Expression of the mRNAs encoding the limbic system-associated membrane protein (LAMP): I. Adult rat brain.

The search for molecular markers common to neural structures that are functionally related has become an attractive strategy for neurobiologists interested in identifying mechanisms involved in the formation of patterned connections. One such molecule is the limbic system-associated membrane protein (LAMP), a 64-68 kDa glycoprotein that is expressed in the soma and dendrites of subpopulations of adult neurons in the brain that are functionally associated with classic limbic structures. Such patterned molecular specificity is established prenatally; LAMP is detected during development on the surface of neurons, axonal membranes and pathfinding growth cones. This molecule has now been cloned (lamp) and has been shown to be highly conserved in rat and human. It is a new immunoglobulin superfamily member that has three Ig domains and a glycosyl-phosphatidylinositol (GPI) anchor to the cell membrane. In this study, the distribution of the lamp transcript in the adult rat brain was determined by using in situ hybridization. Generally, the distribution of lamp corresponds well with that of the LAMP protein. Within the cerebral cortex, the transcript is more abundant in areas that are associated with learning/memory and viscerosensory tasks. It is less abundant in somatic sensory and motor areas. The lamp transcript is also ubiquitous in the basal forebrain, amygdala, and preopticohypothalamic areas. In short, the lamp transcript is expressed heavily in areas of the forebrain and diencephalon that have been classically considered limbic and sparsely or moderately in nonlimbic midbrain and hindbrain regions. Correlative analysis of the connectivity patterns of the regions that express greater amounts of the transcript is consistent with a stronger limbic-associated function relative to the regions expressing less lamp. These quantitative differences may be significant in determining the function of LAMP in the adult brain.