Behavioral disturbances in transgenic mice overexpressing the V717F beta-amyloid precursor protein

PDAPP transgenic mice have been shown to develop age dependently much of the cerebral histopathology associated with Alzheimer's disease. PDAPP mice (3-10 months old) were tested in a battery of memory tasks to determine whether they develop memory-behavioral deficits and whether these deficits occur before or after amyloid deposition. PDAPP mice manifest robust impairments in a radial-maze spatial discrimination task at all ages tested. Mild deficits were observed in a barpress learning task in 3-month-old PDAPP mice. In contrast, PDAPP mice show an age-dependent decrease in spontaneous object-recognition performance that appears to be severe at ages when amyloid deposition is known to occur. Thus, the PDAPP mouse shows severe deficits in the radial maze well before amyloid plaque deposition, whereas object-recognition performance decreases with age and may be associated with amyloid deposition.

GF 109203X, a selective inhibitor of protein kinase C, impairs retention performance in an operant task

The effects of post-training administration of GF 109203X (5 and 50 ng i.c.v.), a selective inhibitor of protein kinase C, on retention performance were investigated in a positively reinforced lever press task, in male Swiss mice. Both doses of GF 109203X suppressed the spontaneous improvement of performance observed in control animals between the last 5 min of the acquisition session and the first 5 min of the retention session 24 h later. GF 109203X had no effect on food intake and locomotor activity. These data suggest that GF 109203X selectively interferes with mechanisms underlying post-training organization of information and that protein kinase C is involved in this memory process.

Characterization of bromine-76-labelled 5-bromo-6-nitroquipazine for PET studies of the serotonin transporter

The development of suitable radioligands for brain imaging of the serotonin transporter is of great importance for the study of depression and other affective disorders. The potent and selective serotonin transporter ligand, 5-iodo-6-nitro-2-piperazinylquinoline, has been labelled with iodine-123 and used as a radioligand for single photon emission computerized tomography. To evaluate the potential of the bromine-76-labelled analogue, 5-bromo-6-nitroquipazine, as a radioligand for positron emission tomography (PET), its brain distribution and binding characteristics were examined in rats. In vivo brain distribution and ex vivo autoradiography demonstrated that [76Br]5-bromo-6-nitroquipazine enters the brain rapidly. The regional brain distribution of [76Br]5-bromo-6-nitroquipazine was consistent with the known distribution of serotonin transporters in the midbrain, pons, thalamus, striatum, and neocortex. Specific binding was inhibited by the selective serotonin reuptake inhibitor citalopram. The peripheral metabolism in plasma was rapid, but more than 90% of the radioactivity in brain represented unchanged radioligand 2 h postinjection (p.i.). A preliminary PET study was also performed in a baboon. Following the intravenous injection of [76Br]5-bromo-6-nitroquipazine in a baboon, there was a conspicuous accumulation of radioactivity in thalamus, striatum, and pons. The radioactivity in these brain regions was 1.5 times higher than in the cerebellum at 3 h and 2.5-4 times higher at 24 h. A rapid metabolism of the radioligand in plasma was observed (38% unchanged after 5 min). The results indicate that [76Br]5-bromo-6-nitroquipazine has potential for PET imaging of the serotonin transporter.

Are glutamate receptors specifically implicated in some forms of memory processes?

Convergent data indicate that certain substances that interact with N-methyl-D-aspartate (NMDA) receptors or metabotropic glutamate receptors (mGluRs) do not affect acquisition processes per se, or retrieval, but interfere specifically with the formation of memory traces. This action differs widely in its amplitude and time-course according to the learning task used. We showed that systemic injection of the competitive NMDA receptor antagonists, gamma-L-glutamyl-L-aspartate (gamma-LGLA) and 3-(2-carboxypiperazin-4-yl)propyl-1-phosphonate (CPP), or intracerebroventricular infusion of D-2-amino-5-phosphonovalerate (D-AP5), immediately following acquisition of a Y-maze avoidance learning task in mice, deeply impaired retention of the temporal component of the task (leaving the start alley within the first 5 s of a trial), which significantly improved in controls during the hours following acquisition. In contrast the same substances had no or only slight effects on retention of the discrimination component (choice of the correct alley), which did not improve over time in control animals. This retention deficit did not appear to be due to an action on acquisition, retrieval and/or forgetting processes, or to state-dependent effects. Moreover, gamma-LGLA, CPP or AP5, when administered immediately after partial acquisition of a food-reinforced bar-press task, suppressed the spontaneous improvement in post-training performance observed in control mice 24 h after the training session. (R,S)-alpha-methyl-4-carboxyphenylglycine (MCPG), an antagonist of mGluRs, also suppressed the post-training performance increment and its effects were antagonized by the co-administration of trans-ACPD, an agonist of mGluRs. Post-training improvement of performance over time is thought to reflect an active and dynamic process, leading to the organization of memory traces. According to this hypothesis, our results suggest that synaptic plasticity mediated by NMDA receptors and/or mGluRs activation is involved in mechanisms underlying long-term consolidation of memory traces.

Memory-enhancing effects of secreted forms of the beta-amyloid precursor protein in normal and amnestic mice

When administered intracerebroventricularly to mice performing various learning tasks involving either short-term or long-term memory, secreted forms of the beta-amyloid precursor protein (APPs751 and APPs695) have potent memory-enhancing effects and block learning deficits induced by scopolamine. The memory-enhancing effects of APPs were observed over a wide range of extremely low doses (0.05-5,000 pg intracerebroventricularly), blocked by anti-APPs antisera, and observed when APPs was administered either after the first training session in a visual discrimination or a lever-press learning task or before the acquisition trial in an object recognition task. APPs had no effect on motor performance or exploratory activity. APPs695 and APPs751 were equally effective in the object recognition task, suggesting that the memory-enhancing effect of APPs does not require the Kunitz protease inhibitor domain. These data suggest an important role for APPss on memory processes.

Changes in pyloric resistance induced by erythromycin

Erythromycin increases gastric emptying but the characteristics of transpyloric flow and the contribution of pyloric resistance to the mechanisms of increased flow are unknown. Transpyloric outflow and gastroduodenal pressures were studied in eight anaesthetized pigs during intravenous infusion of erythromycin (10 mg kg-1). Erythromycin increased emptying of saline through an increased stroke volume of individual flow pulses (13.7 +/- 1.24 vs. 3.6 +/- 1.30 mL) rather than by decreasing the interval between flow pulses (3.9 +/- 0.55 vs. 3.2 +/- 0.30 pulse.min-1). This flow pattern was associated with more frequent antral contractions of larger amplitude originating from the upper part of the gastric antrum, suppression of isolated pyloric pressure waves and significant reduction of the pyloric resistance to flow (2.3 +/- 0.21 vs. 4.6 +/- 0.46 mmHg mL-1 s-1). The decreased resistance originated from a different temporal relationship between antropyloric pressure event and flow pulses that occurred almost simultaneously during erythromycin.

Load-sensitive rat gastric vagal afferents encode volume but not gastric nutrients

To assess nutrient sensitivity in a population of gastric load-sensitive vagal afferents, their neurophysiological activity was examined in anesthetized rats with inflated pyloric cuffs after gastric infusion of a range of volumes of nutrient and equiosmotic saline solutions. Responses to physiological saline loads (1, 2, 4, and 8 ml) were compared with responses elicited by the same volume range of carbohydrate (12.5% glucose), protein (12.5% peptone), and equiosmotic hypertonic (750 mosM) saline. The threshold load volume of physiological saline required to increase gastric vagal afferent activity was 1 ml. Thereafter, there was a dose-dependent relationship between increasing gastric volume and firing rate and between gastric volume and pressure. The dose-response relationships elicited by glucose, peptone, and equiosmotic hypertonic saline loads did not differ from those elicited by physiological saline loads. These data identify a population of gastric load-sensitive vagal afferents unresponsive to the chemical composition of gastric contents and are consistent with a role for vagal gastric volume signals but not gastric nutrient content in the negative feedback control of ingestion.

Erythromycin gastrokinetic activity is partially vagally mediated

Erythromycin overcomes postvagotomy gastroparesia in patients without a distal stomach and functional pylorus. We investigate the role of the vagus in gastric emptying increased by erythromycin, using a model that preserves the physiology of the distal stomach and pylorus. The effects of erythromycin lactobionate (10 mg/kg) on transpyloric flow pattern and pyloric resistance were evaluated during repetitive bilateral vagal cooling in anesthetized pigs. Vagal cooling during erythromycin infusion produced a marked decreased of pyloric outflow (23 +/- 1.1 vs 50 +/- 2.6 ml/min) related to a reduced stroke volume of the flow pulses (7.8 +/- 3.31 vs. 14.1 +/- 2.44 ml). The amplitude and frequency of gastric and duodenal pressure events were unchanged or slightly reduced during vagal cooling. The smaller stroke volume of flow pulse was the consequence of increased pyloric resistance (6.2 +/- 1.98 vs. 2.3 +/- 0.21 mmHg.ml-1.s), which is associated with changes in the temporal relationship between a pyloric pressure event and flow pulse. In conclusion, erythromycin activity on the pylorus requires the integrity of vagal pathways. Enhancement of gastric outflow by erythromycin is also modulated by the vagus, since pyloric resistance was able to overcome increased gastric motility.

5-HT receptor types in the rat ileum longitudinal muscle: focus on 5-HT2 receptors mediating contraction

The 5-hydroxytryptamine (5-HT) receptor(s) that mediate(s) contraction of the rat ileum longitudinal muscle was studied. 5-HT and alpha-methyl-5-HT equipotently induced contractions, whereas 5-methoxytryptamine and 2-methyl-5-HT (partial agonist) were less potent; this rank order of potency suggests involvement of a 5-HT2 receptor. Neither tetrodotoxin nor atropine affected the contraction to 5-HT, suggesting a smooth muscle localization of these 5-HT2 receptors. The presence of either a selective 5-HT2B (SB 204741), 5-HT3 (granisetron) or 5-HT4 (SB 204070) antagonist, slightly affected the contractions to 5-HT. Thus, they were also included in the organ bath solution in all subsequent experiments in order to pharmacologically isolate the main contractile component. Using (if possible) 5-HT2A receptor-selective concentrations, ketanserin, ritanserin, metergoline, spiperone, mianserin, methiothepin, mesulergine, methysergide and cisapride all inhibited the contractions to 5-HT, causing a depression of the curve to 5-HT (i.e. surmountable antagonism was not observed with any of the above agents). Comparison of the affinities of these compounds for the various 5-HT2 receptor subtypes revealed that the receptor involved in the contractions to 5-HT most closely resembles the 5-HT2A receptor. However, cinanserin at a concentration expected to inhibit 5-HT2A receptor-mediated effects, failed to affect the contractions to 5-HT. It is thus concluded that on the longitudinal smooth muscle of the rat ileum, at least a part of the contraction to 5-HT is mediated by 5-HT receptors resembling the 5-HT2A receptor subtype.

Measurement of gastric emptying by intragastric gamma scintigraphy

Gastric emptying is usually measured in animals and humans by dilution/sampling or external scintigraphy. These methods are either time consuming or require expensive equipment. The capacity of a miniature gamma counter positioned in the stomach to measure emptying of liquid and solid meals was evaluated. In eight conscious pigs fitted with gastric and duodenal cannulae, gastric emptying of saline (500 mL), dextrose (20%, 500 mL), porridge (300 g) and scrambled eggs (300 g), all labelled with 3.5 MBq 99mTC, was evaluated. When positioned in the antrum the probe was unable to quantify gastric emptying. In contrast, measurements of the fractional emptying of saline over 4-min periods by the probe positioned in the corpus and quantification of radioactivity in the duodenal effluent correlated closely (r = 0.88, P < 0.05). Gastric emptying (50% emptying time) of saline and both solid meals measured by the probe was not significantly different from quantification of the duodenal effluent volume. No difference was observed also for the dextrose meal but only while gastric acid secretion was suppressed by omeprazole. We conclude that an intragastric gamma counter permits measurement of gastric emptying of homogeneous meals provided meal stimulation of gastric secretion was not extensive. This was possible probably by monitoring emptying from the proximal stomach.

Influence of jejunal nutrients on transpyloric flow and pyloric resistance in pigs

The effects of small intestinal infusion of nutrients on the transpyloric flow and pyloric resistance were evaluated in anaesthetized pigs. Saline versus isocaloric solutions of dextrose, triglycerides and casein were infused into a jejunal loop during saline gastric loading. Antropyloroduodenal pressures were measured with a sleeve/side-hole manometric assembly and the transpyloric flow with an electromagnetic flowmeter probe. Fundic pressure was maintained constant. Although the overall gastric emptying rate was not affected by nutrients, the stroke volume of the transpyloric flow pulses was significantly increased as a consequence of larger peak flow (dextrose) or longer duration of flow pulses (triglycerides and casein). Pyloric resistance was reduced by all nutrients owing to a change in the temporal relationship between the onset of pyloric pressure events and flow pulses so that flow pulses occurred after pyloric pressure events. In conclusion, under controlled fundic pressure, nutrient infusions decrease pyloric resistance.

Mapping quantitative trait loci for open-field behavior in mice

By performing a whole genome screen in an F2 intercross of two strains of mice (A/J and C57BL/6J), which differ markedly in their behavioral response to a brightly lit open field (O-F), we have mapped several quantitative trait loci (QTL) for this complex behavioral phenotype. QTL on chromosomes 1 and 10 were identified that affect both initial ambulation in the O-F (initial "response to novelty" ambulation) (lod of 7.1 and 8.8, respectively) and vertical rearings (lod of 4.5 and 8.5, respectively). For habituated O-F behavior, QTL were identified on chromosomes 3 and 10 for ambulation (lod of 4.1 and 14.7, respectively) and on chromosomes 1, 10, and 19 for vertical rearings (lod of 5.8, 6.0, and 4.7, respectively). The QTL on chromosome 1 (near D1Mit116; 101 cM) was specific for initial O-F ambulation behavior, whereas the QTL on chromosome 10 (near D10Mit237; 74 cM) affected both initial and habituated rearing behavior. Additional suggestive QTL (lod, > 2.8) were mapped to chromosomes 1, 8, 11, 15, and 19. The QTL on chromosomes 1, 10, and 19 individually explain from 3.2 to 12.7%. Collectively, the multiple independent QTL explain from 16.3 to 24.1% of the F2 population's phenotypic variance, depending on the trait. These identified QTL should prove useful for dissecting the genetic and behavioral dimensions of O-F behavior, fostering an understanding of individual differences.

Scopolamine-induced deficits in a two-trial object recognition task in mice

The purpose of the present study was to design an object recognition task in mice and characterize the effects of scopolamine in this paradigm. This task consisted of exposing mice for 6 or 10 min to an object in an open field (trial 1) and, after a delay (1-24 h), testing mice for 10 min with the object and a novel object (trial 2). Mice explored the novel object more than the familiar object as the inter-trial delay decreased and/or the duration of trial 1 increased. Administration of scopolamine (0.3, 1 and 3 mg kg-1, s.c.) before trial 1 reduced recognition performance on trial 2 after a 3 h inter-trial delay and induced other behavioural effects, including an increase in locomotor activity on trial 1. Methylscopolamine (1 mg kg-1) had no effect on recognition performance. The present results show that this task is a useful model to test recognition memory in mice and that blocking the central cholinergic system impairs this form of memory.

Assessment of the efficacy of sacroiliac corticosteroid injections in spondylarthropathies: a double-blind study

Despite previously carrying out a first open study of sacroiliac injection of long-acting corticosteroid, it was not possible to evaluate the role of a placebo effect. We therefore performed a double-blind study in 10 patients/13 articulations, suffering painful sacroiliitis. At 1 month, 5/6 sacroiliac joints injected with corticosteroid described a relief of > 70%, in comparison to 0/7 of the placebo group (P < 0.05). Dolometry showed a marked decrease in the corticosteroid group from (mean +/- S.E.M.) 6.8 +/- 0.6 to 1.3 +/- 0.3, and decreases were mild in the placebo group: 7.0 +/- 0.6 to 5.2 +/- 0.5 (P < 0.005). Six of the seven sacroiliac joints of the placebo group and two patients with failure and relapse of the corticosteroid group were reinjected with corticosteroid. At 1 month, 12/14 (85.7%) were assessed as having a good result. Results were still significant at 3 months (62%) and 6 months (58%). Tolerance was good or very good in 86% of the cases, and we did not report any notable complication. This technique is safe and very efficient, and it has to be considered more widely in patients with contraindications or complications with NSAID, or if the medical treatment is unable to control sufficiently the active sacroiliitis.

The neurosteroid pregnenolone sulfate reduces learning deficits induced by scopolamine and has promnestic effects in mice performing an appetitive learning task

The effects of the neurosteroid pregnenolone sulfate (PS) on learning as well as on scopolamine-induced learning deficits were studied in Swiss mice using an appetitively reinforced Go-No Go visual discrimination task. Subcutaneous (SC) administration of scopolamine (0.3-3 mg/kg) after the first session of training dose-dependently impairs learning during the following sessions in this task. Moreover, intracerebroventricular (ICV) administration of PS (0.01-10 nmol) dose-dependently blocks learning deficits induced by scopolamine (3 mg/kg), with the most potent effects at the dose of 0.5 nmol PS. In addition to antagonizing the amnestic effects of scopolamine, PS (0.5 nmol ICV) has a memory-enhancing effect, when administered alone after the first training session. Scopolamine (3 mg/kg SC) also produced substantial deficits on retrieval performance in the Go-No Go visual discrimination task, and caused motor disturbances, when administered 15 min before testing. PS (0.5 nmol ICV) also reduced scopolamine-induced deficits on retrieval but had no effect on scopolamine-induced motor impairments in the traction reflex test. Such a rapid effect of PS on memory processes may be mediated via NMDA and/or GABAA receptors.

The neurosteroid pregnenolone sulfate blocks deficits induced by a competitive NMDA antagonist in active avoidance and lever-press learning tasks in mice

The neurosteroid pregnenolone sulfate (PREG-S) has been shown to modulate positively NMDA receptor activity and to have memory enhancing properties in mice. The present study was designed to evaluate the effects of post-training administration of PREG-S, alone or in combination with D-2-amino-5-phosphonovalerate (D-AP5), a competitive NMDA receptor antagonist, in Y-maze avoidance and appetitively motivated lever-press learning tasks and in a traction reflex test in mice. Intracerebroventricular (i.c.v.) administration of PREG-S (0.01-0.1 nmol/mouse) blocked the selective retention deficits induced by 0.02 nmol D-AP5 in the Y-maze avoidance task. PREG-S (0.1 nmol, i.c.v.) also blocked the retention deficits induced by 0.02 nmol D-AP5 in the lever-press task. Post-training administration of PREG-S alone (0.001-0.1 nmol, i.c.v.) had no effect on retention performance in the Y-maze and the lever-press tasks. PREG-S (1-10 nmol, i.c.v.) significantly reduced the impairment of the traction reflex induced by 2 nmol D-AP5. The ability of PREG-S to block retention performance deficits as well as motor impairment induced by D-AP5 is in agreement with its positive modulatory action at NMDA receptors.

Genetic analysis of anxiety-related behaviors and responses to benzodiazepine-related drugs in AXB and BXA recombinant inbred mouse strains

Recombinant inbred (RI) strains derived from the C57BL/6J and A/J mouse strains were used for behavioral studies designed to estimate the number and location of chromosomal loci responsible for anxiety-related behaviors and differential sensitivity to agonists and inverse agonists of the gamma-aminobutyric acidA (GABAA)/benzodiazepine receptor complex. The phenotypes of the parental inbred strains and of 28 RI strains were characterized for the number of transitions in the light<-->dark exploratory model, anxiolytic response to diazepam, vertical and ambulatory activities in an open field, and sensitivity to the convulsant properties of methyl-beta-carboline-3-carboxylate (beta-CCM). The strain distribution patterns and estimates of the minimal number of loci obtained for each trait suggest that multiple chromosomal loci contribute to differences in anxiety-related behavioral phenotypes and the behavioral responses to diazepam and beta-CCM between C57BL/6J and A/J mice. The best probabilities of linkage were found between the variables characterizing response to diazepam and loci on chromosomes 1 (Xmv-41) and 10 (D10Mit2) and between the sensitivity to the convulsant actions of beta-CCM and locus D15Mit5 on chromosome 15.

Vagal control of pyloric resistance

Pyloric resistance is probably a major factor regulating gastric emptying of liquids, but its nervous control is unknown. The role of efferent vagal pathways in pyloric resistance was evaluated in 13 anesthetized pigs. Pyloric resistance was assessed by simultaneous recording of gastropyloroduodenal motility and transpyloric flow during gastric emptying of saline. Cervical vagotomy suppressed all antral pressure events, increased the number of pressure events localized at the pylorus, and decreased the frequency of the flow pulses (P < 0.05), without affecting either pyloric resistance or the characteristics of flow pulses. Electrical stimulation of the cervical and the thoracic vagi both decreased pyloric resistance by about 60% and increased the stroke volume of flow pulses (P < 0.05). The reduced pyloric resistance was mainly related to an alteration of the temporal relationship between flow pulses and pyloric pressure events. These results indicate that vagal efferents could provide inhibitory inputs to pyloric resistance. A reduction in pyloric resistance contributes to the increased flow rate observed during vagal stimulation.