1. γ-Aminobutyric acid (GABA) a and b receptors mediate the stimulatory effects of GABA on the human sperm acrosome reaction: interaction with progesterone 
Aldo E Calogero, M.D., Nunziatina Burrello, Ph.D., Emanuela Ferrara, M.D., Jenny Hall, Ph.D., Simon Fishel, Ph.D., Rosario D’Agata, M.D. 
Fertility and Sterility 
Volume 71, Issue 5, Pages (May 1999)
DOI: /S (99)

2. FIGURE 1
Effects of γ-aminobutyric acid (GABA) on the acrosome reaction of human spermatozoa obtained from 10 normozoospermic subjects. ∗P<.05 (vs. 0); †P<.05 (vs. GABA 1 μM); ‡P<.05 (vs. GABA 10 μM).
Fertility and Sterility  , DOI: ( /S (99) )

3. FIGURE 2
Effects of bicuculline (BICU) (n = 12), a GABAA receptor antagonist (upper panel), or saclofen (SACL) (n = 9), a GABAB receptor antagonist (lower panel), on the spontaneous acrosome reaction of human spermatozoa and in response to 10 μM of γ-aminobutyric acid (GABA). ∗P<.05 (vs. no-treatment control); †P<.05 (vs. GABA 10 μM).
Fertility and Sterility  , DOI: ( /S (99) )

4. FIGURE 3
Effects of increasing concentrations of progesterone on the acrosome reaction of human spermatozoa obtained from eight normozoospermic subjects. ∗P<.05 (vs. 0); †P<.05 (vs. progesterone 10 μM); ‡P<.05 (vs. progesterone 30 μM).
Fertility and Sterility  , DOI: ( /S (99) )

5. FIGURE 4
Effects of the GABAA receptor antagonist bicuculline (BICU) on the progesterone (Prog)–stimulated acrosome reaction of human spermatozoa obtained from 10 normozoospermic subjects. ∗P<.05 (vs. 0); †P<.05 (vs. progesterone alone).
Fertility and Sterility  , DOI: ( /S (99) )