An immunochemical and biochemical study of catecholaminergic activity in dissociated hypothalamic cultures

Prolactin: structure, function, and regulation of secretion

Prolactin is a protein hormone of the anterior pituitary gland that was originally named for its ability to promote lactation in response to the suckling stimulus of hungry young mammals. We now know that prolactin is not as simple as originally described. Indeed, chemically, prolactin appears in a multiplicity of posttranslational forms ranging from size variants to chemical modifications such as phosphorylation or glycosylation. It is not only synthesized in the pituitary gland, as originally described, but also within the central nervous system, the immune system, the uterus and its associated tissues of conception, and even the mammary gland itself. Moreover, its biological actions are not limited solely to reproduction because it has been shown to control a variety of behaviors and even play a role in homeostasis. Prolactin-releasing stimuli not only include the nursing stimulus, but light, audition, olfaction, and stress can serve a stimulatory role. Finally, although it is well known that dopamine of hypothalamic origin provides inhibitory control over the secretion of prolactin, other factors within the brain, pituitary gland, and peripheral organs have been shown to inhibit or stimulate prolactin secretion as well. It is the purpose of this review to provide a comprehensive survey of our current understanding of prolactin's function and its regulation and to expose some of the controversies still existing.

Differing neurotoxic potencies of methamphetamine, mazindol, and cocaine in mesencephalic cultures

The potent reinforcing effects of methamphetamine and cocaine are thought to be mediated by their interactions with CNS dopamine neurons. Both stimulants share the ability to block dopamine uptake potently, and methamphetamine can release cytoplasmic dopamine as well. There is also abundant evidence demonstrating the neurotoxic effects of methamphetamine. There are, however, limited studies that attempt to discern the neurotoxic mechanisms of these agents. The purpose of the present study was to characterize and compare the chronic in vitro effects of methamphetamine, cocaine, and the dopamine uptake blocker, mazindol, on cultured fetal mesencephalic dopamine neurons. Our studies examined biochemical mechanisms to evaluate the contribution of reuptake blockade versus release of dopamine. Using a dispersed cell preparation of fetal mesencephalon, cultures were treated for 5 days with the three uptake blockers. Dopamine function was assessed by measuring high-affinity [3H]dopamine uptake and by examining cultures for the presence of tyrosine hydroxylase-immunopositive neurons. Nonspecific neurotoxicity was assessed by staining for neuron-specific enolase and measuring lactate dehydrogenase activity. The results indicate that repeated administration of high concentrations of methamphetamine (10(-4) and 10(-3) M) caused a generalized neurotoxicity whereas the effects of 10(-5) M methamphetamine appeared to be specific to dopamine cells. Likewise, treatment of the cultures with mazindol (10(-6) M) resulted in reduced dopamine uptake while not significantly affecting neuron-specific enolase or tyrosine hydroxylase immunostaining. On the other hand, repeated exposure to cocaine (10(-5) and 10(-4) M) did not alter dopaminergic function in these cultures. The different mechanisms of action of these stimulants may explain the differences in neurotoxic potency of these compounds.(ABSTRACT TRUNCATED AT 250 WORDS)