Glutamic acid decarboxylase immunoreactivity in sector CA 1 of the human Ammon's horn

Summary The distribution of glutamic acid decarboxylase (GAD) immunoreactive neurons, fibres and punctae in sector CA 1 of the adult human Ammon's horn was studied in Vibratome sections (40 m thick) of tissue obtained at surgery and autopsy. On light microscopical examination, the materal did not show pathological changes. The antibody was visualized by the unlabelled antibody enzyme method. GAD-immunoreactive neurons, fibres and punctae were present in all layers. Most immunoreactive neurons were located in the stratum pyramidale and stratum lacunosum. Their size ranged from 8 m in the stratum lacunosum to about 50 m in the stratum oriens. The somata offered a wide range of shapes, multiform to fusiform with the long axis aligned parallel or vertically to the alveus. All somata belonged to the heterogeneous group of non-pyramidal neurons. The dendrites either radiated in all directions or tended to run in two opposite directions. After bleaching the chromogen and staining for lipofuscin pigment granules and basophilic material, it turned out that within the stratum pyramidale all formerly GAD-immunoreactive neurons belonged to the group of lipofuscin-laden non-pyramidal neurons. Within the other layers, a few formerly GAD-immunoreactive neurons were devoid of lipofuscin pigment. The highest density of GAD-immunoreactive punctae was found in the stratum lacunosum. In addition to numerous GAD-immunoreactive punctae in the pyramidal layer and in the stratum radiatum there were thin GAD-immunoreactive fibres of varying length extending into various directions.Abbreviations CA cornu ammonis - CCK cholecystokinin - CN 4-chloro-1-naphthol - GABA -aminobutyric acid - GAD glutamic acid decarboxylase - lac stratum lacunosum - mol stratum moleculare - or stratum oriens - pyr stratum pyramidale - rad stratum radiatum - VIP vasoactive intestinal polypeptide