Ganglia nicotinic receptors

In addition to autonomic ganglia, nicotinic receptors are found in a variety of organs, and their stimulation will produce quite different results in these different tissues. Activation of nicotinic receptors on the plasma membrane of the cells of the adrenal medulla leads to the exo-cytotic release of epinephrine and norepinephrine stimulation of nicotinic receptors at the neuromuscular junction results in the contraction of skeletal muscle (see... 

Ganglionic nicotinic receptors are found on postsynaptic neurons in both parasympathetic and sympathetic ganglia and in the adrenal gland. Ganglionic nicotinic receptors appear in tissues of neural crest embryonic origin and exhibit identical properties in sympathetic and parasympathetic ganglia. 

Nicotine, lobeline, trimethylammonium, and DMPP stimulate all autonomic ganglia by simple combination with ganglionic nicotinic receptors on the postsynaptic membrane. This leads to membrane depolarization, an influx of sodium and calcium ions, and the generation of a fast EPSP. These agents produce general stimulation of autonomic ganglia and a complex pattern of mixed sympathetic and parasympathetic responses. 

Large doses of nicotine produce a prolonged blockade of ganglionic nicotinic receptors. Unlike the blockade of... 

Ganglionic nicotinic receptors, like those of the skeletal muscle neuromuscular junction, are subject to both depolarizing and nondepolarizing blockade (see Chapters 7 and 27). Nicotine itself, carbamoylcholine, and even acetylcholine (if amplified with a cholinesterase inhibitor) can produce depolarizing ganglion block. 

It was concluded that the nicotinic activity of choline phenyl ether and of choline o-tolyl ether is a reflection of the ability of the molecule to assume a "planar" conformation when interacting with the ganglionic nicotinic receptor. In contrast, the inactive 2,6-xylyl ether of choline cannot assume this planar disposition. Evaluation of additional conformation-ally restricted aiyl choline ethers (44-47) revealed that only the piperidine derivative (47) is a ganglionic stimulant (98). 

Antagonists of ganglionic nicotinic receptor sites are not therapeutically useful since they cannot distinguish between the ganglia of the sympathetic nervous system and the ganglia of the parasympathetic nervous system (both use nicotinic receptors). Consequently, they have many side-effects. 

Nicotine and several other compounds stimulate ganglionic nicotinic receptors (Figure 9 ). Nicotine... 

Hexamethonium (Fig. 16.28) is a quaternary ammonium agent. It was the first successful antihypertensive treatment. However, its side effects led to discontinuation of its use. It is thought to exert its action by blocking the ion channel rather than the acetylcholine active site. Blocking the ganglionic nicotinic receptor will stop the... 

Ganglionic blocking agent. A drug that blocks neurotransmission at the nicotinic receptors of the sympathetic ganglia, thus blocking vascular reflexes. 

The answer is d. (Hardman, pp 142—M3.) ACh will stimulate both muscarinic and nicotinic receptors. Skeletal muscle contraction is mediated through NM receptors, and ganglionic stimulation is an effect of NN receptors All of the other effects listed in the question occur following muscarinic receptor activation and will be blocked by atropine and scopolamine, both of which are muscarinic receptor antagonists. Skeletal muscle contraction will not be affected by these drugs rather, a neuromuscular blocker (e.g., tubocurarine) is required to antagonize this effect of ACh. 

FIGURE 11-3 Structure of compounds important to the classification of receptor subtypes at cholinergic synapses. Compounds are subdivided as nicotinic (N) and muscarinic (Ad). The compounds interacting with nicotinic receptors are subdivided further according to whether they are neuromuscular (N,) or ganglionic (N2). Compounds with muscarinic subtype selectivity (M M2, M3, M4) are also noted. 

Badio B, Padgett WL, Daly JW. (1997). Ibogaine a potent noncompetitive blocker of ganglionic/neuronal nicotinic receptors. Mol Pharmacol. 51(1) 1-5. 

So, parasympathetic nerves use acetylcholine as a neurotransmitter and cholinomimetic drugs mimic the action of acetylcholine at its receptors. Muscarinic receptor subtypes are found on neuroeffector junctions. Nicotinic receptor subtypes are found on ganglionic synapses. Chohnomimetics can be classified as ... 

Atropine, an alkaloid from Atropa belladonna, is the classical parasympatholytic compound. It competes with acetylcholine for the binding at the muscarinic receptor. Its affinity towards nicotinic receptors is very low, so that it does not interfere with the ganglionic transmission or the neuromotor transmission, at least in therapeutic dosages. However, in the central nervous system muscarinic receptor do play an important role and while atropine can penetrate the blood-brain barrier it exerts pronounced central effects. Atropine, like all other antagonists of the muscarinic acetylcholine receptor inhibit the stimulatory influence of the parasympathetic branch of the autonomous nervous system. All excretory glands (tear, sweat, salivary, gasto-intestinal, bronchi) are... 

The basis for the antihypertensive activity of the ganglionic blockers lies in their ability to block transmission through autonomic ganglia (Fig. 20.2C). This action, which results in a decrease in the number of impulses passing down the postganglionic sympathetic (and parasympathetic) nerves, decreases vascular tone, cardiac output, and blood pressure. These drugs prevent the interaction of acetylcholine (the transmitter of the preganglionic autonomic nerves) with the nicotinic receptors on postsynaptic neuronal membranes of both the sympathetic and parasympathetic nervous systems. 

Schematic diagram comparing some anatomic and neurotransmitter features of autonomic and somatic motor nerves. Only the primary transmitter substances are shown. Parasympathetic ganglia are not shown because most are in or near the wall of the organ innervated. Cholinergic nerves are shown in blue noradrenergic in red and dopaminergic in green. Note that some sympathetic postganglionic fibers release acetylcholine or dopamine rather than norepinephrine. The adrenal medulla, a modified sympathetic ganglion, receives sympathetic preganglionic fibers and releases epinephrine and norepinephrine into the blood. ACh, acetylcholine D, dopamine Epi, epinephrine M, muscarinic receptors N, nicotinic receptors NE, norepinephrine.

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