Full-genome RNAi profiling of early embryogenesis in Caenorhabditis elegans.

A key challenge of functional genomics today is to generate well-annotated data sets that can be interpreted across different platforms and technologies. Large-scale functional genomics data often fail to connect to standard experimental approaches of gene characterization in individual laboratories. Furthermore, a lack of universal annotation standards for phenotypic data sets makes it difficult to compare different screening approaches. Here we address this problem in a screen designed to identify all genes required for the first two rounds of cell division in the Caenorhabditis elegans embryo. We used RNA-mediated interference to target 98% of all genes predicted in the C. elegans genome in combination with differential interference contrast time-lapse microscopy. Through systematic annotation of the resulting movies, we developed a phenotypic profiling system, which shows high correlation with cellular processes and biochemical pathways, thus enabling us to predict new functions for previously uncharacterized genes.

In vivo voltammetry--prospects for the next decade.

In vivo voltammetry has been in existence for more than ten years. The technique now benefits from smaller, more selective sensors-true 'chemical microelectrodes'. The scope of experimentation has widened dramatically both in vivo and in vitro as new applications are reported. The speed of measurements has increased giving high temporal and spatial resolution, approaching 'real time'. This article discusses the progress of the past decade and looks forward to the advances of the next ten years.

Control of dorsal raphé 5-HT function by multiple 5-HT(1) autoreceptors: parallel purposes or pointless plurality?

The serotonergic cells of the dorsal raphé nucleus innervate much of the forebrain and are thought to be involved in the mechanism of action of antidepressants. Dysfunction of these cells might be involved in the neural mechanisms underlying depression and suicide. The traffic in pathways emanating from the dorsal raphé nucleus is controlled by 5-HT(1) autoreceptors. Until recently it was thought that the autoreceptors in the dorsal raphé nucleus were solely of the 5-HT(1A) subtype. In this article, we discuss evidence that the situation is more complex and that multiple 5-HT(1) subtypes govern different aspects of 5-HT function in the dorsal raphé nucleus presenting new therapeutic opportunities.

Early age-dependent changes in noradrenaline efflux in the bed nucleus of stria terminalis: voltammetric data in rat brain slices.

Fast cyclic voltammetry (FCV) was applied to the detection of stimulated noradrenaline (NA) efflux in the bed nucleus of stria terminalis (BSTV) of the superfused rat brain slice from rats of different ages. Three age groups were compared: young (5 weeks; 130 +/- 8 g), adult (12 weeks; 308 +/- 12 g), and mature rats (36 weeks; 575 +/- 21 g). The effect of train duration (20-99 pulses at 100 Hz) and frequency of stimulation (50 pulses at 10-500 Hz) on NA efflux were examined. The effect of the alpha 2 antagonist yohimbine (1 microM) was also investigated. NA efflux was significantly (p < 0.05) greater in young than adult or mature rats on all train durations and stimulus frequencies tested: Maximal NA efflux on the longest train (99 pulses, 100 Hz, 10 mA, 0.2 ms) was 423 +/- 48 nM (young), 135 +/- 24 nM (adult), and 155 +/- 26 nM (mature). There were no significant differences between adult and mature rats. Yohimbine (1 microM) elevated NA efflux to a greater extent at lower (10 & 20 Hz) than higher frequencies in all age groups. Yohimbine also potentiated NA efflux more (p < 0.05) in young and adult rats than in mature animals. There were no significant differences between young and adult rats. The results indicate early maturational differences in both NA efflux and its control by alpha 2 adrenoceptors. Interestingly, the decreases in NA efflux and in yohimbine response were not temporally linked.

Serotonin efflux in the rat ventral lateral geniculate nucleus assessed by fast cyclic voltammetry is modulated by 5-HT1B and 5-HT1D autoreceptors.

Fast cyclic voltammetry (FCV) was used to measure electrically stimulated monoamine efflux in the rat ventral lateral geniculate nucleus (vLGN). The electrochemical characteristics of the released species resembled 5-HT but not dopamine or noradrenaline. Amine efflux was abolished by the sodium channel blocker tetrodotoxin (0.1 microM), Ro 4-1284 (1.0 microM), the fast-acting reserpine analogue, and removal of Ca2+ from the superfusate. Amine efflux was unaffected by the monoamine oxidase inhibitor clorgyline (0.1 microM). Of paroxetine (0.1 microM), desipramine (50 nM) and vanoxerine (0.5 microM), selective blockers of 5-HT, noradrenaline and dopamine uptake respectively, only paroxetine increased monoamine efflux (to 194 +/- 25%, mean +/- SEM) and prolonged the removal half-life (to 638 +/- 105%). The non-specific 5-HT1 antagonist methiothepin (0.2 microM) increased 5-HT efflux on long (20 pulses at 20 Hz) but not short trains (20 pulses at 100 Hz). When tested on pseudo-one-pulse stimulations (5 pulses, 100 Hz), the selective 5-HT1A agonist 8-OHDPAT (1.0 microM) had no effect. CP 93129 (0.3 microM), the selective 5-HT1B agonist, decreased 5-HT efflux to 37 +/- 4% of control and was antagonised by the 5-HT1B blocker isamoltane (0.5 microM) and by the 5-HT1D/B antagonist GR 127935 (50 nM). The preferential 5-HT1D agonist sumatriptan (0.5 microM) also decreased 5-HT efflux, to 55 +/- 6% and was antagonised by GR 127935 (50 nM) but not isamoltane (0.5 microM). These results suggest that 5-HT released in the vLGN can be measured by FCV. Furthermore, released 5-HT is taken up by the 5-HT transporter and may be under the influence of 5-HT1B and 5-HT1D autoreceptors.

Multiple 5-HT(1) autoreceptor subtypes govern serotonin release in dorsal and median raphé nuclei.

The present study investigated the possibility of multiple 5-HT(1) autoreceptor subtypes in the rostral raphé nuclei. Slices (350 microm) of rat dorsal or median raphé nucleus (DRN/MRN) were taken from male Wistar rats and superfused with artificial cerebrospinal fluid at 32 degrees C. Fast cyclic voltammetry at carbon fibre microelectrodes was used to monitor serotonin (5-HT) release following local electrical stimulation. In both DRN and MRN, 5-HT release on short trains was reduced by the selective 5-HT(1A) agonist 8-OH-DPAT (1 microM), an effect blocked by the selective 5-HT(1A) antagonist WAY 100635 (0.1 microM) but not by SB 216641 (0.05 and 0.2 microM) or BRL 15572 (0.5 microM), selective antagonists at the 5-HT(1B) and 5-HT(1D) receptors respectively. The selective 5-HT(1B) agonist CP 93129 (0.3 microM) also reduced 5-HT release in both nuclei. Its effect was blocked by SB 216641 but not by WAY 100635 or BRL 15572. The 5-HT(1D/1B) agonist sumatriptan (0.5 microM) decreased 5-HT release in both DRN and MRN. In DRN, the effect of sumatriptan was blocked by BRL 15572 but not by WAY 100635 or SB 216641. In MRN, the effect of sumatriptan was not blocked by any of the above antagonists. BRL 15572 increased 5-HT release on long stimulations in DRN and MRN while WAY 100635 had no effect. SB 216641 increased 5-HT release in MRN but not DRN. WAY 100635 potentiated the effect of SB 216641 in DRN but not MRN. The data suggest that 5-HT release in DRN is controlled by 5-HT(1A), 5-HT(1B) and 5-HT(1D) autoreceptors. 5-HT release in MRN is controlled by 5-HT(1A) and 5-HT(1B) autoreceptors and another, as yet unidentified mechanism.

Noradrenergic modulation of serotonin release in rat dorsal and median raphé nuclei via alpha(1) and alpha(2A) adrenoceptors.

The rat rostral raphé nuclei receive catecholaminergic innervation from the locus coeruleus and other areas. In the present study, we investigated noradrenergic modulation of 5-HT release in rat dorsal and median raphé nuclei (DRN and MRN) slices (350 microm thick) superfused with artificial cerebrospinal fluid (aCSF). The raphé was locally stimulated (0.1 ms pulses, 10 mA) and 5-HT release was monitored at carbon fibre microelectrodes using fast cyclic voltammetry. The selective noradrenaline reuptake inhibitor desipramine (50 nM) did not increase stimulated (20 pulses, 100 Hz) 5-HT release but significantly slowed 5-HT reuptake in both DRN and MRN. On short stimulus trains (10 pulses, 200 Hz), the alpha(2)-selective agonist dexmedetomidine (10nM) decreased evoked 5-HT release in DRN and MRN (to 44+/-3 and 43+/-7% of pre-drug values, respectively, at minimum). In both nuclei, this response was antagonised by the selective alpha(2A)-antagonist BRL 44408 (1 microM: P<0.001 vs. dexmedetomidine) but not by the selective alpha(2B/C)-adrenoceptor antagonist ARC 239 (500 nM), the selective 5-HT(1A) antagonist WAY 100635 (100 nM) or the alpha(1)-selective antagonist prazosin (1 microM), suggesting that the effect of dexmedetomidine is wholly attributable to alpha(2A)-receptor activation. The alpha(1)-adrenoceptor agonist phenylephrine (5 microM) significantly decreased 5-HT release (to 49+/-7 and 41+/-4% of pre-drug values in DRN and MRN, respectively). The response was blocked by prazosin (P<0.001) and BRL 44408 (P<0.01) in DRN and by prazosin, BRL 44408 and WAY 100635 (all P<0.05) in MRN, suggesting that the effect of phenylephrine is, under these conditions, only partly mediated via alpha(1)-adrenoceptors. On long stimuli (30 pulses, 10 Hz), BRL 44408 (1 microM) increased evoked 5-HT efflux to 187+/-17 and 178+/-2% of pre-drug values in DRN and MRN, respectively (both P<0.001 vs. vehicle). Collectively, these data show that activation of both alpha(1) and alpha(2A)-adrenoceptors can decrease stimulated 5-HT release in the rostral raphé nuclei. Since the effect of dexmedetomidine was not antagonised by prazosin, we suggest that its effect was mediated directly, possibly through alpha(2A) receptors located on 5-HT cell elements, and not transduced indirectly through alpha(1)-adrenoceptor activation, as previously suggested by others.

Dissociation of the actions of uptake blockers upon dopamine overflow and uptake in the rat nucleus accumbens: in vivo voltammetric data.

Fast cyclic voltammetry, at carbon fibre microelectrodes, was used to monitor stimulated overflow and uptake of DA in the nucleus accumbens of the rat. Several recognised blockers of neuronal uptake of DA were examined for their actions on each process. Benztropine, cocaine, GBR 12909 and nomifensine elevated the overflow of DA, while only nomifensine and bupropion blocked uptake. The actions of the drugs upon uptake did not correlate with their effects on overflow of DA. It is therefore concluded that the mechanisms by which the drugs influence overflow and uptake are different. It cannot be assumed that the elevation of extracellular DA is solely the result of blockade of uptake by these drugs.

Activity of two primary human metabolites of nomifensine on stimulated efflux and uptake of dopamine in the striatum: in vitro voltammetric data in slices of rat brain.

Several antidepressant drugs have active metabolites. This study sought to establish whether two of the main human metabolites of nomifensine (M2: 8-amino-2-methyl-4-(3-methoxy-4-hydroxyphenyl)-1,2,3,4- tetrahydroisoquinoline and M3: 8-amino-2-methyl-4-(3-hydroxy-4-methoxyphenyl)-1,2,3,4- tetrahydroisoquinoline) had actions on the release and uptake of dopamine (DA). Experiments were conducted in superfused striatal slices of the rat. The efflux of DA was evoked by single constant-current pulses (0.1 msec, 10 mA) and trains (20 pulses, 50 Hz), applied alternately every 10 min and monitored using fast cyclic voltammetry at carbon fibre microelectrodes. Nomifensine (5 x 10(-7) M) significantly increased the efflux of DA on both single pulse (302% of pre-drug) and train stimuli (529%) and increased the uptake half-life (178% of pre-drug). The M2 metabolite had similar potency on the efflux of DA (260%: pulse, 570%: train) but without any effect on uptake of DA. Nomifensine and M2 increased efflux of DA more on trains than on single pulses. The M3 metabolite (5 x 10(-7) M) increased efflux of DA only moderately. The selective blocker of the uptake of DA, GBR 12909 (3 x 10(-7) M), increased efflux of DA on single pulse (430%) and train stimuli (645%) and blocked uptake of DA (t1/2: 292%). Amfonelic acid, the psychomotor stimulant (10(-7) M) blocked uptake of DA (t1/2: 234%) and elevated efflux of DA to a greater extent on trains (1007%) than on single pulses (495%).(ABSTRACT TRUNCATED AT 250 WORDS)

Sodium channel blockade unmasks two temporally distinct mechanisms of striatal dopamine release during hypoxia/hypoglycaemia in vitro.

Massive striatal dopamine release during cerebral ischaemia has been implicated in the resulting neuronal damage. Sodium influx is an early event in the biochemical cascade during ischaemia and blockade of sodium channels may increase resistance to ischaemia by reducing energy demand involved in compensation for sodium and potassium fluxes. In this study, we have determined the effects of opening and blockade of voltage-gated sodium channels on hypoxia/hypoglycaemia-induced dopamine release. Slices of rat caudate nucleus were maintained in a slice chamber superfused by an oxygenated artificial cerebrospinal fluid containing 4 mM glucose. Ischaemia (hypoxia/hypoglycaemia) was mimicked by a switch to a deoxygenated artificial cerebrospinal fluid containing 2 mM glucose and dopamine release was measured using fast cyclic voltammetry. In drug-free (control) slices, there was a 2-3 min delay after the onset of hypoxia/hypoglycaemia followed by a rapid dopamine release event which was associated with anoxic depolarization. In slices treated with the Na+ channel opener, veratridine (1 microM), the time to onset of dopamine release was shortened (101 +/- 20 s, compared with 171 +/- 8 s in controls, P < 0.05). Conversely, phenytoin (100 microM), lignocaine (200 microM) and the highly selective sodium channel blocker, tetrodotoxin (1 microM) markedly delayed and slowed dopamine release vs paired controls. In the majority of cases, dopamine release was biphasic after sodium channel blockade: a slow phase preceded a more rapid dopamine release event. The latter was associated with anoxic depolarization. Neither the fast nor the slow release events were affected by pretreatment with the selective dopamine uptake blocker GBR 12935 (0.2 microM), suggesting that uptake carrier reversal did not contribute to these events. In conclusion, sodium channel antagonism delays and slows hypoxia/hypoglycaemia-induced dopamine release in vitro. Furthermore, sodium channel blockade delays anoxic depolarization and its associated neurotransmitter release, revealing an earlier dopamine release event that does not result from reversal of the uptake carrier.

Evidence that 5-hydroxytryptamine release in rat dorsal raphé nucleus is controlled by 5-HT1A, 5-HT1B and 5-HT1D autoreceptors.

Electrically stimulated 5-hydroxytryptamine (5-HT) release was monitored in slices of rat dorsal raphé nucleus (DRN) by fast cyclic voltammetry. Pseudo-single pulse stimulations (5 pulses at 100 Hz) were used to enable the effect of various receptor agonists to be seen without competition from endogenously released transmitter. The selective 5-HT1A receptor agonist, (+)-8-OH-DPAT (1.0 microM) decreased stimulated 5-HT release to 31 +/- 3% of controls. This decrease was inhibited by the 5-HT1A receptor antagonists, (+)-WAY-100135 (1.0 microM) and WAY-100635 (0.1 microM) but not by the 5-HT1D/B antagonist, GR127935 (0.05 microM). The selective 5-HT1B receptor agonist, CP-93129 (0.3 microM) decreased stimulated 5-HT release to 61 +/- 4% of control. This effect was antagonized by the 5-HT1B receptor antagonist, isamoltane (0.5 microM) but not by (+)-WAY-100135. The 5-HT1D agonist, sumatriptan (0.5 microM) decreased stimulated 5-HT release to 52 +/- 2% of controls. This decrease was blocked by GR-127935 but not by WAY-100635. These results suggest that 5-HT release in the rat DRN is under the control of 5-HT1A, 5-HT1B and 5-HT1D autoreceptors.

Actions of dopamine antagonists on stimulated striatal and limbic dopamine release: an in vivo voltammetric study.

1. Fast cyclic voltammetry at carbon fibre microelectrodes was used to study the effects of several dopamine antagonists upon stimulated dopamine release in the rat striatum and nucleus accumbens. 2. In both nuclei, stimulated dopamine release was increased by D2-receptor-selective and mixed D1/D2-receptor antagonists. The D1-selective antagonist SCH 23390 had no effect. 3. Striatal and limbic dopamine release were elevated by cis- but not trans-flupenthixol. 4. The 'atypical' neuroleptics (clozapine and thioridazine) did not cause a selective elevation of dopamine release in the limbic terminal region, whereas the non-antipsychotic drug metoclopramide increased dopamine release more in striatum than nucleus accumbens. 5. We conclude from this study that striatal and limbic dopamine release are under the control of a stereoselective dopamine D2-autoreceptor on the nerve terminal and that atypical neuroleptics do not show a limbic-selective effect at this receptor after acute administration.

Differential effects of dopamine agonists upon stimulated limbic and striatal dopamine release: in vivo voltammetric data.

1. Fast cyclic voltammetry at carbon fibre microelectrodes was used in rats anaesthetized with chloral hydrate to monitor dopamine release in the caudate and nucleus accumbens evoked by electrical stimulation of the median forebrain bundle. Stimulation trains (50 Hz sinusoidal current, 100 +/- 10 microA r.m.s., 2s duration) were repeated every 5 min throughout the experiment. 2. The actions of the dopamine agonists quinpirole, pergolide, SKF 38393, bromocriptine, (+)-3-(3-hydroxyphenyl)-N-n-propylpiperidine ((+)-3PPP) and (-)-3PPP were compared in the two nuclei. 3. Bromocriptine (10 mg kg-1, i.p.) did not affect release in either nucleus while SKF 38393 caused a fleeting decrease in limbic but not striatal dopamine release at a high dose (20 mg kg-1, i.p.). 4. Quinpirole and pergolide (both 1 mg kg-1, i.p.) decreased stimulated dopamine release in the nucleus accumbens while in the caudate the drugs each caused a transient, though not quite significant, elevation of stimulated dopamine release followed by decrease in release of the same magnitude as that seen in the nucleus accumbens. 5. The (-)-enantiomer of 3PPP (20 mg kg-1, i.p.), a partial agonist at the dopamine autoreceptor, increased stimulated dopamine release in both nuclei although the action in the caudate was larger and more prolonged. (+)-3PPP (20 mg kg-1, i.p.), a full agonist, decreased release in the nucleus accumbens. A small, transient and not significant increase in the caudate was followed by decreased release. 6. The results are interpreted as being evidence for differences in the dopamine autoreceptor in the two nuclei, possibly in the affinity state of the receptor in each nucleus.

(+)-WAY 100135, a partial agonist, at native and recombinant 5-HT1B/1D receptors.

1. We have studied the effects of the purportedly selective 5-HT1A receptor antagonist (+)-WAY 100135 on electrically stimulated 5-hydroxytryptamine (5-HT) efflux in the ventrolateral geniculate nucleus (vLGN), and its affinity at human 5-HT1B and 5-HT1D receptors stably expressed in Chinese hamster ovary (CHO) cells. 2. On short 'pseudo single pulse' stimulations (20 pulses at 100 Hz, 190 ms train duration), (+)-WAY 100135 (1.0 microM) decreased 5-HT efflux in the vLGN to 68 +/- 8% of pre-drug values (P < 0.01). This decrease could be blocked by the 5-HT1D/1B receptor antagonist GR 127935 (50 nM). Conversely, when long stimulations (20 pulses at 20 Hz, 950 ms train) were used, (+)-WAY 100135 had no effect on 5-HT efflux (84 +/- 8% of pre-drug values) although both methiothepin (200 nM) and GR 127935 (50 nM) caused significant increases (to 175 +/- 18 and 130 +/- 10% of pre-drug values, respectively). 3. Paroxetine (100 nM), the selective 5-HT reuptake inhibitor, increased stimulated 5-HT efflux and reuptake half-life (to 145 +/- 18% and 649 +/- 121%, respectively) on pseudo single pulse stimulations. When (+)-WAY 100135 was added in combination with the uptake blocker, the effect of paroxetine on stimulated 5-HT efflux was potentiated to 282 +/- 48% (P < 0.01) without further effect on the 5-HT reuptake half-life. 4. The affinity and intrinsic activity of (+)-WAY 100135 were determined at recombinant human 5-HT1B and 5-HT1D receptors expressed in CHO cells, by use of radioligand binding and [35S]-GTP gamma S binding (+)-WAY 100135 was a partial agonist at human 5-HT1B and 5-HT1D receptors with moderately high affinity for 5-HT1D receptors (pEC50 = 7.61). 5. In conclusion, (+)-WAY 100135 was found to be not a selective 5-HT1A autoreceptor antagonist but may act as a partial agonist at the 5-HT1B/1D receptor, displaying agonist or antagonist properties depending on the stimulation protocol used and the resultant 5-HT 'tone' at the receptor.

Voltammetric evidence that subsensitivity to reward following chronic mild stress is associated with increased release of mesolimbic dopamine.

Chronic exposure to mild unpredictable stress caused a decrease in rats' consumption of a palatable weak sucrose solution, which was reversed by chronic (5 weeks) administration of imipramine (5 mg/kg/day). Dopamine (DA) release in the nucleus accumbens (NAc) and caudate putamen (CPu) was measured in vivo using fast cyclic voltammetry, following electrical stimulation of the medial forebrain bundle. Experiments were performed under chloral hydrate anaesthesia 48 h after the termination of stress and the final imipramine injection. DA release was increased in the NAc of both stressed and imipramine-treated animals; imipramine did not normalize the increased DA release in stressed animals. In a further experiment, brain slices from stressed animals tended to be subsensitive to the inhibition of DA release in the NAc by quinpirole. No changes were observed in the CPu in any experiment. We discuss the relationship of these effects to stress-induced anhedonia.

Effect of chronic paroxetine treatment on 5-HT1B and 5-HT1D autoreceptors in rat dorsal raphe nucleus.

This study reports the effect of chronic paroxetine (10 mg/kg p.o., 21 days) on 5-HT1B and 5-HT1D autoreceptors controlling stimulated 5-HT efflux in slices of rat dorsal raphe nucleus. Electrically evoked 5-HT (10 pulses, 200 Hz, 0.1 ms, 10 mA) was measured using fast cyclic voltammetry. 5-HT efflux was inhibited by CP 93129 (10 nM-10 microM) and by sumatriptan (1 nM-1 microM) agonists at 5-HT1B and 5-HT1D receptors, respectively. Chronic paroxetine did not, initially, appear to alter the sensitivity of the 5-HT1B autoreceptors to CP 93129. However, when constructed in the presence of WAY 100635 (10 nM) the selective and silent 5-HT1A antagonist, there was a significant (P < 0.001) rightward shift of the CP 93129 concentration-response curve in the paroxetine-treated rats but not in the controls, implying a desensitisation of the 5-HT1B autoreceptor by paroxetine. Chronic paroxetine did not affect the sumatriptan concentration-response curve, even with WAY 100635 present, implying that there was no (de)sensitisation of the 5-HT1D autoreceptor. These data suggest that chronic paroxetine treatment may desensitise 5-HT1B autoreceptors in the dorsal raphe nucleus but that this effect is unmasked only when the dominant 5-HT1A autoreceptor control is antagonised.

Comparison of ketamine stereoisomers on tissue metabolic activity in an in vitro model of global cerebral ischaemia.

Ketamine (2-o-chlorophenenyl-2-methylaminocyclohexanone hydrochloride) is a dissociative general anaesthetic with neuroprotective properties. Since ketamine is optically active, we compared the neuroprotective efficacy of the (+)- or (-)-enantiomers in global cerebral ischaemia. Rat corticostriatal slices superfused with, or incubated in, artificial CSF at 34 degrees C were subjected to a brief ischaemic insult. Dopamine efflux was measured using fast cyclic voltammetry. Tissue metabolism was determined with 2,3,5-triphenyltetrazolium chloride staining, a marker of mitochondrial enzyme activity. In control slices, ischaemia caused rapid striatal dopamine release (to 122 microM over 18 s) after an initial delay of 149s. Racemic ketamine (100 micromol/l) significantly delayed (by 24%, P<0.05), slowed (by 63%, P<0.01) and reduced (by 27%, P<0.05) ischaemia-induced dopamine release. Ischaemia (10 min) also caused significant decreases in striatal (25%, P<0.01) and cortical (31%, P<0.001) metabolic activity, manifested as a drop in mean TTC staining intensity. Racemic ketamine and its (+)- and (-)-enantiomers (each 100 microM) attenuated the loss of metabolic activity in the striatum. However, in the cortex, only (+)-ketamine (100 microM) was significantly neuroprotective. We conclude that neuroprotection by ketamine in cerebral ischaemia is both region- and isomer-dependent.

Contrasting effects of chronic paroxetine on 5-HT1A control of dorsal raphe cell firing and 5-HT release.

To test the role of 5-HT1A receptors in the action of antidepressants, we investigated the effect of chronic paroxetine (10 mg/kg, p.o. for 21 days) on functional assays of 5-HT1A sensitivity. We constructed cumulative concentration response curves to the selective 5-HT1A agonist (+)-8-OH-DPAT on both extracellular recordings of 5-HT neurones and electrically stimulated 5-HT release in dorsal raphe brain slices. Chronic paroxetine desensitized the 5-HT1A receptors controlling firing, with an increase in EC50 from 10.7 nM to 46.2 nM 8-OH-DPAT. Chronic paroxetine did not, however, desensitize the 5-HT1A receptors controlling 5-HT release but increased the 8-OH-DPAT Emax from 54.9% to 79.2% inhibition of 5-HT release. These data suggest that there are either two distinct populations of 5-HT1A receptors or separate second messenger systems, one controlling 5-HT release and another influencing firing. Furthermore chronic paroxetine treatment can differentially modulate these different populations.

Rauwolscine potentiates the effect of desipramine on limbic noradrenaline efflux.

Desipramine, like most antidepressants, does not exert clinical benefit until 2-3 weeks after the onset of treatment. It has been suggested that this delay might be due to enhanced autoreceptor activation, counteracting the acute uptake blockade. We therefore tested whether autoreceptor blockade might enhance the response to acute uptake blockade, using voltammetry at carbon fibre microelectrodes to monitor stimulated noradrenaline (NA) efflux in rat bed nucleus of stria terminalis brain slices. Desipramine significantly increased NA efflux and slowed NA uptake. The combination of rauwolscine and desipramine increased NA efflux significantly more than desipramine alone. We suggest that alpha 2 autoreceptor blockade functionally mimics alpha 2 autoreceptor down-regulation and thus may allow the full therapeutic effect of desipramine to be manifested more rapidly.

Effects of dizocilpine (MK 801) on noradrenaline, serotonin and dopamine release and uptake.

In the present study, we examined the actions of the NMDA antagonist dizocilpine (MK801) on electrically evoked release and uptake of noradrenaline (NA) in the locus coeruleus (LC), serotonin (5-HT) in the dorsal raphe nucleus (DRN) and dopamine (DA) in the nucleus accumbens (NAc), measured by fast cyclic voltammetry (FCV) in rat brain slices. Dizocilpine (10 microM) significantly increased NA (to 248 +/- 15%) and 5-HT release (to 184 +/- 29%) and slowed monoamine uptake in the LC (t1/2 = 853 +/- 129%) and the DRN (t1/2 = 387 +/- 70%), respectively. However, dizocilpine had no effect on DA release or uptake in NAc. Actions on monoamines are thus likely and should be considered in the interpretation of data regarding dizocilpine.