Ganglionic Stimulants and Blockers Overview

Ganglionic Stimulant and Blockers

• Ganglionic stimulants and blockers affect the autonomic nervous system.
• Learning objectives include understanding the predominant tone in the autonomic nervous system, describing the effects of ganglion stimulants and blockers, and listing therapeutic uses of ganglionic blockers.
• The peripheral nervous system has sensory/afferent and motor/efferent divisions.
• The efferent division has somatic and autonomic nervous systems.
• The autonomic nervous system is further divided into sympathetic and parasympathetic divisions.
• The somatic nervous system controls skeletal muscles (voluntary actions).
• The autonomic nervous system controls smooth and cardiac muscles (involuntary actions).
• The sympathetic division is associated with "fight or flight" responses - raising heart rate, constricting blood vessels, and releasing glucose.
• The parasympathetic division is associated with "rest and digest" responses - digestion, waste expulsion, and general maintenance.
• The sympathetic division originates from thoracic and lumbar regions of the spinal cord, with short preganglionic and long postganglionic fibers.
• The parasympathetic division originates from brain and sacral regions of the spinal cord, with long preganglionic and short postganglionic fibers.
• The neurotransmitter for all preganglionic autonomic fibers, parasympathetic postganglionic fibers, and some postganglionic sympathetic fibers is acetylcholine (ACh).
• Most effector tissues and organs receive innervation from both sympathetic and parasympathetic systems; only one sets the predominant tone.
• The heart's predominant tone is parasympathetic at rest, causing a lower heart rate.
• Ganglionic blockers disrupt the parasympathetic system, allowing the sympathetic system to dominate and increase heart rate.
• Different effector sites (e.g., heart, veins, iris) have predominant tone from either sympathetic or parasympathetic divisions, and various receptors (e.g., M2 cholinergic, β1 adrenergic).

Types of Ganglionic Stimulants

• Stimulants can be selective (nicotinic) or non-selective (nicotinic/muscarinic). -Nicotine, in small doses, is a selective nicotinic agonist.
• Other agonists include dimethyl phenyl piperazinium, and tetramethyl ammonium.
• Varenicline blocks nicotine from activating receptors, reducing smoking's reinforcing effects, and used in smoking cessation.
• Anticholinesterases increase ACh levels.
• Acetylcholine, carbachol, and pilocarpine are muscarinic agonists.

Ganglionic Blockers

• Their clinical use is less common due to more selective agents but has some applications in specific emergencies.
• Examples include Trimethaphan.
• Ganglionic blockers cause vasodilation by blocking sympathetic ganglia.
• They inhibit reflex tachycardia by blocking sympathetic and parasympathetic input to the heart.
• In emergencies, they rapidly lower blood pressure by inducing hypotension.
• Also used for controlled hypotension during surgery to decrease bleeding, though less common now due to other targeted vasodilators.

Nicotine Replacement Therapy (NRT)

• Using nicotine patches, gum, lozenges, or nasal spray to quit smoking.
• Mimics the effects of smoking in the autonomic nervous system and central nervous system.
• Reduces withdrawal symptoms and cravings by offering a controlled amount of nicotine.

Normal Physiological Function of Ganglionic Neurons

• Ganglionic neurons require an optimal amount of neurotransmitter (ACh/N); too little results in no effect; too much blocks the receptor.
• Nicotine (small dose) simulates the normal function, leading to depolarization via sodium ion channels..
• Nicotine (large dose) and anticholinesterases (big dose) lead to chronic or continuous stimulation, thus causing continuous influx of Na+, making the neuron dormant.