VPT 321: Veterinary Neuropharmacology (2+1) copy 1

PHARMACOLOGICAL ACTIONS OF GANGLIONIC STIMULANTS

• Central nervous system
  • Nicotine is an extremely toxic substance that transiently stimulates and then depresses the CNS.
  • Death is from respiratory paralysis of the diaphragm and chest muscles resulting from descending paralysis.
  • Nicotine is absorbed through the chitinous shell of insects after a direct spraying or after contacting a sprayed surface and kills the insect by paralysis.
• Cardiovascular system
  • Small doses of nicotine activate both caridoaccelerator and cardioinhibitory nerves. Since cardioinhibitory nerve is more predominant, decreased pulse rate is noticed.
  • Due to paralysis of the autonomic ganglia after a large dose of nicotine, the heart rate returns towards normal.
  • Small doses of nicotine can cause a pressor response due to the sympathetic stimulation.
  • Peripheral vasodilatation results after a large dose due to autonomic ganglionic blockade.
• Gastrointestinal system
  • Activates both the smooth muscles and secretory glands of the digestive tract and produce excessive salivation, increased gastric secretion, vomiting, increased peristalsis and defecation.
• Skeletal muscle
  • Initially stimulates nicotinic receptors of the motor end plate and in large doses produces a depolarising muscle paralysis.
• Acute nicotine poisoning
  • Excitement, hyperapnea, salivation, pulse rate irregularities, diarrhoea and emesis. After this transient stimulatory phase, a depressed state characterised by incoordination, tachycardia, dyspnoea, coma and death from respiratory paralysis.