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M L Porceddu

Publications and source records attributed to M L Porceddu.

54 records · Page 3Linked to original sources
PubMed1978

Stimulation of "regulatory" dopamine receptors by bromocriptine (CB-154).

Bromocriptine produces long-lasting hypomotility and decreases brain dihydroxyphenylacetic acid (DOPAC) in mice. These effects are obtained with doses much lower than those which produce hypermotility. The decrease of brain DOPAC is correlated to the hypomotility both on a dose and on a time basis. Potent DA receptor blockers as pimozide, benzperidol and droperidol antagonize the hypomotility and the decrease of brain DOPAC produced by bromocriptine. These effects are obtained with very low doses (0.05-0.3 mg/kg) of neuroleptics which per se do not affect motility or brain DOPAC. The maximal decrease of brain DOPAC produced by bromocriptine is similar to that produced by apomorphine and the combination of these drugs does not result in a further decrease. On the basis of these results it is postulated that bromocriptine decreases DA turnover and produces hypomotility by acting on "regulatory" DA receptors different from the postsynaptic ones of the "terminal" dopaminergic areas.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1978

Self-inhibitory dopamine-receptors and central effects of apomorphine.

Apomorphine, a central dopamine-receptor agonist, is well known to produce excitatory effects in animals. However, low doses exert depressant effects as hypomotility, sedation and sleep. The mechanism of these effects are discussed in terms of a stimulation by apomorphine of DA-receptors, different from the post-synaptic ones, provided of an inhibitory effect on DA-synthesis and on the firing of dopaminergic neurons.

Animals↗
PubMed1977

Changes in gastro-intestinal serotonin content associated with fasting and satiation.

Rats fasted for 24 h were fed for 3 h, after which time food was removed. Food intake decreased serotonin levels in the stomach and duodenum by 30 and 40%, respectively. These changes persisted for about 3 h. Food intake did not change tryptophan content in the stomach, while, in the duodenum, tryptophan level rose by 100% at the end of the feeding period and remained elevated for about 9 h.

Animals↗
PubMed1977

Evidence for selective and long-lasting stimulation of "regulatory" dopamine-receptors by bromocriptine (CB 154).

Bromocriptine, an ergot-derivate with DA-receptor stimulating properties in vivo, produces long-lasting hypomotility in mice not accustomed to the motility cage and decreases brain DOPAC and HVA without affecting brain DA. These effects are obtained with doses 25 times lower than those which produce hypermotility. The decrease of brain DOPAC is correlated to the hypomotility both on a dose- and on a time-basis. Potent neuroleptics as pimozide, benzperidol and droperidol, which are considered to be fairly specific DA-receptor blockers, antagonize the hypomotility and the decrease of brain DOPAC produced by bromocriptine. These effects are obtained with very low doses (0.05--0.3 mg/kg) of neuroleptics which per se do not affect motility or brain DOPAC. The maximal decrease of brain DOPAC and HVA produced by bromocriptine is similar to that produced by apomorphine and the combination of these drugs does not result in a further decrease of brain DOPAC or HVA. On the basis of these results it is postulated that bromocriptine decreases brain DA-turnover and produces hypomotility by acting on "regulatory" DA-receptors different from the post-synaptic ones of the "terminal" dopaminergic areas.

3,4-Dihydroxyphenylacetic Acid↗
PubMedDate not supplied

Failure of dark adaptation to upregulate D-1 dopamine receptors in retina of senescent rats.

The effect of aging on the binding parameters of 3H-SCH 23390, the most selective ligand of D-1 DA receptors, was studied in membrane preparations from the rat retina. DA-stimulated adenylate cyclase activity was also measured in order to better characterize the changes in retinal D-1 DA receptors induced by aging. The binding studies revealed that the density of 3H-SCH 23390 was increased (34 and 73%) in the retina of 14- and 26-month-old rats, when compared to young adult animals, respectively. In contrast, aging failed to alter the sensitivity of the adenylate cyclase to the action of DA. In fact, DA (10(-6) M to 10(-4) M) elicited a similar enhancement in cyclic AMP formation in retinal homogenates of both adult and senescent rats. Since dark adaptation increases the density of D-1 DA receptors in the retina of adult rats we studied the effect of light deprivation on 3H-SCH 23390 binding and DA-sensitive adenylate cyclase activity in the retina of senescent rats. As previously shown (25) light deprivation increased 3H-SCH 23390 binding and enhanced DA-sensitive adenylate cyclase activity in the retina of young adult rats. On the contrary, dark adaptation failed to increase 3H-SCH 23390 binding and to enhance DA-sensitive adenylate cyclase activity in the retina of senescent rats. Taken together these results indicate that D-1 DA receptors in the retina of aged rats have biochemical and functional properties different from those found in the retina of adult animals; these changes may result in an altered response to the physiological stimuli elicited by environmental lighting.

Adenylyl Cyclases↗