<prompt> Autonomic fibres are rich in which type of neurotransmitterAcetylcholineNoradrenalineGABAEpinephrine  <response>: The principal transmitter agents involved in autonomic nervous system are acetylcholine and norepinephrine. The neurons that are cholinergic are 1all preganglionic neurons, 2 all parasympathetic postganglionic neurons, 3 sympathetic postganglionic neurons that innervate sweat glands and 4sympathetic postganglionic neurons that end on blood vessels in some skeletal muscles and produce vasodilation when stimulated. The remaining sympathetic postganglionic neurons which is only minimal are noradrenergic ie, release norepinephrine. Ref: Ganong;s review of medical physiology; 23rd edition; pg: 265-266. 