Activation of the dorsal vagal nucleus increases pancreatic exocrine secretion in the rat

Pancreatic secretion is regulated by the dorsal vagal nucleus (DVN) which is modulated by several neurotransmitters and diverse synaptic inputs. The inhibitory neurotransmitter GABA is a major modulator of the vagal output to the gastrointestinal tract. The present study investigated the effects of GABA_A receptor blockade in the DVN, using bicuculline methiodide (BIM, GABA_A receptor antagonist, 100 pmol/25 nl), on pancreatic exocrine secretion (PES). Male Sprague–Dawley rats anaesthetised with isoflurane were used in all experiments. PES was collected from the common bile-pancreatic duct and was used to determine the pancreatic protein output (PPO). PES and PPO were measured prior to, and after, microinjection of BIM into the DVN. Bilateral microinjection of BIM into the DVN significantly increased PES and PPO from 23.4 ± 3.2 μl/h to 66.1 ± 17.5 μl/h and 19.3 ± 1.7 μg/h to 35.7 ± 3.0 μg/h (P < 0.05), respectively. Atropine methonitrate (100 μg/(kg min), i.v.) blocked the excitatory effect of BIM microinjection on PES and PPO. These results suggest that activation of DVN neurons stimulates pancreatic secretion via a cholinergic muscarinic mechanism.     

Central 5-HT3 receptor-induced hypothermia in mice: Interstrain differences and comparison with hypothermia mediated via 5-HT1A receptor

The selective agonist of serotonin 5-HT₃ receptor 1-(3-chlorophenyl)biguanide hydrochloride (m-CPBG) administered intracerebroventricularly (40, 80 or 160 nmol) produced long-lasting dose-dependent hypothermic response in AKR/2J mice. m-CPBG (160 nmol i.c.v.) induced profound hypothermia (delta t = −4 °C) that lasted up to 7 h. m-CPBG (40 nmol i.c.v.)-induced hypothermia was attenuated by 5-HT₃ receptor antagonist ondansetron pretreatment. At the same time, intraperitoneal administration of m-CPBG in a wide range of doses (0.5, 1.0, 5.0 or 10.0 mg/kg) did not affect the body temperature. These findings indicate: (1) the implication of central, rather than peripheral 5-HT₃ receptor in the thermoregulation; (2) the inability of m-CPBG to cross blood–brain barrier in mice. The comparison of brain 5-HT₃-induced hypothermic reaction in six inbred mouse strains (DBA/2J, CBA/Lac, C57BL/6, BALB/c, ICR, AKR/J) was performed and two highly sensitive to m-CPBG strains (CBA/Lac and C57BL/6) were found. In the same six mouse strains the functional activity of 5-HT_1A receptor was studied. The comparison of hypothermic reactions produced by 5-HT_1A receptor agonist 8-OH-DPAT (1.0 mg/kg i.p.) and m-CPBG revealed significant correlation between 5-HT₃ and 5-HT_1A-induced hypothermia in five out of six investigated mouse strains. 5-HT_1A receptor antagonist p-MPPI pretreatment (1 mg/kg i.p.) diminished hypothermia produced by centrally administered m-CPBG (40 nmol i.c.v.). The data suggest the cross-talk between 5-HT_1A and 5-HT₃ receptors in the mechanism of 5-HT-related hypothermia.     

Bifeprunox and aripiprazole suppress in vivo VTA dopaminergic neuronal activity via D2 and not D3 dopamine autoreceptor activation

Bifeprunox and aripiprazole are two novel antipsychotics presenting partial agonistic activity for the D₂ and D₃ dopamine (DA) receptors. Using in vivo electrophysiological paradigms in anaesthetized rats, we have previously shown that both drugs independently inhibit the spontaneous firing and bursting activity of ventral tegmental area (VTA) dopaminergic neurons and partially reverse the suppressing effect of the full DA receptor agonist apomorphine. Moreover, we have also shown that the D_2/3 receptor antagonist haloperidol prevents the inhibitory effects of these antipsychotics, confirming their partial D₂-like agonistic activities [L. Dahan, H. Husum, O. Mnie-Filali, J. Arnt, P. Hertel, N. Haddjeri, Effects of bifeprunox and aripiprazole on rat serotonin and dopamine neuronal activity and anxiolytic behaviour, J. Psychopharmacol. (2009)]. In the present electrophysiological study, selective antagonists of D₂ and D₃ receptors were used to further characterize the inhibitory role of bifeprunox and aripiprazole on the D₂ and D₃ receptors in vivo. Administration of bifeprunox (250 μg/kg, i.v.) or aripiprazole (300 μg/kg, i.v.) reduced the firing activity of VTA DA neurons by 40–50%. The bursting activity was reduced by 95% and 77% by bifeprunox and aripiprazole, respectively. Systemic administration of the preferential D₃ receptor antagonist GR218,231 (200 μg/kg, i.v.) did not modify the inhibitory effect of bifeprunox or aripiprazole, either on the firing or on the bursting activity. On the other hand, the preferential D₂ receptor antagonist L741,626 (500 μg/kg, i.v.) completely blocked the inhibitory effect of both bifeprunox and aripiprazole on the VTA DA neuronal activity. The present study shows that bifeprunox and aripiprazole behave as partial D₂, but not D₃, receptor agonists in vivo, inhibiting the firing activity (preferentially the phasic activity) of VTA DA cells.     

Organoselenium improves memory decline in mice: Involvement of acetylcholinesterase activity

The present study was designed to investigate the possible neuroprotective effect of p,p′-methoxyl-diphenyl diselenide [(MeOPhSe)₂] in a model of sporadic dementia of Alzheimer's type (SDAT) induced by intracerebroventricular (i.c.v.) injection of streptozotocin (STZ) in mice. Mice were divided into four groups: (I) control, (II) (MeOPhSe)₂, (III) STZ, and (IV) (MeOPhSe)₂ + STZ. Mice were exposed to (MeOPhSe)₂ (25 mg/kg, by gavage) and STZ (2 μl of 2.5 mg/ml solution; i.c.v.) or vehicles. 48 after that the exposure was repeated. Learning and memory were assessed with the step-down-type passive-avoidance (SDPA) and Morris water-maze (MWM) tests at the days 5–6 and 6–9, respectively. At the end of the experimental protocol animals were euthanized and cerebral cortex was removed for acetylcholinesterase (AChE) activity assay. Our results confirmed that i.c.v. STZ caused learning and memory deficits in mice, which were verified using the MWM and SDPA tasks. Furthermore, this study showed that AChE activity was increased in mice that received i.c.v. STZ. The most important findings of the present study are that (MeOPhSe)₂ was able to reverse the learning and memory impairments induced by STZ, and to protect against the increase in AChE activity. All these findings support the neuroprotective role of (MeOPhSe)₂ in a mice model of SDAT induced by i.c.v. STZ.     

Activation of α2-adrenoceptors in the lateral hypothalamus reduces pilocarpine-induced salivation in rats

Anti-hypertensive drugs that act on central α₂-adrenoceptors and imidazoline receptors usually cause dry mouth in patients. A central area important for the control of salivary secretion and also for the effects of α₂-adrenoceptor activation is the lateral hypothalamus (LH). Therefore, in the present study we investigated the effects of the injections of moxonidine (an α₂-adrenoceptor and imidazoline agonist) alone or combined with RX 821002 (α₂-adrenoceptor antagonist) into the LH on the salivation induced by intraperitoneal (i.p.) pilocarpine (cholinergic muscarinic agonist). Male Holtzman rats with stainless steel cannula implanted into the LH were used. Saliva was collected using pre-weighted small cotton balls inserted into the animal’s mouth under ketamine anesthesia. Salivation induced by i.p. pilorcarpine (4 μmol/kg of body weight) was reduced by the injection of moxonidine (10 and 20 nmol/0.5 μl) into the LH (222 ± 46 and 183 ± 19 mg/7 min, vs. vehicle: 480 ± 30 mg/7 min). The inhibitory effect of moxonidine on pilocarpine-induced salivation was abolished by prior injections of RX 821002 (160 and 320 nmol/0.5 μl) into the LH (357 ± 25 and 446 ± 38 mg/7 min). Injections of the α₁-adrenoceptor antagonist prazosin (320 nmol/0.5 μl) into the LH did not change the effects of moxonidine. The results show that activation of α₂-adrenoceptors in the LH inhibits pilocarpine-induced salivation, suggesting that LH is one of the possible central sites involved in the anti-salivatory effects produced by the treatment with α₂-adrenoceptor agonists.     

JAK-STAT pathway modulates the roles of iNOS and COX-2 in the cytoprotection of early phase of hydrogen peroxide preconditioning against apoptosis induced by oxidative stress

Our previous studies have demonstrated that preconditioning with hydrogen peroxide (H₂O₂) activated the JAK-STAT pathway that played an important role in the cytoprotection, and inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) mediated the late phase of cytoprotection induced by high concentration of H₂O₂ after preconditioning. Here we sought to identify the downstream targets of the JAK-STAT axis that mediated H₂O₂ preconditioning and the expression of iNOS and COX-2 in the early phase of H₂O₂ preconditioning. It was shown that (1) Preconditioning with H₂O₂ at 100 μmol/L for 90 min in PC12 cells induced significant expression of iNOS and COX-2. (2) Pretreatment with the iNOS inhibitor AG (10 μmol/L) or the COX-2 inhibitor NS-398 (10 μmol/L) respectively 20 min before H₂O₂ preconditioning not only inhibits the increased expression of iNOS or COX-2 but also abrogates the protective effects of H₂O₂ preconditioning against apoptosis induced by oxidative stress. (3) Pretreatment with the JAK inhibitor AG-490 (10 μmol/L) 20 min before H₂O₂ preconditioning obviously inhibits the up-regulation of iNOS or COX-2 induced by H₂O₂ preconditioning. These results suggested that JAK-STAT pathway modulates the roles of iNOS and COX-2 in the cytoprotection of early phase of H₂O₂ preconditioning.     

Effects of intra-hippocampal injections of the NK2 receptor antagonist saredutant on the elevated plus maze,and the mouse defense test battery

Intracerebroventricular (i.c.v.) or intraperitoneal (IP) administration of saredutant (SR48968), an NK2 receptor antagonist, produces anxiolytic-like effects in rodents in a number of animal models of anxiety. NK2 binding sites are present in several limbic structures in rats, including the hippocampus, thalamus, septum and prefrontal cortex, suggesting involvement in the modulation of emotional processes. The current study investigated the behavioral effects of saredutant infused into the ventral hippocampus (VH), a structure associated with cognitive and emotional processes, to clarify the neural substrate underlying the anxiolytic-like effect of the compound. Saredutant (10, 100 or 500 pmol/0.2 μL) was injected bilaterally into the VH of male CD-1 mice tested in the elevated plus-maze and mouse defense test battery (MDTB). Results from the EPM showed that microinjections of 10 pmol/0.2 μL of saredutant increased entries and time spent in the open arms and enhanced end-arm exploration. In the MDTB, saredutant (500 pmol/0.2 μL) decreased vocalizations and increased escape attempts in mice confronted with a rat. Taken together, these results suggest that hippocampal tachykinin mechanisms are involved in the modulation of anxiety and defensive behaviors.     

Effects of the 5-HT4 receptor agonist RS67333 and paroxetine on hippocampal extracellular 5-HT levels

The 5-HT₄ receptor modulates activity of serotonergic neurons and is a new potential target for antidepressant treatment. This microdialysis study evaluated the effect of the 5-HT₄ receptor agonist, RS67333, on extracellular serotonin (5-hydroxytryptamine, 5-HT) and 5-HIAA levels in rat ventral hippocampus during chloral hydrate anaesthesia, and explored the ability of RS67333 to augment the effect of the selective serotonin reuptake inhibitor paroxetine. The effect of RS67333 was examined after acute and subchronic (3 days) administration. Acute RS67333 (1.5 mg/kg i.v.) had no effect on extracellular 5-HT or 5-HIAA levels, while acute paroxetine (0.5 mg/kg i.v.) increased 5-HT levels by 299 ± 16% and decreased 5-HIAA levels by 25 ± 4%. Administration of RS67333 80 min after paroxetine caused an additional transient increase in 5-HT levels (to 398 ± 52% of baseline). Subchronic RS67333 administration (1.5 mg/kg i.p.) increased basal 5-HT levels by 73 ± 15% and decreased 5-HIAA levels by 27 ± 13%. In conclusion, the 5-HT₄ receptor agonist RS67333 augmented the acute effect of paroxetine on extracellular 5-HT levels in the ventral hippocampus, and after 3 days increased basal hippocampal 5-HT levels.     

Novel 8-(furan-2-yl)-3-benzyl thiazolo [5,4-e][1,2,4] triazolo [1,5-c] pyrimidine-2(3H)-thione as selective adenosine A2A receptor antagonist

Adenosine A_2A receptor (A_2AR) antagonists have emerged as potential drug candidates to alleviate progression and symptoms of Parkinson's disease (PD), and reduce the dopaminergic side effects. The synthesis of novel compound 8-(furan-2-yl)-3-benzyl thiazolo [5,4-e][1,2,4] triazolo [1,5-c] pyrimidine-2-(3H)-thione (BTTP) was carried out to evaluate the potential of BTTP as A_2AR antagonist using SCH58261, a standard A_2AR antagonist. The strong interaction of BTTP with A_2AR (ΔG = −12.46 kcal/mol and K_i = 0.6 nM) in silico analysis was confirmed by radioligand receptor binding studies showing high affinity (K_i = 0.004 nM) and selectivity with A_2AR (A_2A/A₁ = 1155-fold). The effect of CGS21680 (selective A_2AR agonist) induced cAMP concentration (0.1 pmol/ml) in HEK293 cells was antagonized with BTTP (0.065 pmol/ml) and SCH58261 (0.075 pmol/ml). Furthermore, BTTP pre-treated (5, 10 and 20 mg/kg) haloperidol-induced mice demonstrated significant attenuation in catalepsy and akinesia. BTTP induced elevation in the striatal dopamine concentration (2.90 μM/mg of tissue) was comparable to SCH58261 (2.92 μM/mg of tissue) at the dose of 10 mg/kg. The results firmly articulate that BTTP possesses potential A_2AR antagonist activity and can be further explored for the treatment of PD.     

l-Cysteine ethyl ester reverses the deleterious effects of morphine on,arterial blood–gas chemistry in tracheotomized rats

This study determined whether the membrane-permeable ventilatory stimulant, l-cysteine ethylester (l-CYSee), reversed the deleterious actions of morphine on arterial blood–gas chemistry in isoflurane-anesthetized rats. Morphine (2 mg/kg, i.v.) elicited sustained decreases in arterial blood pH, pO₂ and sO₂, and increases in pCO₂ (all responses indicative of hypoventilation) and alveolar–arterial gradient (indicative of ventilation–perfusion mismatch). Injections of l-CYSee (100 μmol/kg, i.v.) reversed the effects of morphine in tracheotomized rats but were minimally active in non-tracheotomized rats. l-cysteine or l-serine ethylester (100 μmol/kg, i.v.) were without effect. It is evident that l-CYSee can reverse the negative effects of morphine on arterial blood–gas chemistry and alveolar–arterial gradient but that this positive activity is negated by increases in upper-airway resistance. Since l-cysteine and l-serine ethylester were ineffective, it is evident that cell penetrability and the sulfur moiety of l-CYSee are essential for activity. Due to its ready penetrability into the lungs, chest wall muscle and brain, the effects of l-CYSee on morphine-induced changes in arterial blood–gas chemistry are likely to involve both central and peripheral sites of action.     

Effect of chronic activation of 5-HT3 receptors on 5-HT3, 5-HT1A and 5-HT2A receptors functional activity and expression of key genes of the brain serotonin system

Among serotonin (5-HT) receptors, the 5-HT₃ receptor is the only ligand-gated ion-channel. Little is known about the interaction between the 5-HT₃ receptor and other 5-HT receptors and influence of 5-HT₃ chronic activation on other 5-HT receptors and the expression of key genes of 5-HT system. Chronic activation of 5-HT₃ receptor with intracerebroventricularly administrated selective agonist 1-(3-chlorophenyl)biguanide hydrochloride (m-CPBG) (14 days, 40 nmol, i.c.v.) produced significant desensitization of 5-HT₃ and 5-HT_1A receptors. The hypothermic responses produced by acute administration of selective agonist of 5-HT₃ receptor (m-CPBG, 40 nmol, i.c.v.) or selective agonist of 5-HT_1A receptor (8-hydroxy-2-(di-n-propylamino)tetralin) (8-OH-DPAT, 1 mg/kg, i.p.) was significantly lower in m-CPBG treated mice compared with the mice of control groups. Chronic m-CPBG administration failed to induce any significant change in the 5-HT_2A receptor functional activity and in the expression of the gene encoding 5-HT_2A receptor. Chronic activation of 5-HT₃ receptor produced no considerable effect on the expression on 5-HT₃, 5-HT_1A, and 5-HT transporter (5-HTT) and tryptophan hydroxylase-2 (TPH-2) genes – the key genes of brain 5-HT system, in the midbrain, frontal cortex and hippocampus. In conclusion, chronic activation of ionotropic 5-HT₃ receptor produced significant desensitization of 5-HT₃ and postsynaptic 5-HT_1A receptors but caused no considerable changes in the expression of key genes of the brain 5-HT system.     

Therapeutic potential of α2 adrenoceptor antagonism for antipsychotic-induced extrapyramidal motor disorders

We examined the effects of JP-1302 (a selective α_2C antagonist), BRL-44408 (a selective α_2A antagonist) and yohimbine (a non-selective α₂ antagonist) on haloperidol-induced bradykinesia and catalepsy in mice to elucidate the role of α₂ adrenoceptor subtypes in modifying extrapyramidal motor disorders. JP-1302 (0.1–1 mg/kg, s.c.) dose-dependently ameliorated haloperidol-induced bradykinesia in the pole-test and reversed the catalepsy time increased by haloperidol. Antibradykinetic and anticataleptic actions of JP-1302 were statistically significant at 0.3 and 1 mg/kg, and these doses did not alter the ambulatory distance, rearing or center–perimeter residence time in the open-field test. BRL-44408 (1–10 mg/kg, s.c.) and yohimbine (0.3–3 mg/kg, i.p.) also ameliorated haloperidol-induced bradykinesia and catalepsy. However, both agents significantly decreased ambulatory distance and rearing in the open-field test, possibly reflecting their anxiogenic actions associated with α_2A antagonism. The present study shows for the first time that blockade of α_2C receptors can alleviate antipsychotic-induced extrapyramidal motor disorders without affecting gross behaviors.     

Cyclooxygenase inhibitors suppress the expression of P2X3 receptors in the DRG and attenuate hyperalgesia following chronic constriction injury in rats

Recent evidence suggests that P2X₃ receptors express abundantly in nociceptive sensory neurons and play an important role in neuropathic pain. Upregulation of prostaglandin E2 (PGE2) after nerve injure is involved in the pathogenesis of neuropathic pain. An increase of P2X₃ receptors after chronic constriction injury (CCI) to the sciatic nerve has also been reported, the mechanisms are not known clearly. In this study, we examined the effects of systemic administration of cyclooxygenase (COX) inhibitors on analgesia and the expression of P2X₃ receptors in the dorsal root ganglia (DRG) in CCI rats. Rats received 0.9% saline, the nonselective COX inhibitor ibuprofen (40 mg kg⁻¹ day⁻¹) or the selective COX-2 inhibitor celecoxib (30 mg kg⁻¹ day⁻¹) by gavage twice daily from 3 to 14 days after surgery. Mechanical allodynia and thermal hyperalgesia induced by CCI were markedly attenuated by celecoxib from 5 to 14 days after surgery, and relieved by ibuprofen treatment from 7 to 10 days after surgery. The increase of P2X₃ receptors in the DRG in CCI rats on day 14 after surgery was also significantly inhibited; the effect of ibuprofen was stronger than that of celecoxib. These results demonstrate that up-regulated COX/PGE2 after nerve damage may play an important role in neuropathic pain. They are highly involved in the expression of P2X₃ receptors in the DRG in CCI rats.     

Protective effect of stilbenes containing extract-fraction from Cajanus cajan L. on Aβ25–35-induced cognitive deficits in mice

Cajanus cajan (L.) is a traditional Chinese herb medicine which contains a lot of potential active components. In the present study, we identified the effects of the stilbenes containing extract-fraction from C. cajan L. (sECC) on Aβ_25–35-induced cognitive deficits, oxidative stress and cholinergic dysfunction in mice. Mice were treated with sECC (100 and 200 mg/kg/d) for 1-week, and then received a single intracerebroventricular (i.c.v.) injection of Aβ_25–35 (5 μg/mice). Behavioral changes and neuron apoptosis in mice were evaluated using Morris water maze and TUNEL tests. Furthermore, superoxide dismutase (SOD), choline acetyl transferase (ChAT) and acetylcholine esterase (AchE) activity in hippocampus and cortex were analyzed by spectrophotometric method. The data showed that consumption of sECC (200 mg/kg) significantly ameliorated the cognitive deficits and neuron apoptosis caused by i.c.v. injection of Aβ_25–35. At the same time, the decreased SOD and ChAT activity in hippocampus and cortex were markedly increased by sECC (200 mg/kg). sECC has no effect on AchE activity in hippocampus and cortex. These findings suggest that sECC may be a potential candidate for the development of therapeutic agents to manage cognitive impairment associated with Alzheimer's disease (AD) through increasing the activity of ChAT and anti-oxidative mechanism.     

Positive feedback regulation of COX-2 expression by prostaglandin metabolites

Objectives: Previous studies in cell lines and tissues derived from mice lacking genes encoding cyclooxygenase (COX)-1 or –2 have demonstrated compensatory regulation between the two isoenzymes. To determine whether this compensation was driven by a mechanism that controls prostaglandin (PG) levels, we investigated the effects of PG availability on the regulation of COX and cytosolic phospholipase A₂ (cPLA₂), an upstream enzyme in the PG pathway.Materials and methods: Mouse lung fibroblast cells were treated with various concentrations of PG metabolites including prostaglandin E₂ (PGE₂), 15-deoxy-^12,14-prostaglandin J₂ (15d-PGJ₂), 6-keto PGF₁ and PGF₂ Cells were harvested for protein and mRNA analyses; culture supernatant was collected for prostaglandin assays.Results: We observed 8- and 20-fold increase in basal COX-2 protein expression levels when cells were exposed to PGE₂ and 15d-PGJ₂, respectively. In the presence of IL-1, PGE₂, 15d-PGJ₂, 6-keto PGF₁ and PGF₂ each enhanced COX-2 protein expression between 5- to 20-fold. Corresponding with the induction of COX-2 protein expression, the latter three PGs induced PGE₂ synthesis in a dose-dependent manner. Only PGE₂ and 15d-PGJ₂ induced COX-2 mRNA expression, although to a lower extent than protein induction. None of the PG metabolites tested showed significant effects on the level of COX-1 or cPLA₂ protein expression, except for PGF₂, which increased IL-1-induced cPLA₂ protein expression slightly.Conclusion: Our results demonstrate that there is positive feedback regulation of COX-2 expression by PG metabolites, but not COX-1, indicating that PG levels per se do not play an important role in the compensatory regulation between the two COX isoenzymes, but may play an important role in mediating increased COX-2 expression and activity.Received 16 August 2004; returned for revision 9 September 2004; accepted by A. Falus 20 December 2004     

Cyclic intermittent hypoxia enhances renal sympathetic response to ICV ET-1 in conscious rats

To test the hypothesis that central changes in sympathoregulation might contribute to sympathoexcitation after cyclic intermittent hypoxia (CIH) we exposed male Sprague–Dawley rats to CIH or to room air sham (Sham) for 8 h/d for 3 weeks. After completion of the exposure we assessed heart rate, mean arterial pressure and renal sympathetic nerve activity in conscious animals before and after intracerebroventricular (i.c.v.) administration of endothelin-1 (ET-1, 3 pmol). CIH-exposed animals had a significantly greater sympathetic response to ET-1 than did Sham-exposed animals (CIH 137.8 ± 15.6% of baseline; Sham 112.2 ± 10.0% of baseline; CIH vs. Sham, P = 0.0373). This enhanced sympathetic response to i.c.v. ET-1 was associated with greater expression of endothelin receptor A (ETA) protein in the subfornical organs of CIH-exposed relative to Sham-exposed rats. We conclude that 3-week CIH exposure enhances central ET-1 receptor expression and the sympathetic response to i.c.v. ET-1 suggesting central endothelin may contribute to the sympathetic and hemodynamic response to cyclic intermittent hypoxia.     

Further antinociceptive effects of myricitrin in chemical models of overt nociception in mice

The present work explored the antinociceptive effects of the flavonoid myricitrin in models of overt nociception triggered by intraplantar injection of chemical algogens into the hind paw of mice. The nociception induced by bradykinin (3 nmol/paw i.pl.) was abolished by prior treatment with myricitrin (10–100 mg/kg, i.p.) with ID₅₀ of 12.4 (8.5–18.1) mg/kg. In sharp contrast, myricitrin failed to affect the nociception elicited by prostaglandin E₂ (3 nmol/paw i.pl.). Cinnamaldehyde (10 nmol/paw i.pl.)-induced nociception was reduced by myricitrin (100 mg/kg, i.p.) and camphor (7.6 mg/kg, s.c.) in 43 ± 10% and 57 ± 8%, respectively. Myricitrin (30–100 mg/kg, i.p.) and amiloride (100 mg/kg, i.p.) inhibited nociceptive responses induced by acidified saline (pH 5/paw i.pl.), with ID₅₀ of 22.0 (16.1–30.0) mg/kg and inhibition of 71 ± 6% and 64 ± 5%, respectively. Moreover, myricitrin (10–30 mg/kg, i.p.) and ruthenium red (3 mg/kg, i.p.) significantly reduced the nociception induced by menthol (1.2 μmol/paw i.pl.) with the mean ID₅₀ of 2.4 (1.5–3.7) mg/kg and inhibition of 95 ± 3% and 51 ± 7%, respectively. In addition, myricitrin administration (30 and 100 mg/kg, i.p.) markedly reduced menthol-induced mechanical allodynia. However, myricitrin (100 mg/kg, i.p.) prevented (only in time of 60 min) cold allodynia induced by menthol. Collectively, the present results extend prior data and show that myricitrin promotes potent antinociception, an action that is likely mediated by an inhibition of the activation of nociceptors by bradykinin and TRPs agonist (i.e. cinnamaldehyde, acidified saline and menthol), probably via inhibition of PKC pathways. Thus, myricitrin could constitute an attractive molecule of interest for the development of new analgesic drugs.     

Commissural NTS lesions enhance the pressor response to central cholinergic and adrenergic activation

Electrolytic lesions of the commissural nucleus of the solitary tract (commNTS) in rats enhance the pressor response to bilateral carotid occlusion or to intravenous infusion of hypertonic NaCl without changing baroreflex responses. In an opposite direction, commNTS lesions abolish the pressor responses to peripheral chemoreflex activation. These opposite effects of commNTS lesions apparently result from an impairment of sympathetic activation in one case and in a facilitation of vasopressin secretion in the others. In the present study, we investigated the effects of the electrolytic lesions of the commNTS in the pressor responses that depend on sympathetic activation and vasopressin secretion produced by central cholinergic or adrenergic activation with intracerebroventricular (i.c.v.) injections of carbachol or noradrenaline, respectively, in unanesthetized rats. Male Holtzman rats (280–320 g, n = 8–15/group) with acute (1 day) or chronic (21 days) sham or commNTS lesions (1 mA × 10 s) and a stainless steel cannula implanted in the lateral ventricle were used. Acute commNTS lesions increased the pressor response to i.c.v. injection of carbachol (0.5 nmol/1 μ1) (52 ± 2, vs. sham: 37 ± 2 mmHg) or noradrenaline (80 nmol/1 μl) (45 ± 6, vs. sham: 30 ± 3 mmHg), whereas chronic commNTS lesions did not affect the pressor responses to the same treatments. Lesions of the commNTS impaired chemoreflex responses produced by intravenous KCN, without changing baroreflex responses. The results suggest that commNTS-dependent inhibitory signals are involved in the modulation of the pressor responses to central cholinergic and adrenergic activation, probably limiting vasopressin secretion.     

Differential hippocampal pharmacokinetics of phenobarbital and carbamazepine in repetitive seizures induced by 3-mercaptopropionic acid

Previous evidence has shown that chronic 3-mercaptopropionic acid (MP) administration induced brain P-glycoprotein (P-gp) overexpression altering target site accumulation of phenytoin. The aim of the present work was to assess the involvement of P-glycoprotein in carbamazepine and phenobarbital hippocampal pharmacokinetics in an experimental model of epilepsy, induced by repetitive MP administration. Seizures were induced in Wistar rats by injection of MP (45 mg kg⁻¹, i.p.) during 10 days. Control rats (C) were injected with saline solution. In order to monitor extracellular brain antiepileptic levels, a concentric probe was inserted into the hippocampus. Animals were administered with carbamazepine (10 mg kg⁻¹, i.v.) or phenobarbital (20 mg kg⁻¹, i.v.) 30 min after intraperitoneal administration of vehicle or nimodipine (2 mg kg⁻¹), a well known P-glycoprotein inhibitor. No differences were found in hippocampal concentrations of carbamazepine comparing all groups. In vehicle pre-treated rats, hippocampal phenobarbital concentrations were lower in MP (maximal concentration, C_max: 6.0 ± 0.6 μg ml⁻¹, p < 0.05) than in C animals (C_max: 9.4 ± 0.9 μg ml⁻¹). Control rats pre-treated with nimodipine showed similar results (C_max: 10.7 ± 0.6 μg ml⁻¹) than those pre-treated with vehicle. Nimodipine pre-treatment in MP rats enhanced hippocampal phenobarbital concentrations (C_max: 10.2 ± 1.0 μg ml⁻¹, p < 0.05) as compared with vehicle pre-treatment.     

SKF 83566 attenuates the effects of ghrelin on performance in the object location memory task

Increasing research implicates ghrelin, a metabolic signaling peptide, in memory processes including acquisition, consolidation, and retention. The present study investigated the effects of ghrelin on spatial memory acquisition by utilizing the object location memory task paradigm. Given the co-expression of ghrelin and dopamine D₁ receptors within hippocampal neurons, we examined a potential interaction between these two systems on memory performance. When injected into the dorsal third ventricle (D3V) of male Sprague-Dawley rats, proximal to hippocampal tissue, ghrelin (500 pmol) increased the amount of time spent with objects in novel locations. This effect was completely reversed by the D₁ antagonist SKF 83566 (100 μg/kg IP), although when administered alone, the antagonist had no effect on task performance (10-100 μg/kg). We also examined the feeding effects of D3V ghrelin and found that the peptide reliably increased food intake (500 pmol) but that this effect was not blocked by SKF 83566 (100 μg/kg). When given alone, SKF 83566 did not alter food intake (10-100 μg/kg). Our findings indicate that, in addition to an orexigenic effect, ghrelin improves acquisition of spatial location memories. Furthermore, D₁ receptor activation is necessary for ghrelin to improve the encoding of spatial memories but does not impact the increase in food intake elicited by the peptide.