Emesis pathways

Emesis. Figure 1 Afferent pathways involved in vomiting. Some stimuli for initiation of vomiting from the various locations are shown in the boxes. The presence of receptors at a particular location does not imply that they are necessarily involved in normal transmission of the vomiting reflex. 

These include atropine, scopolamine (hyoscine), trihexyphenidyl (benzhexol) and benzatropine. They block central muscarinic receptors involved in various afferent pathways of the vomiting reflex (Fig. 1). They have been used to control motion sickness, emesis in Meniere s disease and postoperative vomiting. Currently, hyoscine is largely restricted to the treatment of motion sickness where it has a fast onset of action but a short duration (4-6 h). Administration of hyoscine by transdermal patch produces a prolonged, low-level release of the drug with minimal side effects. To control postoperative vomiting, it should be applied >8 h before emesis is anticipated. 

Emesis No distinct pathway DA receptors in chemoreceptor pathway zone Vomiting Anti-emetic (not motion sickness) D2 ... 

Some trichothecene-induced effects may be due to neurotransmitter alteration in the central nervous system. Emesis or vomiting, which occurs with many of the trichothecenes when given at high doses, has been attributed to the stimulation of the chemoreceptor trigger zone in the area postrema of the medulla oblongata. However, studies with T-2 toxin in cats indicated that other mechanisms, such as the neural afferent pathways from the abdomen, implicated in radiation-induced emesis, may also be involved (Borison and Goodheart, 1989). DON alters serotonin activity in the central nervous system of swine which is important in... 

Buclizine (50 mg p.o. 30 minutes prior to travel) is a centrally acting antiemetic agent used for the control of the nausea, vomiting, and dizziness of motion sickness. Buclizine depresses conduction in vestibular-cerebellar pathways and hence reduces labyrinth excitability (antivertigo action), and it inhibits the chemotrigger zone for emesis (antiemetic action) (see also Figures 73 and 81). 

The transmitters involved in the pathways concerned with emesis are not fully known. However, the CTZ is rich in dopamine-D, and 3HT, receptors. Cholinergic and hisiaminergic synapses are involved in transmission from the vestibular apparatus to the vomiting centre. 

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