The effect of DOPA on segmental reflexes in rat pups]

In acute experiments on spinal 5-30-day rat puppies, studies have been made of the effect of DOPA (100 mg/kg intraperitoneally) on monosynaptic reflex in extensors (evaluated by parameters of H-reflex) as well as on polysynaptic segmentary reflexes. In 5-7-day animals, mainly the inhibitory effect was observed with a short phase of facilitation of monosynaptic reflex. From the 10th day, facilitatory effect of DOPA becomes a predominant one reaching maximum to the 16th day. Within first 16 days of postnatal life, DOPA exhibits facilitatory effect on short-latent polysynaptic reflexes and inhibits long-latent ones. To the 30th day, reactions which are typical of adult animals are observed: inhibition of short-latent and facilitation of long-latent polysynaptic discharges. The data obtained indicate that in early postnatal development the effect of DOPA on mono- and polysynaptic reflexes qualitatively differs from that in adult animals.     

Aspirin and the reversal of antifertility effect of iproniazid in rats

Iproniazid, a specific monoamine oxidase inhibitor which is known to exert its primary influence by interfering in the metabolism of catecholamines, showed its antifertility efficacy by causing luteolysis in rats. A concomitant regimen of iproniazid and aspirin, a very potent inhibitor of prostaglandin biosynthesis and release, consistently prevented the iproniazid-induced luteolysis and embryonic resorption in the test animals. It has been proposed that iproniazid-induced luteolysis in rats is probably mediated through an increased production of endogenous prostaglandins as a result of an abnormally higher concentration of catecholamines both at central and peripheral levels.     

The effect of reserpine on the pars intermedia of the rat pituitary

Summary Reserpine has a stimulatory effect on the pars intermedia of the rat pituitary, probably mediated by its action on regulatory catecholaminergic nerves. The effect of single intraperitoneal injections of 0.1–20 mg/kg b.w. of reserpine was studied in adult male rats. Reserpine at a dose of 2 mg/kg b.w. induced degranulation, orientation of the secretory granules along the cell membrane and loss of formaldehyde-chloral-induced fluorescence, accompanied by an activation of the granular endoplasmic reticulum and the Golgi apparatus. With higher doses progressive degranulation and loss of fluorescence were observed. The effect was, however, heterogeneous, and with all doses cells displaying normal ultrastructure and normal fluorescence were regularly present.To study the release of granular products (containing a different components of the pro-opiomelanocortin chain) from individual cells, formaldehyde-chloral induced fluorescence and -MSH- and -endorphin immunoreactivies were demonstrated in consecutive sections from pituitaries of rats given 8 mg/kg body weight of reserpine 24 h before sacrifice. The results indicate coordinated release of these granular products at the cellular level after reserpine treatment.This work was supported by Finska Läkaresällskapet     

The possible mode of action of iproniazid. I. Differential luteolytic effect of iproniazid before and after the establishment of placental adolescence.

Iproniazid, a very specific monoamine oxidase inhibitor, at a dose level of 200 mg/kg body weight induced luteolysis and caused lysis of deciduomata as well as resorption of the established embryos. Exogenous replacement of prolactin, a most consistent stimulant of the endocrine functioning of corpus luteum, or progesterone absolutely reversed the adversity developed following iproniazid injection. Moreover, failure of iproniazid even at a higher dose level in the deviation of the normal sequence of pregnancy after the establishment of placental adolescence strongly tempting to suggest that iproniazid could only show its luteolytic effect when the hypothalamic-pituitary complex is exclusively involved in the maintennance of pregnancy.     

Cytomorphological alterations of mossy fiber boutons of the hippocampus produced by 3-acetylpyridine,methoxypyridoxine, reserpine,and iproniazid

Summary The hippocampal mossy fiber boutons of the rabbit were studied with phase and electron microscopy. The injection of 3-acetylpyridine, methoxypyridoxine, and reserpine diminishes the conspicuous osmiophilic density of the mossy fiber boutons in comparison to similar regions from nontreated animals as observable in phase microscopy. However, electron micrographs of the same samples show little or no diminution in the number of those synaptic vesicles consisting of a clear homogeneous center (Type I). Treatment with monoamine liberator, reserpine, results in the same cytomorphological appearance of the boutons as with convulsant agents. The number of synaptic dense-core vesicles (Type II) is not altered after treatment with the convulsant agents or reserpine.A certain extra-vesicular substance and a certain granular component of the vesicular membranes of Type I vesicles is progressively reduced after treatment with all of these drugs. It is suggested that this accounts for the decreased density by phase microscopy.The monoamine oxidase inhibitor, iproniazid, increases the density of the extra-vesicular substance as well as the particles attached to the vesicular membranes of Type I vesicles.It is suggested that these osmiophilic particles contain the biogenic monoamines (in this instance probably serotonin and/or histamine) and that in acute experiments the liberation of these neurotransmitters is not related to a disappearence of dense-core vesicles concommitant with a depletion of neurotransmitters but is from particles in the extra-vesicular substance and the granular component of the vesicular of the Type I vesicles.Furthermore, the functional role of zinc in the synaptic vesicles of mossy fiber boutons of the hippocampus is discussed in regard to a possible storage mechanism for biogenic monoamines.This study was partly supported by USPHS Grant 5 P10 ESOO159.