Investigation of the connection between the substantia nigra and the medullary reticular formation in the rat

Unfixed, slide-mounted tissue sections from the rat forebrain have been incubated in the presence of 20 and 100 nM [3H]kainic acid ([3H]KA). For the last 2 min of incubation, 10 micrometers unlabelled KA was added to displace [3H]KA from binding sites with high on-off rate. Washed and dried slices were exposed on [3H]Ultrofilm for 178 days. Our results confirm the high density of KA receptors in the terminal field of the hippocampal mossy fibre system which is shown to be due to receptors with slow dissociation rate. Furthermore, the concentration dependency of the specific labelling, as quantified by microdensitometry, allows some suggestions concerning the local binding affinities involved.