Inhibition of nitric oxide synthase dramatically potentiates seizures induced by kainic acid and pilocarpine in rats

We investigated whether the severity of convulsions evoked by kainic acid and pilocarpine is modified in nitric oxide synthase inhibitor-treated rats. We found that chronic treatment (4 days) withN_w-nitro-l-arginine greatly potentiates seizures induced by both convulsants suggesting a potential role for nitric oxide in mechanisms regulating seizure induction and propagation.     

The yohimbine-induced anticonflict effect in the rat,part I. Involvement of noradrenergic,serotonergic and endozepinergic(?) mechanisms

Summary The ₂-adrenoceptor antagonist yohimbine has in several previous studies been found to produce anticonflict effects comparable to those produced by the benzodiazepines (BDZ) in rat punished conflict models. In this and a following paper we have tried to elucidate the neurochemical mechanisms underlying these effects in a modified Vogel's drinking conflict test. Since yohimbine previously has been demonstrated to interfere both with noradrenaline (NA) and serotonin (5-HT) neurochemistry, and, in addition, shows affinity for the BDZ binding site, we have focused on the putative involvement of these neuronal systems in the yohimbine-induced anticonflict effect. The ₂-adrenoceptor agonist clonidine (10 g/kg, i.p.) completely antagonized the anticonflict effect of yohimbine (4.0 mg/kg, i.p.), whereas the ₁-adrenoceptor agonist ST 587 (1.0 mg/kg, i.p.) had no effect. The anticonflict effect of yohimbine was totally abolished also following lesioning of NA neurons with 6-hydroxy-dopamine. A high dose of the mixed ₁ and ₂ adrenoceptor antagonist propranolol (8.0 mg/kg, i.p.) caused a partial blockade of the yohimbine-induced effect in intact animals, whereas the selective ₁-adrenoceptor antagonist metoprolol (4.0 mg/kg, i.p.) had no significant effect and the ₁-adrenoceptor antagonist prazosin instead potentiated the anticonflict action. The anticonflict effect of yohimbine was dose-dependently antagonized also by the 5-HT precursor L-5-hydroxytryptophan (25–100 mg/ kg, i.p.). The BDZ receptor antagonist flumazenil (10 mg/kg, p.O.), as well as Ro 15-4513 (1.0 mg/kg, p.o.), a partial inverse agonist at BDZ receptors, partly, but significantly, counteracted the yohimbine-induced anticonflict effect, whereas low doses of both the chloride channel blocker picrotoxin and the GABA_A antagonist bicuculline only tended to counteract the yohimbine effect. Taken together, the results in the present behavioral paper indicate that the anticonflict effect of yohimbine involves both increased NA and decreased 5-HT activity, and that direct or indirect activation of BDZ receptors may also be involved. Neurochemical findings related to these behavioral results are presented in a following paper.     

Evidence for the involvement of the 5-HT1A receptor in CCK induced satiety in rats

The present study was designed to examine possible interactions between exogenous CCK and the 5-HT_1A receptor subtype mediated serotonergic effects on feeding in rats. The somatodendritic 5-HT_1A receptor agonist 8-OH-DPAT (0.32 mg/kg sc) evoked feeding in freely feeding rats. This effect was attenuated by treatment with CCK-8 (1, 5 and 25 g/kg ip). In food deprived rats, CCK-8 (40 g/kg ip) significantly reduced the size of a test meal. Treatment with the 5-HT_1A receptor antagonist WAY-100135 (10 mg/kg ip) antagonized this anorectic effect of CCK-8. WAY-100135 on its own did not affect food intake. These results suggest the involvement of the 5-HT_1A receptor subtype in mediating 5-HT-CCK interactions in the control of food intake in rats.     

Selective blockade of muscarinic M2 receptors in vivo by the new antagonist tripitramine

The antimuscarinic effects of tripitramine (1, 1, 24--tris [[5, 11-dihydro-6-oxo-6H-pyrido [2, 3-b][1, 4]-benzodiazepin-11-yl)(carbonyl] methyl]-8, 17-dimethyl-1, 8, 17, 24-tetraazatetracosane tetraoxalate), a member of a series of polymethylene tetraamines with in vitro cardioselectivity, were assessed in two in vivo preparations: anaesthetized and pithed rats. The well-known M₂ selective antagonist methoctramine was used in a comparative study. Tripitramine (0.0202 mol/kg i.v.) proved to be a potent antagonist at cardiac M₂ receptors that mediate the decrease in heart rate in the pithed rat; the same dose of this antagonist in the anaesthetized rat did not significantly affect the depressor action of methacholine mediated by vascular M₃ receptors. In the pithed rat, this dose did not affect the ganglionic M₁ receptor-mediated tachycardia and pressor response to muscarme or McN-A-343. These in vivo data are consistent with the in vitro findings and confirm that tripitramine is a more potent and selective muscarinic M₂ receptor antagonist than methoctramine.     

Lead-induced blockade of kainate-sensitive receptor channels

The effects of bivalent lead on ion channels activated by kainate and -amino-3-hydroxy-5-methyl-4-isoxazolpropionate (AMPA) were studied using Xenopus oocytes microinjected with mRNA from rat brain. Lead reduced kainate-induced membrane currents in a reversible and dose-dependent manner, without affecting membrane currents induced by AMPA. Lead decreased the kainate currents with a concentration of 0.1 mol/l to 0.93 ± 0.01 and with a concentration of 100 mol/l to 0.41 ± 0.04 of the control values. The blocking effect of lead on kainate responses was voltage dependent. The inhibition was strongest at - 90 mV to - 70 mV and became weaker at more positive membrane potentials. The effect of lead on the kainate-induced membrane currents remained unchanged when the concentration of kainate was increased. Hence lead probably represents a noncompetitive channel-blocking agent for non-N-methyl-d-aspartate (NMDA) receptor channels activated by kainate.     

Cultured chick sympathetic neurons: ATP-induced noradrenaline release and its blockade by nicotinic receptor antagonists

The ATP-induced increase in tritium outflow from cultured chick sympathetic neurons prelabelled with [³H]-noradrenaline was investigated.Seven days-old dissociated cell cultures of embryonic paravertebral ganglia, loaded with [³H]-noradrenaline (0.05 M), were superfused in the presence of (+)-oxaprotiline and exposed to ATP, ATP-analogues, or 1,1-dimethyl-4-piperazinium (DMPP) for 2 min. ATP (3 LM-3 mM), 2-methylthio-ATP (3–100 M), as well as DMPP (10 and 100 M) induced a significant overflow of tritium. The EC₅₀-value of ATP was 20 M. Both the ATP-induced and the DMPP-induced tritium overflow was Ca²⁺-dependent and sensitive to tetrodotoxin (0.3 M) and -conotoxin (0.1 M); in addition, it was inhibited by the ₂-adrenoceptor agonist 5-bromo-6-(2-imidazoline-2-ylamino)-quinoxaline (UK-14,304; 1 M). The effects of ATP and DMPP were not additive. The ATP-induced as well as the DMPP-induced overflow of tritium was diminished by the P₂-purinoceptor antagonists suramin (300 M) and reactive blue 2 (3 M); in all 4 cases, the inhibition amouted to approximately 40%. The tritium overflow induced by ATP or DMPP was almost abolished by the nicotinic receptor antagonist mecamylamine (10 M) and markedly inhibited by hexamethonium (100 M). Neither ATP nor electrical stimulation caused an overflow of tritium from cultures loaded with [³H]-choline.The results suggest that ATP at molar concentrations induces noradrenaline release from cultured chick sympathetic neurons via an action on a subclass of the nicotinic cholinoceptor.     

Association of Epidermal Growth Factor-related Peptides and Type I Receptor Tyrosine Kinase Receptors with Prognosis of Human Colorectal Carcinomas

The frequency of expression and localization of cripto-1 (CR-1),amphiregulin (AR), transforming growth factor alpha (TGF), epidermalgrowth factor receptor (EGFR) and erbB-2 were examined by immunohistochemistryin 45 carcinomas and adjacent non-involved normal colon mucosa.Thirty (66.7%), 24 (53.3%), 23 (51.1%), 23 (51.1%) and 13 (28.9%)of the 45 carcinomas showed positive staining for CR-1, AR,TGF, EGFR and erbB-2, respectively, whereas 7 (15.5%), 17 (37.7%),15 (33.3%), 20 (44.4%) and 0 (0%) of the corresponding non-involvednormal mucosa specimens were reactive. Among 13 carcinomas withlymph node involvement, 10 (76.9%), 8 (61.5%), 10 (76.9%), 8(61.5%) and 7 (53.8%) exhibited positive staining for CR-1,AR, TGF-, EGFR and erbB-2, respectively. There was a statisticallysignificant association between the frequency of either TGF(P<0.05) or erbB-2 (P<0.05) expression and lymph nodemetastasis. In addition, a signficantly higher frequency ofpositive staining for TGF was observedin Dukes' grade C carcinomas(P<0.05). Finally, significant trends for coexpression ofEGFR and either TGF (P<0.01) or AR (P<0.05) were detectedin carcinomas. These data suggest that AR and TGF may play animportant role in the development of colorectal carcinomas throughan autocrine mechanism involving EGFR, and demonstrate thatTGF and erbB-2 may be more reliable indicators of metastasisor prognosis than CR-1, AR or EGFR in human colon cancers.     

Effects of benzodiazepine receptor partial inverse agonists in the elevated plus maze test of anxiety in the rat

The present series of experiments examined the effects of five benzodiazepine receptor (BZR) partial inverse agonists on the behaviour of rats on an elevated plus maze. The drugs were tested in a standard plus maze with 3-cm walls added to the open arms, as this has been shown to increase the sensitivity of the plus maze to anxiogenic-like drug effects (Jones and Cole 1995). The drugs tested were FG 7142 (0–100 mg/kg),-CCE (0–30 mg/kg), ZK 132 556 (0–100 mg/kg), ZK 90 886 (0–30 mg/kg) and Ro 15–4513 (0–30 mg/kg). In addition, to allow a comparison with previous studies, the effects of three reference substances, DMCM (0–2.5 mg/kg), pentylenetetrazol (PTZ; 0–30 mg/kg) and yohimbine (0–5 mg/kg), were also examined. These three reference compounds produced a dose-dependent reduction in the duration of open arm exploration and the total number of open arm entries, indicative of anxiogenic-like effects. DMCM produced significant effects at the doses of 1.25 and 2.5 mg/kg, PTZ at 30 mg/kg, and yohimbine at 5 mg/kg. The BZR partial inverse agonist FG 7142 (10, 30 and 100 mg/kg) also reduced the duration of open arm exploration and the total number of arm entries. The minimally effective dose resulted in a receptor occupancy of approximately 80%. Ro 15–4513 also produced anxiogenic-like effects, but only at a dose (30 mg/kg) that resulted in a receptor occupancy of approximately 95%. In contrast, the other BZR partial inverse agonists, ZK 132 553 and ZK 90 886, did not significantly reduce the duration of open arm exploration, even at doses that produced greater than 95% receptor occupancies.-CCE also did not reduce open arm exploration at any dose tested (0–30 mg/kg). The GABA shift, a biochemical index of intrinsic activity, indicates that these latter three compounds are more inverse agonistic than Ro 15–4513. In summary, these results demonstrate that not all BZR receptor partial inverse agonists have anxiogenic-like activity in the rat plus maze, and that the GABA shift, a biochemical index of intrinsic efficacy, does not predict which BZR partial inverse agonists are anxiogenic.     

The effects of d-cycloserine and MK-801 on the performance of rats in two spatial learning and memory tasks

The present study was undertaken to investigate the effects of modulation of the (NMDA) receptor on learning and memory. Thus, the performance of rats treated with d-cycloserine, a partial agonist at the glycine recognition site of the NMDA receptor complex, and MK-801, a noncompetitive NMDA receptor antagonist, either alone or concurrently were assessed in radial arm maze and water maze tasks. Administration of MK-801 (0.1 mg/kg, i.p.) impaired acquisition in the water maze (increased escape latency and distance) and working memory in the radial arm maze (increased re-entries) in rats. Moreover, in the radial arm maze, MK-801 disrupted locomotion (increased latencies and decreased arm entries per minute) and impaired the acquisition of reference memory (increased number of errors) performance of rats. d-Cycloserine (0.03, 0.3, 1.0, 3.0, 10 mg/kg, i.p.) had no effects on acquisition or memory performance of control or MK-801-treated rats in either of these tasks. However, d-cycloserine (0.03, 0.3, 3.0 mg/kg) reversed the MK-801-induced disruption in locomotion. Furthermore, 3.0 mg/kg d-cycloserine increased behavioral activity and also decreased the time needed to complete the task in control animals. To conclude, our results suggest that the consequences of NMDA receptor modulation on learning and memory processes and sensorimotor functions may be functionally different or have distinct anatomical locations.