Veterinary Neuropharmacology

CHOLINOMIMETIC ALKALOIDS

• Cholinomimetic alkaloids  stimulate the muscarinic receptors of cells innervated by post ganglionic cholinergic nerves. They are also effective in chronically denervated tissue and are not dependent upon endogenous acetylcholine.
• Pilocarpine, muscarine and arecoline are naturally occuring parasympathomimetic alkaloids with minimal nicotinic effects.

Pilocarpine

• It is obtained from Pilocarpus jaborandi and Pilocarpus microphyllus.
• It is a potent parasympathomimetic.
• It produces all the muscarinic responses of acetylcholine.
  • Increases secretion of exocrine glands - salivary, sweat, mucous, gastric, pancreatic secretions.
  • Causes contraction of the gastrointestinal tract smooth muscles and increases peristalsis.
  • Pupillary constriction is the most important effect observed.

Arecoline

• It is obtained from Areca catechu.
• It has some nicotinic agonistic activity.
• It has been used as an anthelmintic to paralyze tapeworms.
• Acts on the muscarinic receptors of effector cells of glands, smooth muscle and myocardium. It is more potent than pilocarpine.
• Depresses the heart rate and blood pressure and causes dyspnoea.
•  Secretions of the glands of the digestive tract are increased and peristalsis is also increased

Muscarine

• It is obtained from the mushroom Amanita muscaria.
• It is a potent parasympathomimetic.
• It is not used clinically. If taken accidentally, the toxic effects include severe colic, diarrhoea, exocrine secretions, miosis, dyspnoea, hypotension and bradycardia.
• The antidote of choice is atropine.
• Oxotremorine is a synthetic agent.