Expression of messenger RNA coding for the nerve growth factor receptor trkA in the hippocampus of the adult rat

Nerve growth factor is a member of the neurotrophin gene family and acts as a neurotrophic factor on a variety of neuronal populations.(7,23) Nerve growth factor biological action is mediated by binding to the transmembrane tyrosine kinase trkA, although the low affinity neurotrophin receptor p75 may also play a role.(1,7) TrkA messenger RNA in the central nervous system is localized within a small number of specific neuronal populations,(10,19,26) as opposed to the widespread expression of the other members of the trk family, trkB and trkC. In particular, cholinergic neurons of the basal forebrain, the prototype of nerve growth factor-sensitive neurons in the brain(9,14,17,25) express trkA. Several lines of evidence indicate that other populations of central neurons, in particular hippocampal neurons, may be responsive to nerve growth factor as well. In fact, nerve growth factor rescues hippocampal neurons from ischemic cell death in vivo(6,22,27) and increases neurotrasmitter release from hippocampal neurons in culture.(11) Moreover, nerve growth factor has been implicated in spatial learning, a process known to be dependent on the hippocampal formation.(8,18,24) The following paper reports expression of trkA messenger RNA in the rat hippocampus by in situ hybridization and reverse transcription-polymerase chain reaction. This finding supports the notion of hippocampal neurons as an nerve growth factor-sensitive population.