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Cellular Localization of GABA and GABA_B Receptor Subunit Proteins During Spermiogenesis in Rat Testis

KEIKO OKAMOTO

SAKASHI NOMURA

TAKESHI KANEKO

RYUICHI SHIGEMOTO

From the ^* Department of Anatomy, Osaka Medical College, Takatsuki, Osaka, Japan; the Department of Morphological Brain Science, Kyoto University Graduate School of Medicine, Yoshida Konoecho, Sakyouku, Kyoto, Japan; the School of Health Sciences, Faculty of Medicine, Kyoto University, Yoshida Konoecho, Sakyouku, Kyoto, Japan; the Division of Cerebral Structure, National Institute for Physiological Science, Okazaki, Aichi, Japan; and the ^|| Department of Urology, Osaka Medical College, Takatsuki, Osaka, Japan.

Correspondence to: Masahito Watanabe, Department of Anatomy, Osaka Medical College, Takatsuki, Osaka 569-8686, Japan (e-mail: an2002{at}art.osaka-med.ac.jp).

The GABAergic system, a major inhibitory regulator in the central nervous system, may also play important roles in peripheral nonneuronal tissues and cells. Recent studies showed that GABA_B receptor is expressed in testis and sperm. To understand the role of the GABAergic system in spermiogenesis, we examined cellular localization of GABA and GABA_B receptor subunits in rat spermatids by immunocytochemistry. Immunoreactivity for GABA was detected around acrosomal granules of spermatids during the Golgi and cap phases. GABA_B(1) immunoreactivity was observed in the acrosomal vesicle of spermatids in Golgi phase, and during cap phase, this reactivity expanded to the entire region of the acrosome covering the nuclear membrane. The level of reactivity decreased gradually with maturation of spermatids. In contrast, GABA_B(2) immunoreactivity was not observed in spermatids during Golgi phase but was detected in the equatorial region during cap phase. Both GABA immunoreactivity and GABA_B(2) immunoreactivity were transferred to the residual cytoplasm during the release of spermatozoa. Electron microscopic immunocytochemistry revealed that, during cap phase, GABA and GABA_B(1) were distributed within the whole acrosomal vesicle but not in the acrosomal granule. GABA_B(2) immunoreactivity was observed in the narrow space between the inner acrosomal and nuclear membrane and was limited to the equatorial region of the spermatid head. These results indicate that the GABAergic system might be involved in regulation of spermiogenesis.

     Key words: Spermatid, immunocytochemistry, acrosome, GABAergic system

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