Giovanni Vitale

The antinociceptive action of paracetamol is associated with changes in the serotonergic system in the rat brain

The antinociceptive activity of paracetamol in the hot plate and formalin tests was studied to establish the relationship between antinociceptive activity and the central serotonergic system. Significant antinociceptive activity of paracetamol was observed in the formalin test at the dose of 300 mg/kg, while, at the dose of 400 mg/kg, the drug was active both in the formalin and in the hot-plate test. Serum paracetamol levels remained sub-toxic and the behavioral profile remained unchanged. Depletion of brain serotonin with p-chlorophenylalanine prevented the antinociceptive effect of paracetamol in the hot-plate test and in the first phase of the formalin response. Paracetamol significantly increased the serotonin content in the pontine and cortical areas (by 75 and 70%, respectively). The pretreatment with p-chlorophenylalanine reduced the 5-hydroxytryptamine (5-HT) content in cortical and pontine areas to 12 and 19% of baseline values, respectively, and prevented the enhancement induced by paracetamol. The maximum number of cortical 5-HT2 receptors was reduced by paracetamol, while the number of 5-HT1A receptors in both cortical and pontine areas was unchanged. Pre-treatment with p-chlorophenylalanine prevented the reduction in the number of 5-HT2 receptors induced by paracetamol. These results provide evidence for the involvement of the central serotonergic system in the antinociceptive effect of paracetamol in the hot plate and formalin tests.

ANXIOLYTIC LIKE EFFECT OF NEUROPEPTIDE S IN THE RAT DEFENSIVE BURYING.

Neuropeptide S (NPS) has been recently identified as the endogenous ligand of a previously orphan G-protein-coupled receptor now named NPSR. Both NPS and its receptor are expressed in the brain, where they modulate different functions. In particular, it has been demonstrated that intracerebroventricular (i.c.v.) injection of NPS in rodents increases wakefulness and promotes anxiolytic-like effects. In the present study we used the defensive burying (DB) test in rats to further investigate the action of human NPS (0.1-10 nmol, i.c.v.) on anxiety-related behaviors. Diazepam (1.5mg/kg, i.p.) and caffeine (20mg/kg, i.p.) were used in parallel experiments as standard anxiolytic and anxiogenic drugs, respectively. None of the tested drugs produced statistical differences in the latency to contact the probe, burying behavior latency, number of shocks received or immobility/freezing duration. Caffeine increased cumulative burying behavior and the buried bedding height in a statistically significant manner thus promoting anxiogenic like effects. Opposite results were obtained with diazepam that significantly reduced these behavioral parameters. The anxiolytic-like action of diazepam was mimicked by NPS that reduced cumulative burying behavior in a dose dependent manner. Collectively, robust anxiolytic-like effects were recorded in response to NPS in the DB test. These results are of particular interest since the outcome of this assay is marginally influenced by drug effects on locomotor activity. In conclusion, we provide further evidence that NPS evokes genuine anxiolytic-like effects in the rat; therefore NPSR selective agonists are worthy of development as innovative drugs for the treatment of anxiety disorders.

Effect of Hypericum perforatum Extract in an Experimental Model of Binge Eating in Female Rats

Purpose. The present study evaluated the effect of Hypericum perforatum dry extract in an experimental model of binge eating (BE). Methods. BE for highly palatable food (HPF) was evoked in female rats by three 8-day cycles of food restriction/re-feeding and acute stress on the test day (day 25). Stress was induced by preventing access to HPF for 15 min, while rats were able to see and smell it. Hypericum perforatum dry extract was given by gavage. Results. Only rats exposed to both food restrictions and stress exhibited BE. The doses of 250 and 500 mg/kg of Hypericum perforatum extract significantly reduced the BE episode, while 125 mg/kg was ineffective. The same doses did not affect HPF intake in the absence of BE. The dose of 250 mg/kg did not significantly modify stress-induced increase in serum corticosterone levels, suggesting that the effect on BE is not due to suppression of the stress response The combined administration of 125 mg/kg of Hypericum perforatum together with Salidroside, active principle of Rhodiola rosea, produced a synergic effect on BE. Conclusions. The present results indicate for the first time that Hypericum perforatum extracts may have therapeutic properties in bingeing-related eating disorders.

Effect of acute and chronic treatment with triiodothyronine on serotonin levels and serotonergic receptor subtypes in the rat brain

Hyperthyroidism is often associated with behavioral disorders, and thyroid hormones modify receptor sensitivity as well as the synthesis and/or turnover rate of many neurotransmitters. We evaluated the influence in adult rats of triiodothyronine (T3), administered s.c. (100 micrograms/kg) acutely (once only) or chronically (once a day for 3 or 7 consecutive days), on brain serotonin concentration and on the density and affinity of two brain serotonin (5-HT) receptor subtypes mainly involved in behavioral effects. After both acute and chronic T3 treatment, serotonin levels increased in the cerebral cortex but not in the hippocampus. The density and affinity of 5-HT1A receptors (using [3H]-8-OH-DPAT as ligand) were not affected, while there was a significant decrease in the number of 5-HT2 receptors in the cerebral cortex (using [3H]ketanserin as ligand). This observation might indicate that thyroid hormones enhance 5-HT concentration in certain brain areas, thus causing a down-regulation of 5-HT2 receptors. The serotonergic system could be involved in the complex brain-neurotransmitter imbalance underlying hyperthyroidism-linked behavioral changes.

Effect of rofecoxib on nociception and the serotonin system in the rat brain

Abstract.Objective and design: The purpose of the present study was to determine whether the antinociceptive activity of rofecoxib is mediated, at least in part, through changes in the brain serotonergic system.¶Materials and subjects: Male Wistar rats weighing 180-200 g (groups of eight) were subjected to the hot-plate and formalin tests after rofecoxib treatment. Cortical areas were removed for serotonin (5-HT) level, 5-HT2 and μ-receptor evaluation.¶Treatment: Rofecoxib was administered orally at doses of 5, 10, 20 and 50 mg/kg for the time course evaluation in the hot-plate test (30, 60 and 120 min), and at the dose of 10 mg/kg for the formalin test and biochemical determinations.¶Methods: The tests performed were the hot-plate and the formalin assays. HPLC was used to determine 5-HT levels and radioligand-binding assays were utilized to evaluate the characteristics of 5-HT2 and μ-receptors. The data were analysed by ANOVA or Students t test.¶Results: The lowest active dose of rofecoxib in the hot-plate test was 10 mg/kg. The percentage of the maximum possible effect (%MPE) values were: control = 1.7 ± 3.4; treated 23.4 ± 6.5 (p<0.05). The same dose had a significant effect on both phases of the formalin test. Pretreatment with p-chlorophenylalanine (PCPA) significantly decreased the activity of rofecoxib in the hot-plate test. Rofecoxib treatment increased serotonin levels and decreased the maximum number of 5-HT2 receptors. 5-HT levels (ng/g) were: control = 240.1 ± 28.5, rofecoxib = 326.1 ± 19.9 in the frontal cortex. The characteristics of μ-receptors did not change.¶Conclusions: These results suggest that rofecoxib may exert its therapeutic effect, at least in part, through the central serotonergic system. The opioidergic system, on the other hand, seems to be unaffected.

Glutamate-mediated astrocyte-to-neuron signalling in the rat dorsal horn

By releasing neuroactive agents, including proinflammatory cytokines, prostaglandins and neurotrophins, microglia and astrocytes are proposed to be involved in nociceptive transmission, especially in conditions of persistent, pathological pain. The specific action on dorsal horn neurons of agents released from astrocytes, such as glutamate, has been, however, poorly investigated. By using patch‐clamp and confocal microscope calcium imaging techniques in rat spinal cord slices, we monitored the activity of dorsal horn lamina II neurons following astrocyte activation. Results obtained revealed that stimuli that triggered Ca2+ elevations in astrocytes, such as the purinergic receptor agonist BzATP and low extracellular Ca2+, induce in lamina II neurons slow inward currents (SICs). Similarly to SICs triggered by astrocytic glutamate in neurons from other central nervous system regions, these currents (i) are insensitive to tetrodotoxin (TTX), (ii) are blocked by the NMDA receptor (NMDAR) antagonist d‐AP5, (iii) lack an AMPA component, and (iv) have slow rise and decay times. Ca2+ imaging also revealed that astrocytic glutamate evokes NMDAR‐mediated episodes of synchronous activity in groups of substantia gelatinosa neurons. Importantly, in a model of peripheral inflammation, the development of thermal hyperalgesia and mechanical allodynia was accompanied by a significant increase of spontaneous SICs in dorsal horn neurons. The NMDAR‐mediated astrocyte‐to‐neuron signalling thus represents a novel pathway that may contribute to the control of central sensitization in pathological pain.

Anxiolytic-like effects of nociceptin/orphanin FQ in the elevated plus maze and in the conditioned defensive burying test in rats

Different reports suggest that nociceptin/orphanin FQ (N/OFQ) may have either anxiolytic- or anxiogenic-like effect in rodents. Since N/OFQ elicits hypolocomotion, which undergoes rapid tolerance, and hypolocomotion may be associated to emotional consequences, the present study was designed to investigate the effect of N/OFQ on anxiety after development of tolerance to its hypolocomotor effect. The effect of single or double intracerebroventricular (i.c.v.) injection of N/OFQ was evaluated on anxiety-related behaviors in rats, in the elevated plus maze (EPM) and conditioned defensive burying (CDB) tests. After single administration, N/OFQ displayed an anxiogenic-like pattern of response on the elevated plus maze but hypolocomotion was also observed. Conversely, in the CDB test, N/OFQ induced a clear-cut anxiolytic pattern. To produce tolerance to N/OFQ-induced hypolocomotion the peptide was administered by two i.c.v. injections separated by 120 min; in these conditions it decreased the expression of anxiety-related behaviors in both tests without affecting locomotor activity. The nociceptin/orphanin FQ peptide (NOP) receptor antagonist UFP-101 significantly reduced the effects of N/OFQ to control values in either tests. Corticosterone levels were significantly increased after a single N/OFQ administration (not in a dose-dependent manner) but this increase did not reach significance after double administration (1 nmol/rat). Our results support the idea that N/OFQ may act as an anxiolytic-like agent in the rat; the apparent anxiogenic-like effect observed following its single administration in the EPM may be consequent to its effect on locomotion.

Streptozotocin-induced diabetes provokes changes in serotonin concentration and on 5-HT1A and 5-HT2 receptors in the rat brain

Since reduced levels of brain serotonin are known to cause behavioural abnormalities, to which diabetics are also prone, we investigated the effect, in rats, of chronic diabetes on brain serotonin concentration and on the numbers of 5-HT(1A) and 5-HT2 receptors in cerebral cortex and brainstem. Our data show that streptozotocin induces a longlasting hyperglicemia that is associated with a decrease in cerebral concentration of serotonin and with an accompanying increase in the maximum number of 5-HT(1A) and 5-HT2 receptors in the brain areas studied. Our results may suggest that changes in serotonergic transmission in the CNS play a role in diabetes-related behavioural abnormalities.

Further studies on the pharmacological profile of the neuropeptide S receptor antagonist SHA 68.

Neuropeptide S (NPS) regulates various biological functions by selectively activating the NPS receptor (NPSR). Previous studies demonstrated that the non-peptide molecule SHA 68 acts as a selective NPSR antagonist. In the present study the pharmacological profile of SHA 68 has been further investigated in vitro and in vivo. In cells expressing the mouse NPSR SHA 68 was inactive per se up to 10microM while it antagonized NPS-stimulated calcium mobilization in a competitive manner showing a pA(2) value of 8.06. In the 10-50mg/kg range of doses, SHA 68 counteracted the stimulant effects elicited by NPS, but not those of caffeine, in mouse locomotor activity experiments. In the mouse righting reflex assay SHA 68 fully prevented the arousal-promoting action of the peptide. The anxiolytic-like effects of NPS were slightly reduced by SHA 68 in the mouse open field, fully prevented in the rat elevated plus maze and partially antagonized in the rat defensive burying paradigm. Finally, SHA 68 was found poorly active in antagonizing the NPS inhibitory effect on palatable food intake in rats. In all assays SHA 68 did not produce any effect per se. In conclusion, the present study demonstrated that SHA 68 behaves as a selective NPSR antagonist that can be used to characterize the in vivo actions of NPS. However the usefulness of this research tool is limited by its poor pharmacokinetic properties.

Effect of salidroside, active principle of Rhodiola rosea extract, on binge eating

Stress is a key determinant of binge eating (BE). Since Rhodiola rosea is known to modulate stress responses, its effect in a model of BE was investigated. BE for highly palatable food (HPF) was evoked in female rats by three 8-day cycles of food restriction/re-feeding (for 4days 66% of the usual chow intake; for 4days food ad libitum) and acute stress on the test day (day 25). R. rosea dry extract (3% rosavin, 3.12% salidroside) or its active principles were given by gavage 1h before access to HPF. Only rats exposed to both food restrictions and stress exhibited BE in the first 15-60min after the stressful procedure. R. rosea extract 10mg/kg significantly reduced and 20mg/kg abolished the BE episode. R. rosea extract 20mg/kg abolished also stress-induced increase in serum corticosterone levels. The R. rosea active principle salidroside, but not rosavin, at doses present in the extract, dose-dependently reduced or abolished BE for the period in which it was elicited. In conclusion results indicate that R. rosea extracts may have therapeutic properties in bingeing-related eating disorders and that salidroside is the active principle responsible for this effect.