Biomedical subjects
Publications and source records attributed to C Missale.
Na+-dependent binding of 3H-Cocaine is located on dopaminergic terminals and is related to the dopamine uptake system. Studies on senescent rats indicate a decrease in 3H-Cocaine binding density in the striatum. In the same tissue an increase in the Km for dopamine uptake is observed. These changes might be relevant in the age-dependent alterations in dopaminergic function.
Neurotensin (NT) is now reasonably well established as a neurotransmitter or neuromodulator candidate in the CNS. In the present study, we characterized the NT receptors in dispersed cells from the anterior lobe of rat pituitary and investigated the involvement of both cyclic AMP and calcium in the release of prolactin (PRL) induced by NT receptor stimulation. The [3H]NT binding to membranes from anterior pituitary dispersed cells was found saturable and stereospecific. Scatchard analysis of the data gave a straight line indicating a Bmax value of 121 +/- 11 fmol/mg protein and a KD value of 1.4 +/- 0.2 nM. The calculated IC50 values for [3H]NT binding were 5.8 nM for NT, 7.8 nM for L-Phe-NT, and 3,000 nM for the pharmacologically inactive form D-Phe-NT. NT, up to a concentration of 1 microM, did not affect the cyclic AMP generating system in homogenates of anterior pituitary from male or lactating female rats. The same pattern of results was obtained for cyclic AMP formation in intact cells. NT and its analogs stereospecifically enhanced the influx of calcium into dispersed cells from rat anterior pituitary. The effect was time- and dose-dependent. It appeared to be associated with neurotransmitter-operated calcium channels since: preincubation of the cells with tetrodotoxin did not affect the increase in calcium influx induced by NT; concentrations of verapamil that counteract the influx of calcium induced by potassium lacked the capacity to modify the influx of calcium induced by NT; and NT lost its capacity to release PRL in the absence of extracellular calcium.(ABSTRACT TRUNCATED AT 250 WORDS)
The present study demonstrates that 3,4-dihydroxyphenylethylamine (DA, dopamine) prevents neurotensin (NT) stimulation of both prolactin (PRL) release and calcium influx by interacting with specific receptors that are functionally linked to calcium channels. As shown by the studies with dispersed cells from rat anterior pituitary, the pharmacology of the control of PRL release and calcium influx, both induced by NT, was found to be typical of a DAergic process. This was demonstrated by the order of potency of agonists in inhibiting PRL release and calcium influx (DA greater than epinephrine greater than norepinephrine much greater than isoproterenol); by the high affinity of antagonists such as haloperidol and fluphenazine for this process; and by the high degree of stereoselectivity of sulpiride. Specific D2 receptor agonists, such as bromocriptine and lisuride, and the specific D2 receptor antagonist (-)-sulpiride were found to be highly potent on the DA receptors negatively coupled with calcium channels and PRL release. DA was found to lack the capacity to change the influx of calcium induced by either the sodium channel activator veratridine or high extracellular potassium levels, thus indicating a specific action of this amine on calcium channels sensitive to NT. In a range of concentrations that are effective in inhibiting either the calcium influx or the PRL release, both induced by NT, DA did not alter the cyclic AMP generating system. DA (from 1.0 nM to 50 nM) did not affect adenylate cyclase activity in rat pituitary gland homogenates and did not modify intracellular cyclic AMP levels in pituitary cells.(ABSTRACT TRUNCATED AT 250 WORDS)
Dopamine (DA) may participate in the control of aldosterone secretion. We report that two different receptors for DA are present in rat adrenal glomerulosa: D-1, associated with stimulation of adenylate cyclase, and D-2, whose action inhibits adenylate cyclase. The adenylate cyclase system was stimulated by DA (EC50, 7.2 microM) and different DA agonists. When the D-1 receptor blocker SCH 23390 was added to the incubation medium, DA elicited a dose-dependent inhibition of adenylate cyclase (IC50, 10 microM); (-)sulpiride specifically blocked this effect. Furthermore, DA blocked angiotensin II-induced aldosterone release from glomerulosa slices in vitro. This effect was prevented by (-)sulpiride, but not by SCH 23390. The results suggest that the D-2 receptor acts to inhibit the cAMP-generating system and may be physiologically involved in the regulation of aldosterone secretion.
A body of experimental and clinical data was generated over the last decade and now constitutes the basis for a new level of categorization of central dopamine (DA) receptors. Pharmacological and biochemical criteria were used in particular in our laboratories to separate those DA receptors which are linked in a stimulatory way to the enzyme adenylate cyclase and those which are not. We have indeed defined D1 and D2 receptors those DA receptors associated or unassociated to the generation of cyclic AMP, respectively. It should be stressed that the studies on DA receptors in the central nervous system and peripheral tissue were greatly facilitated following the discovery of specific agonist and antagonist drugs for the different DA receptors. As originally proposed by our group, DAergic ergot derivatives and substituted benzamides are now generally accepted as classes of drugs, endowed with agonist and antagonist properties, respectively, on DA D2 receptors. Taking into account the intracellular modifications following the interaction between DA and its own recognition sites, it can be suggested that in cerebral and peripheral tissue the recognition sites for DA are coupled to various of amplifier systems with different molecular mechanisms. According to the data presented and discussed in the text, DA D1 recognition sites appear to be linked to adenylate cyclase through a G/F protein (Ns unit) in a stimulatory way whereas DA D2 recognition sites are associated with adenylate cyclase through a G/F protein (Ns unit) in an inhibitory way or, at least in pituitary, are functionally coupled with inhibition of calcium entry into the cells.
Dopamine receptors in bovine adrenal cortex have been studied by using 3H-(-)sulpiride as selective ligand. The specific binding is saturable and the Scatchard analysis reveals a single component with a Kd of 6.2 nM and a Bmax of 8 fmoles/mg protein. The characterization indicates that the binding is rapid, reversible, stereospecific, Na+ - and temperature- dependent. Moreover its pharmacological profile is superimposable to that of D-2 receptors in the striatum, thus suggesting that central and peripheral D-2 receptors are identical.
Measuring adenylate cyclase activity as a biochemical index of dopamine (DA) receptors, it was found that the selective D1 DA receptor agonist, SKF 82526, was able to stimulate the cAMP formation in rabbit renal and mesenteric arteries, an effect blocked by haloperidol and by SCH 23390. The D2 DA receptor agonist, bromocriptine, elicited a concentration-dependent inhibition of adenylate cyclase activity in both arteries of either normal or 6-hydroxydopamine pretreated rabbits, this effect being prevented by (-)-sulpiride but not by (+)-sulpiride. These data indicate that both D1 and D2 postsynaptic DA receptors, associated with stimulation or inhibition of adenylate cyclase activity, are present on the wall of rabbit renal and mesenteric arteries.
Explore the source record for details and available documents.
Active uptake of 3,4-dihydroxyphenylethylamine (dopamine) is sodium- and temperature-dependent, strongly inhibited by benztropine and nomifensine, and present in corpus striatum and nucleus accumbens. In rat striatum dopamine uptake is related to a receptor that is specifically labelled by [3H]cocaine in the presence of Na+ and is located on dopaminergic terminals. The dopamine uptake is differentially affected in the two areas by single or repeated injections of cocaine. Cocaine inhibits dopamine uptake in slices of corpus striatum. Moreover Na+-dependent [3H]cocaine binding is not detectable in nucleus accumbens. Nomifensine inhibits [3H]dopamine uptake by interacting with low- and high-affinity sites in corpus striatum, but shows only low affinity for dopamine uptake in nucleus accumbens. The present data indicate that different mechanisms are involved in the regulation of dopamine uptake in corpus striatum and nucleus accumbens.
Explore the source record for details and available documents.
Dopamine release and uptake were investigated in striatum and nucleus accumbens slices of rats chronically exposed to lead. No indication of altered endogenous dopamine release under basal or depolarized conditions was observed in both areas. On the other hand lead intoxication inhibited striatal dopamine uptake while stimulating it at the mesolimbic level. Cocaine binding, that is related to the uptake system, appeared to be down-regulated in the striatum and unaffected in the nucleus accumbens. The results suggest that chronic lead might interfere with dopaminergic transmission at the presynaptic level through specific and differential interactions with the uptake process depending on the area examined.
Met-enkephalin levels were measured in various spinal cord regions of rats chronically suffering from the inflammation of a single paw following a treatment with Freund's adjuvant. The results indicate that chronic localized pain induces a selective increase of met-enkephalin immunoreactive material (ME-IR) in the dorsal horn of the spinal cord segment which receives a direct projection from the inflamed paw. In order to gain information on the functional meaning of these data, either the plexus brachialis or the sciatic nerve were sectioned peripherally before inducing inflammation. Denervation prevented the increase of ME-IR concentration induced by the injection of Freund's adjuvant. Our observations suggest that chronic localized pain in a limb induces a change in ME-IR content which is selective for the spinal cord segment receiving a direct projection from the inflamed paw. This increase depends on an intact innervation.
The behavioural and neurochemical effects of caffeine were examined in rats. The intraperitoneal administration of different doses of caffeine significantly decreased DOPAC concentrations in striatum, hypothalamus and frontal cortex, but increased them in nucleus accumbens. These observations suggest that the effects of caffeine on the central nervous system (cns) are at least partially mediated through an interaction with the dopaminergic system.
Met-enkephalin immunoreactive material content was found to be decreased in the cervical and thoracic segments of the spinal cord from rats aged 25 months as compared to young, 3-month-old, rats. No age-related variations were detectable at the lumbar level. Bio-Gel P 30 column chromatography of thoracic segment extracts indicates that the composition of the immunoreactive material is similar in the two age-groups investigated. At the thoracic level opiate receptor binding was also measured. Opiate receptor number is increased in the thoracic segments of the spinal cord from older rats. These age-related changes in immunoreactive Met-enkephalin content and opiate receptor number at spinal levels may contribute to determine an altered pain sensitivity during aging.
Enkephalin like peptides seem to have an important regulatory role at ganglia level. The aim of the present study is to investigate whether the content of enkephalin-like peptides in sympathetic ganglia is affected by the aging process. The results show that the enkephalin like peptides content is low in superior cervical and coeliac ganglia of aged rats (25 months). The age-related decrease of enkephalin content in these structures may be of importance in determining an altered sympathetic control during aging.
Suloctidil is a drug used in the elderly endowed with a mechanism of action at neuronal level which has not been completely explored. The results of the present study indicate that acute treatment with suloctidil induces a decrease of serum prolactin levels and a decrease of 3,4-diidroxyphenylacetic acid concentrations in various rat brain areas. In addition, the repeated injection of small Suloctidil doses produces a down-regulation of dopaminergic receptors. These data suggest that Suloctidil has dopamino-mimetic properties in vivo. This pharmacological activity may be of importance in the clinical action of Suloctidil in the elderly.
The amounts of beta-endorphin- and Met-enkephalin-immunoreactive material are higher in the pituitary of aged rats. However, the aging process decreases the content of beta-endorphin-, but does not affect that of Met-enkephalin-immunoreactive material, in hypothalamus. Thus, it seems that the regulatory mechanisms in the two areas are differentially affected by increasing age. On the other hand, the pituitary increase of these peptides is in line with the assumption that in the elderly the hormonal response to stress is impaired.
Explore the source record for details and available documents.