Nicotinic receptors are a type of cholinergic receptors besides the muscarinic receptors.
In the body, they are stimulated by the neurotransmitter acetylcholinesterase and butyrylcholinesterase.
But unlike Muscarinic receptors, they are specifically stimulated by the alkaloid nicotine.
Hence they are named as nicotinic receptors.
They are specifically blocked by the alkaloid D-tubocurarine (arrow poison).
Structurally they are ligand-gated cation channel receptors.
Due to being ligand-gated channels, the response to the ligand is very quick. The response time is in a fraction of seconds or microseconds.
So they are located in places where such high-speed responses are required.
These receptors are of two types as
Types of Nicotinic Receptors
Nicotinic receptors are basically of two types like
- NM Receptors
- NN Receptors
They are classified so based on their location in the body. NM is present in neuromuscular junction or skeletal muscle endplate. NN is present in the neuronal ganglia and synapses.
NM Receptors: These are stimulated by phenyl trimethyl-ammonium and blocked by D-tubocurarine.
Function: NM Receptors transmit signal for skeletal muscle contraction.
NN Receptors: These receptors are present in the ganglion of both the sympathetic and parasympathetic nervous systems. Besides they are also present in brain, spinal cord and adrenal medulla.
They are stimulated specifically by phenypiperanzinium and blocked by hexamethonium. Their main function is the transmission of nerve signals at the ganglion.
- They stimulate both sympathetic and parasympathetic ganglia and process post ganglion impulses.
- Stimulate the release of adrenalin from the adrenal medulla
- Involved in and excitation and inhibition of CNS (site specifically).
In the lab, nicotinic receptors’ actions can be demonstrated by the rabbit head drop method. Wherein the rabbit when given an injection of D-tubocurarine (DTC ) will be unable to hold its head erect. It just hangs until the effect of DTC is exhausted.
In the forest, large animals elephants could be arrested by using an arrow stained with DTC. The elephant skeletal muscles get paralyzed for a while and hence will be unable to move. This helps them to be captured by hunters.