| Non-Scientific Abstract In animal brain, the processes of learning
and memory formation are believed to involve synaptic plasticity. Synaptic plasticity is a
property of the brain cells that enables them to adjust their responsiveness to the incoming
signal. There are many types of receptors, which are like an antenna for receiving television
waves. In the vertebrate central nervous system, glutamate receptor (GluR) mediates most of the
signal transmission of the brain. One of the glutamate subunits, δ 2, is restrictively
found in Purkinje cells of the cerebellum and is believed to play a key role in long-term
depression (LTD)‹ a condition marked by a reduction in the responsiveness to the stimulation. In
Purkinje cell LPD, both AMPA, a type of GluR, and δ 2 receptors are internalized,or taken
inside the cells.However, the exact mechanistic role of δ 2 in LTD is unknown. We propose
that glutamate stimulation of δ 2 induces the internalization of other receptors. Our
results show that the redistribution of the endogenous δ 2 receptors on the Purkinje cell
membrane is reproducible,which was the first step of this project.Next,we expressed exogeneous
δ 2 receptors,with and without genetic modification, by using Sindbis virus expression
system as a vehicle to introduce the genes into the cells.
Abstract
Glutamate receptor subunits Glutamate receptor subunits δ 2 are selectively expressed in
parallel-fiber-Purkinje cell synapses and play a key role in cerebellum-dependent motor learning
and coordination and long-term depression (LTD) of parallel-fiber-Purkinje cell transmission.
However, its mechanistic role that leads to these cellular functions remains unclear because δ 2
receptor has never exhibited any glutamate binding or channel properties. Cerebellar LTD has
been shown to involve internalization of δ 2 receptor as well as AMPA receptor that actually
mediates the synaptic transmission. Therefore, we hypothesize that δ 2 receptor triggers the
internalization process upon binding with glutamate. To test this hypothesis, we examined the
localization of endogenous and exogenous δ 2 receptor with and without mutation before and after
glutamate stimulation by immunostaining. The exogenous δ 2 receptors were introduced into
dissociated Purkinje cell culture via Sindbis virus expression system.We found that endogenous
receptors are internalized upon glutamate stimulation. Exogenous δ 2 can be introduced by the
Sindbis virus, and they localize in the same manner as the endogenous receptors at the dendritic
spines.However, the Purkinje cells are sensitive to viral toxicity and a balance point between
infectivity and toxicity needs to be further determined. |
