Cognitive dysfunction is a core characteristic of schizophrenia, which can often persist when other symptoms, particularly positive symptoms, may be improved with drug treatment. The non-competitive NMDA receptor antagonist, phencyclidine (PCP), is a psychomotor stimulant drug that has been shown to induce symptoms characteristic of schizophrenia in humans and animals. The aim of these studies was to use the sub-chronic PCP model in rats to investigate cognitive dysfunction in behavioural tests which have been highlighted as relevance by the MATRICS initiative (MATRICS.ucla.edu). The main tests used were attentional set-shifting, operant reversal learning, and novel object recognition tasks. The pharmacology of antipsychotics was studied in the reversal learning task using receptor selective compounds. Following this, experiments were carried out using in vitro electrophysiology and in vivo microdialysis in an attempt to investigate the mechanisms underpinning the PCP-induced cognitive deficits. The attentional set-shifting task is a test of executive function, the extra-dimensional shift (EDS) phase relates to the ability to shift attention to a different stimulus dimension; this is impaired in patients with schizophrenia. The studies presented in chapter 2 showed that sub-chronic PCP administration impaired attentional set-shifting performance selectively in the EDS phase, a deficit which was significantly attenuated by sub-chronic administration of clozapine and risperidone, but not haloperidol. The effect of PCP was also shown to be more robust in female rats compared to males. A deficit in set-shifting ability was also observed in isolation reared rats. However, the deficits produced by PCP were more robust than the deficit produced by isolation rearing. The reversal learning task is another test of executive function. Chapter 3 reported that sub-chronic PCP administration impairs reversal learning ability in an operant task, as demonstrated by reduced percent correct responding in the reversal phase of the reversal learning task. It was found that a D1 agonist (SKF-38398), a 5-HT1A partial agonist (buspirone), a 5-HT2C antagonist (SB-243213A) and an agonist and positive allosteric modulator of the alpha 7 nACh receptor (PNU-282987 and PheTQS respectively) are able to reverse the sub-chronic PCP-induced deficit in reversal learning. Although many antipsychotics have affinity for muscarinic M1 and histamine H1 receptors, selective agents at these receptors were not able to improve the PCP-induced deficit. In chapter 4, the atypical antipsychotics, clozapine and risperidone, when given alone to naïve rats had no effect on reversal learning. Haloperidol when given to naïve rats impaired performance at the highest dose. Sub-chronic PCP was again found to impair reversal learning performance. Investigative experiments revealed that the 2 min time-out could be important as a cue. Following a double reversal, olanzapine-treated rats lost the ability to switch between the rules, whereas clozapine and risperidone-treated rats could perform the double reversal. Experiments with the extended (15 min) reversal phase could allow the investigation of the time-course effects of antipsychotics or selective compounds. The studies presented in chapter 5 found a reduction in gamma oscillations in the CA3 region of the hippocampus, following sub-chronic PCP treatment (2-5 weeks post treatment) that was paralleled by a deficit in parvalbumin immunoreactive (IR) cell density, at a similar time point (2 weeks post treatment). In contrast, a time-dependent increase in gamma oscillations was observed (6-8 weeks post treatment), at which point parvalbumin IR cell density was unchanged (8 weeks post treatment). Gamma oscillations were unchanged in the prefrontal cortex (PFC) following the PCP treatment regime. Locomotor activity tests were also carried out to ensure that the sub-chronic PCP treatment was successful. In-vivo microdialysis revealed that vehicle-treated rats show an increase in dopamine in the PFC which is selective for the retention trial of the novel object recognition task. PCP-treated rats were unable to distinguish between the novel and familiar objects and the increase in dopamine observed in vehicle rats was absent. As a control experiment it was also shown that sub-chronic PCP did not induce anxiety-like symptoms in the elevated plus maze and open field tests. These studies suggest that sub-chronic PCP induces cognitive deficits in behavioural tasks, and these deficits may be due to GABAergic mediated processes in the hippocampus and dopaminergic dysfunction in the PFC. These behavioural and neurochemical results are concurrent to findings observed in schizophrenia.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

In the absence of ligand, certain growth factor receptors can be activated via G protein-coupled receptor (GPCR) activation in a process termed transactivation. Serotonin (5-HT) receptors can transactivate the receptor tyrosine kinase (RTK) platelet-derived growth factor (PDGF) ?? receptors in smooth muscle cells, but it is not known if similar pathways occur in neuronal cells. Here, it is shown that 5-HT can transiently increase the phosphorylation of PDGF?? receptors in a time- and concentration-dependent manner in SH-SY5Y neuroblastoma cells. This transactivation pathway was pertussis-toxin sensitive, and was dependent on phospholipase C activity, intracellular calcium signaling and subsequent protein kinase C activation. Exogenous application of non-lethal concentrations of H2O2 induced the phosphorylation of PDGF?? receptors in a concentration-dependent fashion, similar to that observed with 5-HT. Further investigation revealed reactive oxygen species (ROS) production as a necessary component in the transactivation pathway, as scavenging ROS eliminated PDGF?? receptor phosphorylation. NADPH oxidase was determined to be the likely source of ROS given that the NADPH oxidase inhibitors diphenyleneiodonium chloride and apocynin abrogated PDGF?? receptor transactivation. The role of Src tyrosine kinase was also investigated, and its location in this signaling cascade was determined to be downstream of calcium signaling, but upstream of NADPH oxidase activity. In addition, the activation of ERK1/2 in this system was elucidated to be independent of PDGF?? receptor transactivation. Interestingly, 5-HT also transactivated TrkB receptors, another RTK whose function is implicated in clinical depression. Expectedly, the enzymes in this mechanism were consistent with those revealed in 5-HT-to-PDGF?? receptor signaling. This cross-talk between 5-HT and RTKs such as TrkB and PDGF?? receptors identifies a potentially important signaling link between the serotonergic system and neurotrophic factor signaling in neurons that could have implications in mental health disorders including depression. Furthermore, although transactivation pathways are commonly initiated by a GPCR, recent reports have demonstrated that selective serotonin reuptake inhibitors (SSRIs) were able to block 5-HT-induced transactivation of PDGF?? receptors, suggesting that in addition to GPCRs, monoamine transporters may also be involved in RTK transactivation. SH-SY5Y cells pretreated with the SSRI fluoxetine blocked 5-HT-induced transactivation of the PDGF?? receptors, but not PDGF-induced PDGF?? receptor activation. Upon further examination, it was discovered that during the pretreatment period, fluoxetine itself was transiently transactivating the PDGF?? receptor via 5-HT2 receptors. By the end of the pretreatment period, the effects of fluoxetine on PDGF?? receptor phosphorylation had returned to baseline, and a subsequent transactivating stimulus (5-HT) failed to ???re-transactivate??? the PDGF?? receptor. Additional investigations demonstrated that 5-HT pretreatment can block dopamine-induced PDGF?? receptor transactivation, but not PDGF-induced PDGF?? receptor activation. This is the first demonstration of the heterologous desensitization of an RTK via a transactivation pathway, and this phenomenon is specific for transactivation pathways because in all cases the PDGF?? receptor ligand PDGF-BB was able to directly stimulate receptor activity in spite of GPCR agonist pretreatment. Heterologous desensitization in transactivation signaling reveals a previously unknown short-term ???blackout??? period wherein no further transactivation signaling can occur to potentially exploit the mitogenic effects of RTK activation.

In zebrafish, the ventilatory response to hypoxia first develops at 3 days post-fertilization (d.p.f.) before O2-chemoreceptive neuroepithelial cells (NECs) of the gill appear at 7 d.p.f. This indicates the presence of extrabranchial chemoreceptors in embryos and a developmental transition to primarily gill O2 sensing. This thesis examined the skin NECs, which reach peak density in embryos but decline as gill NECs appear. Exposure of embryos and larvae to chronic hypoxia prevented the loss of skin NECs, shifted peak basal ventilation to a later developmental stage, and induced a hypoventilatory response to acute hypoxia. Chronic exposure to hyperoxia rapidly diminished skin NECs, shifted peak ventilation to earlier stages and eliminated the response to acute hypoxia. Administration of the neurotoxin 6-hydroxydopamine degraded nerve terminals that contact skin NECs and reduced both basal ventilation frequency and the hypoxic ventilatory response. Thus, skin NECs are candidates for extrabranchial O2 chemoreceptors in developing zebrafish.

In zebrafish, the ventilatory response to hypoxia first develops at 3 days post-fertilization (d.p.f.) before O2-chemoreceptive neuroepithelial cells (NECs) of the gill appear at 7 d.p.f. This indicates the presence of extrabranchial chemoreceptors in embryos and a developmental transition to primarily gill O2 sensing. This thesis examined the skin NECs, which reach peak density in embryos but decline as gill NECs appear. Exposure of embryos and larvae to chronic hypoxia prevented the loss of skin NECs, shifted peak basal ventilation to a later developmental stage, and induced a hypoventilatory response to acute hypoxia. Chronic exposure to hyperoxia rapidly diminished skin NECs, shifted peak ventilation to earlier stages and eliminated the response to acute hypoxia. Administration of the neurotoxin 6-hydroxydopamine degraded nerve terminals that contact skin NECs and reduced both basal ventilation frequency and the hypoxic ventilatory response. Thus, skin NECs are candidates for extrabranchial O2 chemoreceptors in developing zebrafish.

Interindividual differences in animal behaviour that are relatively consistent over time and context are referred to as animal personality. Personality has been recognized throughout the entire animal kingdom, in an array of species like molluscs, arthropods, fish, birds and mammals. The personality of non-human animals has been suggested to vary along five different axes, or continua; boldness-shyness, avoidanceexploration, activity, sociability and aggressiveness. Having a relatively fixed personality may seem nonadaptive compared to infinite behavioural plasticity so the individual would be able to respond adaptively to any changes in the environment. There can be physiological limitations to the phenotypic expressions of any trait, including behaviour. Variation in neuroendocrinology may thus explain why animals have personality. A candidate neurochemical that potentially proximately influences and forms personality, is serotonin (5- HT), one of the most omnipotent neurotransmitter of the animal body. In the many realms of the serotonergic system, there may arise individual differences which forms a proximate basis for differences in personality. In this review paper, I discuss the impact of the serotonergic system on a few different personality traits. Depending on the individual’s motivational state, serotonin can dampen or enhance aggression. Serotonin correlates negatively to anxious traits. Feeding behaviour is affected by serotonin in seemingly opposing directions. Overall, serotonin seem to underlie many behaviours that describe animal personality.

Recent studies suggest that patients identified by the Rome III criteria for functional constipation (FC) and irritable bowel syndrome with constipation (IBS-C) are not distinct groups. Previous studies have shown that patients with IBS-C exhibit no or limited 5-HT response to meal ingestion, with plasma concentrations remaining similar to those under fasting conditions. The aim of this study was to determine whether patients with FC show a similar 5-HT response to meal ingestion as patients with IBS-C, and to investigate any relationship to gastrointestinal transit and visceral sensitivity. 23 female IBS-C patients, 11 female FC patients and 23 healthy female volunteers (HV) were recruited. Platelet depleted plasma 5-HT concentrations were measured under fasting (2hrs) and fed (4hrs) conditions. Within 2 weeks, oro-caecal (hydrogen breath test) and colonic (radio-opaque markers followed by X-ray) transit, along with rectal sensitivity (barostat) were determined. The main findings of the study are: 1. The FC patients had no 5-HT response to meal ingestion, as previously seen in patients with IBS-C, compared with healthy volunteers. 2. Patients with FC had abdominal and bowel movement associated symptoms as well as delayed colonic transit (whole gut transit), similar to that seen in IBS-C compared with healthy volunteers. 3. The mean pain threshold in patients with FC was similar to that seen in healthy volunteers, with more patients with hyposensitivity or insensitivity in this group compared with IBS-C and no patients with hypersensitivity. 4. Patients with FC had a shift towards higher fasting and postprandial PDP 5-HT levels, unlike patients with IBS-C, compared to healthy volunteers.This study show that based on symptoms, IBS-C and FC patients have more similarities than differences. However, although patients with FC had a similar 5-HT response to a test meal, they had different fasting 5-HT levels and some different physiological findings on assessment of visceral sensitivity with barostat.

Neonatal 6-hydroxydopamine (6-OHDA) treatment of rats is associated with supersensitization of the dopamine D1 agonist induction of oral activity. The present study was conducted to determine whether induced oral responses to serotonin (5-HT) agonists would be similarly altered in this rat model. At 3 days after birth, rats received desipramine HCl (20 mg/kg, IP) 1 h before 6-OHDA HBr (100 μg in each lateral ventricle) or saline-ascorbic acid (0.1%) vehicle. At approximately 9 mo, rats were challenged with the mixed 5-HT1C and 5-HT2 receptor agonist, m-chlorophenylpiperazine diHCl (m-CPP 2HCl; 0.30-6.0 mg/kg, IP) and were then observed for 1 min every 10 min over a 60-min period. m-CPP induced oral activity in both the vehicle and 6-OHDA groups, with the responses of the 6-OHDA group being much greater. An m-CPP dose of 3.0 mg/kg produced a maximal response of 63.6 ± 3.2 oral movements in the 6-OHDA group. A bell-shaped response curve was obtained, with lower and higher doses of m-CPP producing less of an effect. Attenuation of the m-CPP-induced response by the 5-HT receptor antagonist, mianserin HCl (1.0 mg/kg, IP, 30 min before m-CPP), indicates that the m-CPP effect is receptor mediated. These findings demonstrate that neonatal 6-OHDA treatment produces ontogenic long-lived supersensitization of a 5-HT receptor system in rats.

Grooming behavior in rats has so far been known to be induced mainly by dopamine agonists type D1. In order to explore the involvement of serotonine (5-HT) and its receptors in such a behavior, rats were exposed to two phases of treatment: to the serotonin neurotoxin 5,7-dihydroxytryptamine (5,7-DHT), injected intraventricularly three days after birth, and to the serotonin partial agonist m-chlorophenylpiperazine (mCPP), administered in two dose levels, two months later. Grooming behavior was monitored immediately before and after the higher dose of mCPP, while brain levels of 5-HT and its major metabolite 5-HIAA were assayed one week after mCPP administration. It is documented that while a low dose of mCPP in the non-lesioned rats increased the grooming-time by 5.7-fold, the higher mCPP dose in the non-lesioned non-primed rats increased grooming behavior by 3.6-fold. The 5,7-DHT lesions caused a 6.7-fold increase in the non-primed rats, and a 4.2-fold increase in the primed ones. These increases were noticeable only in male rats. When a higher dose of mCPP followed its lower dose in the 5,7-DHT-lesioned rats, a 3.6-fold decrease was recorded only in the female rats. A 88% and 94% drop in 5-HT and 5-HIAA levels in the brain neostriatum of the 5,7-DHT-lesioned rats was noticed in both sexes, one week after mCPP administration. These findings are the first to demonstrate that the 5-HT2 partial agonist mCPP is capable of modifying grooming behavior, and that 5,7,-DHT brain lesions increase basal grooming time, suggesting that 5-HT neurons and receptors are involved in grooming behavior in rats.

The aim of this study was to determine histamine content in the brain and the effect of histamine receptor antagonists on behavior of adult rats lesioned as neonates with the serotonin (5-HT) neurotoxin 5,7-dihydroxytryptamine (5,7-DHT). At 3 days after birth Wistar rats were pretreated with desipramine (20 mg/kg ip) before bilateral icv administration of 5,7-DHT (37.5 μg base on each side) or saline-ascorbic (0.1%) vehicle (control). At 10 week levels of 5-HT and its metabolite 5-hydroxyindole acetic acid (5-HIAA) were determined in frontal cortex, striatum, and hippocampus by an HPLC/ED technique. In the hypothalamus, frontal cortex, hippocampus and medulla oblongata, the level of histamine was analyzed by an immunoenzymatic method. Behavioral observations (locomotion, exploratory-, oral-, and stereotyped activity) were performed, and effects of DA receptor agonists (SKF 38393, apomorphine) and histamine receptor antagonists S(+)chlorpheniramine (H1), cimetidine (H2), and thioperamide (H3) were determined. We confirmed that 5,7-DHT profoundly reduced contents of 5-HT and 5-HIAA in the brain in adulthood. Histamine content was also reduced in all examined brain regions. Moreover, in 5,7-DHT-lesioned rats the locomotor and oral activity responses to thioperamide were altered, and apomorphineinduced stereotype was intensified. From the above, we conclude that an intact central serotoninergic system modulates histamine H3 receptor antagonist effects on the dopaminergic neurons in rats.