Synaptic Morphology of the Mouse Striatal Cholinergic Neurons in the Early Postnatal Life

Hann, Hoo Jae; Lee, Hee Lai

Abstract

The cholinergic neurons in the striatal complex are the major interneurons that integrate the informations incoming to and outflowing from the striatum. The shape of synapses may change even after birth and the synaptic morphology reflects the functional state of synapse. However, it is not well known about the synaptic morphology of the mouse striatal cholinergic neurons in their early postnatal life. Thus, we investigated the synaptic morphology of the mouse striatal cholinergic neurons in their early postnatal life by the electron microscopy combined with immunohis-tochemistry. In addition, we investigated the trends of change in synaptic morphology and whether the difference between two compartments exists or not. Experimental animals which are ICR mice, were divided into 5 groups according to their postnatal age: 3-day, 1-week, 2-week, 4-week, and 6-week. Pre-embedding immunohisto-chemistry was done with anti-choline acetyl transferase antibody. The results were as follows. 1. In synapses that immunoreactive terminals constitute the presynaptic components, most of synapses are symmetric type in all age groups (p<0.05). Most of synapses in the dorsal striatum are symmetric form from 1-week of postnatal age, but it is not prominent in the ventral striatum until 2-week of postnatal age. 2. In synapses that immunoreactive terminals constitute the postsynaptic components, both symmetric and asymmetric synapses are noted in similar proportions (p<0.05). There are no difference in the synaptic morphology between dorsal and ventral striatum. 3. No specific findings are observed in synaptic curve according to the postnatal age or compartment. In conclusion, the synaptic morphology of mouse striatal cholinergic neurons is similar to mature pattern from 2-week of postnatal age. And it is thought that period between birth and 2-week of postnatal age is the critical period for synaptogenesis. The synaptic curve does not reflect the degree of synaptic maturity. Further investigations will be required to generalize the synaptic curve as a marker for synaptic maturity.