Biomedical subjects

D Parolaro

Publications and source records attributed to D Parolaro.

At least 55 records · Page 3Linked to original sources

PubMed1993

Cholera toxin antagonizes morphine-induced catalepsy through a cyclic AMP-independent mechanism.

We studied the effect of intracerebroventricular pretreatment with pertussis toxin and cholera toxin on morphine catalepsy in rats. Pertussis toxin (1 micrograms/rat, two, three and six days before) did not affect catalepsy evoked by central morphine. Cholera toxin (1 micrograms/rat) did not affect morphine catalepsy after 24 h and 48 h, but significantly reduced it (about 60%) after three and five days. Ten days later the morphine response had totally recovered. This effect was selective, since morphine analgesia was not modified. The reduction of catalepsy appeared unrelated to the ability of cholera toxin to raise cAMP levels, as demonstrated by the different time course of changes in striatal cholera toxin-stimulated adenylate cyclase activity. The effect required an intact cholera toxin molecule and did not occur with a similar dose of cholera toxin-B subunit. These findings demonstrate that catalepsy is an opioid effect not linked to pertussis toxin-sensitive G proteins and suggest that the Gs protein might be involved.

Adenylate Cyclase Toxin↗

PubMed1993

In situ hybridization reveals specific increases in G alpha s and G alpha o mRNA in discrete brain regions of morphine-tolerant rats.

In situ hybridization histochemistry has been used to detect the basal distribution of mRNA encoding the alpha subunit of Gs, Go and Gi2 proteins throughout the rat brain. Based on these data we investigated the effect of chronic morphine on the content of these G protein alpha subunits mRNA. We observed an increase in the expression of alpha s and alpha o messages of chronically morphine-treated animals, while no changes were seen in alpha i2 mRNA. Specifically a 30% increase in expression for alpha s was seen only in the paraventricular nucleus of hypothalamus and a 20% elevation for alpha o was detected in the claustrum and endopiriform nucleus. Immunoblotting analysis was used to correlate the changes in alpha s and alpha o messages with equivalent changes in protein levels. Chronic morphine significantly increased alpha s amounts in the hypothalamus (70%), and produced a minor elevation (30%) in G alpha o levels in the olfactory area. Our results indicate that in discrete brain regions altered G protein expression is part of the adaptive changes underlying opiate tolerance.

Animals↗

PubMed1992

Influence of pertussis toxin on thermic responses to morphine and neurotensin in rats.

The influence of pertussis toxin (PTX) on thermic responses elicited by morphine and neurotensin was evaluated in unrestrained rats kept at 22 degrees C. High doses of morphine (9-36 micrograms/rat i.c.v.) lowered body temperature and low doses (1.25, 2.5 micrograms/rat i.c.v.) produced hyperthermia. The hyperthermic effect was more resistant than the hypothermic effect to naloxone antagonism. Neurotensin (50, 100 micrograms/rat i.c.v.) induced marked hypothermia followed by hyperthermia. I.c.v. injection of PTX (1 microgram), six days before morphine (18 micrograms/rat i.c.v.), replaced the opiate hypothermia by consistent hyperthermia and reduced by 60% the hyperthermia elicited by morphine (2.5 micrograms/rat i.c.v.). The toxin also affected the thermic responses induced by neurotensin (50 micrograms/rat i.c.v.) administered six days after PTX (1 microgram/rat i.c.v.). The initial hypothermia was enhanced by 173% and the late hyperthermia was fully antagonized. It thus appears that PTX-sensitive G-proteins play different roles in the molecular events underlying the thermoregulatory responses to morphine and neurotensin.

Animals↗

PubMed1992

Influence of omega-conotoxin on morphine analgesia and withdrawal syndrome in rats.

The effect of omega-conotoxin on opiate analgesia and withdrawal syndrome was investigated in rats. omega-Conotoxin given i.c.v. and i.p. caused weak analgesia in the tail-flick test. When the toxin (20 ng/rat) was given i.c.v. immediately before morphine (1.5 micrograms/rat i.c.v.) the resultant analgesic effect was additive. In contrast, the analgesia elicited by morphine (3 micrograms/rat i.c.v.) was greatly reduced after 24-h pretreatment with the toxin (20 ng/rat i.c.v.). The systemic administration of the toxin (10 micrograms/kg i.p.) did not affect morphine analgesia whether omega-conotoxin was coadministered with morphine (2.5 mg/kg i.p.) or was given 24 h before the opiate (5 mg/kg i.p.). omega-Conotoxin i.c.v. injected in morphine-dependent rats 15 min before naloxone challenge significantly attenuated the abstinence syndrome. On the contrary systemic administration of omega-conotoxin failed to suppress the morphine withdrawal syndrome. The present results suggest that omega-conotoxin affects both acute and chronic effects of morphine.

Analgesia↗

PubMed1992

Further investigations on the antipropulsive effect of centrally administered histamine and its relation with morphine.

The effect of intracerebroventricularly (i.c.v.) administered histamine (100 micrograms/rat) on intestinal myoelectrical activity was investigated in the jejunum of fasted rats. Histamine caused the disappearance of phase III and a partial reduction of phase II of migrating myoelectric complexes. This effect was antagonized by i.c.v. pretreatment with mepyramine (10 micrograms/rat), an H1 receptor antagonist. Lesions of central noradrenergic neurons by i.c.v. injection of the neurotoxin 6-hydroxydopamine strongly reduced both the inhibition of intestinal propulsion and the migrating myoelectric complexes profile induced by i.c.v. histamine, whereas pretreatment with p-chlorophenylalanine, a selective depletor of serotonin stores, had no effect. It thus appears that aminergic pathways are involved in the visceral effects of central histamine. Mepyramine (200 micrograms/rat i.c.v.) partially reduced the slowing of intestinal transit induced by high doses of morphine. Pretreatment with compound 48/80 (10 micrograms/rat i.c.v.), a mast cell degranulator, but not with alpha-fluoromethylhistidine, an irreversible inhibitor of histidine decarboxylase, reduced the antipropulsive action of i.c.v. morphine to the same extent as mepyramine, suggesting that histamine released from cerebral mast cells by high doses of morphine could contribute to the intestinal inhibition by morphine.

Animals↗

PubMed1991

Pertussis toxin pretreatment affects opiate/nonopiate and stress-induced analgesia differently.

Intracerebroventricular injection of pertussis toxin (PTX, 1 microgram/rat) six days before the hot plate test abolished analgesia induced by central morphine. The toxin did not affect analgesia evoked by central neurotensin or ASU 1-7 eel calcitonin. PTX pretreatment also attenuated footshock-induced analgesia (FSIA) delivered to all four paws. When the shock was restricted to the front paws, PTX consistently lowered postshock tail flick latencies, but did not reduce analgesia resulting from shock delivered to the hind paws. It thus appears that PTX-sensitive G-proteins are an essential transduction step needed to initiate the molecular events underlying opiate analgesia evoked by either morphine or shock. In contrast, the signal transduction mechanism subsequent to the stimulation of neurotensin or calcitonin receptors, and to the nonopiate FSIA, appears not to involve PTX-sensitive G-proteins.

Animals↗

PubMed1990

Pertussis toxin modifies the effect of central morphine on rat intestinal motility.

To find whether the antipropulsive effect of morphine administered intracerebroventricularly (i.c.v.) depends on a G-protein-mediated mechanism, we studied the effect of i.c.v. pertussis toxin (PTX) pretreatment on morphine-induced inhibition of intestinal motility. The influence of PTX was evaluated on intestinal transit (charcoal meal test) and by monitoring of intestinal myoelectrical activity. The antitransit effect of morphine (10 micrograms/rat) was antagonized by about 70% 3, 6, 9 and 12 days after PTX pretreatment (1 microgram/rat) and it was partially restored after 25 days. I.c.v. morphine abolished the regular appearance of the myoelectric migrating complex (MMC) recorded in the rat jejunum and this effect was completely antagonized by PTX pretreatment. When morphine was injected 25 days after PTX, it significantly reduced MMC frequency, confirming the partial recovery seen in the transit experiments. The pertussis toxin-catalyzed ADP ribosylation of a 39-41 kDa substrate in membranes prepared from hypothalamus and midbrain of rats injected with toxin 6 days before was strongly reduced as compared to the controls. On the contrary, after 25 days, ADP ribosylation was the same in treated and control rats. Thus the antipropulsive effect of central morphine could be initiated at receptor sites which interact with G-protein substrates of pertussis toxin.

Adenosine Diphosphate↗

PubMed1990

Pertussis toxin inhibits morphine analgesia and prevents opiate dependence.

Six days after intracerebroventricular pretreatment of rats with pertussis toxin (PTX 0.5 microgram/rat) there was a marked decrease in the antinociceptive effect of morphine, regardless of the route of opioid administration (into the periaqueductal gray matter, intrathecally or intraperitoneally) or the analgesic test used (tail flick and jaw opening reflex). PTX pretreatment also partially attenuated the naloxone-precipitated withdrawal syndrome in morphine-dependent rats, significantly reducing teeth chattering, rearing and grooming. These in vivo findings indicate that G-protein-dependent mechanisms are involved in morphine analgesia and dependence. The biochemical mechanism could be related to ADP ribosylation of Gi coupled to the adenylate cyclase system, but an interaction of PTX with other G-proteins linked to different second messengers or directly to ionic channels cannot be excluded.

Adenylate Cyclase Toxin↗

PubMed1989

Histamine as a central modulator of rat intestinal transit.

Histamine (HA) injected i.c.v. to rats inhibited intestinal propulsion in linear relation to the log of the administered doses (in the range from 20-100 micrograms/rat). In the same dose range HA also induced a dose-related analgesic effect (tail-flick test). The dose of HA maximally active by the i.c.v. route (100 micrograms/rat) showed neither of these effects when injected i.v. or i.p. HA-induced intestinal inhibition and analgesia were antagonized competitively by i.c.v. mepyramine (10 micrograms/rat), an H1 receptor antagonist, whereas cimetidine (10 micrograms/rat), an H2 receptor antagonist, had no effect. Repeated i.c.v. injections of HA resulted in tachyphylaxis of both intestinal inhibition and analgesia. Pretreatment with i.c.v. naloxone (20 micrograms/rat) antagonized the antipropulsive effect of HA in a noncompetitive fashion, but did not affect its antinociceptive action. The relevance of the central histaminergic system in the modulation of gastrointestinal motility and its relationship with the opioid system are discussed.

Analgesia↗

PubMed1988

Supraspinal cerebral areas involved in morphine's intestinal inhibition and analgesia.

To explore the neuroanatomical pathways involved in mediating the antipropulsive effect and analgesia of morphine (M) in the periaqueductal gray matter (PAG), we examined the influence of the vagus nerve and the role of serotonergic neurotransmission. M-induced inhibition of intestinal transit was unaffected by subdiaphragmatic vagotomy. In contrast, electrolytic lesions in the raphe magnus nucleus (NRM) and pretreatment with a selective neurotoxin (5,6-DHT, 15 micrograms/rat) in the same region, both significantly reduced M-induced inhibition of intestinal transit. Analgesia was only slightly affected. p-CPA pretreatment (100 mg/kg IP) induced the same results. Finally some other central brain regions were found to be sensitive to M's intestinal inhibition and analgesia such as the mid-line thalamus, the dorsal and lateral hypothalamus, and the bulbar reticular formation. Negative results were obtained for frontal cortex, caudate and amygdala. Some considerations are put forward about the existence in the central nervous system of selective areas involved in intestinal modulation and their relation with those mediating pain transmission.

Analgesia↗

PubMed1988

Cerebral extract from morphine-tolerant rats shows antiopiate properties in guinea pig ileum bioassay.

The existence of an endogenous antiopiate system which counteracts endogenous opiate effects has been proposed. The present study set out to seek substance/s with morphine-antagonist activity in the brain and serum of morphine-tolerant rats. Cerebral extracts were partly purified on Sephadex G 25 and serum was ultrafiltered through membranes with pore diameter smaller than 0.005 micron. On the guinea pig ileum myenteric plexus longitudinal muscle a fraction of the cerebral extract and the serum ultrafiltrate in toto did increase electrically induced contractions, and antagonized the depressant effect of morphine. The serum ultrafiltrate also enhanced longitudinal smooth muscle tone. Preliminary findings suggest that levels of endogenous morphine-antagonist substance/s are higher in morphine-tolerant rats than in controls. Only cerebral extract, not serum ultrafiltrate, inhibited [3H]-naloxone binding to cerebral opiate receptors. In the guinea pig bioassay both the cerebral extract and serum ultrafiltrate antagonized, to some extent, the inhibition elicited by morphine, norepinephrine and adenosine. These observations support the existence of endogenous compound/s which may be functional antagonist/s of opiates and play a role in the development of tolerance and dependence.

Animals↗

PubMed1987

Binding studies of dermorphin and its L-form on rat brain opioid receptors.

It is well known dermorphin is a potent and long-acting opioid peptide while its synthetic L-form is almost completely devoid of biological activity. We investigated whether the L-Ala2 residue might affect the affinity of the compound for opioid receptors or make [L-Ala2] dermorphin more sensitive to metabolic degradation. Dermorphin and [L-Ala2] dermorphin were assayed in [3H]naloxone binding to opioid receptors in rat brain preparations in the absence and presence of peptidase inhibitors bestatin, captopril and thiorphan. The synthetic [L-Ala2] dermorphin showed very low affinity for the opioid receptors. This was only slightly increased in the presence of the peptidase inhibitor bestatin, alone and in combination with captopril and thiorphan. The low affinity of [L-Ala2] dermorphin was not improved even when the binding assay was carried out at 0 degrees C. We suggest that the D-Ala2 residue is essential for the binding of dermorphin to the opioid receptors as well as for its pharmacological activity.

Alanine↗

PubMed1987

Further investigations on neurotensin as central modulator of intestinal motility in rats.

Previous studies have shown that neurotensin (NT) administered intracerebroventricularly (i.c.v.) to rats provokes an inhibition of intestinal propulsion linearly related to the log of administered doses. In the present study it is demonstrated that, in contrast to morphine, repeated i.c.v. administrations of NT (2.5 nmol/rat/day) did not result in tolerance to the intestinal effect. Naloxone (Nx) administered i.c.v. fully antagonized the intestinal inhibition of i.c.v. morphine, but did not significantly alter the NT effect. However, centrally administered thyrotropin-releasing hormone (TRH) inhibited NT-induced (but not morphine-induced) intestinal inhibition. Direct microinjections of NT into the periaqueductal gray matter (PAG) produced complete inhibition of intestinal propulsion when the microinjections were localized in the dorsal portion. Finally, subdiaphragmatic vagotomy totally abolished the inhibition induced by NT into the PAG, while morphine was not affected. Some considerations are put forward concerning the existence in the central nervous system of a peptidergic pathway modulating intestinal function.

Animals↗

PubMed1986

Pertussis toxin inhibits the antinociceptive action of morphine in the rat.

The influence of pertussis toxin (PTX) injected intracerebroventricularly (i.c.v., 0.5 micrograms) on the analgesic effect induced in the rat by i.c.v. injection of morphine (5 micrograms) was studied. Morphine analgesia was unaffected 24 h after toxin administration, but there was a significant decrease after 6 days. Therefore a PTX-sensitive substrate, probably a guanine nucleotide regulatory protein could be involved in the coupling of opiate receptors to cellular effectors responsible for the expression of the antinociceptive action of morphine.

Analgesics↗

PubMed1986

Intestinal effect and analgesia: evidence for different involvement of opioid receptor subtypes in periaqueductal gray matter.

Periaqueductal gray matter (PAG) has been shown to be one of the sites in the central nervous system where microinjections of morphine strongly inhibit intestinal transit. To investigate the nature of opioid receptor populations involved in this central effect, selective opioid agonists, FK 33824 for mu, DALA for delta, dynorphin for kappa and tentatively beta-endorphin for epsilon, were microinjected in all PAG areas previously identified as morphine-sensitive for intestinal inhibition. The PAG-induced inhibition of intestinal transit appears to be mediated mainly by mu receptors and possibly by epsilon receptors. kappa and delta receptors seem not to be involved.

Analgesia↗

PubMed1985

Cerebral sites of central action of dermorphin on intestinal motility in the rat.

Dermorphin (DM), microinjected at 0.4 nmoles/rat into various sites of the periaqueductal gray matter (PAG), provokes complete inhibition of intestinal propulsion always coupled with full analgesia and catalepsy. When electrolytic lesions were made in the raphe magnus nucleus (NRM) a slight but significant reduction of intestinal inhibition evoked by DM into the PAG was observed. In contrast, pretreatment into the NRM 10 days before DM with a selective antiserotoninergic agent (5,6 DHT 15 microgram/rat), did not influence intestinal inhibition. As expected, both lesions reduced DM-induced analgesia but catalepsy was not affected. DM-induced inhibition of intestinal transit was therefore unaffected by subdiaphragmatic vagotomy. Finally, some other central brain regions were found sensitive to DM for the above effects such as the lateral and medial hypothalamus and mid-line thalamus. Negative results were obtained for the supraoptic nuclei and postero-medial cortical amygdaloid nucleus. Some considerations are put forward about the existence in the central nervous system of selective areas involved in intestinal modulation and their relationship with those mediating other opiate behavioural effects.

Amygdala↗

PubMed1985

Central pharmacological activities and opiate receptor binding studies of some dermorphin analogs.

A series of dermorphin-like compounds were injected intracerebroventricularly in the rat to assess in vivo their effects on intestinal motility and analgesia. In vitro they were tested by binding assay using 3H-naloxone as radioligand or by guinea pig ileum bioassay. The synthetic peptides were less potent than dermorphin in inhibiting intestinal transit and in producing analgesia, or even inactive up to doses 30 times the dermorphin ED50. This reduction in pharmacological activity was coupled with a decrease in binding potency. The 3H-naloxone binding studies in the absence or presence of Na+ indicated that Na+ reduced the interaction of dermorphin and its analogs with brain opiate receptors. Only the dibenzyl derivative was slightly affected by sodium, suggesting a dual action for this peptide, as confirmed by preliminary data from guinea pig ileum bioassay.

Amino Acid Sequence↗

PubMed1984

Dermorphin interaction with peripheral opioid receptors.

The interaction of dermorphin with different peripheral opioid receptor subtypes was investigated in vitro, using the guinea pig ileum as representative tissue for mu, the mouse vas deferens for delta, the rabbit vas deferens for kappa and the rat vas deferens for epsilon. The effect of dermorphin on each tissue preparation was compared with that of selective mu, delta, kappa epsilon agonists respectively morphine, met-enkephalinamide, ethylketocyclazocine and camel beta-endorphin. Antagonism with naloxone was also tested and calculated as Ke. It is concluded that dermorphin mainly interacts with the mu receptors, although it also binds to epsilon receptors; the interaction with delta receptors is questionable, and the kappa receptors are unaffected.

Animals↗