Receptor Antagonist WAY-100635 Research Articles

Role of 5-HT 1A receptors in the lower brainstem on the cardiovascular response to dorsomedial hypothalamus activation

The dorsomedial hypothalamus (DMH) is an essential brain region for the integration of the physiological response to psychological stressors. The cardiovascular components of the response include increases in blood pressure, heart rate and the activity of sympathetic nerves to the kidney, skin, brown adipose tissue, and heart. Neurons in the rostral ventrolateral medulla (RVLM) and in the region of the medullary raphe are important components of the descending pathways that mediate the cardiovascular response to the DMH activation. Activation of 5-hydroxytryptamine 1A (5-HT 1A) receptors in the brain leads to a suppression of the cardiac and sympathetic vasomotor components of the DMH-evoked response and of the response to acute psychological stress. In this study we showed that intracisternal injection of a low dose (1 µg/kg) of the 5-HT 1A receptor agonist, 8-hydroxy-2-(di- n-propylamino)tetralin (8-OH-DPAT), significantly reduced the increases in heart rate and renal sympathetic nerve activity evoked by disinhibition of the DMH, but had no effect on these responses when injected intravenously. Subsequent intracisternal administration of the 5-HT 1A receptor antagonist WAY-100635 restored the DMH-evoked cardiovascular responses to levels observed before 8-OH-DPAT administration. Bilateral microinjections of 8-OH-DPAT (200pmol on each side) into the RVLM, however, did not significantly affect the cardiovascular response to disinhibition of the DMH. These observations demonstrate that activation of 5-HT 1A receptors within the lower brainstem, but not in the RVLM, can powerfully suppress the cardiovascular response evoked from the DMH.

Serotonergic and noradrenergic facilitation of the visceromotor reflex evoked by urinary bladder distension in rats with inflamed bladders

Bladder inflammation resulting from intravesical administration of zymosan significantly enhances the visceromotor reflex (VMR) evoked by urinary bladder distension (UBD). The present study examined whether intrathecal (i.t.) administration of receptor antagonists to either norepinephrine (NE) or serotonin (5-HT) altered this enhancement effect. I.t. administration of the non-specific 5-HT receptor antagonist methysergide (30 microg), the 5-HT(3) receptor antagonist ondansetron, or the 5-HT(1A) receptor antagonist WAY 100635 eliminated the enhancement effect produced by intravesical zymosan and also tended to reduce electromyographic (EMG) responses to UBD in non-inflamed rats. I.t. administration of either the non-specific NE receptor antagonist phentolamine (30 microg) or the alpha(1) antagonist WB 4101 also eliminated the enhancement effect, whereas i.t. administration of the alpha(2) antagonist yohimbine failed to significantly affect the enhancement effect. The effects of phentolamine and methysergide were not mediated by changes in bladder compliance. This is the first study to demonstrate that bladder hypersensitivity resulting from bladder inflammation is partly mediated by 5-HT and NE facilitatory effects. Based on these and previous findings we conclude that the net nociceptive response to bladder distension under conditions of bladder inflammation represents a complex interaction of facilitatory influences of spinal 5-HT and NE, and inhibitory influences of spinal opioids.

Interplay between glutamate and serotonin within the dorsal periaqueductal gray modulates anxiety-related behavior of rats exposed to the elevated plus-maze

Several neurotransmitters, including glutamate and serotonin, modulate defensive behaviors related to anxiety in the rat dorsal periaqueductal gray (PAG). Although both glutamate N-methyl- d-aspartic acid (NMDA) and serotonin type 1-A (5-HT 1A) receptors have been shown to interfere with these subtle responses, such as inhibitory avoidance, a possible interaction between them remains to be examined. To address this issue, the present study investigated whether the activation or the blockage of 5-HT 1A receptors located in the dorsal PAG would interact with NMDA function in animals exposed to the elevated plus-maze task. The effect of the NMDA (25 pmol) was evaluated in rats pretreated with the 5-HT 1A receptor antagonist WAY-100135 (2.0 or 5.0 nmol). In addition, the effect of the NMDA (100 pmol) was evaluated in rats pretreated with the 5-HT 1A receptor agonist 8-OH-DPAT (2.0 or 8.0 nmol). Intra-dorsal PAG injection of NMDA (25 pmol) increased inhibitory avoidance behavior. This anxiogenic-like effect of the NMDA was counteracted by the pretreatment with WAY-100135 (5.0 nmol). Although 100 pmol of NMDA failed to increase inhibitory avoidance in the vehicle-pretreated group, in rats pretreated with 8-OH-DPAT this NMDA dose produced an anxiogenic-like effect. These results suggest that 5-HT 1A and NMDA receptors interact in the dorsal PAG to modulate the anxiety-related behavior.

Contractile effects of 5‐hydroxytryptamine (5‐HT) in the equine jejunum circular muscle: Functional and immunohistochemical identification of a 5‐HT1A‐like receptor

Prokinetic drugs used to treat gastrointestinal ileus in man have equivocal results in horses. In man, prokinetic drugs have 5-hydroxytryptamine4(5-HT4) receptors as their target, but little is known about the 5-HT-receptor subtypes in the equine small intestine. Functional and immunohistochemical identification of the serotonin receptor subtype(s) responsible for the 5-HT induced contractile response in the equine circular jejunum. Isometric organ-bath recordings were carried out to assess spontaneous and drug-evoked contractile activity of equine circular jejunum. Histological investigations by immunofluorescence analyses were performed to check for presence and localisation of this functionally identified 5-HT receptor subtype. Tonic contractions were induced by 5-HT in horse jejunal circular muscle. Tetrodotoxin, atropine and NG-nitro L-arginine did not modify this response. A set of 5-HT receptor subtype selective antagonists excluded interaction with 5-HT1B, 1D, 2A, 3, 4 and 7 receptors. The selective 5-HT1A receptor antagonists WAY 100635 and NAN 190 caused a clear rightward shift of the concentration-response curve to 5-HT. The contractile effect of 5-CT, that can interact with 5-HT1A, 1B, 1D, 5 and 7 receptors was also antagonised by WAY 100635, identifying the targeted 5-HT receptor as a 5-HT1A-like receptor. Immunohistology performed with rabbit polyclonal anti-5-HT1A receptor antibodies confirmed the presence of muscular 5-HT1A receptors in the muscularis mucosae, and both longitudinal and circular smooth muscle layers of the equine jejunum. Contractile responses in equine jejunal circular smooth muscle induced by 5-HT involves 5-HT1A-like receptors.

Expression level of 5‐HT1A receptor alters firing rate and concentration‐dependency in YFP‐labeled 5‐HT dorsal raphe neurons

The serotonin (5‐HT) 1A receptor is implicated in the etiology of anxiety and depression. Depressed suicide victims show increased expression of the 5‐HT1A receptor, and transgenic 5‐HT1A receptor knockout (KO) mice have an anxiety phenotype. Both in vivo and in vitro electrophysiological recording techniques were used to assess the effects of 5‐HT1A receptor KO and overexpression (OE) on extracelullarly recorded firing rate and 5‐HT1A receptor mediated responses. There was no difference in firing rate between KO and wild‐type (WT) mice measured extracellularly in vivo or in brain slices in which YFP labeled 5‐HT neurons were activated with 10mM phenylephrine. 5‐HT1A receptor activation with 5‐CT inhibited firing in 5‐HT neurons in raphe brain slices from WT, but not KO, mice. 5‐HT neurons from OE mice showed decreased basal firing and a leftward shift of the 5‐HT1A concentration‐response (C‐R) curve compared to WT. The 5‐HT1A receptor antagonist WAY 100635 (100nM) had no effect on basal firing rate of OE or WT neurons, but blocked the inhibition by 5‐CT. Interestingly, whole cell recordings showed no difference in the C‐R curve for 5‐HT1A receptor‐mediated outward current. These results show that KO mice have no 5‐HT neuronal response to 5‐HT1A receptor activation, whereas OE mice have increased sensitivity compared to WT depending on the active state of the neuron. Supported by MH63078.

The 5‐HT7Dro Serotonin Receptor: Expression in the CNS and Function

Serotonin (5‐HT) influences behaviors that include circadian, sleep, appetite, aggression, locomotion, perception, and sexual behavior. The effects of 5‐HT are mediated through G‐protein coupled receptors, which initiate multiple effector pathways. Disregulation of 5‐HT signaling in humans has been implicated in neuropsychiatric disorders including depression, anxiety disorders, anorexia and schizophrenia. The fruit fly, Drosophila melanogaster, expresses orthologs of three mammalian 5‐HT receptor subtypes: 5‐HT1A, 5‐HT2, and 5‐HT7. The 5‐HT7Dro receptor is orthologous to the mammalian 5‐HT7 receptor and activates adenylate cyclase through Gαs. We show that in fly 3rd instar larvae brain, 5‐HT7Dro expression is observed in discreet populations of neurons in the hemispheres as well as in neurons of the ventral ganglia. In adult brains, 5‐HT7Dro is highly expressed in neurons that innervate the ellipsoid body, a region believed to be involved in higher order behaviors. 5‐HT7Dro neurons also cluster with PDF‐positive circadian pacemaker neurons. Pharmacological studies using the 5‐HT1A/7 receptor agonist 8‐OH‐DPAT with the 5‐HT1A receptor antagonist WAY100635 eliminated circadian activity. These results suggest that 5‐HT7Dro may modulate circadian activity in the fly. Further studies to determine the role of 5‐HT7Dro in additional behaviors are ongoing. Supported by NIMH 1R21MH078454

Effect of co-administration of the selective 5-HT 1A receptor antagonist WAY 100,635 and selective 5-HT 1B/1D receptor antagonist GR 127,935 on anxiolytic effect of citalopram in conditioned fear stress in the rat

This study investigated the effect of co-administration of the selective 5-HT 1A receptor antagonist WAY 100,635 and selective 5-HT 1B/1D receptor antagonist GR 127,935 with a subactive dose of citalopram [selective serotonin (5-HT) reuptake inhibitor (SSRI)] on the expression of conditioned freezing, an index of fear. In the present study, acute administration of citalopram (s.c.) reduced freezing significantly at high doses (10, 30 and 100 mg/kg), while showing no significant effect at low doses (1 and 3 mg/kg). Co-administration of WAY 100,635 (0.15 mg/kg) with citalopram (3 mg/kg) reduced freezing markedly and significantly, as compared with either drug alone. However, the addition of GR 127,935 (4 mg/kg) did not potentiate the effects of citalopram (3 mg/kg) on freezing and did not enhance the effect of WAY 100,635 (0.15 mg/kg) with citalopram (3 mg/kg). Co-administration of WAY 100,635 (0.15 mg/kg) or GR 127,935 (4 mg/kg) gave no effect on high-dose citalopram (30 mg/kg)-induced inhibition of freezing behavior. These results suggest that co-administration of WAY 100,635 (0.15 mg/kg) strengthens the anxiolytic effect of citalopram (3 mg/kg) by facilitating central 5-HT neurotransmission. Since GR 127,935 (4 mg/kg) failed to accelerate the inhibition of freezing induced by citalopram (3 mg/kg) with WAY 100,635 (0.15 mg/kg) or citalopram (3 mg/kg) alone, it is suggested that blocking 5-HT 1A receptors is more effective in facilitating the anxiolytic effect of citalopram than blocking 5-HT 1B/1D receptors.

5-HT1A receptors of the lateral septum regulate inhibitory avoidance but not escape behavior in rats

Serotonin in the lateral septum (LS) has been implicated in the modulation of defensive behaviors and in anxiety. However, it is currently unknown whether changes in 5-HT mechanisms in this brain area may selectively affect defensive responses associated with specific subtypes of anxiety disorders recognized in clinical settings. To address this question, we evaluated the effect of the intra-LS injection of the 5-HT 1A/7 receptor agonist 8-OH-DPAT (0.6, 3.0, 15.0 nmol) in male Wistar rats exposed to the elevated T-maze animal model of anxiety. This test allows the measurement of two behavioral defensive responses in the same rat: inhibitory avoidance and escape behavior. In clinical terms, these responses have been respectively related to generalized anxiety and panic disorder. The effects of 8-OH-DPAT were compared to those caused by a standard anxiolytic compound, the benzodiazepine receptor agonist midazolam (MDZ, 20 nmol). We also investigated whether the intra-LS injection of the 5-HT 1A receptor antagonist WAY-100635 (0.37 nmol) was able to block the effects of 8-OH-DPAT. All animals were also tested in an open field for locomotor activity assessments. Results showed that whereas intra-LS administration of MDZ decreased avoidance latencies, suggesting an anxiolytic action, 8-OH-DPAT caused the opposite effect. Neither drug affected the escape performance. Intra-LS administration of WAY-100635 blocked the anxiogenic effect caused by 8-OH-DPAT. No changes to locomotion were detected in the open field. The data suggests that LS 5-HT 1A receptors are involved in the control of inhibitory avoidance behavior and that a failure in this regulatory mechanism may be of importance to the physiopathology of generalized anxiety disorder.

5-HT1A and 5-HT1B receptors in the ventrolateral striatum differentially modulate apomorphine-induced jaw movements in rats

The ability of serotonin 5-HT(1A) and 5-HT(1B) receptors in the ventrolateral striatum to modulate dopamine receptor-mediated jaw movements was investigated in freely moving rats, using a magnet-sensing system combined with an intracerebral drug microinjection technique. Apomorphine (1 mg/kg i.v.) has been found to elicit repetitive jaw movements. Bilateral injections of the 5-HT(1A) receptor agonist 8-OH-DPAT (1 and 4 microg/0.2 microl in each side) into the ventrolateral striatum partially but significantly reduced apomorphine-induced repetitive jaw movements. The 5-HT(1A) receptor antagonist WAY-100635 (1 microg), which alone did not affect the effects of apomorphine, antagonized the inhibitory effects of 8-OH-DPAT (4 microg). Bilateral injections of the 5-HT(1B) receptor agonist CP93129 (1 and 10 microg) also reduced apomorphine-induced repetitive jaw movements in a dose-dependent manner. However, the 5-HT(1B) receptor antagonist GR55562 (1 and 10 microg) did not antagonize the inhibitory effects of CP93129 (10 microg). These results suggest that 5-HT(1A), but not 5-HT(1B), receptors in the ventrolateral striatum play a modulatory role in the production of dopamine receptor-mediated jaw movements.

Fish on prozac: Effect of serotonin reuptake inhibitors on cognition in goldfish.

The authors studied the effect of fluoxetine (a specific serotonin reuptake inhibitor--SSRI) on active avoidance learning in fish. In an active, two-way, shuttle-box avoidance task we compared escape and avoidance of shock among fish receiving chronic administration of fluoxetine (Prozac), others receiving a 5-HT(1A) receptor antagonist (WAY 100,635; Sigma, St. Louis, MO) and controls. The receptor-blocked group performed significantly more Avoids than the fluoxetine group, which was lowest in performance, or than controls, which were slightly higher, and not significantly different from, the fluoxetine group. This conforms to results reported in rats. Active avoidance learning may be stimulated by the 5-HT(1A) receptor antagonist. Fluoxetine-treated fish seemed less active in their home tanks than controls or blocker-treated fish. These results suggest that at the dosages used in this experiment, the 5-HT(1A) receptor antagonist WAY 100,635 may have positive effects on cognition in fishes and its action may not necessarily be restricted to blockage of 5 HT reuptake inhibition. It seems that serotonin mechanisms may be highly conserved in vertebrate evolution.

Predatory Stress as an Experimental Strategy to Measure Fear and Anxiety-related Behaviors in Non-human Primates

Natural defense-inducing stimuli are being increasingly exploited as a means to investigate the neural mechanisms underlying normal and pathological anxiety, as well as for the screening of new compounds with potential therapeutic use in human anxiety disorders. Such an approach, frequently used in rodents, has recently been employed in the Marmoset Predator Confrontation Test (MPCT). In this method, marmoset monkeys are individually confronted with a taxidermized predator (wild oncilla cat) in a previously habituated maze environment, while several easily discernable fear/anxiety-related behaviors are measured. Confrontation with the cat stimulus significantly altered ongoing behaviors, each habituating distinctively during repeated exposures; e.g. complete rapid habituation (alarm call), complete slow habituation (exploration, vigilance) or only partial habituation (proximity avoidance). Pharmacological validating studies with diazepam and buspirone induced a significant dose-dependent reversal of the fear-induced proximic avoidance and scratching/scent-marking behaviors, while exploration (smell/lick the maze, leg stand) was found to increase. The neuropeptide substance P and the selective 5-HT1A receptor antagonist WAY100635 resulted in a similar anxiolytic-like profile. The response pattern observed was not influenced by social isolation, handling/manual restraint, novel environment exposure or habituation to the stimulus or its location. Persistent defensive behavior and response pattern to diazepam was observed when naive versus MPCT-experienced marmosets were tested following a recent predatory stress. Taken together, the results indicate that the MPCT is a valuable experimental procedure to measure fear and anxiety-related behaviors in nonhuman primates.

Phencyclidine-induced cognitive deficits in mice are improved by subsequent subchronic administration of the antipsychotic drug perospirone: Role of serotonin 5-HT 1A receptors

Accumulating evidence suggests that the serotonin 5-HT 1A receptor may play a role in the pathophysiology of schizophrenia. The present study was undertaken to examine the effects of perospirone, an atypical antipsychotic drug with 5-HT 1A receptor agonism, on cognitive deficits in mice after repeated administration of the NMDA receptor antagonist phencyclidine (PCP). Subsequent subchronic (14 days) administration of perospirone (1.0, 3.0, or 10 mg/kg) significantly attenuated PCP (10 mg/kg)-induced cognitive deficits in mice, in a dose-dependent manner. The effects of perospirone (10 mg/kg) were significantly antagonized by co-administration of the selective 5-HT 1A receptor antagonist WAY100635 (1.0 mg/kg). Furthermore, hypothermia by the 5-HT 1A receptor agonist 8-OH DPAT (0.25 mg/kg) was significantly attenuated in mice treated with PCP. Moreover, a receptor binding assay using [ 3H]WAY100635 revealed that levels of 5-HT 1A receptors in the hippocampus, but not in the frontal cortex, of PCP-treated mice were significantly lower than those of saline-treated mice. These findings suggest that repeated PCP administration alters 5-HT 1A receptor function in the mouse brain, and that subsequent subchronic administration of perospirone ameliorates PCP-induced cognitive deficits via 5-HT 1A receptors. Therefore, perospirone could be a potential therapy for the cognitive deficits observed in schizophrenic patients.

Activation of 5-HT1Areceptors in medullary raphé disrupts sleep and decreases shivering during cooling in the conscious piglet

Activation of 5-HT1A receptors in the medullary raphé decreases sympathetically mediated brown adipose tissue (BAT) thermogenesis and peripheral vasoconstriction when previously activated with leptin, LPS, prostaglandins, or cooling. It is not known whether shivering is also modulated by medullary raphé 5-HT1A receptors. We previously showed in conscious piglets that activation of 5-HT1A receptors with (+/-)-8-hydroxy-2-(dipropylamino)-tetralin (8-OH-DPAT) in the paragigantocellularis lateralis (PGCL), a medullary region lateral to the raphé that contains substantial numbers of 5-HT neurons, eliminates rapid eye movement (REM) sleep and decreases shivering in a cold environment, but does not attenuate peripheral vasoconstriction. Hoffman JM, Brown JW, Sirlin EA, Benoit AM, Gill WH, Harris MB, Darnall RA. Am J Physiol Regul Integr Comp Physiol 293: R518-R527, 2007. We hypothesized that, during cooling, activation of 5-HT1A receptors in the medullary raphé would also eliminate REM sleep and, in contrast to activation of 5-HT1A receptors in the PGCL, would attenuate both shivering and peripheral vasoconstriction. In a continuously cool environment, dialysis of 8-OH-DPAT into the medullary raphé resulted in alternating brief periods of non-REM sleep and wakefulness and eliminated REM sleep, as observed when 8-OH-DPAT is dialyzed into the PGCL. Moreover, both shivering and peripheral vasoconstriction were significantly attenuated after 8-OH-DPAT dialysis into the medullary raphé. The effects of 8-OH-DPAT were prevented after dialysis of the selective 5-HT1A receptor antagonist WAY-100635. We conclude that, during cooling, exogenous activation of 5-HT1A receptors in the medullary raphé decreases both shivering and peripheral vasoconstriction. Our data are consistent with the hypothesis that neurons expressing 5-HT1A receptors in the medullary raphé facilitate spinal motor circuits involved in shivering, as well as sympathetic stimulation of other thermoregulatory effector mechanisms.

Characterization of clozapine-induced changes in synaptic plasticity in the hippocampal–mPFC pathway of anesthetized rats

Synaptic plasticity expressed as long-term potentiation (LTP) in the hippocampal–medial prefrontal cortex (mPFC) pathway is considered to be involved in cognitive function and learning and memory processes, but its synaptic mechanism remains unknown. The present study characterized LTP in the mPFC using the atypical antipsychotic clozapine, with a focus on dopaminergic modulation. The magnitude of LTP was facilitated by pretreatment with clozapine (20 mg/kg, i.p.), but not by the typical antipsychotic haloperidol (1 mg/kg, i.p.). Clozapine-induced LTP augmentation was blocked by the dopamine D 1 receptor antagonist SCH-23390 (10 μg/rat, i.c.v.), but not by the D 2 receptor antagonist remoxipride (10 μg/rat, i.c.v.) or the 5-HT 1A receptor antagonist WAY-100635 (20 μg/rat, i.c.v.). SCH-23390 (10 μg/rat, i.c.v.) by itself did not affect LTP induction. The D 1 receptor agonist SKF-38393 (10 μg/kg, i.c.v.) facilitated LTP, mimicking the clozapine-induced response. Furthermore, in vivo microdialysis showed that transient increases in mPFC dopamine levels induced by tetanic stimulation sustained facilitation following clozapine administration (20 mg/kg, i.p.). These results demonstrate the importance of the D 1 receptor as a mediator of clozapine-induced LTP augmentation through enhanced dopaminergic activity. Augmentation of synaptic plasticity in the hippocampal-mPFC pathway via D 1 receptors appears to be responsible for the therapeutic effects of clozapine.

The selective 5-HT1A receptor antagonist WAY-100635 inhibits neuronal activity of the ventromedial prefrontal cortex in a rodent model of Parkinson’s disease

The ventral part of the medial prefrontal cortex (mPFC) plays an important role in initiation and control of voluntary movement, mood and cognition. However, after the degeneration of the nigrostriatal pathway, the neuronal activity of the ventral mPFC and the role of serotonin(1A) (5-hydroxytryptamine, 5-HT(1A)) receptors in the firing of the neurons are still unknown. The present study is to investigate the change of neuronal activity in the ventral mPFC and the effect of systemic administration of the selective 5-HT(1A) receptor antagonist WAY-100635 on the activity of the neurons in normal and 6-hydroxydopamine (6-OHDA)-lesioned rats. Single unit responses were recorded extracellularly with glass microelectrodes from ventral mPFC neurons in normal rats and 6-OHDA unilaterally lesioned rats in vivo. 6-OHDA lesion of the substantia nigra pars compacta (SNc) significantly increased the firing rate with no change in the firing pattern of neurons of the ventral mPFC in rats. Systemic administration of WAY-100635 (0.1 mg/kg, i.v.) did not change the mean firing rate and firing pattern of ventral mPFC neurons in normal rats. In contrast, WAY-100635 significantly decreased the mean firing rate of the neurons in rats with 6-OHDA lesion of the SNc. These data suggest that the degeneration of the nigrostriatal pathway results in an increase of neuronal activity of ventral mPFC and dysfunction of 5-HT(1A) receptor.

Reciprocal effects of combined administration of serotonin, noradrenaline and dopamine reuptake inhibitors on serotonin and dopamine levels in the rat prefrontal cortex: the role of 5-HT1A receptors

The purpose of the present study was to examine, by in vivo microdialysis technique, the effects of triple acting monoamine reuptake inhibitors, constructed by combinations of a selective serotonin reuptake inhibitor citalopram with a noradrenaline/dopamine reuptake inhibitor methylphenidate and a serotonin/noradrenaline reuptake inhibitor venlafaxine with a dopamine reuptake inhibitor GBR12909, on extracellular levels of serotonin (5-HT), noradrenaline (NA) and dopamine (DA) in the prefrontal cortex (PFC) of anaesthetized rats. At the highest dose tested, adjunctive methylphenidate (10 mg/kg s.c.) to citalopram markedly attenuated by 63% the extracellular levels of 5-HT as compared to the levels induced by citalopram (5 mg/kg i.p.) alone, whereas the overall DA concentrations significantly increased to about 149% of those induced by methylphenidate alone. Similarly, the combination of venlafaxine with GBR12909 (10 mg/kg s.c.) caused a reduction of 5-HT levels to 66% of the levels induced by venlafaxine (10 mg/kg i.p.) alone, whereas the overall DA levels increased to 151% of the venlafaxine-treated group. The extracellular levels of NA were only marginally affected by the treatments with combined reuptake inhibitors compared to the effects induced by methylphenidate or venlafaxine alone. The modulatory effects of combined administration of the DA/NA reuptake inhibitors with the 5-HT reuptake inhibitors (citalopram and venlafaxine) on potentiation of DA and attenuation of 5-HT efflux were completely reversed by a pre-treatment with the 5-HT(1A) receptor antagonist WAY-100635. These findings suggest a crucial role played by the 5-HT(1A) receptors in balancing the reuptake inhibitory efficacy for the enhancement of 5-HT and DA transmission in the PFC by the drugs combining the reuptake inhibition of all three monoamines.

The neurotensin analog NT69L enhances medial prefrontal cortical dopamine and acetylcholine efflux: Potentiation of risperidone-, but not haloperidol-, induced dopamine efflux

NT69L is a novel neurotensin (8–13) analog that produces atypical antipsychotic-like effects in animal models. Because atypical antipsychotic drugs increase dopamine (DA) and acetylcholine (ACh) efflux in the medial prefrontal cortex and DA efflux in the nucleus accumbens, the present study sought to further evaluate the putative antipsychotic-like effects of NT69L by assessing DA and ACh efflux in these regions. Dual probe microdialysis was conducted in awake freely moving male rats, without using an acetylcholinesterase inhibitor in the perfusion medium. NT69L (1.0 and 3.0 mg/kg) produced significant increases in extracellular DA and ACh efflux in the medial prefrontal cortex. NT69L (1.0 mg/kg, but not 3.0 mg/kg) produced a significant increase of DA, but not ACh, efflux in the nucleus accumbens. Pretreatment with the serotonin (5-HT) 1A receptor antagonist WAY100635 (0.2 mg/kg) significantly attenuated the 3.0 mg/kg NT69L-induced increase in medial prefrontal cortical DA efflux. Pretreatment with NT69L (1.0 mg/kg) significantly potentiated the effects of the atypical antipsychotic drug risperidone (0.1 mg/kg) on DA, but not ACh, efflux in the medial prefrontal cortex, while pretreatment with NT69L 1.0 mg/kg failed to alter the effects of haloperidol (0.1 mg/kg) on DA or ACh efflux in either region. These findings further suggest that NT analogs may be useful alone or adjunctively for the treatment of schizophrenia.

Activation of septal 5‐HT1A receptors alters spatial memory encoding, interferes with consolidation, but does not affect retrieval in rats subjected to a water‐maze task

Using Long-Evans rats tested in a water maze, this study assessed the role of 5-HT1A/5-HT7 receptors of the medial septum in encoding, consolidation, and retrieval of spatial information. The testing protocol (acquisition: daily four-trial sessions over three consecutive days; retention: probe trial on day 4) was first validated by showing that intraseptal infusions of lidocaine (LIDO; 40 microg/0.5 microL) disrupted acquisition and retrieval of the task. 8-OH-DPAT (4 microg/0.5 microL) infused before each acquisition session prevented learning/retention of the platform location, an effect attenuated by pretreatment with the 5-HT1A receptor antagonist WAY 100635. With the 5-HT7 antagonist SB 269970, the 8-OH-DPAT-induced acquisition deficit seemed attenuated, but there was no subsequent retention. When infused immediately, 1, 4, or 6 h after each acquisition session, 8-OH-DPAT did not hinder consolidation. When the infusions were performed 2 h postacquisition, however, consolidation was disrupted. Finally, when infused before a probe trial after drug-free acquisition, 8-OH-DPAT had no effect, suggesting no interference with retrieval processes. We also established that 8-OH-DPAT had no effects when the platform was visible, and altered neither home-cage activity nor anxiety-related behavior (elevated plus-maze). Altogether, these results show that 5-HT1A receptors in the septal region contribute both to declarative-like information encoding and subsequently, within a given postacquisition time window, to its consolidation. They do not participate in the retrieval of recently learned declarative-like information. These observations suggest that 5-HT1A receptors of the medial septum contribute to a serotonin-mediated mechanism involved in the encoding and consolidation, not the retrieval of spatial hippocampal-dependent knowledge. These results might have some relevance to approaches aimed at modifying serotonergic functions in the brain for the treatment of disorders such as depression, anxiety, post-traumatic stress, and amnesia.

Receptor mediation of exaggerated responses to serotonin-enhancing drugs in serotonin transporter (SERT)-deficient mice

Administration of serotonin-enhancing drugs induces a distinctive behavioral syndrome in rodents. We previously reported that mice with a targeted disruption of the serotonin transporter (SERT) display some of these behaviors spontaneously, in the absence of drug. In the current studies, we assessed the drug-induced serotonin syndrome in SERT wildtype (+/+), heterozygous (+/−) and knockout (−/−) mice. In SERT −/− mice, the monoamine oxidase inhibitor (MAOI) tranylcypromine (1 mg/kg) or the serotonin precursor 5-hydroxy- l-tryptophan (5-HTP; 80 mg/kg) led to markedly exaggerated serotonin syndrome behaviors relative to SERT +/+ mice, with an intermediate phenotype in SERT +/− mice. SERT +/+ mice developed significant serotonin syndrome behaviors only with the combination of the MAO-A/B inhibitor tranylcypromine (0.5 or 1 mg/kg) or the MAO-A-selective inhibitor clorgyline (1.2 mg/kg) plus 5-HTP. In evaluations of underlying mechanisms, pretreatment with the Htr1a receptor antagonist WAY 100635 (1 mg/kg), but not the Htr7 antagonist SB 269970 (3 mg/kg) or the Htr2a antagonist MDL 11,939 (5 mg/kg), markedly decreased the exaggerated 5-HTP-induced behaviors in SERT −/− mice. Subsequent experiments showed that the Htr1a agonist 8-OH-DPAT (1 or 2 mg/kg) elicited serotonin syndrome behaviors in a dose-dependent manner, blocked by WAY 100635 (1 mg/kg), in mice of all three genotypes, confirming the role of Htr1a receptors. The current data document markedly enhanced behavioral sensitivity to serotonin-enhancing drugs in SERT-deficient mice. These studies also show that the exaggerated behavioral responses observed in SERT +/− and −/− mice are mediated by postsynaptic Htr1a receptors, and suggest intact postsynaptic Htr1a function in SERT −/− mice.

WAY-100635 has high selectivity for serotonin 5-HT1A versus dopamine D4 receptors

The serotonin 5-HT(1A) receptor antagonist WAY-100635 was recently reported to have potent agonist properties at dopamine D(4) receptors (Chemel et al., 2006, Psychopharmacology 188, 244-251.). Herein WAY-100635 (pK(i) at human (h) serotonin 5-HT(1A) receptors=9.51; pK(i) at dopamine hD(4.4) receptors=7.42) stimulated [(35)S]GTPgammaS incorporation in membranes of Chinese Hamster Ovary cells expressing dopamine hD(4.4) receptors with only moderate potency and modest efficacy (pEC(50)=6.63; E(max)=19% of dopamine). Moreover, in antagonism experiments, WAY-100635 had a much lower potency at dopamine hD(4.4) receptors (pK(B)=7.09), than at serotonin h5-HT(1A) receptors (pK(B)=9.47). These data demonstrate that WAY-100635 has high selectivity for serotonin h5-HT(1A)versus dopamine hD(4.4) receptors.