GABAergic input of cholecystokinin-immunoreactive neurons in the hilar region of the rat hippocampus. An electron microscopic double immunostaining study.

Double immunostaining was performed for electron microscopy to analyze the synaptic connections between glutamate decarboxylase (GAD)-immunoreactive axons and cholecystokinin (CCK)-immunoreactive neurons in the hilar region of the rat hippocampal formation. Following immunostaining for CCK, the diaminobenzidine (DAB) reaction product was silver-intensified and gold-substituted. In a subsequent second immunostaining for GAD, the immunoreactive elements were labeled using a single DAB reaction. Electron microscopic analysis of the double-stained Vibratome sections demonstrated that the single DAB-labeled GAD-immunoreactive boutons form symmetrical synaptic connections on the soma and primary dendrites of the DAB-gold-labeled CCK-immunoreactive neurons.