The relationship between GABA and GnRH in the brain of the sea lamprey using in situ hybridization

The amino acid neurotransmitter gamma aminobutyric acid (GABA) is the primary inhibiting neurotransmitter in the central nervous system across all vertebrates, however there is recent evidence indicating an alternate role for GABA as a stimulating agent. GABA and agents that alter GABAergic function have considerable regulatory effects on reproductive processes by acting on the hypothalamus and pituitary. GABA has also been shown to play an important role in the regulation of gonadotropin-releasing hormone (GnRH) synthesis and release in vertebrates. Much of this control is due to regulation of GABA receptors on GnRH neurons. Glutamic acid decarboxylase (GAD) is the rate-limiting enzyme that catalyzes the synthesis of GABA from glutamate. Therefore, in order to examine GABA, we determined the expression of GAD in brain tissues. Our objective of this study was to determine the relationship between GABA and GnRH in the brain of the sea lamprey, Petromyzon marinus, by investigating GAD and lamprey GnRH-I and -III expression using in situ hybridization. Sense and antisense riboprobes were synthesized and tested using freshly prepared cryostat tissue sections of larval and adult sea lamprey brains. Hybridization was performed and tissue sections were then examined for presence and location of probe binding. Results of this study have demonstrated the presence of both lamprey GnRH-I, and -III and GAD transcripts in the preoptic anterior hypothalamus of the larval lamprey brain, as well as the presence of lamprey GnRH-I and -III transcripts in the adult lamprey brains. Supported by NSF to SAS.