Slower spontaneous excitatory postsynaptic currents in spiny versus aspiny hilar neurons

In the hilar region of the rat hippocampus, large spontaneous excitatory postsynaptic currents (sEPSCs) mediated by non-NMDA glutamate receptors are present in both excitatory spiny mossy cells and inhibitory aspiny hilar interneurons, making these neurons ideal candidates for a comparative study using the tight seal whole-cell recording technique. Although sEPSCs have similar amplitude distributions, the rise and decay times are significantly slower in spiny versus aspiny neurons. Similar kinetic differences are observed in synaptic currents evoked by mossy fiber stimulation. These results demonstrate a physiological difference between the excitatory drive to excitatory and inhibitory neurons in the hilus that certainly contributes to differences in synaptic strength and that may be applicable to other brain regions. Furthermore, since the development or modification of individual spines or groups of spines may affect synaptic strength, these results may be pivotal in establishing a role for spines in modulating synaptic activity.