A.H.J. Herremans

Effects of infusion of cholinergic drugs into the prefrontal cortex area on delayed matching to position performance in the rat

Rats trained on a Delayed Matching To Position (DMTP) task displayed mediating behavior during delays to solve the task. Infusion of the cholinergic antagonist scopolamine into the medial Prefrontal Cortex area (mPFC), dose dependently impaired performance independent of delay. These results indicate that scopolamine does not specifically affect working memory. Infusion of the cholinesterase inhibitor physostigmine, muscarinic subtype receptor antagonists, the dopamine (D1) antagonist SCH23390, and of the GABA-A receptor antagonist bicuculline, did not affect performance in the DMTP task. In a post-hoc analysis scopolamine was found to impair discriminability in a delay-dependent manner only in animals that used mediating behavior in the majority of the trials. Furthermore, a time sampling method indicated that scopolamine infusions into the mPFC disrupted mediating behavior during the task. Results suggest that cholinergic systems in the mPFC play a role in directing attention to task relevant behavior.

Behavioural changes after different stress paradigms: prepulse inhibition increased after physical, but not emotional stress

Physical (PS) and emotional (ES) stress have opposite long-term effects on open field behaviour, i.e., response to novelty. PS induced a long-term reduction in locomotor activity, while ES increased it. Additionally, sensitivity to rewarding stimuli was differentially affected by PS and ES. Whether the stress effects were specific for locomotor activity and reward or if these two stress treatments also have differential effects on other behaviours and brain functions is not known. In the present study, temperature regulation, sensory gating, learning capacity, locomotor activity and coping style were examined. PS consisted of a repeated mild foot shock treatment, which the ES animals witnessed. The tests pose additional challenges, to which all groups can respond differently depending on their previous experience. All tests were performed several days after the last stress treatment. Stress effects were specifically observed on locomotor activity, startle response and prepulse inhibition (PPI). The PS animals showed a potentiated inhibition of the startle when a prepulse (PPI) was used, although the initial startle response was already significantly lower than that of controls. ES animals did not differ from controls on PPI and startle. Additionally PS animals showed an initial decrease in activity, which turned into an increase when the tests continued. ES showed a constant increase in activity compared to controls. Stress effects on the tests for other brain processes and behaviour were not found. In addition, PS animals appeared to be less sensitive to the dopamine agonist apomorphine than control animal. In summary, physical and emotional stress induce differential changes on locomotor activity, startle response and PPI. Underlying mechanisms explaining the differences in stress effects are discussed, i.e., the role of the mesolimbic dopamine system and opioid systems.

SLV313 (1-(2,3-dihydro-benzo[1,4]dioxin-5-yl)-4- [5-(4-fluoro-phenyl)-pyridin-3-ylmethyl]-piperazine monohydrochloride): a novel dopamine D2 receptor antagonist and 5-HT1A receptor agonist potential antipsychotic drug.

Combined dopamine D2 receptor antagonism and serotonin (5-HT)1A receptor agonism may improve efficacy and alleviate some side effects associated with classical antipsychotics. The present study describes the in vitro and in vivo characterization of 1-(2,3-dihydro-benzo[1,4]dioxin-5-yl)-4-[5-(4-fluoro-phenyl)-pyridin-3-ylmethyl]-piperazine monohydrochloride (SLV313), a D2/3 antagonist and 5-HT1A agonist. SLV313 possessed high affinity at human recombinant D2, D3, D4, 5-HT2B, and 5-HT1A receptors, moderate affinity at 5-HT7 and weak affinity at 5-HT2A receptors, with little-no affinity at 5-HT4, 5-HT6, α1, and α2 (rat), H1 (guinea pig), M1, M4, 5-HT3 receptors, and the 5-HT transporter. SLV313 had full agonist activity at cloned h5-HT1A receptors (pEC50=9.0) and full antagonist activity at hD2 (pA2=9.3) and hD3 (pA2=8.9) receptors. In vivo, SLV313 antagonized apomorphine-induced climbing and induced 5-HT1A syndrome behaviors and hypothermia, the latter behaviors being antagonized by the 5-HT1A antagonist WAY100635. In a drug discrimination procedure SLV313 induced full generalization to the training drug flesinoxan and was also antagonized by WAY100635. In the nucleus accumbens SLV313 reduced extracellular 5-HT and increased dopamine levels in the same dose range. Acetylcholine and dopamine were elevated in the hippocampus and mPFCx, the latter antagonized by WAY100635, suggesting possible 5-HT1A-dependent efficacy for the treatment of cognitive and attentional processes. SLV313 did not possess cataleptogenic potential (up to 60 mg/kg p.o.). The number of spontaneously active dopamine cells in the ventral tegmental area was reduced by SLV313 and clozapine, while no such changes were seen in the substantia nigra zona compacta following chronic administration. These results suggest that SLV313 is a full 5-HT1A receptor agonist and full D2/3 receptor antagonist possessing characteristics of an atypical antipsychotic, representing a potential novel treatment for schizophrenia.

The putative 5-HT1A receptor antagonist DU125530 blocks the discriminative stimulus of the 5-HT1A receptor agonist flesinoxan in pigeons

Twelve homing pigeons were trained to discriminate the 5-HT1A receptor agonist flesinoxan (0.25 mg/kg p.o.) from its vehicle in a fixed ratio (FR) 30 two-key operant drug discrimination procedure. Tests for generalization and antagonism showed that compounds with agonistic action at the 5-HT1A receptor, such as 8-OH-DPAT (8-hydroxy-2-(di-n-propylamino)tetralin), buspirone and ipsapirone all substituted for the flesinoxan cue. Compounds with mixed agonistic action at the 5-HT(1A/1B) receptor fully (eltoprazine) or partially (RU24969 (5-methoxy-3-(1,2,3,6-tetrahydropyridin-4-yl-1H-indole)) substituted for flesinoxan. TFMPP (1-(3-trifluoromethylphenyl)piperazine) and mCPP (1-(3-chlorophenyl)piperazine), both acting at the 5-HT(1B/2C) receptor, did not substitute for flesinoxan, neither did the selective 5-HT re-uptake inhibitor fluvoxamine. The results of the antagonism tests showed that the 5-HT1A receptor antagonists NAN-190 (1-(2-methoxyphenyl)-4-[4-(2-phthalimido)butyl]piperazine), WAY 100635 ((N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl)cyclo-he xane-carboxamide) and the newly developed DU125530 (2-[4-[4-(7-chloro-2,3-dihydro-1,4-benzodioxin-5-yl)-1-piperazinyl ]butyl]-1,2-benzisothiazol-3(2H)-one-1,1-dioxide) fully (more than 80%) blocked the flesinoxan cue without having substantial effects when given alone. WAY100135 (N-tert-butyl-3-(4-(2-methoxyphenyl)piperazine-1-yl)-2-phenylpropanamide ), (+/-)-pindolol and (S)-UH-301 ((S)-5-fluoro-8-hydroxy-2-(dipropylamino)-tetralin) all partially antagonized the flesinoxan cue. However, both WAY100135 as well as (+/-)-pindolol also partially substituted for flesinoxan in generalization tests. NAN190, (S)-UH-301, WAY100635 and DU125530 were without any activity in the generalization test at the doses tested. The putative 5-HT1A receptor antagonist S15535 (4-benzodioxan-5-yl) 1-(indan-2-yl)piperazine) was identified as a full agonist in the present procedure. Taken together these results suggest that the flesinoxan cue in pigeons is mediated by the 5-HT1A receptor and that DU125530 acts as a full antagonist on the 5-HT1A receptor.

SLV330, a cannabinoid CB(1) receptor antagonist, attenuates ethanol and nicotine seeking and improves inhibitory response control in rats.

Cannabinoid CB(1) receptor (CB(1)R) signaling has been shown to play a role in the regulation of addictive behavior. In the present study, our aim was to investigate whether the CB(1)R antagonist SLV330 could reduce ethanol and nicotine self-administration and cue-induced reinstatement of ethanol and nicotine seeking behavior in Wistar rats. In operant chambers, rats were learned to emit a specific response (nose poke) in order to receive an ethanol solution or intravenous injections of nicotine. Discrete light and tone cues were presented during ethanol and nicotine delivery. These cues are particularly important for drug self-administration behavior and, through Pavlovian conditioning, acquire conditioned reinforcing and motivational properties and are therefore able to generate and maintain drug-seeking behavior. Subsequently, the CB(1)R antagonist SLV330 (doses ranging from 1 to 10mg/kg, given orally, p.o.) was administered to investigate the effects on drug self-administration. In addition, responding for ethanol and nicotine was extinguished. Then, the animals were tested for cue-induced reinstatement of ethanol and nicotine seeking and treated with vehicle or SLV330. Finally, the effects of SLV330 were studied on the number of anticipatory responses in the 5-choice serial reaction time task (5-CSRTT) in order to determine whether this compound could also increase impulse control in Wistar rats. The CB(1) antagonist SLV330 was effective in reducing ethanol self-administration at a lowest effective dose (LED) of 10mg/kg (p.o.) and reinstatement of ethanol seeking at a LED of 3mg/kg (p.o.). SLV330 was also effective in reducing nicotine self-administration and reinstatement of nicotine seeking, although at a LED of 10mg/kg (p.o.). Finally, SLV330 decreased time delay-dependent anticipatory responding (LED of 3.0mg/kg, p.o.), indicating an increased inhibitory control. These findings are in agreement with results reported with other CB(1) antagonists. The combined action of reducing the reinforcing and motivational properties of nicotine and alcohol and the improvement of impulse control supports the idea that the cannabinoid system is a promising target for anti-relapse medication.

The object delayed non-matching to sample task in rats does not depend on working memory

Four rats were trained on an object delayed non-matching to sample task to measure working memory (WM). On separate trials a sample object was presented to the rat, which was presented again along with another object after a 3 s delay rats were rewarded with food if they chose the novel object. In this procedure the choice objects are positioned in a fixed order (the novel object was positioned at first, followed by the sample object). When the order of placement of the choice objects was reversed performance dropped from 87% to 28% correct, showing that the rats always chose the object that was first positioned into the choice area. When the order of positioning of the choice objects was randomized during training, rats were not able to learn the task. It is suggested that performance is based on a discrimination between choice objects instead of WM.

The delayed-conditional-discrimination task improves measurement of working memory in rats

The validity of delayed-matching-to-sample (DMTS) and related tasks executed in skinner boxes as an animal model for human working memory (WM) is confounded by the occurrence of mediating behaviour during delays. True matching, a supplementary task during delays and response similarity are ways to deal with this problem. However, until now rats have not been able to learn a true matching task in Skinner boxes and introduction of a supplementary task during delays does not sufficiently prevent mediating behaviour. Response similarity, on the other hand, effectively prevents the use of mediating behaviour by reducing the discriminative value of the behaviour during delays. Furthermore, it is argued that the interpretation of drug effects is confounded by baseline performance and mediating behaviour. It is shown that high baseline levels and high amounts of mediating behaviour can induce delay dependent drug effects, suggesting a specific effect on WM. We therefore assert that examination of delay-dependency of a drug effect alone is not sufficient to claim specific effects of a drug on WM. The delayed-conditional-discrimination (DCD) task uses response similarity to effectively reduce mediating behavior and does not generate high levels of baseline performance. The DCD task is therefore preferred over other tasks for the measurement of WM in rats using Skinner boxes.

Effects of cholinergic drug infusions into the dorsal part of the medial prefrontal cortex on delayed conditional discrimination performance in the rat.

Effects of bilateral infusions of cholinergic drugs into the dorsal part of the medial prefrontal cortex (dmPFC) on performance in a delayed conditional discrimination (DCD) task were examined in rats. Scopolamine dose-dependently impaired performance. No delay-dependent effect was found indicating that scopolamine did not specifically affect working memory (WM). Physostigmine alone induced a slight improvement of DCD performance independent of delay and co-administration of physostigmine with scopolamine attenuated the scopolamine-induced impairment of DCD performance. Infusion of the muscarinic M2 antagonist AQRA-471, the M3 antagonist 4-DAMP and the mixed M1-M3 antagonist UH-AH 37 did not affect performance in the DCD task, suggesting that the effect of scopolamine is not mediated by a single muscarinic receptor subtype. The results furthermore indicate that the cholinergic system in the dmPFC does not play a specific role in WM processes in the DCD task. Furthermore, the results suggest that the dmPFC cholinergic system plays a role in the attentional processes involved in the DCD task.

Stimulus properties of the selective 5-HT reuptake inhibitor fluvoxamine in conditioned taste aversion procedures.

Previous attempts to train pigeons and rats to discriminate between the antidepressant fluvoxamine and its vehicle as assessed in a drug discrimination paradigm have been without success. The present experiments were, therefore, designed to assess in a conditioned taste aversion procedure (CTA) whether or not fluvoxamine possesses stimulus properties. Rats were exposed to a conditioned taste aversion (CTA) procedure. In Experiment I, subjects were given 15 mg/kg fluvoxamine p.o. or vehicle after drinking a novel tasting saccharin solution. In Experiment II, a comparison was made between the effects of 15 mg/kg fluvoxamine i.p., 30 mg/kg fluvoxamine i.p., NaCl, and lithium chloride (LiCl). In Experiment III, subjects were treated with either 10 mg/kg fluoxetine i.p., 30 mg/kg fluvoxamine i.p., or LiCl. CTA was observed after treatment with LiCl, but never after treatment with fluvoxamine or fluoxetine, suggesting that fluvoxamine does not have clear stimulus properties, which can serve as a discriminative stimulus in operant procedures. In a crossfamiliarization CTA procedure in mice, however, fluvoxamine elicited a reliable CTA, suggesting that under certain conditions (species, dose?) selective serotonin reuptake inhibitors (SSRIs) may lead to certain discriminable effects. It is as yet unclear why SSRIs apparently produce such weak and species or situation-dependent discriminable effects.

The 5-HT1A receptor agonist flesinoxan shares discriminative stimulus properties with some 5-HT2 receptor antagonists.

Ten homing pigeons were trained to discriminate the selective 5-HT1A receptor agonist flesinoxan (0.25 mg/kg p.o.) from its vehicle in a fixed-ratio (FR) 30 two-key operant drug discrimination procedure. The 5-HT2 receptor antagonist mianserin (ED50 = 4.8 mg/kg) fully substituted for flesinoxan, whereas ketanserin, ritanserin, mesulergine, and SB200646A substituted only partially, suggesting an interaction between 5-HT1A and 5-HT2 receptors. However, the 5-HT2 receptor agonists [DOI (0.6 mg/kg), TFMPP (10 mg/kg), mCPP (4 mg/kg)] were unable to antagonize the flesinoxan cue. The 5-HT1A receptor antagonists DU125530 (0.5-13 mg/kg) and WAY100,635 (0.1-1 mg/kg) partially antagonized the generalization of mianserin to flesinoxan. Taken together, these results are in accordance with the hypothesis that 5-HT1A receptor activation exerts an inhibitory effect on activation of 5-HT2 receptors. These results are in broad agreement with existing theories on 5-HT1A and 5-HT2 receptor interaction. Furthermore, it is argued that the discriminative stimulus properties of a drug may undergo qualitative changes with prolonged training.