Implantation of D-[3H]aspartate loaded gel particles permits restricted uptake sites for transmitter-selective axonal transport.

Intracerebral pressure injections of small molecular tracers such as D-[3H]aspartate are usually followed by considerable spread which makes it difficult to assess the effective uptake area and precludes analysis of short axonal connections. As an attempt to circumvent these problems, D-[3H]aspartate was adsorbed onto gel beads that were subsequently packed into glass capillaries and implanted in the brain. Model experiments suggested that the loaded beads gradually release the tracer to the nerve tissue. The implantations resulted in small and sharply circumscribed tracer deposits which enabled us to study long axonal projections, as well as short intrahippocampal and intraamygdaloid pathways that are not easily resolved after pressure injections.