The use of Quetol 651 for the post-embedding immunohistochemical demonstration of gamma-aminobutyric acid on semithin sections

Summary Quetol 651 was used as an embedding medium for the demonstration of aminobutyric acid (GABA) in semithin sections by the peroxidase—anti-peroxidase method. In order to demonstrate the immunoreactivity, the embedding medium was partially dissolved using absolute ethanol containing 0.8–1m NaOH or KOH for 5–7 min. The experimental procedure was elaborated by testing the GABAergic sites in the endings surrounding the small neurones of the anterior exterolateral nucleus of a mormyrid fish and in the pyramidal cells of the electrosensory lateral line lobe of gymnotoid fish by applying anti-GAD (glutamic acid decarboxylase) antiserum. To test the general validity of the use of Quetol 651, GABAergic sites were also identified in the central nervous system of an insect, the honey bee, with anti-GABA and anti-GAD antisera. The intensity of labelling revealed by immunoperoxidase applied to Quetol 651-embedded semithin sections, demonstrated high precision and gave good resolution for light microscopical observations.