Ovarian hormone elevations are associated with enhanced learning/memory. During behavioral estrus or pregnancy, progestins, such as progesterone (P 4 ) and its metabolite 5a-pregnan-3a-ol-20-one (3a,5a-THP), are elevated due, in part, to corpora luteal and placental secretion. During 'pseudopregnancy', the induction of corpora luteal functioning results in a hormonal milieu analogous to pregnancy, which ceases after about 12 days, due to the lack of placental formation. Multiparity is also associated with enhanced learning/memory, perhaps due to prior steroid exposure during pregnancy. Given evidence that progestins and/or parity may influence cognition, we investigated how natural alterations in the progestin milieu influence cognitive performance. In Experiment 1, virgin rats (nulliparous) or rats with two prior pregnancies (multiparous) were assessed on the object placement and recognition tasks, when in high-estrogen/P 4 (behavioral estrus) or low-estrogen/P 4 (diestrus) phases of the estrous cycle. In Experiment 2, primiparous or multiparous rats were tested in the object placement and recognition tasks when not pregnant, pseudopregnant, or pregnant (between gestational days (GDs) 6 and 12). In Experiment 3, pregnant primiparous or multiparous rats were assessed daily in the object placement or recognition tasks. Females in natural states associated with higher endogenous progestins (behavioral estrus, pregnancy, multiparity) outperformed rats in low progestin states (diestrus, non-pregnancy, nulliparity) on the object placement and recognition tasks. In earlier pregnancy, multiparous, compared with primiparous, rats had a lower corticosterone, but higher estrogen levels, concomitant with better object placement performance. From GD 13 until post partum, primiparous rats had higher 3a,5a-THP levels and improved object placement performance compared with multiparous rats.

Rationale Human immunodeficiency virus (HIV) infection is associated with substantial increases in generalized anxiety. The HIV regulatory protein, transactivator of transcription (Tat), has been implicated in the neuropathogenesis related to HIV-1 infection. However, direct examination of the effect of Tat on behavioral measures of anxiety has not been demonstrated. Objective To identify whether expression of the Tat1-86 protein exerts dose-dependent and persistent anxiety-like effects in a whole animal model, the GT-tg bigenic mouse. Methods GT-tg mice and C57BL/6J controls were administered doxycycline in a dose- (0, 50, 100, or 125 mg/kg, i.p., for 7 days) or duration- (100 mg/kg, i.p., for 0, 1, 3, 5, or 14 days) dependent manner to induce Tat1-86 in brain. Mice were assessed for anxiety-like behavior in an open field, social interaction, or marble burying task 0, 7, and/or 14 days later. Central expression of Tat1-86 protein was verified with Western blot analyses. Results Doxycycline produced no effects on C57BL/6J controls that lacked the Tat1-86 transgene. Among GT-tg mice, doxycycline (100 mg/kg for 3, 5, or 7 days) significantly increased anxiety-like behavior in all tasks, commensurate with enhanced Western blot labeling of Tat1-86 protein in brain, displaying optimal effects with the 7-day regimen. Greater exposure to doxycycline (either 125 mg/kg for 7 days or 100 mg/kg for 14 days) impaired locomotor behavior; whereas, lower dosing (below 100 mg/kg) produced only transient increases in anxiety-like behavior. Conclusions Expression of HIV-1-Tat1-86 in GT-tg mouse brain produces exposure-dependent, persistent increases in anxiety-like behavior.

Summary Decline in the ovarian steroid, estradiol (E2), with the menopause transition may influence cognitive and affective processing of older women and there is evidence that hormone replacement therapies (HRTs) with E2-mimetics may provide benefit in some, but not all, women. The parameters that play a role in determining whether the response to HRTs is positive are of interest. It may be that the likelihood for positive responses is related to the timing of E2-replacement following E2 decline. As such, in the present study an animal model was utilized to investigate this. We investigated the effects of long- vs. short-term E2 replacement by examining cognitive (object placement task), anxiety (open field, mirror maze, light-dark transition task), and depression (forced swim task) behavior of female rats that were ovariectomized (OVX) at middle-age (14 months) or older (19 months) and implanted with E2–filled implants at the time of surgery or after a delay of 5 months, or OVX at 14 months of age and never replaced with E2. Rats were tested at 20 months of age. The hypothesis that was tested was that rats would have reduced anxiety and depression behavior and improved cognitive performance with E2-replacement at ovarian cessation, compared to with a delay in E2-replacement. Performance in the object placement task was improved in rats that were OVX and then received continuous E2-replacement, compared to those that were OVX and continuously administered placebo vehicle. In the open field and forced swim task, there was an increase in anti-anxiety and anti-depressive behavior, respectively, among rats that were OVX and then received continuous E2-replacement, compared to OVX rats administered vehicle or those that experienced a delay in E2 replacement. In the mirror maze and light-dark transition task, E2-replacement at OVX, or after a delay, reduced anxiety-like behavior. Thus, E2 replacement reduced anxiety and depression behavior and improved cognitive performance of aged female rats; however, delay in E2 treatment influenced whether there were favorable effects of E2 in some tasks.

REPRODUCTION RESEARCHEngaging in paced mating, but neither exploratory, anti-anxiety, nor social behavior, increases 5a-reduced progestin concentrations in midbrain, hippocampus, striatum, and cortex AbstractSequential actions of 17b-estradiol (E 2 ) and progesterone (P 4 ) in the hypothalamus and the P 4 metabolite, 5a-pregnan-3a-ol-20-one (3a,5a-THP), in the midbrain ventral tegmental area (VTA) respectively mediate the initiation and intensity of lordosis of female rats and may also modulate anxiety and social behaviors, through actions in these, and/or other brain regions. Biosynthesis of E 2 , P 4 , and 3a,5a-THP can also occur in brain, independent of peripheral gland secretion, in response to environmental/behavioral stimuli. The extent to which engaging in tasks related to reproductive behaviors and/or mating increased E 2 or progestin concentrations in brain was investigated. In Experiment 1, proestrous rats were randomly assigned to be tested in individual tasks, including the open field, elevated plus maze, partner preference, social interaction, or no test control, in conjunction with paced mating or no mating. Engaging in paced mating, but not other behaviors, significantly increased dihydroprogesterone (DHP) and 3a,5a-THP levels in midbrain, hippocampus, striatum, and cortex. In Experiment 2, proestrous rats were tested in the combinations of the above tasks (open field and elevated plus maze, partner preference, and social interaction) with or without paced mating. As in Experiment 1, only engaging in paced mating increased DHP and 3a,5a-THP concentrations in midbrain, hippocampus, striatum, and cortex. Thus, paced mating enhances concentrations of 5a-reduced progestins in brain areas associated with reproduction (midbrain), as well as exploration/anxiety (hippocampus and striatum) and social behavior (cortex).

As a major neuropathogenic factor associated with human immunodeficiency virus (HIV) infection, HIV-1 Tat protein is known to synergize with psychostimulant drugs of abuse to cause neurotoxicity and exacerbate the progression of central nervous system pathology. However, the functional consequences of the interaction between HIV-1 Tat and abused drugs on behavior are little known. We tested the hypothesis that HIV-1 Tat expression in brain would modulate the psychostimulant effects of cocaine. Using the GT-tg bigenic mouse model, where brain-selective Tat expression is induced by activation of a doxycycline (Dox) promotor, we tested the effects of Tat on cocaine (10 mg/kg, s.c.) induced locomotion and conditioned place preference (CPP). Compared with uninduced littermates or C57BL/6J controls, cocaine-induced hyperlocomotion was sustained for a significantly longer duration among Tat-induced mice. Moreover, although all groups displayed similar saline-CPP, Tat-induced GT-tg mice demonstrated a three-fold increase in cocaine-CPP over the response of either uninduced littermates or Dox-treated C57BL/6J control mice. Induction of Tat also increased the magnitude of a previously established cocaine-CPP after an additional cycle of cocaine place-conditioning. Despite Tat-induced potentiation, extinction of place preference occurred within 21 days, commensurate with cocaine-extinction among saline-treated littermates and C57BL/6J controls. Re-exposure to cocaine produced reinstatement of an equivalent place preference in Tat-induced GT-tg or C57BL/6J mice; however, induction of Tat protein after the extinction of CPP also produced reinstatement without additional exposure to cocaine. Together, these data suggest that central HIV-1 Tat expression can potentiate the psychostimulant behavioral effects of cocaine in mice.