Lamina-specific synaptic activation causes domain-specific alterations in dendritic immunostaining for MAP2 and CAM kinase II.

Polyribosomal complexes are selectively localized beneath postsynaptic sites on neuronal dendrites; this localization suggests that the translation of the mRNAs that are present in dendrites may be regulated by synaptic activity. The present study tests this hypothesis by evaluating whether synaptic activation alters the immunostaining pattern for two proteins whose mRNAs are present in dendrites: the dendrite-specific cytoskeletal protein MAP2 and the alpha-subunit of CAMKII. High-frequency stimulation of the perforant path projections to the dentate gyrus, which terminate in a discrete band on the dendrites of dentate granule cells, produced a two-stage alteration in immunostaining for MAP2 in the dendritic laminae. Five minutes of stimulation (30 trains) caused a decrease in MAP2 immunostaining in the lamina in which the activated synapses terminate. After more prolonged periods of stimulation (1-2 hr), there was an increase in immunostaining in the sideband laminae just proximal and distal to the activated band of synapses. The same stimulation paradigm produced a modest increase in immunostaining for alpha-CAMKII in the activated laminae, with no detectable changes in the sideband laminae. The alterations in immunostaining for MAP2 were diminished, but not eliminated, by inhibiting protein synthesis; the increases in CAMKII were not. These findings reveal that patterned synaptic activity can produce domain-specific alterations in the molecular composition of dendrites; these alterations may be caused in part by local protein synthesis and in part by other mechanisms.