Question

1. Opioids inhibit nerve activity in several different ways, depending on where the receptors are located. Please explain the effects of the following, in detail:

a) Postsynaptic inhibition (5pts):

a.

b) Axoaxonic Inhibition (5pts):

a.

c) Presynaptic autoreceptors (5pts):

a.

Answer 1

Opioids drugs produce their pharmacological action, including analgesia, by acting on receptor located on neuronal cell membrane.

The presynaptic action of opioids to inhibit neurotransmitter release is considered to be their major effects in the nervous system. There are three type of opioids receptor m, d and k are coupled to intracellular mechanisms by G-Protein. Opioids produce effects on neurons by acting on receptors. The opioids receptors and many other receptors are coupled to guanine nucleotide binding G-Protein.

Opioids have actions at two sites, the presynaptic nerve terminal and the postsynaptic neuron.

          The post synaptic opioids are usually inhibitory and the presynaptic action on opioids is to inhibit neurotransmitter release, and this is considered to be their major effects on nervous system, however the final effects of an opioids in the brain is the result not only its action at multiple presynaptic sites on both inhibitory and excitatory neurons but also of its postsynaptic effects.

For example, presynaptic inhibition of neurotransmitter release many results in excitatory effects in a target neurons if the neurotransmitter normally produce an inhibitory effect. However if the opioids also has a postsynaptic inhibitory effect on the target neuron, the excitatory may not occur.

The location and density of opioids receptors on the neuron determine the overall effects of opioids on the neuron.

The nervous system comprise neuron of many different types which differ in size, shape, function and chemical nature of neurotransmitter released from their terminals to carry information to other neurons.