Depression by neuropeptide Y of noradrenergic inhibitory postsynaptic potentials of locus coeruleus neurones

Summary Intracellular recordings were performed in a pontine slice preparation of the rat brain containing the locus coeruleus (LC). The spontaneous firing of action potentials was prevented by passing continuous hyperpolarizing current via the recording electrode. Focal electrical stimulation evoked a synaptic depolarization (PSP) followed by a hyperpolarization (IPSP). Neuropeptide Y (NPY; 0.1 mol/l) inhibited the IPSP only. Pressure ejection of noradrenaline produced hyperpolarization which was potentiated in the presence of NPY (0.1 mol/l). Hence, NPY appears to inhibit the release of noradrenaline from dendrites or recurrent axon collaterals of LC neurones. Correspondence to: P. Illes at the above address     

The pharmacology of DMP696 and DMP904, non-peptidergic CRF1 receptor antagonists

CRF(1) antagonists DMP696 and DMP904 were designed as drug development candidates for the treatment of anxiety and depression. Both compounds display nanomolar affinity for human CRF(1) receptors, and exhibit >1000-fold selectivity for CRF(1) over CRF(2) receptors and over a broad panel of other proteins. DMP696 and DMP904 block CRF-stimulated adenylyl cyclase activity in cortical homogenates and cell-lines expressing CRF(1) receptors. Both compounds inhibit CRF-stimulated ACTH release from rat pituitary corticotropes. Binding and functional studies indicate that DMP696 and DMP904 behave as noncompetitive full antagonists. DMP696 and DMP904 exhibit anxiolytic-like efficacy in several rat anxiety models. In the defensive withdrawal test, both compounds reduce exit latency with lowest effective doses of 3 and 1 mg/kg, respectively. The anxiolytic-like effect is maintained over 14 days of repeated dosing. In the context of a novel environment used in this test, DMP696 and DMP904 reverse mild stress-induced increases in plasma CORT secretion but at doses 3-4-fold greater than those required for anxiolyticlike efficacy. DMP696 and DMP904 are ineffective in three depression models including the learned helplessness paradigm at doses up to 30 mg/kg. At lowest anxiolytic-like doses, DMP696 and DMP904 occupy >50% CRF(1) receptors in the brain. The in vivo IC(50) values (plasma concentrations required for occupying 50% CRF(1) receptors) estimated based upon free, but not total, plasma concentrations are an excellent correlation with the in vitro IC(50) values. Neither compound produces sedation, ataxia, chlordiazepoxide-like subjective effects or adverse effects on cognition at doses 10-fold higher than anxiolytic-like doses. Neither compound produces physiologically significant changes in cardiovascular, respiratory, gastrointestinal or renal functions at anxiolytic-like doses. DMP696 and DMP904 have favorable pharmacokinetic profiles with good oral bioavailabilities. The overall pharmacological properties suggest that both compounds may be effective anxiolytics with low behavioral side effect liabilities.     

Histamine excites noradrenergic neurons in locus coeruleus in rats

Histamine is implicated in the control of many brain functions, in particular the control of arousal. Histaminergic neurons send dense projections through the entire brain, including the locus coeruleus (LC)--the main noradrenergic (NAergic) nucleus. In this study, we have examined the effect of bath-applied histamine on cells in the LC by single-unit recordings in slices and the expression of histamine receptors in this area by single-cell RT-PCR. Histamine (10 microM) increased the firing of NAergic cells to 130+/-9% of control, 100 microM to 256+/-58% of control. This excitation was unaffected by blocking synaptic transmission. Histamine-mediated excitation was blocked by an H1 receptor antagonist, mepyramine, in 78% of cells and by cimetidine, an H2 receptor antagonist, in 42% of cells, but not by the H3 receptor antagonist, thioperamide. RT-PCR revealed that mRNA for the H1 receptor was expressed in 77% of isolated LC neurons, mRNA for the H2 receptor in 41% of LC neurons and H3 receptors in 29%. These findings underline the coordination between aminergic systems and suggest that the arousal induced by the histamine system could involve excitation of noradrenergic neurons in the locus coeruleus.     

The CRF(1) receptor antagonist DMP696 produces anxiolytic effects and inhibits the stress-induced hypothalamic-pituitary-adrenal axis activation without sedation or ataxia in rats

Abstract Rationale. CRF₁ antagonists may be effective in the treatment of anxiety disorders while having fewer side effects compared with classical benzodiazepines. Objectives. The effects of a small molecule selective CRF₁ antagonist DMP696 on anxiety-like behaviors and stress-induced increases in corticosterone in rats exposed to a novel environment and on locomotor activity and motor coordination were determined in rats. These effects of DMP696 were compared with those produced by the classical benzodiazepine chlordiazepoxide (CDP). Methods. DMP696 or CDP were administered PO, 60 minutes before behavioral testing in rats. Their effects on latency to exit a dark chamber and stress-induced increase in corticosterone in the Defensive Withdrawal test (an animal model of anxiety), locomotor activity, and rotorod performance (measure of ataxia) were determined. Results. DMP696 significantly reduced exit latency and reversed the stress-induced increase in corticosterone in the Defensive Withdrawal test at doses of 3.0–10 mg/kg and higher. In contrast, CDP significantly decreased exit latency at 10 and 30 mg/kg, but not at 100 mg/kg, due to concurrent non-specific side effects. Unlike DMP696, CDP had no effect on the stress-induced increase in corticosterone at lower doses, but resulted in a significant increase at higher doses. DMP696 did not reduce locomotor activity or impair motor coordination at doses up to 30-fold higher than doses effective in the Defensive Withdrawal model. In contrast, CDP produced significant sedation and ataxia at the same doses that were effective in reducing exit latency. Conclusions. These data suggest that the CRF₁ antagonist DMP696 might retain the therapeutic benefits of classical benzodiazepines but have fewer motoric side effects. Electronic Publication     

Involvement of locus coeruleus noradrenergic neurons in supraspinal antinociception by alpha,beta-methylene-ATP in rats

We reported previously that intracerebroventricular (i.c.v.) administration of P2X-receptor agonists produced antinociception and the effect was attenuated by i.c.v. pretreatment with beta(2)-adrenergic receptor antagonists. The present study examined the involvement of noradrenergic neurons arising from the locus coeruleus (LC) in the supraspinal antinociception by the P2X-receptor agonist alpha,beta-methylene-ATP in rats. We found that pretreatment with DSP-4 (50 mg/kg, i.p.), which is a neurotoxin to selectively disrupt noradrenergic neurons arising from the LC, significantly attenuated the antinociception by i.c.v. administration of alpha,beta-methylene-ATP (10 nmol/rat). Microinjection of alpha,beta-methylene-ATP (0.1 and 1 nmol/side) into the bilateral LC significantly elevated the nociceptive threshold more potently than the i.c.v. administration at a dose of 10 nmol/rat. The antinociception by intra-LC injection of alpha,beta-methylene-ATP (1 nmol/side) was significantly attenuated by co-injection of pyridoxal-phosphate-6-azophenyl-2',4'-disulphonic acid (1 nmol/side), a non-selective P2X-receptor antagonist. These results suggest that noradrenergic neurons arising from the LC are involved in the supraspinal antinociception by alpha,beta-methylene-ATP through P2X receptors in the LC.     

CRF1受体阻滞剂类新型抗抑郁药DMP696的合成新方法

目的：合成促肾上腺皮质激素释放激素1(CRF1)受体阻滞剂类新型抗抑郁药DMP696。方法：以2,4-二氯苯乙腈为起始原料,经乙酰化、两次环化、氯代、偶联共5步合成DMP696。结果：目标化合物的总收率为10.5%,结构经1H-NMR、MS确证。结论：该方法合成路线短,试剂廉价易得,反应条件温和易控。     

Modulation of the firing activity of noradrenergic neurones in the rat locus coeruleus by the 5-hydroxtryptamine system

1. The aim of the present study was to investigate the putative modulation of locus coeruleus (LC) noradrenergic (NA) neurones by the 5-hydroxytryptaminergic (5-HT) system by use of in vivo extracellular unitary recordings and microiontophoresis in anaesthetized rats. To this end, the potent and selective 5-HT_1A receptor antagonist WAY 100635 (N-{2-[4(2-methoxyphenyl)-1-piperazinyl]ethyl}-N-(2-pyridinyl)cyclohexanecarboxamide trihydroxychloride) was used.
2. In the dorsal hippocampus, both local (by microiontophoresis, 20 nA) and systemic (100 μg kg⁻¹, i.v.) administration of WAY 100635 antagonized the suppressant effect of microiontophorectically-applied 5-HT on the firing activity of CA₃ pyramidal neurones, indicating its antagonistic effect on postsynaptic 5-HT_1A receptors.
3. WAY 100635 and 5-HT failed to modify the spontaneous firing activity of LC NA neurones when applied by microiontophoresis. However, the intravenous injection of WAY 100635 (100 μg kg⁻¹) readily suppressed the spontaneous firing activity of LC NA neurones.
4. The lesion of 5-HT neurones with the neurotoxin 5,7-dihydroxytryptamine increased the spontaneous firing activity of LC NA neurones and abolished the suppressant effect of WAY 100635 on the firing activity of LC NA neurones.
5. In order to determine the nature of the 5-HT receptor subtypes mediating the suppressant effect of WAY 100635 on NA neurone firing activity, several 5-HT receptor antagonists were used. The selective 5-HT₃ receptor antagonist BRL 46470A (10 and 100 μg kg⁻¹, i.v.), the 5-HT_1D receptor antagonist GR 127935 (100 μg kg⁻¹, i.v.) and the 5-HT_1A/1B receptor antagonist (−)-pindolol (15 mg kg⁻¹, i.p.) did not prevent the suppressant effect of WAY 100635 on the firing activity of LC NA neurones. However, the suppressant effect of WAY 100635 was prevented by the non-selective 5-HT receptor antagonists spiperone (1 mg kg⁻¹, i.v.) and metergoline (1 mg kg⁻¹, i.v.), by the 5-HT₂ receptor antagonist ritanserin (500 μg kg⁻¹, i.v.). It was also prevented by the 5-HT_1A receptor/α_1D-adrenoceptor antagonist BMY 7378 (1 mg kg⁻¹, i.v.) and by the α₁-adrenoceptor antagonist prazosin (100 μg kg⁻¹, i.v.).
6. These data support the notion that the 5-HT system tonically modulates NA neurotransmission since the lesion of 5-HT neurones enhanced the LC NA neurones firing activity and the suppressant effect of WAY 100635 on the firing activity of NA neurones was abolished by this lesion. However, the location of the 5-HT_1A receptors involved in this complex circuitry remains to be elucidated. It is concluded that the suppressant effect of WAY 100635 on the firing activity of LC NA neurones is due to an enhancement of the function of 5-HT neurones via a presynaptic 5-HT_1A receptor. In contrast, the postsynaptic 5-HT receptor mediating this effect of WAY 100635 on NA neurones appears to be of the 5-HT_2A subtype.

     

Stimulatory effects of clonidine,cirazoline and rilmenidine on locus coeruleus noradrenergic neurones: possible involvement of imidazoline-preferring receptors

Summary Clonidine and related drugs not only interact with ₂-adrenoceptors but also recognise non-adrenoceptor sites in the brain. The involvement of these imidazoline-preferring receptors in the regulation of the activity of locus coeruleus noradrenergic neurones (NA-LC) was investigated after inactivation of ₂-adrenoceptors with N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ). In EEDQ-pretreated rats (6 mg/kg, i.p., 6 h), the characteristic inhibitory effect of low doses of clonidine on these neurones was abolished and a paradoxical, dose-dependent increase in firing rate was observed at higher doses (640–5120 g/kg, i.v.) (ED₅₀ = 702 g/kg, E_max = 83 %, n = 14). Guanfacine (0.3–20 mg/kg) did not modify neuronal activity but antagonised the stimulatory effect of clonidine. Cirazoline (80–640 g/kg) and rilmenidine (0.3–10 mg/kg) also stimulatedneuronal activity(ED₅₀ = 192 g/kg, E_max = 102%, n = 5; ED₅₀ = 1563 g/kg, E_max = 70%, n = 1–5, respectively) by an ₂-adrenoceptor-independent mechanism. The results suggest that these drugs can modulate the activity of locus coeruleus noradrenergic neurones through the activation of I₁-imidazoline-preferring receptors.     

The stimulatory effect of clonidine through imidazoline receptors on locus coeruleus noradrenergic neurones is mediated by excitatory amino acids and modulated by serotonin

Clonidine and other imidazoline/oxazoline drugs, such as cirazoline and rilmenidine, have been shown to stimulate the activity of noradrenergic neurones in the locus coeruleus (NA-LC) by an ₂-adrenoceptor-independent mechanism through the activation of I-imidazoline receptors. The endogenous modulation of the stimulatory effect of clonidine on NA-LC neurones was further investigated after inactivation of ₂-adrenoceptors with N-ethoxycarbonyl-2-ethoxy-1, 2-dihydroquinoline (EEDQ). In EEDQ-pretreated rats (6 mg/kg, i.p., 6h), clonidine caused a rapid and dose-dependent (320–5120 g/kg, i.v.) increase in the firing rate of NA-LC neurones (ED₅₀ = 809 g/kg, E_max = 90%). The stimulatory effect of clonidine on NA-LC neurones was completely blocked by pretreatment of rats with the excitatory amino acid receptor antagonist kynurenic acid (1–3 mol in 10–30 mol i.c.v., 2–5 min before clonidine). In contrast, the stimulatory effect of clonidine on NA-LC neurones was potentiated by pretreatment with reserpine (5 mg/kg, s.c., 18 h) (E_max increased by 63%). Pretreatment with -methyl-p-tyrosine (250 mg/kg, i.p., 24 h) did not alter the stimulatory effect of clonidine, but pretreatment with p-chloro-phenylalanine (400 mg/kg, i.p., 24 h) markedly enhanced the stimulatory effect of clonidine on NA-LC neurones (E_max increased by 139%). The present results indicate that the imidazoline receptor-mediated stimulatory effect of clonidine on NA-LC neurones is an indirect effect dependent on an excitatory amino acid pathway and modulated by an inhibitory serotonin mechanism.     

Opiate activation of potassium conductance inhibits calcium action potentials in rat locus coeruleus neurones.

Opiates act on mu-receptors to increase the potassium conductance of rat locus coeruleus neurones. Opiates also depress the rate of rise and peak amplitude of calcium action potentials in these cells. The action of opiates on calcium action potentials was prevented by two procedures which blocked the opiate-induced potassium current, intracellular caesium and extracellular barium. This indicates that the opiate reduction in calcium entry is secondary to an increased potassium current.     

Dependence-induced increases in ethanol self-administration in mice are blocked by the CRF1 receptor antagonist antalarmin and by CRF1 receptor knockout

Models of dependence-induced increases in ethanol self-administration will be critical in increasing our understanding of the processes of addiction and relapse, underlying mechanisms, and potential therapeutics. One system that has received considerable attention recently is the CRF(1) system that may mediate the link between anxiety states and relapse drinking. C57BL/6J mice were trained to lever press for ethanol, were made dependent and then were allowed to self-administer ethanol following a period of abstinence. The effect of the CRF(1) antagonist, antalarmin, was examined on this abstinence-induced self-administration in a separate group of mice. Finally, dependence-induced changes in ethanol self-administration were examined in CRF(1) knockout and wild type mice. The results indicated that ethanol self-administration was increased following the induction of dependence, but only after a period of abstinence. This increase in ethanol self-administration was blocked by antalarmin. Furthermore, CRF(1) knockout mice did not display this increased ethanol self-administration following dependence and abstinence. These studies, using both a pharmacological and genetic approach, support a critical role for the CRF(1) system in ethanol self-administration following dependence. In addition, a model is presented that may be useful for studies examining underlying mechanisms of the ethanol addiction process as well as for testing potential therapeutics.     

Effect of vinpocetine on noradrenergic neurons in rat locus coeruleus

Conventional extracellular single unit recordings were used to investigate the effect of vinpocetine on locus coeruleus noradrenergic neurons in chloral hydrate-anesthetized rats. Vinpocetine produced a significant and dose-dependent increase in the firing rate of locus coeruleus neurons (ED30 = 0.75 mg/kg i.v.) up to 1 mg/kg i.v., followed by a complete blockade of spiking activity at doses higher than this. The effective dose range was in very good agreement with the dose range corresponding to the memory-enhancing effects of the compound. Our results supplied direct electrophysiological evidence that vinpocetine increases the activity of ascending noradrenergic pathways. This effect can be related to the cognitive-enhancing characteristics of the compound.     

Intracerebroventricular and locus coeruleus microinjections of somatostatin antagonist decrease REM sleep in rats

In order to study the role of endogenous somatostatin in the physiologic modulation of REM sleep (REMS), we measured the effect of intracerebroventricular (ICV) injection of somatostatin antagonist (SA) cyclo-(7-aminoheptanoyl-phe-d-trp-lys-thr(bzl)) on sleep in rats. The effect of ICV SA was also tested after 24-h REMS deprivation with the platform method. To study the role of locus coeruleus (LC) as a site of the sleep inducing action for somatostatin and galanin we microinjected SA, somatostatin, and galanin locally into LC. In all experiments, vigilance state was analyzed visually from 6 h post-injection EEG/EMG recording. Injection of 0.5 and 2 nmol of SA ICV reduced spontaneous REMS and 2 nmol dose reduced also rebound REMS after REMS deprivation when compared with controls (artificial cerebrospinal fluid vehicle). Microinjection of 0.25 nmol of SA into LC reduced REMS, whereas microinjection of somatostatin, galanin, and a combined injection of them were not effective to induce REMS. The results suggest that endogenous somatostatin may contribute to facilitation of REMS. Somatostatin receptors in the LC may be one possible mediator of this effect.     

Nociceptin receptor coupling to a potassium conductance in rat locus coeruleus neurones in vitro.

1. In this study we have examined the effects of nociceptin, an endogenous ligand for the opioid-like receptor ORL1 on the membrane properties of rat locus coeruleus (LC) neurones in vitro, using intracellular and whole cell patch clamp recording. 2. When locus coeruleus neurones were voltage clamped to -60 mV, application to nociceptin caused an outward current in all cells examined (n = 49), with an EC50 of 90 nM. Neither the potency nor the maximal effect of nociceptin was altered in the presence of the peptidase inhibitors, bestatin (20 microM) or thiorphan (2 microM). 3. The outward currents caused by nociceptin in 2.5 mM extracellular K+ reversed polarity at -123 mV, more negative than the predicted K+ reversal potential of -105 mV. Increasing extracellular K+ to 6.5 mM resulted in a shift of the reversal potential of +25 mV, a shift consistent with a K+ conductance. The conductance activated by nociceptin showed mild inward rectification. 4. Application of a high concentration of nociceptin (3 microM) occluded the current produced by simultaneous application of high concentrations of Met-enkephalin (10 microM), (3 microM) somatostatin and UK 14304 (3 microM), indicating that nociceptin activated the same conductance as mu-opioid and somatostatin receptors and alpha 2-adrenoceptors. 5. The actions of nociceptin were weakly antagonized by the opioid antagonist, naloxone, with pKb's estimated from 2 cells of -4.23 and -4.33. The mu-opioid antagonist, CTAP (D-Phe-Cys-Tyr-D-Trp-Arg-Pen-Thr-NH2, 1 microM), the opioid antagonist, nalorphine (30 microM) or the somatostatin antagonist, CPP (cyclo(7-aminoheptanoyl-Phe-D-Trp-Lys-Thr[Bz1]) 3 microM) did not affect the nociceptin-induced current. 6. Dynorphin A (microM), another putative endogenous ligand for ORL1, caused a robust outward current in locus coeruleus neurones that was, however, completely antagonized by moderate concentrations of naloxone (300 nM-1 microM). 7. Continuous application of nociceptin (3 microM) resulted in a decrease of the outward current to a steady level of 70% of the maximum response with a t1/2 of 120s. Desensitization was largely homologous because simultaneous application of Met-enkephalin (30 microM) during the desensitized period of the nociceptin response resulted in an outward current that was 92% of control responses to Met-enkephalin in the same cells. Conversely, continuous application of Met-enkephalin (30 microM) resulted in a decrease of Met-enkephalin current to a steady level that was 54% of the initial current. During this desensitized period application of nociceptin (3 microM) resulted in a current that was 78% of the control responses to nociceptin in the same cells. 8. Thus nociceptin potently activates an inwardly rectifying K+ conductance in locus coeruleus neurones, with a pharmacological profile consistent with activation of the ORL1 receptor. Dynorphin A does not appear to be a ligand for ORL1 in rat locus coeruleus neurones.     

The analgesic effect of N-arachidonoyl-serotonin, a FAAH inhibitor and TRPV1 receptor antagonist, associated with changes in rostral ventromedial medulla and locus coeruleus cell activity in rats

We evaluated the effects of intra-periaqueductal grey (PAG) N-arachidonoyl-serotonin (AA-5-HT), a compound with a “dual” ability to inhibit the fatty acid amide hydrolase (FAAH) and to antagonize transient receptor vanilloid type 1 (TRPV1) receptors, on endocannabinoid levels, rostral ventromedial medulla (RVM) ON and OFF cell activities, thermal nociception (tail flick in anaesthetized rats) and formalin-induced nocifensive responses in awake rats. AA-5-HT increased endocannabinoid levels in the PAG and induced analgesia. Paradoxically, it also depressed the RVM OFF cell, as well as the ON cell activities. The effect of AA-5-HT was mimicked by co-injecting the selective FAAH inhibitor URB597 and the selective TRPV1 antagonist I-RTX into the PAG, which also induced analgesia and inhibition of ON and OFF cell ongoing activities. The recruitment of “alternative” pathways, such as PAG-locus coeruleus (LC)-spinal cord might be responsible for AA-5-HT effect since we found evidence that (i) intra-PAG AA-5-HT increased LC neuron firing activities, and (ii) intrathecal phentolamine or ketanserin prevented the analgesic effect of AA-5-HT. Moreover, intra-PAG AA-5-HT prevented the changes in the ON and OFF cells firing activity induced by intra-paw formalin, and it inverted the formalin-induced increase in LC adrenergic cell activity. All AA-5-HT effects were antagonized by cannabinoid CB₁ and TRPV1 receptor antagonists thus suggesting that co-localization of these receptors in the PAG can be an appropriate neural substrate for AA-5-HT-induced analgesia.     

Footshock-induced responses in ventral subiculum neurons are mediated by locus coeruleus noradrenergic afferents

The ventral subiculum (vSub) of the hippocampus is critically involved in mediating the forebrain's response to stress, particularly with regard to psychogenic stressors. Stress, in turn, is known to aggravate many psychiatric conditions including schizophrenia, depression, anxiety, and drug abuse. Pathological alterations in hippocampal function have been identified in all these disorders; thus, it is of interest to understand how stress affects this brain region. The vSub receives dense projections from the stress-related locus coeruleus (LC); however, it is not known what role this input plays in signaling stressful stimuli. In this study, the direct LC innervation of the vSub was investigated as a potential mediator of stress responses in this region. To examine responses to an acute stressor, the effect of footshock on single vSub neurons was tested in rats. Footshock inhibited 13%, and activated 48% of neurons in this region. Importantly, responses to footshock were correlated with LC stimulation-evoked responses in single neurons, and LC inactivation blocked these responses. Furthermore, prazosin, an alpha-1 antagonist, reversed footshock-evoked inhibition, revealing an underlying activation. Inactivation of the basolateral amygdala (BLA) did not block phasic footshock-evoked activation; however, it reduced tonic activity in the vSub. These results suggest that the LC NE system plays an important role in mediating stress responses in the vSub. Footshock evokes both inhibition and excitation in the vSub, by activating noradrenergic inputs from the LC. These responses may contribute to stress adaptation; while an imbalance of this system may lead to pathological stress responses in mental disorders.     

Elevated concentrations of CRF in the locus coeruleus of depressed subjects.

Research evidence that corticotropin-releasing factor (CRF) plays a role in the pathophysiology of major depressive disorder (MDD) has accumulated over the past 20 years. The elevation of lumbar cerebrospinal fluid (CSF) concentrations of CRF decreased responsiveness of pituitary CRF receptors to challenge with synthetic CRF, and increased levels of serum cortisol in MDD subjects support the hypothesis that CRF is chronically hypersecreted in at least the endocrine circuits of the hypothalamic-pituitary-adrenal (HPA) axis and may also involve other CRF brain circuits mediating emotional responses and/or arousal. One such circuit includes the excitatory CRF input to the locus coeruleus (LC), the major source of norepinephrine in the brain. Furthermore, there are now reports of decreased levels of CRF in lumbar CSF from MDD patients after symptom relief from chronic treatment with antidepressant drugs or electroconvulsive therapy. Whether this normalization reflects therapeutic effects on both endocrine- and limbic-associated CRF circuits has not yet been effectively addressed. In this brief report, we describe increased concentrations of CRF-like immunoreactivity in micropunches of post-mortem LC from subjects with MDD symptoms as established by retrospective psychiatric diagnosis compared to nondepressed subjects matched for age and sex.     

Valproate enhances GABA-A mediated inhibition of locus coeruleus neurones in vitro

Summary It has previously been claimed that the anti-convulsant valproate acts by augmenting GABA-ergic transmission, however, the data supporting this claim is controversial. Here we demonstrate that valproate strongly and reversibly potentiates the depressant effects of the GABA-A receptor agonist muscimol on locus coeruleus neurones recorded extracellularly from a midpontine slice preparation of the rat. The depressant effect of muscimol (2 M) is augmented by bath applied valproate at concentrations of 50 M, 100 M and 1 mM. The effect of GABA is also potentiated by valproate. The potentiating effect is selective since the cell inhibition elicited by the GABA-B receptor agonist baclofen is not affected. Valproate on its own had no effect on the firing frequency. Send of print requests to H.-R. Olpe at the above address