4. List the role of glutamate in synaptic transmission between photoreceptor 
    and bipolar cells. What is meant by neuroprotection 
The neurotransmitter of neurons of the vertical pathways through the retina is glutamate.
All photoreceptor types, rods and cones, probably use the excitatory amino acid glutamate to transmit signals to the next order neuron (bipolar cells) in the chain.The action of the photoreceptor neurotransmitter upon the second-order neurons is through two different types of sensory channels. The one type of postsynaptic receptor type is a metabotropic glutamate channel that involves a second messenger cascade and cyclic GMP for activation of the channel (in the ON-center bipolar cell) whereas the other is an ionotropic channel via AMPA receptors and Na ions (OFF-center bipolar and horizontal cell) 

Neuroprotection means preventing the nerve from being damaged. In ophthalmology, this usually applied to optic nerve and retinal ganglia. Two theories are thought to be involved in neuroprotection: one is to prevent cell apoptosis;  the other is to improve vascular health for healthier ganglia. Betoptic eyedrop is thought to have neuroprotection property because it has the additional effect of increasing optic nerve flow because of it calcium channel blocking capabilities.

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