Blood platelets as models for neurons: uses and limitations.

Platelets show similarities with 5-hydroxytryptaminergic neurons with respect to (1) uptake kinetics of 5-hydroxytryptamine (5-HT) at the plasma membrane, (2) inhibitory effects of tricyclic antidepressants and neuroleptics on 5-HT uptake, (3) granular storage of 5-HT and possibly catecholamines, (4) action of drugs interfering with granular and possibly extragranular amine storage and (5) reaction of the 5-HT receptor at the plasma membrane to 5-HT agonists and antagonists. Dissimilarities include (1) the uptake of catecholamines at the plasma membrane, (2) the biosynthesis of biogenic amines (absent in platelets, present in neurons) and (3) the turnover of 5-HT (slow or absent in platelets, fast in neurons). Although the above mentioned similarities are not absolute, platelets may be considered as reasonable models for some functions of 5-hydroxytryptaminergic neurons e.g. 5-HT uptake at the plasma membrane, intracellular storage of monoamines and reactions of 5-HT receptors to drugs. In addition, the shape change reaction of platelets can probably be used to identify those basic proteins and polypeptides which cause neuronal depolarization. The significance of disturbances of the monoamine system of platelets in neuropsychiatric disorders including Parkinson's syndrome is not yet clear in all respects. Therefore, some of the current ideas about the validity of platelets as models for neurons will be briefly reviewed in this article.