Serotonin 5-HT1A receptors might control the output of cortical glutamatergic neurons in rat cingulate cortex

Common and contrasting effects of 5-HTergic signaling in pyramidal cells and SOM interneurons of the mouse cortex

Serotonin (5-hydroxytryptamine, 5-HT) is a powerful modulator of neuronal activity within the central nervous system and dysfunctions of the serotonergic system have been linked to several neuropsychiatric disorders such as major depressive disorders or schizophrenia. The anterior cingulate cortex (aCC) plays an important role in cognitive capture of stimuli and valence processing and it is densely innervated by serotonergic fibers from the nucleus raphe. In order to understand how pathophysiological 5-HT signalling can lead to neuropsychiatric diseases, it is important to understand the physiological actions of 5-HT on cortical circuits. Therefore, we combined electrophysiological recordings with pharmacology and immunocytochemistry to investigate the effects of 5-HT on Somatostatin-positive interneurons (SOM-INs) and compared these to supragranular pyramidal cells (PCs). This comparison allowed us to identify common and contrasting effects of 5-HT on SOM-INs and PCs of the aCC resulting in a specific modulation of the excitation-to-inhibition balance in PCs but not in SOM-INs.

Prevention of MK-801-induced amnestic effect with combined activation of 5-HT1A and muscarinic receptors in mice

BACKGROUND

Muscarinic or 5-HT1A receptors are crucial in learning and memory processes, and their expression is evident in the brain areas involved in cognition. The administration of the activators of these receptors prevents the development of cognitive dysfunctions in animal models of schizophrenia induced by MK-801 (N-methyl-d-aspartate receptor antagonist) administration. GABAergic dysfunction is considered as one of the most important causes of MK-801-induced spatial learning deficits.

METHODS

Novel object recognition (NOR) and Morris water maze (MWM) tests were used to study the anti-amnestic effect of the biased 5-HT1A receptor agonist (F15599) alone or in combinations with VU0357017 (M1 receptor allosteric agonist), VU0152100 (M4 receptor positive allosteric modulator), and VU0238429 (M5 receptor positive allosteric modulator) on MK-801-induced dysfunctions. The compounds were administered for 5 consecutive days. Animals tested with the MWM underwent 5-day training. Western blotting was used to study the expressions of 5-HT1A receptors and the level of GAD65 in the frontal cortices (FCs) and hippocampi of the animals.

RESULTS

F15599 prevented the amnestic effect induced by MK-801 in the MWM at a dose of 0.1 mg/kg. The co-administration of the compound with muscarinic receptors activators had no synergistic effect. The additive effect of the combinations was evident in the prevention of declarative memory dysfunctions investigated in NOR. The administration of MK-801 impaired 5-HT1A expression in the hippocampi and decreased GAD65 levels in both the FCs and hippocampi. The administration of muscarinic ligands prevented these MK-801-induced deficits only in the hippocampi of MWM-trained animals. No effects of the compounds were observed in untrained mice.

CONCLUSION

Our results indicate that F15599 prevents schizophrenia-related spatial learning deficits in the MWM; however, the activity of the compound is not intensified with muscarinic receptors activators. In contrast, the combined administration of the ligands is effective in the NOR model of declarative memory. The muscarinic receptors activators reversed MK-801-induced 5-HT1A and GAD65 dysfunctions in the hippocampi of MWM-trained mice, but not in untrained mice.

Altered brain serotonin 5-HT1A receptor expression and function in juvenile Fmr1 knockout mice

There are no approved pharmacotherapies for fragile X syndrome (FXS), a rare neurodevelopmental disorder caused by a mutation in the FMR1 promoter region that leads to various symptoms, including intellectual disability and auditory hypersensitivity. The gene that encodes inhibitory serotonin 1A receptors (5-HT1ARs) is differentially expressed in embryonic brain tissue from individuals with FXS, and 5-HT1ARs are highly expressed in neural systems that are disordered in FXS, providing a rationale to focus on 5-HT1ARs as targets to treat symptoms of FXS. We examined agonist-labeled 5-HT1AR densities in male and female Fmr1 knockout mice and found no differences in whole-brain 5-HT1AR expression in adult control compared to Fmr1 knockout mice. However, juvenile Fmr1 knockout mice had lower whole-brain 5-HT1AR expression than age-matched controls. Consistent with these results, juvenile Fmr1 knockout mice showed reduced behavioral responses elicited by the 5-HT1AR agonist (R)-8-OH-DPAT, effects blocked by the selective 5-HT1AR antagonist, WAY-100635. Also, treatment with the selective 5-HT1AR agonist, NLX-112, dose-dependently prevented audiogenic seizures (AGS) in juvenile Fmr1 knockout mice, an effect reversed by WAY-100635. Suggestive of a potential role for 5-HT1ARs in regulating AGS, compared to males, female Fmr1 knockout mice had a lower prevalence of AGS and higher expression of antagonist-labeled 5-HT1ARs in the inferior colliculus and auditory cortex. These results provide preclinical support that 5-HT1AR agonists may be therapeutic for young individuals with FXS hypersensitive to auditory stimuli.

Central norepinephrine transmission is required for stress-induced repetitive behavior in two rodent models of obsessive-compulsive disorder

RATIONALE

Obsessive-compulsive disorder (OCD) is characterized by repetitive behaviors exacerbated by stress. Many OCD patients do not respond to available pharmacotherapies, but neurosurgical ablation of the anterior cingulate cortex (ACC) can provide symptomatic relief. Although the ACC receives noradrenergic innervation and expresses adrenergic receptors (ARs), the involvement of norepinephrine (NE) in OCD has not been investigated.

OBJECTIVE

To determine the effects of genetic or pharmacological disruption of NE neurotransmission on marble burying (MB) and nestlet shredding (NS), two animal models of OCD.

METHODS

We assessed NE-deficient (Dbh -/-) mice and NE-competent (Dbh +/-) controls in MB and NS tasks. We also measured the effects of anti-adrenergic drugs on NS and MB in control mice and the effects of pharmacological restoration of central NE in Dbh -/- mice. Finally, we compared c-fos induction in the locus coeruleus (LC) and ACC of Dbh -/- and control mice following both tasks.

RESULTS

Dbh -/- mice virtually lacked MB and NS behaviors seen in control mice but did not differ in the elevated zero maze (EZM) model of general anxiety-like behavior. Pharmacological restoration of central NE synthesis in Dbh -/- mice completely rescued NS behavior, while NS and MB were suppressed in control mice by anti-adrenergic drugs. Expression of c-fos in the ACC was attenuated in Dbh -/- mice after MB and NS.

CONCLUSION

These findings support a role for NE transmission to the ACC in the expression of stress-induced compulsive behaviors and suggest further evaluation of anti-adrenergic drugs for OCD is warranted.

Cognitive Control as a 5-HT1A-Based Domain That Is Disrupted in Major Depressive Disorder

Heterogeneity within Major Depressive Disorder (MDD) has hampered identification of biological markers (e.g., intermediate phenotypes, IPs) that might increase risk for the disorder or reflect closer links to the genes underlying the disease process. The newer characterizations of dimensions of MDD within Research Domain Criteria (RDoC) domains may align well with the goal of defining IPs. We compare a sample of 25 individuals with MDD compared to 29 age and education matched controls in multimodal assessment. The multimodal RDoC assessment included the primary IP biomarker, positron emission tomography (PET) with a selective radiotracer for 5-HT1A [(11C)WAY-100635], as well as event-related functional MRI with a Go/No-go task targeting the Cognitive Control network, neuropsychological assessment of affective perception, negative memory bias and Cognitive Control domains. There was also an exploratory genetic analysis with the serotonin transporter (5-HTTLPR) and monamine oxidase A (MAO-A) genes. In regression analyses, lower 5-HT1A binding potential (BP) in the MDD group was related to diminished engagement of the Cognitive Control network, slowed resolution of interfering cognitive stimuli, one element of Cognitive Control. In contrast, higher/normative levels of 5-HT1A BP in MDD (only) was related to a substantial memory bias toward negative information, but intact resolution of interfering cognitive stimuli and greater engagement of Cognitive Control circuitry. The serotonin transporter risk allele was associated with lower 1a BP and the corresponding imaging and cognitive IPs in MDD. Lowered 5HT 1a BP was present in half of the MDD group relative to the control group. Lowered 5HT 1a BP may represent a subtype including decreased engagement of Cognitive Control network and impaired resolution of interfering cognitive stimuli. Future investigations might link lowered 1a BP to neurobiological pathways and markers, as well as probing subtype-specific treatment targets.

The effect of NAD-299 and TCB-2 on learning and memory, hippocampal BDNF levels and amyloid plaques in Streptozotocin-induced memory deficits in male rats

RATIONALE

Alzheimer's disease (AD) is the most common form of dementia characterized by a progressive decline in cognitive function. The serotonergic system via the 5-HT1A receptor and 5-HT2A receptor is proposed to affect the cognitive process.

OBJECTIVE

In the present study, the effects of NAD-299 (5-HT1AR antagonist) and TCB-2 (5-HT2AR agonist) on learning and memory processes, hippocampal brain-derived neurotrophic factor (BDNF) levels, neuronal necrosis, and Aβ plaque production have been investigated on the intracerebroventricular (icv) injection of streptozotocin (STZ)-induced memory deficits in rats.

METHODS

Fifty-four adult male Wistar rats (250-300 g) were divided into six groups (n = 9 in each group): control, sham-operated, AD (icv-STZ (3 mg/kg, 10 μl)), AD+NAD-299 (5 μg/1 μl icv for 30 days), AD+TCB-2 (5 μg/1 μl icv for 30 days), and AD+NAD-299 + TCB-2 (NAD-299 (5 μg/0.5 μl icv) and TCB-2 (5 μg/0.5 μl icv) for 30 days). Following the treatment period, rats were subjected to behavioral tests of learning and memory. Then, hippocampal BDNF, amyloid-beta (Aβ) plaque, and neuronal loss were determined by ELISA Kit, Congo red staining, and Nissl staining, respectively.

RESULTS

The results of behavioral tests showed that icv-STZ injection decreased the discrimination index in the novel object recognition (NOR) test. In the passive avoidance learning (PAL) task, icv-STZ injection significantly decreased step-through latency (STLr) and increased time spent in dark compartment (TDC). Treatment with NAD-299, TCB-2, and NAD-299 + TCB-2 attenuated the STZ-induced memory impairment in both NOR and PAL tasks. icv-STZ induced a decrease in hippocampal BDNF levels and increased Aβ plaques production in the brain, whereas treatment with NAD-299, TCB-2, and NAD-299 + TCB-2 reduced Aβ plaques in the brain and increased the hippocampal BDNF level. Results of Nissl staining showed that icv-STZ injection increased neuronal loss in the hippocampus, while treatment with NAD-299, TCB-2, and NAD-299 + TCB-2 reduced hippocampal neurodegeneration.

CONCLUSION

These findings suggest that 5-HT1AR blockade by NAD-299 and 5-HT2AR activation by TCB-2 improve cognitive dysfunction in icv-STZ-treated rats, and these drugs may potentially prevent the progression of AD.

Mechanisms Underlying Serotonergic Excitation of Callosal Projection Neurons in the Mouse Medial Prefrontal Cortex

Serotonin (5-HT) selectively excites subpopulations of pyramidal neurons in the neocortex via activation of 5-HT_2A (2A) receptors coupled to G_q subtype G-protein alpha subunits. G_q-mediated excitatory responses have been attributed primarily to suppression of potassium conductances, including those mediated by K_V7 potassium channels (i.e., the M-current), or activation of non-specific cation conductances that underlie calcium-dependent afterdepolarizations (ADPs). However, 2A-dependent excitation of cortical neurons has not been extensively studied, and no consensus exists regarding the underlying ionic effector(s) involved. In layer 5 of the mouse medial prefrontal cortex, we tested potential mechanisms of serotonergic excitation in commissural/callosal (COM) projection neurons, a subpopulation of pyramidal neurons that exhibits 2A-dependent excitation in response to 5-HT. In baseline conditions, 5-HT enhanced the rate of action potential generation in COM neurons experiencing suprathreshold somatic current injection. This serotonergic excitation was occluded by activation of muscarinic acetylcholine (ACh) receptors, confirming that 5-HT acts via the same G_q-signaling cascades engaged by ACh. Like ACh, 5-HT promoted the generation of calcium-dependent ADPs following spike trains. However, calcium was not necessary for serotonergic excitation, as responses to 5-HT were enhanced (by >100%), rather than reduced, by chelation of intracellular calcium with 10 mM BAPTA. This suggests intracellular calcium negatively regulates additional ionic conductances gated by 2A receptors. Removal of extracellular calcium had no effect when intracellular calcium signaling was intact, but suppressed 5-HT response amplitudes, by about 50%, when BAPTA was included in patch pipettes. This suggests that 2A excitation involves activation of a non-specific cation conductance that is both calcium-sensitive and calcium-permeable. M-current suppression was found to be a third ionic effector, as blockade of K_V7 channels with XE991 (10 μM) reduced serotonergic excitation by ∼50% in control conditions, and by ∼30% with intracellular BAPTA present. Together, these findings demonstrate a role for at least three distinct ionic effectors, including K_V7 channels, a calcium-sensitive and calcium-permeable non-specific cation conductance, and the calcium-dependent ADP conductance, in mediating serotonergic excitation of COM neurons.

Selective Modulation of Axonal Sodium Channel Subtypes by 5-HT1A Receptor in Cortical Pyramidal Neuron

Serotonergic innervation of the prefrontal cortex (PFC) modulates neuronal activity and PFC functions. However, the cellular mechanism for serotonergic modulation of neuronal excitability remains unclear. We performed patch-clamp recording at the axon of layer-5 pyramidal neurons in rodent PFC slices. We found surprisingly that the activation of 5-HT1A receptors selectively inhibits Na+ currents obtained at the axon initial segment (AIS) but not those at the axon trunk. In addition, Na+ channel subtype NaV1.2 but not NaV1.6 at the AIS is selectively modulated by 5-HT1A receptors. Further experiments revealed that the inhibitory effect is attributable to a depolarizing shift of the activation curve and a facilitation of slow inactivation of AIS Na+ currents. Consistently, dual somatic and axonal recording and simulation results demonstrate that the activation of 5-HT1A receptors could decrease the success rate of action potential (AP) backpropagation toward the somatodendritic compartments, enhancing the segregation of axonal and dendritic activities. Together, our results reveal a selective modulation of NaV1.2 distributed at the proximal AIS region and AP backpropagation by 5-HT1A receptors, suggesting a potential mechanism for serotonergic regulation of functional polarization in the dendro-axonal axis, synaptic plasticity and PFC functions.

Modulation of Synaptic Plasticity in the Cortex Needs to Understand All the Players

The prefrontal cortex (PFC) is involved in cognitive tasks such as working memory, decision making, risk assessment and regulation of attention. These functions performed by the PFC are supposed to rely on rhythmic electrical activity generated by neuronal network oscillations determined by a precise balance between excitation and inhibition balance (E/I balance) resulting from the coordinated activities of recurrent excitation and feedback and feedforward inhibition. Functional alterations in PFC functions have been associated with cognitive deficits in several pathologies such as major depression, anxiety and schizophrenia. These pathological situations are correlated with alterations of different neurotransmitter systems (i.e., serotonin (5-HT), dopamine (DA), acetylcholine…) that result in alterations of the E/I balance. The aim of this review article is to cover the basic aspects of the regulation of the E/I balance as well as to highlight the importance of the complementarity role of several neurotransmitters in the modulation of the plasticity of excitatory and inhibitory synapses. We illustrate our purpose by recent findings that demonstrate that 5-HT and DA cooperate to regulate the plasticity of excitatory and inhibitory synapses targeting layer 5 pyramidal neurons (L5PyNs) of the PFC and to fine tune the E/I balance. Using a method based on the decomposition of the synaptic conductance into its excitatory and inhibitory components, we show that concomitant activation of D1-like receptors (D1Rs) and 5-HT_1ARs, through a modulation of NMDA receptors, favors long term potentiation (LTP) of both excitation and inhibition and consequently does not modify the E/I balance. We also demonstrate that activation of D2-receptors requires functional 5-HT_1ARs to shift the E-I balance towards more inhibition and to favor long term depression (LTD) of excitatory synapses through the activation of glycogen synthase kinase 3β (GSK3β). This cooperation between different neurotransmitters is particularly relevant in view of pathological situations in which alterations of one neurotransmitter system will also have consequences on the regulation of synaptic efficacy by other neurotransmitters. This opens up new perspectives in the development of therapeutic strategies for the pharmacological treatment of neuronal disorders.

How Does the Brain Implement Adaptive Decision Making to Eat?

Adaptive decision making to eat is crucial for survival, but in anorexia nervosa, the brain persistently supports reduced food intake despite a growing need for energy. How the brain persists in reducing food intake, sometimes even to the point of death and despite the evolution of multiple mechanisms to ensure survival by governing adaptive eating behaviors, remains mysterious. Neural substrates belong to the reward-habit system, which could differ among the eating disorders. The present review provides an overview of neural circuitry of restrictive food choice, binge eating, and the contribution of specific serotonin receptors. One possibility is that restrictive food intake critically engages goal-directed (decision making) systems and "habit," supporting the view that persistent caloric restriction mimics some aspects of addiction to drugs of abuse.

SIGNIFICANCE STATEMENT

An improved understanding of the neural basis of eating disorders is a timely challenge because these disorders can be deadly. Up to 70 million of people in the world suffer from eating disorders. Anorexia nervosa affects 1-4% of women in United States and is the first cause of death among adolescents in Europe. Studies relying on animal models suggest that decision making to eat (or not) can prevail over actual energy requirements due to emotional disturbances resulting in abnormal habitual behavior, mimicking dependence. These recent studies provide a foundation for developing more specific and effective interventions for these disorders.

Serotoninergic and dopaminergic modulation of cortico-striatal circuit in executive and attention deficits induced by NMDA receptor hypofunction in the 5-choice serial reaction time task

Executive functions are an emerging propriety of neuronal processing in circuits encompassing frontal cortex and other cortical and subcortical brain regions such as basal ganglia and thalamus. Glutamate serves as the major neurotrasmitter in these circuits where glutamate receptors of NMDA type play key role. Serotonin and dopamine afferents are in position to modulate intrinsic glutamate neurotransmission along these circuits and in turn to optimize circuit performance for specific aspects of executive control over behavior. In this review, we focus on the 5-choice serial reaction time task which is able to provide various measures of attention and executive control over performance in rodents and the ability of prefrontocortical and striatal serotonin 5-HT_1A, 5-HT_2A, and 5-HT_2C as well as dopamine D₁- and D₂-like receptors to modulate different aspects of executive and attention disturbances induced by NMDA receptor hypofunction in the prefrontal cortex. These behavioral studies are integrated with findings from microdialysis studies. These studies illustrate the control of attention selectivity by serotonin 5-HT_1A, 5-HT_2A, 5-HT_2C, and dopamine D₁- but not D₂-like receptors and a distinct contribution of these cortical and striatal serotonin and dopamine receptors to the control of different aspects of executive control over performance such as impulsivity and compulsivity. An association between NMDA antagonist-induced increase in glutamate release in the prefrontal cortex and attention is suggested. Collectively, this review highlights the functional interaction of serotonin and dopamine with NMDA dependent glutamate neurotransmission in the cortico-striatal circuitry for specific cognitive demands and may shed some light on how dysregulation of neuronal processing in these circuits may be implicated in specific neuropsychiatric disorders.

Serotonin modulation of cortical neurons and networks

The serotonergic pathways originating in the dorsal and median raphe nuclei (DR and MnR, respectively) are critically involved in cortical function. Serotonin (5-HT), acting on postsynaptic and presynaptic receptors, is involved in cognition, mood, impulse control and motor functions by (1) modulating the activity of different neuronal types, and (2) varying the release of other neurotransmitters, such as glutamate, GABA, acetylcholine and dopamine. Also, 5-HT seems to play an important role in cortical development. Of all cortical regions, the frontal lobe is the area most enriched in serotonergic axons and 5-HT receptors. 5-HT and selective receptor agonists modulate the excitability of cortical neurons and their discharge rate through the activation of several receptor subtypes, of which the 5-HT_1A, 5-HT_1B, 5-HT_2A, and 5-HT₃ subtypes play a major role. Little is known, however, on the role of other excitatory receptors moderately expressed in cortical areas, such as 5-HT_2C, 5-HT₄, 5-HT₆, and 5-HT₇. In vitro and in vivo studies suggest that 5-HT_1A and 5-HT_2A receptors are key players and exert opposite effects on the activity of pyramidal neurons in the medial prefrontal cortex (mPFC). The activation of 5-HT_1A receptors in mPFC hyperpolarizes pyramidal neurons whereas that of 5-HT_2A receptors results in neuronal depolarization, reduction of the afterhyperpolarization and increase of excitatory postsynaptic currents (EPSCs) and of discharge rate. 5-HT can also stimulate excitatory (5-HT_2A and 5-HT₃) and inhibitory (5-HT_1A) receptors in GABA interneurons to modulate synaptic GABA inputs onto pyramidal neurons. Likewise, the pharmacological manipulation of various 5-HT receptors alters oscillatory activity in PFC, suggesting that 5-HT is also involved in the control of cortical network activity. A better understanding of the actions of 5-HT in PFC may help to develop treatments for mood and cognitive disorders associated with an abnormal function of the frontal lobe.

Dopaminergic modulation of axonal potassium channels and action potential waveform in pyramidal neurons of prefrontal cortex

Voltage-gated K(+) (KV) channels play critical roles in shaping neuronal signals. KV channels distributed in the perisomatic regions and thick dendrites of cortical pyramidal neurons have been extensively studied. However, the properties and regulation of KV channels distributed in the thin axons remain unknown. In this study, by performing somatic and axonal patch-clamp recordings from layer 5 pyramidal neurons of prefrontal cortical slices, we showed that the rapidly inactivating A-currents mediated the transient K(+) currents evoked by action potential (AP) waveform command (KAP) at the soma, whereas the rapidly activating but slowly inactivating KV1-mediated D-currents dominated the KAP at the axon. In addition, activation of D1-like receptors for dopamine decreased the axonal K(+) currents, as a result of an increase in the activity of cAMP-PKA pathway. In contrast, activation of D2-like receptors showed an opposite effect on the axonal K(+) currents. Further experiments demonstrated that functional D1-like receptors were expressed at the main axon trunk and their activation could broaden the waveforms of axonal APs. Together, these results show that axonal KV channels were subjected to dopamine modulation, and this modulation could regulate the waveforms of propagating APs at the axon, suggesting an important role of dopaminergic modulation of axonal KV channels in regulating neuronal signalling.

Serotonin 1A receptor genetic variations, suicide, and life events in the Iranian population

AIM

The association of serotonin 1A receptor (5-HTR1A) gene polymorphisms with suicidal behavior has been reported in several previous studies, but the results have been inconsistent, which might be due to ethnic differences. The aim of the present study was therefore to investigate the association between polymorphisms -1019C>G, 47C>T (Pro16Leu) and 815G>A (Gly272Asp) and suicidal behavior, taking into account age, gender, and the presence of stressful life and loss events in 1 year prior to suicide.

METHODS

A total of 191 suicide victims and 218 healthy control subjects were included in the present study. 5-HT1RA gene polymorphisms were determined on polymerase chain reaction-restriction fragment length polymorphism.

RESULTS

The distribution of -1019C>G genotypes was significantly different in suicide victims and healthy controls (P = 0.002), and the GG genotype was associated with a significantly higher number of more stressful life and loss events in the suicide victims (P = 0.017, P = 0.037, respectively). The distribution of 47C>T (Pro16Leu) and 815G>A (Gly272Asp) genotypes was not significantly different in the suicide victims and control subjects (P > 0.05). Moreover, these genotypes were not associated with stressful life and loss events (P > 0.05).

CONCLUSION

The frequency of the -1019G allele in the 5-HTR1A gene was higher in suicide victims (with stressful life events) as compared with the control group. In contrast, neither 47C>T (Pro16Leu) nor 815G>A (Gly272Asp) polymorphisms were related with suicide and stressful life events.

Psilocybin dose-dependently causes delayed, transient headaches in healthy volunteers

BACKGROUND

Psilocybin is a well-characterized classic hallucinogen (psychedelic) with a long history of religious use by indigenous cultures, and nonmedical use in modern societies. Although psilocybin is structurally related to migraine medications, and case studies suggest that psilocybin may be efficacious in treatment of cluster headache, little is known about the relationship between psilocybin and headache.

METHODS

This double-blind study examined a broad range of psilocybin doses (0, 5, 10, 20, and 30 mg/70 kg) on headache in 18 healthy participants.

RESULTS

Psilocybin frequently caused headache, the incidence, duration, and severity of which increased in a dose-dependent manner. All headaches had delayed onset, were transient, and lasted no more than a day after psilocybin administration.

CONCLUSIONS

Possible mechanisms for these observations are discussed, and include induction of delayed headache through nitric oxide release. These data suggest that headache is an adverse event to be expected with the nonmedical use of psilocybin-containing mushrooms as well as the administration of psilocybin in human research. Headaches were neither severe nor disabling, and should not present a barrier to future psilocybin research.

Evidence for the differential co-localization of neurokinin-1 receptors with 5-HT receptor subtypes in rat forebrain

Studies suggest that like selective 5-hydroxytryptamine (5-HT; serotonin) reuptake inhibitors, antagonists at neurokinin-1 receptors (NK(1)Rs) may have antidepressant and anxiolytic properties. NK(1)Rs are present in 5-HT innervated forebrain regions which may provide a common point of interaction between these two transmitter systems. This study aimed to investigate for cellular co-localization between NK(1)Rs and 5-HT receptor subtypes in mood-related brain regions in the rat forebrain. With experiments using fluorescence immunocytochemistry, double-labelling methods demonstrated a high degree of co-localization between NK(1)Rs and 5-HT(1A) receptors in most regions examined. Co-localization was highest in the medial septum (88% NK(1)R expressing cells were 5-HT(1A) receptor-positive) and hippocampal regions (e.g. dentate gyrus, 65%), followed by the lateral/basolateral amygdala (35%) and medial prefrontal cortex (31%). In contrast, co-localization between NK(1)Rs and 5-HT(2A) receptors was infrequent (< 8%) in most areas examined except for the hippocampus (e.g. CA3, 43%). Overall co-localization between NK(1)Rs and 5-HT(1A) receptors was much greater than that between NK(1)Rs and 5-HT(2A) receptors. Thus, these experiments demonstrate a high degree of co-localization between NK(1)Rs and 5-HT(1A) receptors in cortical and limbic regions of the rat forebrain. These findings suggest a novel site of interaction between NK(1)R antagonists and the 5-HT system.

Disruptions in serotonergic regulation of cortical glutamate release in primate insular cortex in response to chronic ethanol and nursery rearing

Early-life stress has been shown to increase susceptibility to anxiety and substance abuse. Disrupted activity within the anterior insular cortex (AIC) has been shown to play a role in both of these disorders. Altered serotonergic processing is implicated in controlling the activity levels of the associated cognitive networks. We therefore investigated changes in both serotonin receptor expression and glutamatergic synaptic activity in the AIC of alcohol-drinking rhesus monkeys. We studied tissues from male rhesus monkeys raised under two conditions: Male rhesus monkeys (1) "mother reared" (MR) by adult females (n=9) or (2) "Nursery reared" (NR), that is, separated from their mothers and reared as a separate group under surrogate/peer-reared conditions (n=9). The NR condition represents a long-standing and well-validated nonhuman primate model of early life stress. All monkeys were trained to self-administer ethanol (4% w/v) or an isocaloric maltose-dextrin control solution. Subsets from each rearing condition were then given daily access to ethanol, water, or maltose-dextrin for 12 months. Tissues were collected at necropsy and were further analyzed. Using real time RT-PCR we found that ethanol-naive, NR monkeys had lower AIC levels of 5-HT(1A) and 5-HT(2A) receptor mRNA compared with ethanol-naive, MR animals. Although NR monkeys consumed more ethanol over the 12-month period compared with MR animals, both MR and NR animals expressed greater 5-HT(1A) and 5-HT(2A) receptor mRNA levels following chronic alcohol self-administration. The interaction between nursery-rearing conditions and alcohol consumption resulted in a significant enhancement of both 5-HT(1A) and 5-HT(2A) receptor mRNA levels such that lower expression levels observed in nursery-rearing conditions were not found in the alcohol self-administration group. Using voltage clamp recordings in the whole cell configuration we recorded excitatory postsynaptic currents in both ethanol-naive and chronic self-administration groups of NR and MR monkeys. Both groups that self-administered ethanol showed greater glutamatergic activity within the AIC. This AIC hyperactivity in MR alcohol-consuming monkeys was accompanied by an increased sensitivity to regulation by presynaptic 5-HT(1A) receptors that was not apparent in the ethanol-naive, MR group. Our data indicate that chronic alcohol consumption leads to greater AIC activity and may indicate a compensatory upregulation of presynaptic 5-HT(1A) receptors. Our results also indicate that AIC activity may be less effectively regulated by 5-HT in ethanol-naive NR animals than in NR monkeys in response to chronic ethanol self-administration. These data suggest possible mechanisms for increased alcohol seeking and possible addiction potential among young adults who had previously experienced early-life stress that include disruptions in both AIC activity and serotonin system dynamics.

Serotonin and prefrontal cortex function: neurons, networks, and circuits

Higher-order executive tasks such as learning, working memory, and behavioral flexibility depend on the prefrontal cortex (PFC), the brain region most elaborated in primates. The prominent innervation by serotonin neurons and the dense expression of serotonergic receptors in the PFC suggest that serotonin is a major modulator of its function. The most abundant serotonin receptors in the PFC, 5-HT1A, 5-HT2A and 5-HT3A receptors, are selectively expressed in distinct populations of pyramidal neurons and inhibitory interneurons, and play a critical role in modulating cortical activity and neural oscillations (brain waves). Serotonergic signaling is altered in many psychiatric disorders such as schizophrenia and depression, where parallel changes in receptor expression and brain waves have been observed. Furthermore, many psychiatric drug treatments target serotonergic receptors in the PFC. Thus, understanding the role of serotonergic neurotransmission in PFC function is of major clinical importance. Here, we review recent findings concerning the powerful influences of serotonin on single neurons, neural networks, and cortical circuits in the PFC of the rat, where the effects of serotonin have been most thoroughly studied.

Comparative pharmacology of antipsychotics possessing combined dopamine D2 and serotonin 5-HT1A receptor properties

RATIONALE

There is increasing interest in antipsychotics intended to manage positive symptoms via D(2) receptor blockade and improve negative symptoms and cognitive deficits via 5-HT(1A) activation. Such a strategy reduces side-effects such as the extrapyramidal syndrome (EPS), weight gain, and autonomic disturbance liability.

OBJECTIVE

This study aims to review pharmacological literature on compounds interacting at both 5-HT(1A) and D(2) receptors (as well as at other receptors), including aripiprazole, perospirone, ziprasidone, bifeprunox, lurasidone and cariprazine, PF-217830, adoprazine, SSR181507, and F15063.

METHODS

We examine data on in vitro binding and agonism and in vivo tests related to (1) positive symptoms (e.g., psychostimulant-induced hyperactivity or prepulse inhibition deficit), (2) negative symptoms (e.g., phencyclidine-induced social interaction deficits and cortical dopamine release), and (3) cognitive deficits (e.g., phencyclidine or scopolamine-induced memory deficits). EPS liability is assessed by measuring catalepsy and neuroendocrine impact by determining plasma prolactin, glucose, and corticosterone levels.

RESULTS

Compounds possessing "balanced" 5-HT(1A) receptor agonism and D(2) antagonism (or weak partial agonism) and, in some cases, combined with other beneficial properties, such as 5-HT(2A) receptor antagonism, are efficacious in a broad range of rodent pharmacological models yet have a lower propensity to elicit EPS or metabolic dysfunction.

CONCLUSIONS

Recent compounds exhibiting combined 5-HT(1A)/D(2) properties may be effective in treating a broader range of symptoms of schizophrenia and be better tolerated than existing antipsychotics. Nevertheless, further investigations are necessary to evaluate recent compounds, notably in view of their differing levels of 5-HT(1A) affinity and efficacy, which can markedly influence activity and side-effect profiles.

Neuronal-immune interactions in mediating stress effects in the etiology and course of schizophrenia: role of the amygdala in developmental co-ordination

Stress, in its many forms, is long associated with the etiology and course of schizophrenia. The mechanisms mediating the impacts of stress are not fully elucidated. Here it is proposed that stress induced cortisol alters kynurenic acid (KA) and quinolinic acid (QA) in the cortex and amygdala/striatum, respectively. These effects are significantly modulated by BAG-1 (bcl-2 associated anthanogene) and involve ROS, IL-18, and the induction of IDO (indoleamine 2,3-dioxygenase). The kynurenine pathway (KP) products response to stress seems to mediate both prenatal etiology and symptom course in adulthood. It is suggested that the effects of cortisol and quinolinic acid in the amygdala, coupled to an increase in dopamine efflux, mediate amygdala driven developmental changes in the cortex and VTA/N.Accumbens junction. This change in patterned brain activity co-ordinates alterations in motivated behaviour and thought outputs. Such developmental alterations determine changes in sensory-amygdala interactions, readily allowing developmental links to changes in lateral inhibition and pre-pulse inhibition. Decreases in vitamin D3 and melatonin further potentiate such stress induced changes. The likely involvement of glia in mediating increases in the KP products suggests that adaptation to stress is driven by neuronal activity as a form of glia to glia communication.

Metabotropic glutamate receptor 4 novel agonist LSP1-2111 with anxiolytic, but not antidepressant-like activity, mediated by serotonergic and GABAergic systems

Our earlier studies have demonstrated that the non-selective group III mGlu receptor agonist, ACPT-I, produced anxiolytic rather than antidepressant-like actions after its peripheral administration. Here, we describe the effects of LSP1-2111 ((2S)-2-amino-4-[hydroxy[hydroxy(4-hydroxy-3-methoxy-5-nitro-phenyl)methyl]phosphoryl]butanoic acid), a novel orthosteric, preferential agonist of the mGlu4 receptor, a member of the group III mGlu receptors family, in the stress-induced hyperthermia (SIH) and elevated plus-maze (EPM) tests in mice. In both tests an anxiolytic-like effect was clearly seen in doses of 2 and 5 mg/kg, i.p. The compound did not produce antidepressant-like effects in the tail suspension test (TST) or in the forced swim test (FST) in mice. The potential anxiolytic effect of LSP1-2111 (5 mg/kg) in the SIH test was inhibited by the benzodiazepine receptor antagonist flumazenil (given i.p., 10 mg/kg), and by a 5-HT(1A) receptor antagonist N-{2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl}-N-(2-pyridynyl)cyclohexane-carboxamide (WAY100635) (0.1 mg/kg, s.c.). At the same time, ritanserin (0.5 mg/kg i.p.), the 5-HT(2A/C) receptor antagonist, did not change the anxiolytic-like effects of LSP1-2111. Moreover, the compound was not effective in 5-HT depleted animals. The results of these studies indicate that the GABAergic and serotonergic systems are involved in the potential anxiolytic action of LSP1-2111.

Cadmium chloride exposure modifies amino acid daily pattern in the mediobasal hypothalamus in adult male rat

The present study was conducted to investigate the possible effects of cadmium exposure on the daily pattern of aspartate, glutamate, glutamine, gamma-aminobutyric acid (GABA) and taurine levels in the mediobasal hypothalamus of adult male rats. For this purpose, animals were treated with cadmium at two different exposure doses (25 and 50 mg l(-1) of cadmium chloride, CdCl(2)) in the drinking water for 30 days. Control age-matched rats received CdCl(2)-free water. After the treatment, rats were killed at six different time intervals throughout a 24 h cycle. CdCl(2) exposure modified the amino acid daily pattern, as it decreased aspartate, glutamate, GABA and taurine levels at 12:00 h with both exposure doses employed. In addition, the treatment with 25 mg l(-1) of CdCl(2) induced the appearance of minimal values at 16:00 h and maximal values between 04:00 and 08:00 h for glutamate, and a peak of glutamine content at 20:00 h. The heavy metal also decreased GABA medium levels around the clock in the mediobasal hypothalamus. However, CdCl(2) did not alter the metabolic correlation between glutamate, aspartate, glutamine and GABA observed in control animals. These results suggest that CdCl(2) induced several alterations in aspartate, glutamate, glutamine, GABA and taurine daily pattern in the mediobasal hypothalamus and those changes may be related to alterations in hypothalamic function.

In-vivo effects of the 1,2,4-piperazine derivatives MM5 and MC1, putative 5-HT agonists, on dopamine and serotonin release in rat prefrontal cortex

Two 1,2,4-substituted derivatives of piperazine were tested for their effect on dopamine and serotonin (5-HT) release in rat prefrontal cortex. Both compounds, 1-[4-(4-chinolin-2-yl-piperazin-1-yl)-butyl]piperidin-2-on (MM5) and 1-[4-(2-methyl-4-chinolin-2-yl-piperazin-1-yl)-butyl]-8-azaspiro [4.5]decano-7,9-dion (MC1), produced hypothermia in mice and showed affinity for 5-HT1A receptors in-vitro. Like the selective 5-HT1A agonist 8-OH-DPAT (0.1 mg kg−1), MM5 given peripherally (30 mg kg−1) decreased the extracellular 5-HT level in rat prefrontal cortex, while MC1 suppressed 5-HT release at a higher dose (40 mg kg−1), but not at a lower one (30 mg kg−1). The effect of both compounds on 5-HT release was abolished by WAY 100635 (0.3 mg kg−1). MC1 (30 and 40 mg kg−1), but not MM5, raised cortical dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC) and extracellular homovanillic acid (HVA) levels. The effect of MC1 on dopamine release was reversed by neither WAY 100635 nor the non-selective 5-HT2 antagonist ritanserin (2 mg kg−1). However, ritanserin prevented the effect of the higher dose of MC1 on 5-HT release. The results of this study suggest that MM5 exhibits the profile of a 5-HT1A agonist devoid of dopaminergic activity. MC1 seems to possess moderate agonist activity at 5-HT1A and 5-HT2A receptors, while acting on 5-HT release in the rat prefrontal cortex. However, the facilitation of dopamine release by this compound does not seem to be related to its affinity for 5-HT1A and 5-HT2A receptors.

Spreading depression: from serendipity to targeted therapy in migraine prophylaxis

Despite the relatively well-characterized headache mechanisms in migraine, upstream events triggering individual attacks are poorly understood. This lack of mechanistic insight has hampered a rational approach to prophylactic drug discovery. Unlike targeted abortive and analgesic interventions, mainstream migraine prophylaxis has been largely based on serendipitous observations (e.g. propranolol) and presumed class effects (e.g. anticonvulsants). Recent studies suggest that spreading depression is the final common pathophysiological target for several established or investigational migraine prophylactic drugs. Building on these observations, spreading depression can now be explored for its predictive utility as a preclinical drug screening paradigm in migraine prophylaxis.

Layer II/III of the prefrontal cortex: Inhibition by the serotonin 5-HT1A receptor in development and stress

The modulation of the prefrontal cortex by the neurotransmitter serotonin (5-HT) is thought to play a key role in determining adult anxiety levels. Layer II/III of the prefrontal cortex, which mediates communication across cortical regions, displays a high level of 5-HT(1A) receptor binding in normal individuals and a significantly lower level in patients with mood and anxiety disorders. Here, we examine how serotonin modulates pyramidal neurons in layer II/III of the rat prefrontal cortex throughout postnatal development and in adulthood. Using whole cell recordings in brain slices of the rat medial prefrontal cortex, we observed that serotonin directly inhibits layer II/III pyramidal neurons through 5-HT(1A) receptors across postnatal development (postnatal days 6-96). In adulthood, a sex difference in these currents emerges, consistent with human imaging studies of 5-HT(1A) receptor binding. We examined the effects of early life stress on the 5-HT(1A) receptor currents in layer II/III. Surprisingly, animals subjected to early life stress displayed significantly larger 5-HT(1A)-mediated outward currents throughout the third and fourth postnatal weeks after elevated 5-HT(1A) expression during the second postnatal week. Subsequent exposure to social isolation in adulthood resulted in the almost-complete elimination of 5-HT(1A) currents in layer II/III neurons suggesting an interaction between early life events and adult experiences. These data represent the first examination of functional 5-HT(1A) receptors in layer II/III of the prefrontal cortex during normal development as well as after stress.

SEROTONERGIC MECHANISMS IN AMYOTROPHIC LATERAL SCLEROSIS

Serotonin (5-HT) has been intimately linked with global regulation of motor behavior, local control of motoneuron excitability, functional recovery of spinal motoneurons as well as neuronal maturation and aging. Selective degeneration of motoneurons is the pathological hallmark of amyotrophic lateral sclerosis (ALS). Motoneurons that are preferentially affected in ALS are also densely innervated by 5-HT neurons (e.g., trigeminal, facial, ambiguus, and hypoglossal brainstem nuclei as well as ventral horn and motor cortex). Conversely, motoneuron groups that appear more resistant to the process of neurodegeneration in ALS (e.g., oculomotor, trochlear, and abducens nuclei) as well as the cerebellum receive only sparse 5-HT input. The glutamate excitotoxicity theory maintains that in ALS degeneration of motoneurons is caused by excessive glutamate neurotransmission, which is neurotoxic. Because of its facilitatory effects on glutaminergic motoneuron excitation, 5-HT may be pivotal to the pathogenesis and therapy of ALS. 5-HT levels as well as the concentrations 5-hydroxyindole acetic acid (5-HIAA), the major metabolite of 5-HT, are reduced in postmortem spinal cord tissue of ALS patients indicating decreased 5-HT release. Furthermore, cerebrospinal fluid levels of tryptophan, a precursor of 5-HT, are decreased in patients with ALS and plasma concentrations of tryptophan are also decreased with the lowest levels found in the most severely affected patients. In ALS progressive degeneration of 5-HT neurons would result in a compensatory increase in glutamate excitation of motoneurons. Additionally, because 5-HT, acting through presynaptic 5-HT1B receptors, inhibits glutamatergic synaptic transmission, lowered 5-HT activity would lead to increased synaptic glutamate release. Furthermore, 5-HT is a precursor of melatonin, which inhibits glutamate release and glutamate-induced neurotoxicity. Thus, progressive degeneration of 5-HT neurons affecting motoneuron activity constitutes the prime mover of the disease and its progression and treatment of ALS needs to be focused primarily on boosting 5-HT functions (e.g., pharmacologically via its precursors, reuptake inhibitors, selective 5-HT1A receptor agonists/5-HT2 receptor antagonists, and electrically through transcranial administration of AC pulsed picotesla electromagnetic fields) to prevent excessive glutamate activity in the motoneurons. In fact, 5HT1A and 5HT2 receptor agonists have been shown to prevent glutamate-induced neurotoxicity in primary cortical cell cultures and the 5-HT precursor 5-hydroxytryptophan (5-HTP) improved locomotor function and survival of transgenic SOD1 G93A mice, an animal model of ALS.

Gene expression in the anterior cingulate cortex and amygdala of adolescent marmoset monkeys following parental separations in infancy

Early life adversities are risk factors for later mood and emotional disorders. Repeated separation of infant marmosets from their parents provides a validated primate model of depression vulnerability, producing in-vivo biochemical and behavioural effects indicative of persistently altered stress reactivity and mild anhedonia. Here we report the long-term effect (in adolescence) of this intervention on the expression of synaptophysin, GAP-43, VGluT1, VGAT, MAP-2, spinophilin, and 5-HT1A and 5-HT2A receptors, in the anterior cingulate cortex (ACC; supragenual and subgenual areas) and amygdala (lateral, basal and central nuclei). These genes and regions are implicated in the response to stress or in mood disorder. The profile of 5-HT1A receptor binding in ACC was affected by early deprivation, notably in the subgenual region, with a decrease in deep laminae but an increase in superficial laminae. Following early deprivation, spinophilin mRNA was reduced in subgenual ACC. In the amygdala, no significant effects of the manipulation were seen, but expression of several transcripts was sexually dimorphic. There were correlations between expression of some transcripts and in-vivo measurements. The results show that early deprivation in a non-human primate has a selective long-term effect on expression of genes in the ACC, particularly the subgenual area. The results differ from those reported in the hippocampus of the same animals, indicating the presence of limbic region-specific long-term molecular responses to early life stress.

Serotoninergic fine-tuning of the excitation-inhibition balance in rat visual cortical networks

Fundamental brain functions depend on a balance between excitation (E) and inhibition (I) that is highly adjusted to a 20-80% set point in layer 5 pyramidal neurons (L5PNs) of rat visual cortex. Dysregulations of both the E-I balance and the serotonergic system in neocortical networks lead to serious neuronal diseases including depression, schizophrenia, and epilepsy. However, no link between the activation of neuronal 5-hydroxytryptamine receptors (5-HTRs) and the cortical E-I balance has yet been reported. Here we used a combination of patch-clamp recordings of composite stimulus-locked responses in L5PN following local electrical stimulations in either layer 2/3 or 6, simultaneous measurement of excitatory and inhibitory conductance dynamics, together with selective pharmacological targeting and single-cell reverse transcriptase-polymerase chain reaction. We show that cortical serotonin shifts the E-I balance in favor of more E and we reveal fine and differential modulations of the E-I balance between 5-HTR subtypes, in relation to whether layer 2/3 or 6 was stimulated and in concordance with the specific expression pattern of these subtypes in pyramidal cells and deep interneurons. This first evidence for the functional segregation of 5-HTR subtypes sheds new light on their coherent functioning in polysynaptic sensory circuits.

Differential effects of M1 and 5-hydroxytryptamine1A receptors on atypical antipsychotic drug-induced dopamine efflux in the medial prefrontal cortex

Systemic administration of the M(1) receptor agonists N-desmethylclozapine (NDMC) and 4-[3-(4-butylpiperidin-1-yl)-propyl]-7-fluoro-4H-benzo[1,4]oxazin-3-one (AC260584) increase dopamine (DA) efflux in rat medial prefrontal cortex (mPFC). This increase is blocked by systemic administration of both telenzepine, a preferential M(1) receptor antagonist, and N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl)cyclohexanecarboxamide (WAY-100635), a 5-hydroxytryptamine(1A) receptor antagonist. The present study sought to determine whether DA efflux in the mPFC induced by the atypical antipsychotic drugs clozapine, risperidone, and olanzapine is also mediated by M(1) receptor stimulation and, specifically, to determine whether these effects are mediated M(1) receptors in the mPFC through use of in vivo microdialysis in awake, freely moving Sprague-Dawley rats. Telenzepine (3 mg/kg) significantly attenuated clozapine- (20 mg/kg), olanzapine- (10 mg/kg), and risperidone- (1.0 mg/kg) induced increases in mPFC DA efflux. Local mPFC perfusion of NDMC, AC260584, clozapine, risperidone, or olanzapine (10-500 microM), significantly increased DA efflux in the mPFC. Local mPFC perfusion of telenzepine (0.1 microM) prevented increases in mPFC DA efflux induced by systemic administration of AC260584 (10 mg/kg), NDMC (20 mg/kg), and clozapine (10 mg/kg), but not by risperidone (1.0 mg/kg) or olanzapine (10 mg/kg). However, local mPFC perfusion of WAY-100635 (0.1 microM) prevented mPFC DA efflux induced by clozapine, risperidone, and olanzapine, but not by AC260584 or NDMC. These results suggest that the AC260584-, NDMC-, and clozapine-induced DA efflux in the mPFC is mediated directly by mPFC M(1) receptors.

The firing activity of pyramidal neurons in medial prefrontal cortex and their response to 5-hydroxytryptamine-1A receptor stimulation in a rat model of Parkinson's disease

The changes in the firing rate and firing pattern of pyramidal neurons in medial prefrontal cortex (mPFC) and the effects of selective 5-hydroxytryptamine-(1A) (5-HT(1A)) receptor agonist (R)-(+)-8-hydroxy-2-(dipropylamino)tetralin hydrobromide (8-OH-DPAT) and antagonist N-(2-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl)-N-2-pyridylcyclohexane carboxamide maleate salt (WAY-100635) on the firing activity of the neurons were studied in sham-lesioned rats and rats with 6-hydroxydopamine lesions of the substantia nigra pars compacta (SNc). The lesion of the SNc increased the firing rate of pyramidal neurons significantly compared to sham-lesioned rats, and the firing pattern of these neurons also changed significantly towards a more burst-firing. The systemic administration of 8-OH-DPAT at doses in the range of 0.5-128 microg/kg showed an excitatory-inhibitory effect on the firing rate of pyramidal neurons in mPFC of sham-lesioned rats. At lower doses, 0.5-32 microg/kg, it evoked excitation of the neurons, and at a high dose, i.e. 128 microg/kg, inhibited the activity of the neurons. In contrast to sham-lesioned rats, 8-OH-DPAT, at the same doses, showed no excitatory effect in the lesioned rats although the inhibitory phase of the effect of 8-OH-DPAT on the firing rate of pyramidal neurons in mPFC was still present. Furthermore, the local application of 8-OH-DPAT, 5 microg, in mPFC inhibited the firing rate of pyramidal neurons in sham-lesioned rats, while having no effect on firing rate in the lesioned rats. The excitatory or inhibitory effects of 8-OH-DPAT were reversed by WAY-100635, indicating that these effects are mediated by 5-HT(1A) receptor. Altogether, these results indicate that the lesion of the SNc leads to hyperactivity of pyramidal neurons in mPFC and the abnormality of response of these neurons to 5-HT(1A) receptor stimulation, suggesting that mPFC may be involved in the pathophysiology of the psychiatric disturbance of Parkinson's disease.

Role of different monoamine receptors controlling MK-801-induced release of serotonin and glutamate in the medial prefrontal cortex: relevance for antipsychotic action

Several studies have demonstrated that systemically administered N-methyl-d-aspartate (NMDA) receptor antagonists increase serotonin (5-HT) and glutamate release in the medial prefrontal cortex (mPFC). Previously we showed that the perfusion of clozapine in the mPFC prevented the MK-801-induced increase in extracellular glutamate and 5-HT whereas haloperidol blocked only the effect of MK-801 on glutamate. To study the contribution of different monoaminergic receptors (for which clozapine and haloperidol exhibit distinct affinities) to these effects, here we used in-vivo microdialysis to examine the role of local blockade of dopamine D2, 5-HT2A and alpha1-adrenergic receptors as well as agonism at dopamine D1 and 5-HT1A receptors in the mPFC on the increased efflux of glutamate and 5-HT elicited by MK-801. The results show that M100907 (5-HT2A antagonist), BAY x 3702 (5-HT1A agonist) and prazosin (alpha1-adrenergic antagonist) blocked the MK-801-induced increase of 5-HT and glutamate in the mPFC. However, raclopride, eticlopride (dopamine D2 antagonists) and SKF-38393 (dopamine D1 agonist) were able to prevent the increased efflux of glutamate (but not that of 5-HT) elicited by MK-801. We propose that D2 receptor antagonists and D1 agonists would act predominantly on a subpopulation of GABAergic interneurons of the mPFC, thus leading to an enhanced cortical inhibition that would prevent an excessive glutamatergic transmission. On the other hand, atypical antipsychotic drugs might further act upon 5-HT2A, 5-HT1A and alpha1-adrenoceptors present in pyramidal cells (including those projecting to the dorsal raphe nucleus), which would directly inhibit an excessive excitability of these cells.

Impaired interhemispheric interactions in patients with major depression

Previous studies have shown that patients with major depression have an interhemispheric imbalance between right and left prefrontal and motor cortex. We aimed to investigate the interhemispheric interactions in patients with major depression using repetitive transcranial magnetic stimulation (rTMS). Thirteen patients with major depression and 14 age-matched healthy subjects participated in this study. Corticospinal excitability before and after 1 Hz rTMS (applied to the left primary motor cortex) was assessed in the left and right motor cortex and these results were compared with those in healthy subjects. There was a significant difference in the interhemispheric effects between patients with depression and healthy subjects. In healthy subjects, 1 Hz rTMS significantly decreased corticospinal excitability in the stimulated, left hemisphere and increased it in the contralateral, right hemisphere. In depressed subjects, 1 Hz rTMS also decreased corticospinal excitability in the left hemisphere; however, it induced no significant changes in corticospinal excitability in the contralateral, right hemisphere. In addition, there was a significant correlation between the degree of interhemispheric modulation and the severity of the depression as indexed by the Beck Depression Inventory scores. Our findings showing a decreased interhemispheric modulation in patients with major depression are consistent with the notion that mood disorders are associated with slow interhemispheric switching mechanisms.

The antipsychotics clozapine and olanzapine increase plasma glucose and corticosterone levels in rats: comparison with aripiprazole, ziprasidone, bifeprunox and F15063

Several novel antipsychotics activate serotonin 5-HT1A receptors as well as antagonising dopamine D2/3 receptors. Such a pharmacological profile is associated with a lowered liability to produce extrapyramidal side effects and enhanced efficacy in treating negative and cognitive symptoms of schizophrenia. However, 5-HT1A receptor agonists increase plasma corticosterone and many antipsychotics disturb the regulation of glucose. Here, we compared the influence on plasma glucose and corticosterone of acute treatments with 'new generation' antipsychotics which target dopamine D2/3 receptors and 5-HT1A receptors, with that of atypical antipsychotics, and with haloperidol. Olanzapine and clozapine, antipsychotics that are known to produce weight gain and diabetes in humans, both at 10 mg/kg p.o., substantially increased plasma glucose (from 0.8 to 1.7 g/l) at 1 h after administration, an effect that returned to control levels after 4 h. In comparison, F15063 (40 mg/kg p.o.) was without effect at any time point. Olanzapine and clozapine dose-dependently increased plasma glucose concentrations as did SLV313 and SSR181507. Haloperidol and risperidone had modest effects whereas aripiprazole, ziprasidone and bifeprunox, antipsychotics that are not associated with metabolic dysfunction in humans, and F15063 had little or no influence on plasma glucose. The same general pattern of response was found for plasma corticosterone levels. The present data provide the first comparative study of conventional, atypical and 'new generation' antipsychotics on glucose and corticosterone levels in rats. A variety of mechanisms likely underlie the hyperglycemia and corticosterone release observed with clozapine and olanzapine, whilst the balance of dopamine D2/3/5-HT1A interaction may contribute to the less favourable impact of SLV313 and SSR181507 compared with that of bifeprunox and F15063.

The effect of a serotonin-induced dissociation between spiking and perisynaptic activity on BOLD functional MRI

The relationship of the blood oxygen-level-dependent (BOLD) signal to its underlying neuronal activity is still poorly understood. Combined physiology and functional MRI experiments suggested that local field potential (LFP) is a better predictor of the BOLD signal than multiunit activity (MUA). To further explore this relationship, we simultaneously recorded BOLD and electrophysiological activity while inducing a dissociation of MUA from LFP activity with injections of the neuromodulator BP554 into the primary visual cortex of anesthetized monkeys. BP554 is a 5-HT1A agonist acting primarily on the membrane of efferent neurons by potassium-induced hyperpolarization. Its infusion in visual cortex reliably reduced MUA without affecting either LFP or BOLD activity. This finding suggests that the efferents of a neuronal network pose relatively little metabolic burden compared with the overall presynaptic and postsynaptic processing of incoming afferents. We discuss implications of this finding for the interpretation of BOLD activity.

F15063, a potential antipsychotic with D2/D3 antagonist, 5-HT 1A agonist and D4 partial agonist properties. I. In vitro receptor affinity and efficacy profile

BACKGROUND AND PURPOSE

Combining 5-HT(1A) receptor activation with dopamine D(2)/D(3) receptor blockade should improve negative symptoms and cognitive deficits in schizophrenia. We describe the in vitro profile of F15063 (N-[(2,2-dimethyl-2,3-dihydro-benzofuran-7-yloxy)ethyl]-3-(cyclopent-1-enyl)-benzylamine).

EXPERIMENTAL APPROACH

F15063 was characterised in tests of binding affinity and in cellular models of signal transduction at monoamine receptors.

KEY RESULTS

Affinities (receptor and pK(i) values) of F15063 were: rD(2) 9.38; hD(2L) 9.44; hD(2S) 9.25; hD(3) 8.95; hD(4) 8.81; h5-HT(1A) 8.37. F15063 had little affinity (40-fold lower than D(2)) at other targets. F15063 antagonised dopamine-activated G-protein activation at hD(2), rD(2) and hD(3) receptors with potency (pK (b) values 9.19, 8.29 and 8.74 in [(35)S]GTP gamma S binding experiments) similar to haloperidol. F15063 did not exhibit any hD(2) receptor agonism, even in tests of ERK1/2 phosphorylation and G-protein activation in cells with high receptor expression. In contrast, like (+/-)8-OH-DPAT, F15063 efficaciously activated h5-HT(1A) (E(max) 70%, pEC(50) 7.57) and r5-HT(1A) receptors (52%, 7.95) in tests of [(35)S]GTP gamma S binding, cAMP accumulation (90%, 7.12) and ERK1/2 phosphorylation (93%, 7.13). F15063 acted as a partial agonist for [(35)S]GTP gamma S binding at hD(4) (29%, 8.15) and h5-HT(1D) receptors (35%, 7.68). In [(35)S]GTP gamma S autoradiography, F15063 activated G-proteins in hippocampus, cortex and septum (regions enriched in 5-HT(1A) receptors), but antagonised quinelorane-induced activation of D(2)/D(3) receptors in striatum.

CONCLUSIONS AND IMPLICATIONS

F15063 antagonised dopamine D(2)/D(3) receptors, a property underlying its antipsychotic-like activity, whereas activation of 5-HT(1A) and D(4) receptors mediated its actions in models of negative symptoms and cognitive deficits of schizophrenia (see companion papers).

Activation of pyramidal cells in rat medial prefrontal cortex projecting to ventral tegmental area by a 5-HT1A receptor agonist

5-HT(1A) receptor agonists increase the activity of dopamine (DA) neurons in the ventral tegmental area (VTA) and DA release in medial prefrontal cortex (mPFC). The mPFC is enriched in 5-HT(1A) receptors and projects to the VTA, where mesocortical dopaminergic neurons originate. We examined whether 5-HT(1A) receptor activation can modulate the activity of mPFC pyramidal neurons projecting to VTA. These were identified by antidromic stimulation from the VTA and were recorded extracellularly in anesthetized rats. The selective 5-HT(1A) agonist BAY x 3,702 (10-80 microg/kg i.v.) increased the firing rate in 14/19 neurons (283 +/- 79%) and reduced the activity of 5/19 neurons (22 +/- 11%), resulting in an overall 2.2-fold increase of the firing rate. Both effects were blocked by the selective 5-HT(1A) antagonist WAY-100635. These results suggest that the increase in dopaminergic activity produced by 5-HT(1A) receptor activation can be driven by an increase in the activity of projection neurons in mPFC.

Multi-target strategies for the improved treatment of depressive states: Conceptual foundations and neuronal substrates, drug discovery and therapeutic application

Major depression is a debilitating and recurrent disorder with a substantial lifetime risk and a high social cost. Depressed patients generally display co-morbid symptoms, and depression frequently accompanies other serious disorders. Currently available drugs display limited efficacy and a pronounced delay to onset of action, and all provoke distressing side effects. Cloning of the human genome has fuelled expectations that symptomatic treatment may soon become more rapid and effective, and that depressive states may ultimately be "prevented" or "cured". In pursuing these objectives, in particular for genome-derived, non-monoaminergic targets, "specificity" of drug actions is often emphasized. That is, priority is afforded to agents that interact exclusively with a single site hypothesized as critically involved in the pathogenesis and/or control of depression. Certain highly selective drugs may prove effective, and they remain indispensable in the experimental (and clinical) evaluation of the significance of novel mechanisms. However, by analogy to other multifactorial disorders, "multi-target" agents may be better adapted to the improved treatment of depressive states. Support for this contention is garnered from a broad palette of observations, ranging from mechanisms of action of adjunctive drug combinations and electroconvulsive therapy to "network theory" analysis of the etiology and management of depressive states. The review also outlines opportunities to be exploited, and challenges to be addressed, in the discovery and characterization of drugs recognizing multiple targets. Finally, a diversity of multi-target strategies is proposed for the more efficacious and rapid control of core and co-morbid symptoms of depression, together with improved tolerance relative to currently available agents.