Different correlations among physiological and morphological properties at single glutamatergic synapses in the rat hippocampus and the cerebellum.

Abstract

Synapses in the mammalian central nervous system show substantial diversity in their physiological and morphological properties. However, the correlations among them have remained elusive. Here, we tried to clarify the correlations by establishing a method to record excitatory postsynaptic currents (EPSCs) at individual synapses and also to observe the morphology at the same time. A pair of pre- and postsynaptic neurons were labeled with different fluorescent dyes, and a presynaptic varicosity was selectively stimulated with a θ-tube glass electrode under conditions in which action potential generation was suppressed. Two representative types of excitatory glutamatergic synapses, one on hippocampal pyramidal neurons and the other on cerebellar Purkinje neurons, were studied. The correlations between the properties of quantal EPSCs (qEPSCs) and those of synaptic morphology were analyzed in rat primary culture preparations. The amplitude and the decay time of qEPSC were correlated with the size of the postsynaptic spine only at hippocampal synapses. In contrast, the size of the presynaptic varicosity was correlated with the size of the postsynaptic spine and the quantal content of evoked EPSCs only at granule neuron-Purkinje neuron synapses in the cerebellum. These results suggest that the interaction between pre- and postsynaptic structures and the coupling of postsynaptic responsiveness and the spine morphology differ between cerebellar and hippocampal glutamatergic synapses.