Preserved induction of long-term potentiation in the stratum radiatum in the CA1 field of hippocampal slices from transgenic mice overexpressing ornithine decarboxylase and overproducing putrescine.

The role of putrescine in synaptic neurotransmission and plasticity was studied using transgenic mice overexpressing ornithine decarboxylase (ODC), a polyamine-synthesizing enzyme. Transgenic mice were produced using the standard microinjection technique leading to elevated levels of putrescine in the periphery and in the brain. The experiments investigated whether or not ODC mice with elevated levels of putrescine show alterations in synaptic transmission and induction of long-term potentiation in the CA1 field of the hippocampus in vitro. Our results indicated that (1) putrescine levels in brain slices of the transgenic mice were more than ten times higher than those in fresh slices of control mice, although the absolute levels of putrescine and spermine decreased (by 15 and 40%, respectively) after 3-6 h incubation in vitro, while the levels of spermidine slightly increased (by 10%), (2) the excitatory synaptic response waveforms were wider (an increased half-width), and paired-pulse facilitation was somewhat reduced in ODC mice as compared to controls, and (3) potentiation of excitatory synaptic responses (measured 30-45 min after theta burst stimulation) did not differ between ODC and control mice. These results indicate that synaptic transmission is affected, but synaptic plasticity in the field CA1 assessed in vitro is not changed by elevated levels of intracellular putrescine.