous mice in the open field and elevated plus maze, but these effects did not significantly interact with Tat-induction. Among ovariectomized mice, doxycycline-induced Tat protein significantly increased anxiety-like behavior in an elevated plus maze and a marble burying task compared to saline-treated mice, but not an open field (where anxiety-like responding was already maximal). Co-administration of progesterone (4mg/kg), but not 17β-estradiol (0.09mg/kg), with doxycycline significantly ameliorated anxiety-like responding in the elevated plus maze and marble burying tasks. When administered together, 17β-estradiol partially antagonized the protective effects of progesterone on Tat-induced anxiety-like behavior. These findings support evidence of steroid-protection over HIV-1 proteins, and extend them by demonstrating the protective capacity of progesterone on Tat-induced anxiety-like behavior of ovariectomized female mice.

Keywords: 17β-estradiol; Elevated plus maze; Estrous cycle; GT-tg bigenic mice; Marble burying; Neuroaids; Open field; Ovariectomy; Tat(1–86); Transactivating transcriptor.

Figure 1

Depicts the experimental design for female GT-tg mice that were intraperitoneally-administered saline (0.9 %) or doxycycline (100 mg/kg; to induce HIV-1 Tat) for 7 days while naturally-cycling (left panel) or ovariectomized and co-administered subcutaneous vehicle, 17β-estradiol (0.09 mg/kg), and/or progesterone (4 mg/kg; right panel). All mice were assessed for anxiety-like behavior in an open field, elevated plus maze, and marble burying task.

Figure 2

(A) Regularly estrous cycling female GT-tg mice were treated with 7 days of saline (as a control; open bars) or doxycycline (to centrally induce HIV-1 Tat protein; striped bars) and tested in the next proestrous (left bars) or diestrous (right bars) phase of their cycle (n = 20 / group). Anxiety-like behavior was assessed in (B) an open field, (C) an elevated plus maze, and (D) a marble burying task. * indicates significant main effect for doxycycline-treated mice to differ from saline-treated mice. † indicates significant main effect for diestrous mice to differ from proestrous mice, p < 0.05.

Figure 3

(A) GT-tg female mice were ovariectomized. After one week of recovery, mice (n = 12 – 16 / group) were intraperitoneally treated with 7 days of saline (as a control; open bars) or doxycycline (to centrally induce HIV-1 Tat protein; striped bars) while subcutaneously co-administered vehicle, estradiol (0.09 mg/kg), and/or progesterone (4 mg/kg). Anxiety-like behavior was assessed in (B) an open field, (C) an elevated plus maze, and (D) a marble burying task. * indicates significant interaction wherein indicated doxycycline-treated group differs from respective saline-treated control group. † indicates significant main effect for estradiol-administered mice to differ from vehicle-treated mice. ‡ indicates significant main effect for progesterone-administered mice to differ from estradiol- or estradiol/progesterone-administered mice. § indicates significant interaction wherein doxycycline/progesterone-treated group differs from doxycycline/vehicle- or doxycycline-estradiol-treated groups, p < 0.05.