Progesterone Promotes Anti-Anxiety/Depressant-like Behavior and Trophic Actions of BDNF in the Hippocampus of Female Nuclear Progesterone Receptor, but Not 5α-Reductase, Knockout Mice

Abstract

Progestogens' anti-anxiety and anti-depressive effects and mechanisms are not well-understood. Progestogens are hypothesized to have anti-anxiety and anti-depressive effects on behavior, independent of actions at nuclear progestin receptors (NPRs) and dependent on allopregnanolone (5α-pregnan-3α-ol-20-one; 3α,5α-THP), a 5α-reduced, neuroactive metabolite of progesterone (P₄). Adult c57 mice in behavioral estrus (proestrus; pro) showed more anti-anxiety-like and anti-depressant-like behavior and higher levels of estradiol (E₂), P₄, and allopregnanolone in the hippocampus/amygdala complex. Proestrus c57 > 5α-reductase knockout (5αRKO) mice made more central entries in an open field than diestrus c57 and 5αRKO mice that were not different. Ovariectomized (OVX) c57 mice administered 1, 2, or 4 mg/kg P₄ SC showed dosage-dependent increases in central entries in an open field (more anti-anxiety-like behavior); 5αRKO mice had maximal increases at 1-2 mg/kg P₄. OVX c57 and 5αRKO mice showed maximum increases in central entries with SC 3α,5α-THP (4 mg/kg), and c57s showed a similar maximal response to P₄ (4 mg/kg), but 5αRKOs response was half at that dosage. P₄ (4 mg/kg SC to OVX c57 or progestin receptor knockout (PRKO) mice decreased immobility (depression-like behavior) in the forced swim task. Effects of E₂ and veh were similar in both groups. Levels of 3α,5α-THP in the hippocampus/amygdala were consistent with effects on central entries in the open field. Levels of brain-derived neurotrophic factor (BDNF) in the hippocampus/amygdala were greater among E₂-primed (0.09 mg/kg, SC) vs vehicle-administered mice. In sum, adult female mice can be responsive to P₄ for anti-anxiety/anti-depressant-like behavior; such effects may be independent of NPRs but require 5α-reduction and E₂'s priming actions at BDNF in the hippocampus/amygdala complex.

Keywords: elevated plus maze; forced swim; neuroactive steroid; neurosteroid; non-genomic; open field.

Figure 1

Putative pathways of allopregnanolone (3α,5α-THP) sources (left side) and some targets of action (right side). 3α,5α-THP can be metabolized in the brain from progesterone by 3α (β)-hydroxysteroid dehydrogenase and 5α-reductase, which estradiol can upregulate. Allopregnanolone is secreted de novo in response to challenges (e.g., open field behavior) that activate the autonomic nervous system to reinstate parasympathetic tone, in part by upregulating pregnane xenobiotic receptor function (PXR) in brain. Targets of allopregnanolone’s actions include steroid binding sites at GABA_A, dopamine, NMDA, and cognate progestin membrane receptors (mPRs) (others not shown), but not nuclear progesterone receptors (NPRs) in physiological concentrations [5,6].

Figure 2

The (left panel) shows anti-anxiety-like behavior in the elevated plus maze. * Time spent in open arms is significantly greater in proestrus (pro; c57Bl/6J (c57) mice indicated in blue bars (n = 10) than diestrus (di, c57 mice indicated in red bars, n = 10) in a 120 sec test. The (right panel) shows anti-depressant-like behavior in the forced swim test of 300 secs. c57 mice in proestrus (n = 10) spent less time immobile than diestrus mice (n = 10). Immobility is considered a sign that one has given up; it is a proxy measure of depression. * represents a difference between groups is greater than p ≤ 0.001.

Figure 3

Diestrus (left side; red) and proestrus (right side; blue) control, c57, wildtype (WT) mice are depicted by solid bars, and 5αRKO mice are depicted by bars with horizontal stripes; n = 10/group. * There was a significant p ≤ 0.001 interaction of cycle and strain as c57, WT mice in proestrus made more central entries compared to all other groups. There were main effects of strain for WT, c57 mice to have more central entries than 5αRKO knockout mice and main effects of the cycle for proestrus mice to have more central entries than diestrus mice.

Figure 4

WT (colored bars) and 5αRKO deficient mice (striped bars) were OVX and administered oil vehicle or E₂ (0.09 mg/kg) and different dosages of P₄ (1 (yellow), 2 (green), or 4 mg/kg (purple) or 3α,5α-THP (4 mg/kg; orange) SC. * Administration of 3α,5α-THP to WT (c57) or 5αRKO mice increased central entries to the open field comparable to that of WT mice administered E₂ and P₄ (solid purple) and greater than that of all other groups. There was the significant interaction of hormones and strain. E₂ (red), compared to the vehicle (blue), increased central entries of WT and 5αRKO mice, E₂ and P₄ (1 (yellow) or 2 mg/kg (green) increased central entries of WT mice, a main effect of hormones, ^ represented by the upside-down caret.

Figure 5

c57, wildtype (WT mice are depicted by solid-colored bars, and 5αRKO mice are depicted by colored bars with horizontal stripes; n = 10/group. * There is a significant interaction of hormone and strain as WT and 5αRKO mice had robust responses to allopregnanolone on central entries to the open field compared to P₄, to WT and 5αRKO mice. There were main effects of the hormone condition for E₂, P₄, and 3α,5α-THP (allopregnanolone) to produce significant increases compared to the vehicle irrespective of. The ^ indicates the significant differences between WT and 5αRKO at this P₄ dosage. The main effect of strain was for WT to have more effects than that of 5αRKO mice on central entries.

Figure 6

c57/Wildtype (left side) and PRKO (right side) mice showed less immobility and depression-like behavior in the forced swim test when administered 4 mg/kg of progesterone; P₄ (green bars) compared to when administered oil vehicle (yellow bars). There are n = 10/group. * There was a significant main effect of P₄ to decrease immobility, but neither an effect of mouse strain nor an interaction of what was administered and strain.

Figure 7

Hippocampus/amygdala-complex brain-derived neurotrophic factor (BDNF) levels in the hippocampus of c57 mice administered vehicle (blue bars) vs mice administered (red bar) E₂ SC. (n = 10/group). There was a main effect of estradiol (E_2; red bar on the right) to increased BDNF in the hippocampus/amygdala-complex compared to the vehicle (veh; blue bar on the left, n = 10 per group).