Regulation of the tuberoinfundibular and nigrostriatal systems. Evidence for different kinds of dopaminergic neurons in the brain.

The tuberoinfundibular dopaminergic (TIDA) neurons appear to present remarkable differences from the nigrostriatal and mesocortical dopaminergic (DA) systems. The hormonal feedback of prolactin on TIDA neurons differs from the neuronal feedback system operating in the striatum and olfactory tubercles. The uptake of dopamine appears to present the characteristics of a high affinity process in the terminals of the striatum and olfactory tubercle, whereas in the median eminence this process exhibits a much lower affinity. The pharmacological properties of postsynaptic receptors in the different DA pathways appear to be similar. However, the intracellular events which are ultimately manifested as physiological responses to dopamine may be completely different in the postsynaptic cells in the neostriatum and in the lactotrophs of the anterior pituitary. In addition, there is evidence suggesting that dopamine receptors in the anterior pituitary are more sensitive to the actions of agonists and antagonists than are dopamine receptors in the striatum.