Aim: 

The primary aim of this study was to determine whether GABAergic cell populations can be studied in the brains of healthy humans who died of non-neurological causes.

Methods: 

For this purpose, the glutamic acid decarboxylase (GAD) immunohistochemistry (IHC) technique was perfected in 20-mm sections of the diencephalon and the anterior cingulate cortex (ACc) blocks. Nissl and Klüver Barrera staining was done in parallel with the GAD-IHC peroxidase-anti-peroxidase (PAP) technique. IHC for GAD was performed on the diencephalon sections with rabbit (Rb) antibody for GAD₆₇ (1: 3000) and on the ACc sections with sheep (Sh) antibody for GAD_Sh (1: 2000). For GAD₆₇–IHC, the sections were then incubated with donkey-anti-Rb antiserum (1: 100), followed by PAP-Rb (1:200). For GAD_Sh-IHC, the sections were subsequently incubated with Rb-Anti-Sh antiserum (1: 50), followed by PAP-Sh (1: 400). The PAP was demonstrated with diaminobenzidine and H₂O₂.

Results: 

GAD₆₇(+)-immunopositive cells of various size and shape were observed in the sections of the anterior dorsal thalamus. In the ACc, some large GAD_Sh(+) cells were detected near some large GAD_Sh(-)immunonegative cells. The GAD_Sh(+) cells were found to be largely heterogeneous and distributed along the different layers of the ACc; the smallest GAD_Sh(+) cells were located in layers VI, III, II and I. A very small subset of magnocellular Betz/Hammarberg/Cajal/von Economo spindle GAD_Sh(+) cells was found in layer Vb of the ACc.

Conclusion: 

The results obtained with the GAD_67/Sh-IHC technique in human brain sections may be useful for specific future studies. The identified GABAergic anterior dorsal thalamic and ACc neurons may, through their different connections, play multiple roles in modulating simple and complex cortical activities and behavioural states. It has been suggested that the "Spindle"-GAD_Sh(+) cells in the ACc play an important role in Alzheimer's Disease, as well as in rapid, sophisticated intuitive assessment of complex situations. Very recently, the glutamatergic/GABAergic/creatine dysfunction hypothesis has been suggested for Simian Immunodeficiency Virus Encephalitis (SIVE-HIV_1-2-HAD-AIDS) diseases.