Regulation of SSAT expression by synaptic activity

Neuronal activity is a requirement for the plasticity and normal developmen t of the central nervous system. We have used differential cloning techniqu es to identify an immediate-early gene (IEG) that is rapidly induced in neu rons by activity in both adult and developmental models of plasticity. Here we describe the key regulatory enzyme of polyamine catabolism, spermidine/ spermine N'-acetyltransferase (SSAT), as a neuronal IEG. In the rat brain, kainate-induced seizures result in a 5.5-fold increase in the amount of SS AT mRNA above basal levels and the enzymatic activity is increased twofold. Expression of SSAT mRNA is rapidly and transiently upregulated in the cere bral cortex and hippocampus by seizure-induced neuronal activation. In hipp ocampal neurons, SSAT expression is dynamically responsive to synaptic acti vity in the long-term potentiation (LTP) paradigm. In developing brain, reg ion-specific expression of SSAT mRNA is first detected at postnatal day 9 ( P9) and subsequently increases through days P15, P20, before reaching maxim al level in adult animals. This dynamic transcriptional and translational c ontrol suggests that SSAT may play a role in activity-dependent neuronal pl asticity and development.