[Use of specific drugs for Alzheimer's disease]. / Utilización de fármacos específicos para la enfermedad de Alzheimer.

OBJECTIVE: To evaluate the consumption evolution and financial impact of specific treatments for Alzheimer's disease (AD) in Aragon (Spain), analyzing consumption patterns and trends, and to estimate the proportion of AD patients treated with these drugs. METHODS: Descriptive study of outpatient utilization of cholinesterase inhibitors and memantine (1996-2004), obtained from the drug packages dispensed by community pharmacists through prescriptions charged to the National Health Service. According to the defined daily doses (DDD) and expenditure data available, data were expressed in DDD per 1,000 inhabitants per day (DHD), DDD per 1,000 inhabitants older than 64 (DHD65), first-last year increase (%), drug consumption pattern, annual cost per inhabitant and daily treatment cost (DTC). To estimate the proportion of treated patients we compared the DHD65 data with the estimated AD prevalence. RESULTS: Overall consumption of these drugs has increased from 0.026 DHD (1996) to 3.235 DHD (2004). Donepezil remains as the most prescribed, though it is proportionally decreasing as a result of the quick introduction of newer alternatives. Overall cost of the DHD dispensed in 2004 reached nearly 6 million euros. DTC decreased about 30% over the study period, but the total cost increased ninety-fold (sixty-fold when non-variable euros from 2004 were considered). According to our estimates, 34% of people with AD were receiving specific treatment. CONCLUSIONS: There is a significant increase in the consumption and economical burden of these drugs, whose cost-effectiveness has been questioned in some studies. More studies including specific patient data are needed in order to identify individual characteristics and evaluate treatment appropriateness.

The expression of nNOS, iNOS and nitrotyrosine is increased in the rat cerebral cortex in experimental hepatic encephalopathy.

The changes in the distribution and amount of nitric oxide (NO) synthases (nNOS and iNOS) and the appearance of nitrotyrosine (NT) in the rat cerebral cortex were investigated following portacaval anastomosis (PCA), an experimental hepatic encephalopathy (HE) model. One month after PCA, rats showed more neurones immunoreactive to nNOS than did control animals. At 6 months post PCA, the number of neurones expressing nNOS had again increased and the intensity of the immunoreactions was stronger. Immunohistochemical analysis also showed that iNOS was increasingly expressed in pyramidal-like cortical neurones and in perivascular astrocytes from 1 to 6 months post PCA. In addition, a significant increase in cerebral iNOS concentration, at both post-PCA periods, was determined by Western blotting. The iNOS induction appears to be correlated with the length of the post-PCA period. PCA also induced the expression of NT, a nitration product of peroxynitrite. NT immunoreactivity was found in pyramidal-like cortical neurones. At 6 months, NT immunoreactivity was also evident in perivascular astrocytes, which was concomitant with a significant increase in NT protein level. PCA therefore not only increases the expression of nNOS but also induces the expression of iNOS and NT in both neurones and astrocytes. Taken together, these findings indicate that the induction of iNOS in pyramidal neurones and cortical astrocytes 6 months after PCA contributes to the generation of NT, and demonstrate the clear participation of NO in the pathogenic process of HE in this model.

The role of hydrogen peroxide in the contractile response to angiotensin II.

In the last years, reactive oxygen species (ROS) have been proposed as mediators of proliferative/hypertrophic responses to angiotensin II (Ang II), both in vivo and in vitro. However, the hypothesis that the Ang II-dependent cell contraction could be mediated by ROS, particularly H2O2, has not been tested. Present experiments were devoted to test this hypothesis and to analyze the possible mechanisms involved. Catalase (CAT) prevented the increased myosin light chain phosphorylation and the decreased planar cell surface area (PCSA) induced by 1 microM Ang II in cultured rat vascular smooth muscle cells (VSMC). This preventive effect of CAT was also detected when 1 microM platelet-activating factor (PAF) was used as a contractile agonist instead of Ang II. Similar results were found when using horseradish peroxidase as an H2O2 scavenger or cultured rat mesangial cells. In vascular smooth muscle cells, CAT modified neither the binding of labeled Ang II nor the Ang II-induced inositol 1,4,5-trisphosphate (IP3) synthesis. However, it completely abolished the Ang II-dependent calcium peak, in a dose-dependent fashion. CAT-loaded cells (increased intracellular CAT concentration over 3-fold) did not show either a decreased PCSA or an increased intracellular calcium concentration after Ang II treatment. Ang II stimulated the H2O2 synthesis by cultured cells, and the presence of CAT in the extracellular compartment significantly diminished the Ang II-dependent increased intracellular H2O2 concentration. The physiological importance of these findings was tested in rat thoracic aortic rings: CAT prevented the contraction elicited by Ang II. In summary, present experiments point to H2O2 as a critical intracellular metabolite in the regulation of cell contraction.

Bombesin induces a reduction of somatostatin inhibition of adenylyl cyclase activity, Gi function, and somatostatin receptors in rat exocrine pancreas.

To analyze the effect of bombesin on the somatostatin (SS) mechanism of action in the exocrine pancreas, male Wistar rats (250-270 g) were injected intraperitoneally with bombesin (10 microg/kg) three times daily at 8-h intervals for 7 or 14 days. Bombesin attenuated the ability of SS to inhibit forskolin-stimulated adenylyl cyclase activity in pancreatic acinar membranes. However, it did not decrease the ability of forskolin to stimulate the adenylyl cyclase catalytic subunit. The ability of 5'-guanylylimidodiphosphate [Gpp(NH)p] (a nonhydrolyzable GTP analog) to inhibit forskolin-stimulated adenylyl cyclase activity was diminished in pancreatic acinar cell membranes from bombesin-treated rats. Bombesin administration did not affect the ADP-ribosylation of a 41-kDa G protein catalyzed by pertussis toxin. The maximal SS binding capacity of pancreatic acinar membranes from bombesin-treated rats was decreased when compared with controls at the two time periods studied. The bombesin/gastrin-releasing peptide antagonist [D-Tpi6,Leu13psi(CH2NH)Leu14]bombesin (6-14) (RC-3095) (10 microg/kg i.p.), injected three times daily at 8-h intervals for 7 or 14 days, had a similar effect to that of bombesin on the SS mechanism of action. The combined administration of bombesin and its antagonist RC-3095 had a greater effect on the SS receptor-effector system than when administered separately. The present study indicates that the pancreatic SS receptor-effector system may be regulated by bombesin in vivo.

Effect of nitric oxide on the somatostatinergic system in the rat exocrine pancreas.

Nitric oxide (NO) and somatostatin (SS) are two important mediators of the exocrine and endocrine pancreas, exerting opposite effects on this organ. There is strong evidence suggesting an interaction between pancreatic NO and SS. The aim of this study was to determine whether L-arginine (L-Arg), the substrate for NO synthase (NOS), and Nomega-nitro-L-arginine methyl ester (L-NAME), a NOS inhibitor, regulate pancreatic somatostatin-like immunoreactivity (SSLI) content and the SS mechanism of action in pancreatic acinar cell membranes. L-Arg (150 mg/kg, intraperitoneally (i.p.)), L-NAME (50 mg/kg, i.p.) or L-NAME plus L-Arg were injected twice daily at 8 h intervals for 8 days. L-Arg decreased pancreatic SSLI content as well as the number of SS receptors in pancreatic acinar cell membranes whereas L-NAME increased both parameters. The stable SS analogue SMS 201-995 induced a significantly lower inhibition of forskolin-stimulated adenylyl cyclase activity in pancreatic acinar cell membranes from L-Arg-treated rats whereas an increased inhibition was observed in pancreatic acinar membranes from L-NAME-treated rats. These results indicate that the NO system may contribute to the regulation of the pancreatic somatostatinergic system.

Acute effects of D1- and D2-receptor agonist and antagonist drugs on somatostatin binding, inhibition of adenylyl cyclase activity and accumulation of inositol 1,4,5-trisphosphate in the rat striatum.

A recent study carried out by our group demonstrated that exogenous dopamine increases the somatostatin (SS) receptor-effector system in the rat striatum. The present study examined the participation of the D1- and D2-dopaminergic systems in the modulation of the rat striatal SS receptor-effector system by use of the D1-receptor agonist and antagonist SKF 38393 and SCH 23390, respectively, and the D2-receptor agonist and antagonist bromocriptine and raclopride, respectively. In view of the rapid onset of dopamine action, the effect of dopaminergic agents on the SS mechanism of action were studied 3 h after their administration. SKF 38393 (4 mg/kg i.p.) or bromocriptine (2 mg/kg i.p.) administered to male Wistar rats increased the number of 125I-Tyr3-SMS receptors in the striatum (52 and 30%, respectively) without changing the affinity constant. The effect of SKF 38393 on 125I-Tyr3-SMS binding was antagonized by the D1-specific antagonist SCH 23390 (0.25 mg/kg i.p.) whereas the effect of bromocriptine was abolished by the D2-specific antagonist raclopride (5 mg/kg i.p.). No change in binding was produced when SKF 38393 or bromocriptine were added directly to the incubation medium. The acute systemic administration of SCH 23390 or raclopride alone had no effect on the binding of 125I-Tyr3-SMS to its receptors. The increase of the number of 125I-Tyr3-SMS receptor induced by SKF 38393 or bromocriptine was accompanied by an increase in the capacity of SMS 201-995 to inhibit basal and forskolin (FK)-stimulated adenylyl cyclase (AC) activity when compared to the control groups. In addition, the effect of SMS 201-995 on the mass accumulation of inositol 1,4,5-trisphosphate (IP3) was investigated. SKF 38393 as well as bromocriptine increased the capacity of SMS 201-995 to accumulate IP3 in the rat striatum although this effect was only statistically significant in the case of SKF 38393. These results suggest that the activation of D1 and D2 receptors increases the activity of the SS receptor-effector system, the effect being greater in the case of D1 receptors. These findings are consistent with a functional interaction between dopamine and SS in the rat striatum.

Influence of fluoxetine and p-chloroamphetamine on the somatostatin receptor-adenylyl cyclase system in the rat frontoparietal cortex.

There is evidence that suggests a reciprocal functional link between the serotonergic and the somatostatinergic system in the rat frontoparietal cortex. However, to date, the role of endogenous 5-hydroxytryptamine (serotonin) on the regulation of the somatostatin (SS) receptor-adenylyl cyclase (AC) system remains unclear. In the present study, the administration of fluoxetine (10 mg/kg i.p.), a 5-hydroxytryptamine uptake inhibitor in a single dose or administered daily for 14 days increased the number of specific [125I]Tyr11-SS receptors, with no change in the receptor affinity, in rat frontoparietal cortical membranes. However, the capacity of SS to inhibit forskolin (FK)-stimulated AC activity in these membranes was lower than in the control groups. The ability of the stable GTP analogue 5'-guanylylimidodiphosphate (Gpp(NH)p) to inhibit FK-stimulated AC activity in frontoparietal cortical membranes was also decreased in rats acutely and chronically treated with fluoxetine. p-Chloroamphetamine (5 mg/kg i.p.), which leads to a lasting reduction of 5-hydroxytryptamine innervation, administered on days 1, 3 and 5 and the rats sacrificed 1 or 3 weeks after the first injection, decreased the number of SS receptors without changing the receptor affinity. In this experimental group, SS also caused a significantly lower inhibition of FK-stimulated AC activity. p-Chloroamphetamine had no effect on the ability of Gpp(NH)p to inhibit FK-stimulated AC activity in frontoparietal cortical membranes at all the time periods studied. The present results suggest that under normal circumstances some SS receptors are under a tonic stimulatory control through the serotonergic system.

Region-selective glutamine synthetase expression in the rat central nervous system following portocaval anastomosis.

Glutamine synthetase (GS) content was investigated using immunohistochemical methods in the hippocampus, cerebellum and spinal cord of rats after long-term portocaval anastomosis (PCA). Six months after surgery, GS content was increased in several areas of each region and decreased in others, compared with controls. In the hippocampus, the CA1-CA3 pyramidal subfields and the dentate molecular layer had a high level of GS expression; PCA reduced GS content in other hippocampal regions, such as the dentate hilus. In the cerebellum, PCA significantly increased GS immunoreactivity in the Bergmann glial processes of the molecular layer and decreased GS immunoreactivity in astrocytes of the granule cell layer. In the spinal cord, GS immunoreactivity increased in the dorsal horn and decreased in the ventral horn. Blood vessels located in zones with GS-immunopositive perineuronal astrocytes in PCA-exposed brains were surrounded by strongly GS-immunostained perivascular processes. These results suggest that PCA exposure had a differential effect on GS expression in different regions of the central nervous system. The increased immunoreactivity of GS-positive cells in PCA-exposed brains correlates with glutamatergic areas, which may contribute to protecting neurons against extracellular glutamate and/or ammonia excess.

Dopamine enhances somatostatin receptor-mediated inhibition of adenylate cyclase in rat striatum and hippocampus.

Although there is evidence that suggests that dopamine (DA) has stimulatory effects on somatostatinergic transmission, it is unknown to date if DA increases the activity of the somatostatin (SS) receptor-effector system in the rat brain. In this study, we evaluated the effects of the administration of DA and the DA D1-like (D1, D5) receptor antagonist SCH 23390 and the D2-like (D2, D3, D4) receptor antagonist spiperone on the SS receptor-adenylate cyclase (AC) system in the Sprague-Dawley rat striatum and hippocampus. An intracerebroventricular injection of DA (0.5 microgram/rat) increased the number of SS receptors and decreased their apparent affinity in the striatum and hippocampus 15 hr after its administration. The simultaneous administration of the DA receptor antagonists SCH 23390 (0.25 mg/kg, ip) and spiperone (0.1 mg/kg, ip) before DA injection partially prevented the DA-induced increase in SS binding. The administration of SCH 23390 plus spiperone alone produced a significant decrease in the number of SS receptors in both brain areas studied at 15 hr after injection, an effect that disappeared at 24 hr. The increased number of SS receptors in the DA-treated rats was associated with an increased capacity of SS to inhibit basal and forskolin (FK)-stimulated (AC) activity in the striatum and hippocampus at 15 hr after injection. This effect had disappeared at 24 hr. By contrast, basal and FK-stimulated enzyme activities were unaltered after DA injection. No significant changes in the levels of the alpha i (alpha i1 + alpha i2) subunits were found in DA-treated rats as compared with control rats. In addition, the immunodetection of the alpha i1 or alpha i2 subunits showed no significant changes in their levels in DA-treated rats when compared with controls. DA injection also induced an increase in SS-like immunoreactive content in the rat striatum but not hippocampus at 15 hr after administration and returned to control values at 24 hr. These results provide direct evidence of a functional linkage between the dopaminergic and somatostatinergic systems at the molecular level.

5-hydroxytryptamine decreases somatostatin receptors and somatostatin-responsive adenylyl cyclase in rat pancreatic acinar membranes.

Pretreatment of pancreatic acini with 5-hydroxytryptamine (5-HT) reduced the binding of the labeled somatostatin (SS) analogue 125I-Tyr3-SMS to pancreatic acinar membranes. This effect was dependent of the dose of 5-HT used and length of pretreatment. This inhibitory effect of 5-HT was abolished when pancreatic acini were pretreated with 5-HT in the presence of the 5-HT1p receptor-antagonist 5-hydroxytryptophyl-5-hydroxytryptophan amide (5-HTP-DP). Pretreatment of pancreatic acini with 5-HT reduced the inhibition by the stable SS analogue SMS 201-995 of basal and forskolin (FK)-stimulated adenylyl cyclase (AC) activity in pancreatic acinar membranes. There was no statistical difference established between IC50 values for the stable GTP analogue 5'-guanylylimidodiphosphate (Gpp(NH)p) which inhibits ligand binding to SMS receptors in controls and in 5-HT treated pancreatic cells, respectively. In addition, no significant differences were seen in the level of Gi proteins in the control and 5-HT treated pancreatic acini. These data suggest that the decrease of the number of 125I-Tyr3-SMS receptors, would explain the decreased sensitivity of AC to SMS 201-995 in membranes from 5-HT-pretreated acini.

The somatostatin receptor-adenylate cyclase system in rat pancreatic acinar membranes after temporary pancreaticobiliary duct ligation.

The mechanism whereby somatostatin (SS) produces beneficial effects in established pancreatitis induced by pancreaticobiliary duct ligation (PBDL) is still not clear. The aim of the work was to evaluate the possibility of a direct action of SS on pancreatic acinar cells from rats with acute pancreatitis. For this purpose, we studied the SS-receptor-adenylate cyclase system in pancreatic acinar membranes from both, control rats and rats with experimentally induced acute pancreatitis. On the other hand, it has been reported that cholecystokinin (CCK) diminishes the number of SS receptors in pancreatic acinar cells. Proglumide, a CCK receptor antagonist reduces the severity of acute pancreatitis in the rat. Therefore, we have also examined the effect of proglumide on the somatostatinergic system in controls and rats with acute pancreatitis. Fourteen hours after PBDL, the SS receptors, the capacity of the SS analogue SMS 201-995 to inhibit forskolin-stimulated adenylate cyclase activity and PTX-catalyzed [32P] ADP-ribosylation of the alpha1 subunits of Gi proteins could not be detected in pancreatic acinar membranes. One month after reopening the closed pancreaticobiliary duct (PBD), the pancreas showed regeneration of acinar cells, and the above-mentioned parameters were significantly lower than in the control group. Two months after reopening the closed PBD, all these parameters had returned to control values. The administration of proglumide (20 mg/kg i.p.), a cholecystokinin receptor antagonist, accelerated pancreatic regeneration and approached all these parameters to control values one month after reopening the closed PBD. The present study suggests that the beneficial effects of SS on established pancreatitis induced by PBDL may not be due to a direct action of the peptide on pancreatic acinar cells at least at 14 hours after PBDL. In addition, these findings suggest that in established pancreatitis the effect of proglumide on the SS receptor-adenylate cyclase system could be due to its action on pancreatic regeneration.

Histamine H1-receptors modulate somatostatin receptors coupled to the inhibition of adenylyl cyclase in the rat frontoparietal cortex.

Since exogenous histamine has been previously shown to increase the somatostatin (SS) receptor-effector system in the rat frontoparietal cortex and both histamine H1-receptor agonists and SS modulate higher nervous activity and have anticonvulsive properties, it was of interest to determine the participation of the H1-histaminergic system in this response. The intracerebroventricular (i.c.v.) administration of the specific histamine H1-receptor agonist 2-pyridylethylamine (PEA) (10 micrograms) to rats 2 h before decapitation increased the number of SS receptors (599 +/- 40 vs 401 +/- 31 femtomoles/mg protein, p < 0.01) and decreased their apparent affinity for SS (0.41 +/- 0.03 vs 0.26 +/- 0.02 nM, p < 0.01) in rat frontoparietal cortical membranes. No significant differences were seen for the basal and forskolin (FK)-stimulated adenylyl cyclase (AC) activities in the frontoparietal cortex of PEA-treated rats when compared to the control group. In the PEA group, however, the capacity of SS (10(-4) M) to inhibit basal and FK (10(-5) M)-stimulated AC activity in frontoparietal cortical membranes was significantly higher than in the control group (34 +/- 1% vs 20 +/- 2%, p < 0.001). The ability of low concentrations of the stable GTP analogue 5'-guanylylimidodiphosphate [Gpp(NH)p] to inhibit FK-stimulated AC activity in frontoparietal cortical membranes was similar in the PEA-treated and control animals. These results suggest that the increased SS-mediated inhibition of AC activity in the frontoparietal cortex of PEA-treated rats may be due to the increase of the number of SS receptors induced by PEA. Pretreatment with the H1-receptor antagonist mepyramine (30 mg/kg, intraperitoneally (IP) prevented the PEA-induced changes in SS binding and SS-mediated inhibition of AC activity. Mepyramine (30 mg/kg, IP) alone had no observable effect on the somatostatinergic system. The in vitro addition of PEA or mepyramine to frontoparietal cortical membranes obtained from untreated rats did not affect the SS binding parameters. Altogether, these results suggest that the H1-histaminergic system modulates the somatostatinergic system in the rat frontoparietal cortex.

Long-term changes in glial fibrillary acidic protein and glutamine synthetase immunoreactivities in the supraoptic nucleus of portacaval shunted rats.

The present study was undertaken to ascertain whether, and to what extent, glial fibrillary acidic protein (GFAP) and glutamine synthetase (GS) expressions in the supraoptic nucleus (SON) could be modulated after one month and six months of portacaval shunting (PCS) in rats. GFAP and GS immunoreactivities were significantly higher in PCS rats than in control rats at one and six months. The increased GFAP and GS immunoreactivities observed in the SON astrocytes were directly related to the duration of PCS. In PCS rats, the number and length of both GFAP and GS immunopositive astroglial processes increased not only in the hypothalamic nucleus but in the perinuclear zone, where glutamatergic pathways have been described, whereas GFAP and GS expressions decreased in the ventral glial lamina. Since GS is one of the glutamate metabolizing enzymes and the SON is one of the areas of glutamatergic activity, our results show that astrocytes respond differentially to glutamate toxicity. This suggests that overexpression of GFAP and GS immunoreactivities could be associated with glutamatergic neurotransmission disorders.

Response of rat cerebral somatostatinergic system to a high ammonia diet.

It has been reported that ingestion of an ammonium-containing diet produces hyperammonemia without encephalopathy, thus permitting the study of the specific effects of ammonia toxicity. The present study investigated the rat cerebral somatostatinergic system using this experimental model of hyperammonemia. Wistar rats were fed a high ammonia diet prepared by mixing a standard diet with ammonium acetate (20% w/w); in addition, 5 mM of ammonium acetate was added to their water supply. Control rats were fed with a standard diet. The animals were sacrificed at 3, 7 and 15 days of ammonia ingestion. Ammonia levels in blood had increased approximately 3-fold at 7 days of ammonia ingestion. These changes were associated with a significant decrease in the specific binding of somatostatin (SS) to putative receptors sites in the frontoparietal cortex and hippocampus at 7 and 15 days after starting the high ammonia diet. Scatchard analysis shows that the decrease in SS binding resulted from a decrease in the number of available SS receptors rather than a change in receptor affinity. No changes in the somatostatin-like immunoreactivity content (SSLI) were detected in either brain area at the three study times. These results suggest that hyperammonemia alone can affect the rat brain somatostatinergic system. However, the animal model of hyperammonemia used here is insufficient to produce encephalopathy despite the significant increase in serum ammonia.

Lactational changes in the rat exocrine pancreas somatostatin receptors and modulation of guanylate cyclase.

Hyperplasia of the pancreatic tissue during late lactation (third week) and lasting for at least the first two weeks after weaning has been observed by several authors. Since the tetradecapeptide somatostatin (SS) inhibits pancreatic growth and its plasma levels are elevated during these periods, the aim of the present study was to determine the possible implication of the somatostatinergic system in the pancreatic changes cited above. Thus, the present study investigated 125I-Tyr(11)-somatostatin (125I-Tyr(11)-SS) binding and the effects of SS on guanylate cyclase activity as well as pancreatic somatostatin-like immunoreactivity (SSLI) levels in pancreatic acinar membranes from control, lactating and weaning rats. SS receptors were identified using 125I-Tyr(11)-SS and isolated pancreatic acinar membranes in vitro. There was an increase in the number of SS receptors after the third week of lactation (244 +/- 6 vs. 155 +/- 12 fmol/mg protein, P < 0.01) and the first two weeks after weaning (327 +/- 8 vs. 164 +/-10 fmol/mg protein, P < 0.001). No change in the affinity of the receptor site was detected at either study time. In addition, SS-stimulated guanylate cyclase activity was markedly increased at the third week of lactation (119%) and at the second week after weaning (158%) when compared with the control group. In contrast, basal guanylate cyclase activity was not modified at either study period. Thus, SS-stimulated guanylate cyclase activity is increased in pancreatic acinar membranes at late lactation and at the second week after beginning weaning probably due to an increase in the number of SS receptors. Significant decreases in SSLI content were observed at the third week of lactation (69%) and the second week after weaning (37%) when compared with the respective controls. The present results suggest that pancreatic acinar cell growth observed at the third week of lactation and the second week after weaning is associated with up-regulation of SS receptors which would represent a mechanism promoted by the cell that would negatively regulate the mitogenic activity of the increased number of pancreatic growth factors observed during both periods.

Effect of dimaprit and cimetidine on the somatostatinergic system in the rat frontoparietal cortex.

A recent study carried out by this laboratory demonstrated that exogenous histamine increases the somatostatin (SS) receptor/effector system in the rat frontoparietal cortex (Puebla and Arilla, 1995). In the present study we examined the participation of the H2-histaminergic system in this modulation by use of the H2-receptor agonist and antagonist dimaprit and cimetidine, respectively. Dimaprit administration [20 micrograms/rat, intracerebroventricularly (ICV)] to rats 2 hours before decapitation increased the number of SS receptors in the frontoparietal cortex without changing the affinity constant. Pretreatment with cimetidine (20 micrograms/rat, ICV) prevented the dimaprit-induced changes in SS binding in the frontoparietal cortex, whereas cimetidine alone (20 micrograms/rat, ICV) had no observable effect on this parameter. The in vitro addition of dimaprit or cimetidine to frontoparietal cortex membranes from untreated rats did not markedly affect the SS binding characteristics. Somatostatin caused a significantly higher inhibition of basal and forskolin (FK)-stimulated adenylyl cyclase (AC) activity in frontoparietal cortex membranes from dimaprit-treated rats than in controls, an effect that was prevented by pretreatment with cimetidine. No significant differences, however, were detected for the basal or FK-stimulated AC enzyme activity in the control, dimaprit-, and/or cimetidine-treated groups, which suggests no impairment of the AC catalytic subunit. In addition, the functional activity of the guanine nucleotide-binding inhibitory protein Gi, as measured by the capacity of the stable GTP analogue 5'-guanylylimidodiphosphate [Gpp(NH)p] to inhibit FK-stimulated AC activity, was not altered by dimaprit. Thus, the increased SS-mediated inhibition of AC activity observed in the dimaprit-treated rats may be caused by the increase in the number of SS receptors. Neither dimaprit nor cimetidine affected somatostatinlike immunoreactivity (SSLI) content. The present results, together with the fact that SS and histamine have been shown to influence locomotor activity and nociception in a similar manner, suggest that some of the neurotransmitter effects of SS may be modulated by histamine via H2-histaminergic receptors.

Modulation by 5-hydroxytryptamine of the somatostatin receptor-effector system and somatostatin levels in rat brain.

The role of 5-hydroxytryptamine (5-HT) in the acute regulation of the rat brain somatostatin (SS) receptor-effector system and somatostatin-like immunoreactivity (SSLI) content was examined. 5-HT administered i.c.v. in a volume of 10 microliters at a dose of 0.5 microgram (pH 3.4) increased the SSLI concentration at 60 min in the Wistar rat frontoparietal cortex and hippocampus (60%, P < 0.05; 72%, P < 0.01; respectively). These changes were associated with a significant increase in the total number of specific SS receptors in the frontoparietal cortex (24%, P < 0.05) and hippocampus (20%, P < 0.05), without changes in the affinity constant as compared with the control group. No significant differences were seen in the basal and forskolin (FK)-stimulated adenylate cyclase (AC) activities in both brain areas of 5-HT-treated rats when compared to the control group. The capacity of SS to inhibit the FK-stimulated AC activity in the frontoparietal cortex and hippocampus of 5-HT-treated rats was lower than in the control groups. The ability of the stable GTP analogue 5'-guanylylimidodiphosphate (Gpp(NH)p) to inhibit FK-stimulated AC activity in frontoparietal cortical and hippocampal membranes was markedly decreased in 5-HT-treated rats. To determine if the above-mentioned changes were related to the 5-HT activation of central 5-HT1 and 5-HT2 receptors, a non-selective 5-HT1 and 5-HT2 receptor antagonist, methysergide, was administered 60 min before the 5-HT injection. Pretreatment with methysergide (5 mg/kg i.p. in a volume of 400 microliters) prevented the 5-HT-induced changes in the SS receptor-effector system and in SSLI levels in both brain areas. Methysergide alone had no observable effect on the somatostatinergic system. These results suggest that the frontoparietal cortical and hippocampal somatostatinergic system can be regulated by 5-HT receptors.

Involvement of presynaptic histamine H3 receptors in the modulation of somatostatin binding and its effects on adenylyl cyclase activity in the rat frontoparietal cortex.

Thioperamide (2 mg/kg, l.p.), a histamine H3-receptor antagonist, increased the number of somatostatin (SS) receptors, with no change in the affinity constant, in the rat frontoparietal cortex. This effect was prevented by treatment with (R)-alpha-methylhistamine (3.2 mg/kg, l.p.), a histamine H3-receptor agonist. Thioperamide also induced an increase in SS binding in rats pretreated with mepyramine, a histamine H1-receptor antagonist, or cimetidine, a histamine H2-receptor antagonist. Pretreatment with mepyramine plus cimetidine administered simultaneously antagonized the thioperamide effect on SS binding. The increase in the number of SS receptors was accompanied by a greater SS-mediated inhibition of basal and forskolin-stimulated adenylyl cyclase (AC) activity in frontoparietal cortical membranes in the thioperamide group. Furthermore, the functional activity of the guanine nucleotide-binding inhibitory protein (G1 protein) was not altered by thioperamide or (R)-alpha-methylhistamine administration in frontoparietal cortical membranes. In rats treated with mepyramine plus thioperamide or cimetidine plus thioperamide, the increase in the number of SS receptors was also accompanied by an increased SS inhibition of AC activity. Thioperamide induced a significant increase in SS-like immunoreactivity content in the frontoparietal cortex. Altogether, these results suggest that frontoparietal cortical histamine may play, at least in part, a role in the regulation of the somatostatinergic system.

Glycine increases the number of somatostatin receptors and somatostatin-mediated inhibition of the adenylate cyclase system in the rat hippocampus.

The glycine and somatostatin (SS) neurotransmission systems in the brain have been implicated in the function of sensory, motor, and nociceptive pathways. To investigate a possible relationship between these two components, we studied the influence of glycine on the binding of 125I-Tyr11-SS to its receptors and on SS-like immunoreactivity (SSLI) levels in the rat hippocampus and frontoparietal cortex. An intracerebroventricular (i.c.v.) dose of 16 or 160 nmol of glycine induced an increase in the total number of specific SS receptors in the hippocampus but not in the frontoparietal cortex at 15 min following injection, with no changes in the affinity constant. This effect seems to be mediated by inhibitory strychnine-sensitive glycine receptors since pretreatment with the antagonist strychnine (80 micrograms/100 g body weight, intravenously) abolished this response. No significant changes in SSLI content were detected in either brain region of glycine- and strychnine plus glycine-treated rats as compared to control values. Since SS receptors are coupled via guanine nucleotide-binding G proteins to the adenylyl cyclase (AC) system, we also examined the inhibitory effects of SS and the guanine nucleotide Gpp(NH)p on AC activity in hippocampal membranes of control, glycine- and strychnine plus glycine-treated rats since the increase in SS receptors was observed only in this brain area. No significant differences were observed for the forskolin (FK)-stimulated AC enzyme activities in hippocampal membranes from all the experimental groups studied. In the hippocampus of the glycine- (160 nmol) treated group, however, basal AC activity was significantly lower, and the capacity of SS to inhibit FK-stimulated AC activity was increased as compared to the control group. Pretreatment with strychnine prevented the increase in SS-mediated inhibition of AC activity. The functional activity of the inhibitory guanine nucleotide-binding protein Gi, as determined by the inhibitory effect of the stable GTP analogue Gpp(NH)p on FK-stimulated AC activity, was significantly higher in hippocampal membranes of glycine- (160 nmol) treated rats as compared to controls. This suggests that the increased inhibition of AC activity by SS in the glycine-treated group may be due to the increase in Gi activity and/or the increase in the number of SS receptors observed. Alternatively, the greater Gi activity may be responsible for the increased binding of 125I-Tyr11-SS to its receptors observed after glycine administration. Altogether, these data suggest that the hippocampal somatostatinergic system can be regulated by strychnine-sensitive glycine receptors in the rat.