<prompt> All are features of neurotransmitters except:Released from presynaptic cleftDegraded from presynaptic cleftExogenous administration will not have any effectProduced in neurons only  <response>: Ans: C exogenous admin... Ref: Ganong, 22nd ed, p. 85, 94Exogenous administration does have effects, for example when adrenaline which is a neurotransmitter is administered; it produces a number of effects like tachycardia, increase in BP etc.Mechanism of neurotransmission Nerve endings convert electrical energy into chemical energy by means of neurotransmitters. These neurotransmitters are stored in synaptic vesicles and released by nerve impulses into the synaptic cleft. These neurotransmitters then act on the post synaptic membrane which results in conduction of impulse. After their action they are rapidly removed from synaptic cleft by diffusion, metabolism or by re- uptake into the presynaptic neuron. Exogenous administration of the neurotransmitter can also cause effects similar to its endogenous counterpart. Noradrenaline which is a neurotransmitter is given in shock to raise BP. 