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Contrasting local effects of MAO inhibitors on caudate tremor activities
Abstract:
Hindlimb tremor was produced in chronic cats by intracaudate microinjection of the monoamine oxidase (MAO) inhibitors tranylcypromine and harmaline throughout a range of doses (150-385 mug). Pargyline, however, was non-tremorgenic within the same range, suggesting that interference with MAO is not sufficient in itself to elicit tremor. Tranylcypromine tremors differed from those of harmaline by exhibiting a slower onset, longer duration and susceptibility to antagonism by hemicholinium. In contrast, ongoing cholinergic tremors following intracaudate physostigmine were variably suppressed by all three MAO inhibitors at comparable dose levels (175-200 mug); pargyline produced the most complete suppression. These results indicate that MAO inhibitors can modify tremor activities in a differential manner dependent both on the functional state of the caudate nucleus and on the ability of cartain MAO inhibitors to exert other local actions.
Insights
Monoamine oxidase (MAO) inhibitors like tranylcypromine and harmaline can induce tremors in cats. However, their effects vary, suggesting MAO inhibition alone isn't enough to cause tremors.
Area of Science:
- Neuropharmacology
- Neuroscience
Background:
- Monoamine oxidase (MAO) inhibitors are known to affect neurotransmitter levels.
- The caudate nucleus plays a role in motor control and tremor generation.
Purpose of the Study:
- To investigate the tremorigenic effects of specific MAO inhibitors administered intracaudately in cats.
- To differentiate the mechanisms underlying tremor induction by MAO inhibitors.
Main Methods:
- Chronic cats received intracaudate microinjections of tranylcypromine, harmaline, and pargyline at various doses.
- Cholinergic tremors induced by physostigmine were also studied in conjunction with MAO inhibitors.
- Tremor characteristics and responses to antagonism were observed.
Main Results:
- Tranylcypromine and harmaline induced hindlimb tremors, while pargyline did not, indicating MAO inhibition is insufficient for tremor.
- Tranylcypromine-induced tremors had a slower onset and longer duration than harmaline-induced tremors.
- MAO inhibitors differentially modulated physostigmine-induced cholinergic tremors, with pargyline showing the most suppression.
Conclusions:
- MAO inhibitors can differentially modify tremor activity in the caudate nucleus.
- The functional state of the caudate nucleus and specific MAO inhibitor actions influence tremor generation.
- MAO inhibitors' effects on tremor are complex and not solely dependent on MAO inhibition.