[Efficacy of psychodynamic therapies: A systematic review of the recent literature]. / L'efficacité des psychothérapies inspirées par la psychanalyse : une revue systématique de la littérature scientifique récente.

AIM: A French governmental institute published, in February 2004, a report assessing the efficacy of psychotherapies in the light of the biomedical literature. It concluded that cognitive psychotherapies effectively cure common mental disorders, while the efficacy of psychodynamic therapies is not proven by scientific studies. Because many French mental health professionals are practicing with reference to psychoanalysis, this conclusion stirred up heated controversy. Since February 2004, numerous studies assessing psychodynamic therapies have been published in peer-reviewed biomedical journals. Moreover, these primary studies have been meta-analyzed in dozens of review articles. Here, we systematically review these meta-analysis articles. METHODS: A systematic search for meta-analyses assessing psychodynamic therapies was performed using PubMed and identified 71 articles published from January 2004 to December 2019. Among them, 25 articles were judged to be relevant because they reported meta-analyses assessing the symptoms of common mental disorders in at least three distinct cohorts of adult patients. Although the primary studies included in these 25 meta-analysis articles often overlap, the selection criteria, calculation methods and results always differ between them. Therefore, we reviewed all of them without further selection. From all the meta-analyses reported in these 25 articles, we systematically present here the most compelling ones, i.e. those calculated from the largest number of primary studies. Results were quantified in terms of effect size (i.e. standardized mean difference). Effect sizes below 0.25 were considered as without clinical significance, whereas those superior to 0.8 were regarded as robust. Because short-term psychodynamic therapies had been assessed in 20 meta-analysis articles published until 2017, we did not search for more recent primary studies. However, because the most recent meta-analysis article about long-term psychodynamic therapies was published in 2013, we also searched, using PubMed, for primary studies assessing psychodynamic therapies lasting for at least one year and published from January 2013 to December 2019. Among the 57 publications retrieved by PubMed, three were identified as randomized controlled trials not included in meta-analyses and were extensively described here. RESULTS: Eight meta-analysis articles have assessed symptom improvement at treatment termination by comparing with baseline symptoms. According to all of them, psychodynamic therapies alleviate symptoms and their effect sizes are always robust. Three meta-analysis articles compared psychodynamic therapies with inactive treatments (e.g. placebo medication, waiting list) and reported clinically significant differences in favor of psychodynamic therapies. Ten meta-analysis articles compared, at treatment termination, psychodynamic therapies to active treatments, including medication and cognitive psychotherapies. Nine of them reported no difference. Only one article concluded that psychodynamic therapies are clinically inferior to cognitive psychotherapies (d=-0.28). Seven meta-analysis articles compared psychodynamic therapies to active treatment at follow-up (i.e. months or years after treatment termination). Five of them reported no significant difference, one reported a medium effect size in favor of psychodynamic therapies over various active treatments (d=0.38), while the other reported a clinically significant difference in favor of cognitive psychotherapies (d=-0.55). Because short-term treatments are often insufficient to prevent relapse, investigations about long-term treatments (i.e. more than one year) are needed, but such published studies are still scarce. Five meta-analysis articles and three primary studies published since 2013 compared long-term psychodynamic therapies to various active treatments of similar duration. According to them, psychodynamic therapies were at least as effective as other active treatments. CONCLUSION: A systematic review about psychodynamic therapies, published in 2015 in Lancet Psychiatry, included 64 randomized controlled trials of which 37 were published after 2003. Therefore, most quality studies assessing psychodynamic therapies have been published since 2003 and have been reviewed in recent meta-analysis articles. All together, this recent literature leads to the conclusion that psychodynamic therapies are as effective as active treatments, including cognitive psychotherapies, to help patients suffering from common mental disorders (unipolar depression, anxiety disorders, eating disorders and personality disorders). Beside this overall conclusion, it appears that randomized controlled trials are not well suited for answering why psychotherapies work in some patients but not in others, and how they work in general. Other approaches are needed, including case studies.

Stimulation of serotonin2C receptors elicits abnormal oral movements by acting on pathways other than the sensorimotor one in the rat basal ganglia.

Serotonin2C (5-HT(2C)) receptors act in the basal ganglia, a group of sub-cortical structures involved in motor behavior, where they are thought to modulate oral activity and participate in iatrogenic motor side-effects in Parkinson's disease and Schizophrenia. Whether abnormal movements initiated by 5-HT(2C) receptors are directly consequent to dysfunctions of the motor circuit is uncertain. In the present study, we combined behavioral, immunohistochemical and extracellular single-cell recordings approaches in rats to investigate the effect of the 5-HT(2C) agonist Ro-60-0175 respectively on orofacial dyskinesia, the expression of the marker of neuronal activity c-Fos in basal ganglia and the electrophysiological activity of substantia nigra pars reticulata (SNr) neuron connected to the orofacial motor cortex (OfMC) or the medial prefrontal cortex (mPFC). The results show that Ro-60-0175 (1 mg/kg) caused bouts of orofacial movements that were suppressed by the 5-HT(2C) antagonist SB-243213 (1 mg/kg). Ro-60-0175 (0.3, 1, 3 mg/kg) dose-dependently enhanced Fos expression in the striatum and the nucleus accumbens. At the highest dose, it enhanced Fos expression in the subthalamic nucleus, the SNr and the entopeduncular nucleus but not in the external globus pallidus. However, the effect of Ro-60-0175 was mainly associated with associative/limbic regions of basal ganglia whereas subregions of basal ganglia corresponding to sensorimotor territories were devoid of Fos labeling. Ro-60-0175 (1-3 mg/kg) did not affect the electrophysiological activity of SNr neurons connected to the OfMC nor their excitatory-inhibitory-excitatory responses to the OfMC electrical stimulation. Conversely, Ro-60-0175 (1 mg/kg) enhanced the late excitatory response of SNr neurons evoked by the mPFC electrical stimulation. These results suggest that oral dyskinesia induced by 5-HT(2C) agonists are not restricted to aberrant signalling in the orofacial motor circuit and demonstrate discrete modifications in associative territories.

A mouse juvenile or adult slice with preserved functional nigro-striatal dopaminergic neurons.

The effect of endogenous dopamine on the activity of target neurons recorded with patch clamp or Ca2+ imaging techniques in slices has been studied to date with intra-striatal stimuli. Yet, this approach is severely handicapped by the nonphysiological and nonspecific stimulation of local neurons and fibers within the striatum. We now report a new juvenile and adult mouse slice preparation in which a component of the nigro-striatal dopaminergic pathway is preserved in its entirety, from cell bodies to axon terminals. This tilted parasagittal slice (380-400 microm) just medial to the subthalamic nucleus contains functional nigro-striatal neurons as assessed by morphological examination of tyrosine hydroxylase positive cell bodies and axons, combined with electrochemical assays of dopamine release in the striatum in response to stimulation of the substantia nigra pars compacta. The nigro-striatal slice constitutes a suitable in vitro preparation to determine the impact of endogenously released dopamine on target neurons of the striatum.

Inhibition of dopamine release via presynaptic D2 receptors: time course and functional characteristics in vivo.

Most neurotransmitters inhibit their own release through autoreceptors. However, the physiological functions of these presynaptic inhibitions are still poorly understood, in part because their time course and functional characteristics have not been described in vivo. Dopamine inhibits its own release through D2 autoreceptors. Here, the part played by autoinhibition in the relationship between impulse flow and dopamine release was studied in vivo in real time. Dopamine release was evoked in the striatum of anesthetized mice by electrical stimulation of the medial forebrain bundle and was continuously monitored by amperometry using carbon fiber electrodes. Control experiments performed in mice lacking D2 receptors showed no autoinhibition of dopamine release. In wild-type mice, stimulation at 100 Hz with two to six pulses linearly inhibited further release, whereas single pulses were inefficient. Dopaminergic neurons exhibit two discharge patterns: single spikes forming a tonic activity below 4 Hz and bursts of two to six action potentials at 15 Hz. Stimulation mimicking one burst (four pulses at 15 Hz) promoted extracellular dopamine accumulation and thus inhibited further dopamine release. This autoinhibition was maximal between 150 and 300 msec after stimulation and disappeared within 600 msec. This delayed and prolonged time course is not reflected in extracellular DA availability and thus probably attributable to mechanisms downstream from autoreceptor stimulation. Thus, in physiological conditions, autoinhibition has two important roles. First, it contributes to the attenuation of extracellular dopamine during bursts. Second, autoinhibition elicited by one burst transiently attenuates further dopamine release elicited by tonic activity.

Amphetamine distorts stimulation-dependent dopamine overflow: effects on D2 autoreceptors, transporters, and synaptic vesicle stores.

Amphetamine (AMPH) is known to raise extracellular dopamine (DA) levels by inducing stimulation-independent DA efflux via reverse transport through the DA transporter and by inhibiting DA re-uptake. In contrast, recent studies indicate that AMPH decreases stimulation-dependent vesicular DA release. One candidate mechanism for this effect is the AMPH-mediated redistribution of DA from vesicles to the cytosol. In addition, the inhibition of stimulation-dependent release may occur because of D2 autoreceptor activation by DA that is released via reverse transport. We used the D2 receptor antagonist sulpiride and mice lacking the D2 receptor to address this issue. To evaluate carefully AMPH effects on release and uptake, we recorded stimulated DA overflow in striatal slices by using continuous amperometry and cyclic voltammetry. Recordings were fit by a random walk simulation of DA diffusion, including uptake with Michaelis-Menten kinetics, that provided estimates of DA concentration and uptake parameters. AMPH (10 microm) promoted the overflow of synaptically released DA by decreasing the apparent affinity for DA uptake (K(m) increase from 0.8 to 32 microm). The amount of DA released per pulse, however, was decreased by 82%. This release inhibition was prevented partly by superfusion with sulpiride (47% inhibition) and was reduced in D2 mutant mice (23% inhibition). When D2 autoreceptor activation was minimal, the combined effects of AMPH on DA release and uptake resulted in an enhanced overflow of exocytically released DA. Such enhancement of stimulation-dependent DA overflow may occur under conditions of low D2 receptor activity or expression, for example as a result of AMPH sensitization.

Adaptive changes in the nigrostriatal pathway in response to increased 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced neurodegeneration in the mouse.

Although several adaptive mechanisms have been identified that mask the existence of Parkinson's disease and delay the onset and aggravation of motor symptoms, the timescale and implications of this compensatory process remain an enigma. In order to examine: (i) the nature of the dopaminergic adaptive mechanisms that come into action; (ii) their sequential activation in relation to the severity of degeneration; and (iii) their efficacy with regard to the maintenance of a normal level of basal ganglia activity, we analysed the brains of mice treated daily with 1-methyl-4-phenyl-1,2,3, 6-tetrahydropyridine (MPTP, 4 mg/kg, i.p.) and killed at 5-day intervals from day 0 (D0) to D20. Our results demonstrate the sequential activation of two compensatory mechanisms: (i) an increase in striatal tyrosine hydroxylase (TH) protein content attested by the persistence of TH immunolabelling up to D15, contrasting with the decrease observed in both the number of nigral TH-immunoreactive neurons (-70.2%) and striatal dopamine content (-38.4%); (ii) a downregulation of DA uptake in surviving terminals at D20 (73.4% of nigral degeneration). At this point, the failure of adaptive mechanisms to maintain striatal dopaminergic homeostasis is also illustrated by an increase in the cytochrome oxidase activity of substantia nigra pars reticulata, a marker of neuronal function. It has been postulated that an increase in dopamine release per pulse could constitute an adaptive mechanism. The data we present from our MPTP mice model infirm this hypothesis. This study explores the link between the degree of nigral degeneration and the sequential activation of dopaminergic compensatory mechanisms in the nigrostriatal pathway and, in so doing, proposes a rethink of the paradigm applied to these mechanisms.

Release and elimination of dopamine in vivo in mice lacking the dopamine transporter: functional consequences.

In mice lacking the dopamine transporter (DAT), the amplitude of dopamine (DA) release and the kinetics of dopamine elimination were measured in vivo using carbon fibre electrodes combined with amperometry. DA release was evoked by electrical stimulation of the medial forebrain bundle. The amplitude of DA release per pulse was lower (7% in striatum and 21% in nucleus accumbens) than in wild-type mice. Inhibition of monoamine oxidases (MAOs) by pargyline, but not of catechol-O-methyltransferase (COMT) by tolcapone, slowed down DA elimination in knockout mice. As DA half-life was two orders of magnitude higher in these mice, the DA diffusion distance was 10-times higher than in wild-types (100 and 10 microm, respectively). In knockout mice, alpha-methyl-p-tyrosine induced a much faster decline of DA release and haloperidol was less effective in potentiating DA release. Therefore, DA release was more dependent on DA synthesis than in normal animals but was less influenced by D2 autoregulation. Dopaminergic neurons exhibit two kinds of discharge activity, i.e. single spikes and bursts of 2-6 action potentials. In wild-type mice, stimuli mimicking bursts evoked significant increases in extracellular DA over its basal level sustained by tonic activity. However, in mice lacking the DAT, low frequency firing resulted in consistently high extracellular DA levels that could not be distinguished from DA levels achieved by high frequency firing. Therefore, the burst firing activity cannot be specifically translated into phasic changes in extracellular DA. This deficit might contribute to the difficulties of these mice in spatial cognitive function.

Increased rewarding properties of morphine in dopamine-transporter knockout mice.

The activation of dopamine (DA) neurotransmission plays a crucial role in the behavioural responses to drugs of abuse. In particular, increased extracellular levels of DA within the mesolimbic pathway have been implicated in the rewarding and locomotor stimulatory properties of morphine. We investigated the behavioural responses to morphine in mice with a genetic disruption of the DA transporter (DAT), resulting in a constitutively high level of extrasynaptic DA. In the conditioned place preference test, DAT-/- mice exhibited a stronger rewarding response to morphine (5 mg/kg, s.c.) compared with control littermates. However, the same dose of morphine failed to increase locomotor activity in DAT-/- mice, whilst enhancing locomotion in DAT+/- and DAT+/+ animals. Morphine-induced analgesia was unaffected in mutant mice, but the behavioural expression of naloxone-induced withdrawal signs was blunted. In vivo voltammetry in the shell of the nucleus accumbens revealed that morphine was able to stimulate DA neurons in DAT-/- mice, resulting in the accumulation of higher extracellular DA levels compared with control animals. Morphine also induced a higher rate of c-fos transcription in the shell of the nucleus accumbens in mutant mice. We conclude that morphine-induced rewarding responses are firmly established in DAT mutant mice despite a DA transmission that is already tonically activated, and independently of any effect on locomotion. These particular behavioural responses to morphine may be associated with the action of the drug on DA release and c-fos expression in the shell of the nucleus accumbens of DAT-/- mice.

Dopamine tone regulates D1 receptor trafficking and delivery in striatal neurons in dopamine transporter-deficient mice.

In vivo, G protein-coupled receptors (GPCR) for neurotransmitters undergo complex intracellular trafficking that contribute to regulate their abundance at the cell surface. Here, we report a previously undescribed alteration in the subcellular localization of D1 dopamine receptor (D1R) that occurs in vivo in striatal dopaminoceptive neurons in response to chronic and constitutive hyperdopaminergia. Indeed, in mice lacking the dopamine transporter, D1R is in abnormally low abundance at the plasma membrane of cell bodies and dendrites and is largely accumulated in rough endoplasmic reticulum and Golgi apparatus. Decrease of striatal extracellular dopamine concentration with 6-hydroxydopamine (6- OHDA) in heterozygous mice restores delivery of the receptor from the cytoplasm to the plasma membrane in cell bodies. These results demonstrate that, in vivo, in the central nervous system, the storage in cytoplasmic compartments involved in synthesis and the membrane delivery contribute to regulate GPCR availability and abundance at the surface of the neurons under control of the neurotransmitter tone. Such regulation may contribute to modulate receptivity of neurons to their endogenous ligands and related exogenous drugs.

Opposite tonic modulation of dopamine and adenosine on c-fos gene expression in striatopallidal neurons.

The impulse flow-dependent dopamine release in the striatum was acutely blocked by unilateral lesion of the medial forebrain bundle with 6-hydroxydopamine. Within 45 min this disruption reduced the striatal extracellular dopamine levels by 80% as determined by in vivo voltammetry. A strong induction of c-fos messenger RNA was detected in the ipsilateral dorsolateral striatum 75 min after 6-hydroxydopamine injection by in situ hybridization. Double labelling demonstrates that this induction was confined to neurons expressing the dopamine D2 receptor messenger RNA. At this time-point, there were no changes in the striatal levels of either tyrosine hydroxylase immunoreactivity or dopamine D2 receptor messenger RNA. The c-fos messenger RNA expression induced by acute 6-hydroxydopamine injection was abolished by intraperitoneal pretreatment with the dopamine D2 receptor agonist, quinelorane (2 mg/kg) and strongly reduced by administration of the selective adenosine A2A receptor antagonist SCH-58261 (5 mg/kg). The results reported here show, by using a novel methodological approach, that an acute decrease of dopamine release causes an induction of c-fos messenger RNA in dopamine D2 receptor-containing striatopallidal neurons. This, together with previous findings, demonstrates that the c-fos gene expression is tonically inhibited by the impulse flow-dependent dopamine release via D2 receptors. In addition, this study provides evidence that endogenous adenosine, acting via adenosine A2A receptors, induces striatal c-fos messenger RNA when extracellular dopamine levels are strongly reduced. Thus endogenous dopamine and adenosine exert opposite effects on the activity of the D2-containing striatopallidal neurons.

Facilitation and depression of ATP and noradrenaline release from sympathetic nerves of rat tail artery.

1. Excitatory junction currents (EJCs) were used to measure ATP release; noradrenaline (NA) oxidation currents and fractional overflow of labelled NA, [3H]NA, were used to monitor the release of endogenous and exogenous NA, respectively, from post-ganglionic sympathetic nerves of rat tail artery. 2. During nerve stimulation with 100 pulses at 5-20 Hz the EJCs initially grew in size (maximally by 23 %, at 2-10 Hz), and then depressed, maximally by 68 % at 20 Hz. 3. The peak amplitude of NA oxidation currents in response to nerve stimulation with 100 pulses at 2-20 Hz grew in size with frequency, while the area was independent of frequency and roughly constant. 4. The size of the NA oxidation currents evoked by nerve stimulation with 4-100 pulses at 20 Hz grew linearly with train length between pulses 4-16. Between pulses 20-100 there was a train length-dependent depression of the signal. 5. Fractional overflow of [3H]NA in response to nerve stimulation with 5-100 pulses at 20 Hz behaved similarly to the EJCs. It initially grew roughly linearly between pulses 5-25, and then showed a dramatic depression similar to that of the EJCs. 6. The alpha2-adrenoceptor antagonists rauwolscine and yohimbine increased the overflow of [3H]NA and the amplitude of NA oxidation currents, but not that of the EJCs. 7. It is concluded that during high-frequency stimulation (i) the release of ATP and NA is first briefly facilitated then markedly depressed, (ii) facilitation and depression of the two transmitters are similar in magnitude and time course, and (iii) alpha2-adrenoceptor antagonists differentially modify EJCs and the NA signals. The results obtained in the absence of drugs are compatible with the hypothesis that ATP and NA are released in parallel, while the effects of alpha2-adrenoceptor antagonists seem to suggest dissociated release.

Internalization of D1 dopamine receptor in striatal neurons in vivo as evidence of activation by dopamine agonists.

To investigate how dopamine influences the subcellular localization of the dopamine receptors in the striatal dopaminoceptive neurons, we have used immunohistochemistry to detect D1 dopamine receptors (D1R) after modifications of the dopamine environment. In normal rats, D1R are located mostly extrasynaptically at the plasma membrane of the cell bodies, dendrites, and spines. The intrastriatal injection of the full D1R agonist SKF-82958 and the intraperitoneal injection of the same molecule or of amphetamine (which induces a massive release of dopamine in the striatum) induce modifications of the pattern of D1R immunoreactivity in the dorsal and ventral striatum. Whereas normal rats display homogenous staining of the neuropile with staining of the plasma membrane of the cell bodies, either treatment provokes the appearance of an intense immunoreactivity in the cytoplasm and the proximal dendrites. The labeling pattern is heterogeneous and more intense in the striosomes than in the matrix. Analysis of semithin sections and electron microscopy studies demonstrates a translocation of the labeling from the plasma membrane to endocytic vesicles and endosomes bearing D1R immunoreactivity in the cytoplasm of cell bodies and dendrites. Injection of D1R antagonist (SCH-23390) alone or injection of D1R antagonist, together with amphetamine or SKF-82958, do not provoke modification of the immunoreactivity, as compared with normal rat. Our results demonstrate that, in vivo, the acute activation of dopamine receptors by direct agonists or endogenously released dopamine provokes dramatic modifications of their subcellular distribution in neurons, including internalization in the endosomal compartment in the cytoplasm. This suggests that modifications of the localization of neurotransmitter receptors, including extrasynaptic ones, may be a critical event that contributes to the postsynaptic response in vivo.

Paired pulse analysis of ATP and noradrenaline release from sympathetic nerves of rat tail artery and mouse vas deferens: effects of K+ channel blockers.

1. The paired pulse stimulus paradigm - two pulses of equal strength delivered at variable interpulse intervals was used to study the release of ATP and noradrenaline (NA) from post ganglionic sympathetic nerves of rat tail artery and mouse vas deferens. 2. Excitatory junction currents (EJCs) were used to measure the release of ATP, and differential pulse amperometry to measure that of NA. 3. At interpulse intervals of 0.1 - 1 s paired pulse stimulation caused an increase in the size of the second EJC, both in rat tail artery and mouse vas deferens. As the interpulse interval was increased to 10 s or more, the two EJCs became of equal size. 4. In both preparations the K+ channel blockers tetraethylammonium (TEA, 20 mM) and 4-aminopyridine (4-AP, 1 mM) prolonged the duration of the nerve terminal spike and greatly amplified the first EJC of the pair. 5. In the presence of TEA and 4-AP in rat tail artery paired pulse stimulation caused a dramatic depression of the second EJC without markedly affecting the nerve terminal spike. The depression of the second EJC decreased with increasing interpulse intervals, and also when external Ca2+ was reduced to 0.2 mM. In mouse vas deferens, TEA and 4-AP caused only a modest depression of the second EJC. 6. In rat tail artery in the presence of TEA and 4-AP paired pulse stimulation caused a depression of the NA oxidation current evoked by the second pulse, which was similar in magnitude and time course to that of the EJC. Similar TEA and 4-AP induced depression of the second pulse response was also observed when the purinergic and noradrenergic components of the contractile response were investigated. 7. The results show that in rat tail artery K+ channel blockers cause a dramatic paired pulse depression of the release of ATP and NA. The similarity in the depression of the EJC, the NA oxidation current, and the purinergic and noradrenergic components of the contractile response is compatible with the hypothesis that ATP and NA are released in parallel from the same neuronal sources.

Prolonged and extrasynaptic excitatory action of dopamine mediated by D1 receptors in the rat striatum in vivo.

The spatiotemporal characteristics of the dopaminergic transmission mediated by D1 receptors were investigated in vivo. For this purpose dopamine (DA) release was evoked in the striatum of anesthetized rats by train electrical stimulations of the medial forebrain bundle (one to four pulses at 15 Hz), which mimicked the spontaneous activity of dopaminergic neurons. The resulting dopamine overflow was electrochemically monitored in real time in the extracellular space. This evoked DA release induced a delayed increase in discharge activity in a subpopulation of single striatal neurons. This excitation was attributable to stimulation of D1 receptors by released DA because it was abolished by acute 6-hydroxydopamine lesion and strongly reduced by the D1 antagonist SCH 23390. Striatal neurons exhibiting this delayed response were also strongly excited by intravenous administration of the D1 agonist SKF 82958. Whereas the DA overflow was closely time-correlated with stimulation, the excitatory response mediated by DA started 200 msec after release and lasted for up to 1 sec. Moreover, functional evidence presented here combined with previous morphological data show that D1 receptors are stimulated by DA diffusing up to 12 micron away from release sites in the extrasynaptic extracellular space. In conclusion, DA released by bursts of action potentials exerts, via D1 receptors, a delayed and prolonged excitatory influence on target neurons. This phasic transmission occurs outside synaptic clefts but still exhibits a high degree of spatial specificity.

Exocytosis in single chromaffin cells: regulation by a secretory granule-associated Go protein.

1. Besides having a role in signal transduction, trimeric G proteins may also be involved in membrane trafficking events. In chromaffin cells, G alpha o has been found associated with the membrane of secretory granules. Here we examined the role of Go in regulated exocytosis using pressure microinjection combined with amperometric measurement of catecholamine secretion from individual chromaffin cells. 2. Microinjection of GTP gamma S and mastoparan strongly inhibits the amperometric response to either nicotine or high K+. 3. The presence of mastoparan in the cell incubation medium had no effect on K(+)-evoked secretion, suggesting that mastoparan blocks the exocytotic machinery through an intracellular target protein not located just beneath the plasma membrane. 4. Microinjection of anti-G alpha o antibodies potentiates by more than 50% the K(+)-evoked secretion, whereas anti-G alpha i1/2 antibodies have no effect. 5. Thus an inhibitory Go protein, probably associated with secretory granules, controls exocytosis in chromaffin cells. The intracellular proteins controlling organelle-associated G proteins are currently unknown. The neuronal cytosolic protein GAP-43 stimulates G alpha o in purified chromaffin granule membranes and inhibits exocytosis in permeabilized cells. We show here that microinjection of a synthetic peptide corresponding to the domain of GAP-43 that interacts with Go inhibits secretion. We suggest that GAP-43 or a related cytosolic protein controls the exocytotic priming step in chromaffin, cells by stimulating a granule-associated Go protein.

Neurochemical characteristics of amisulpride, an atypical dopamine D2/D3 receptor antagonist with both presynaptic and limbic selectivity.

The benzamide derivative amisulpride shows a unique therapeutic profile being antipsychotic, at high doses, and disinhibitory, at low doses, while giving rise to only a low incidence of extrapyramidal side effects. In vitro, amisulpride has high affinity and selectivity for the human dopamine D2 (Ki = 2.8 nM) and D3 (Ki = 3.2 nM) receptors. Amisulpride shows antagonist properties toward D3 and both pre- and postsynaptic D2-like dopamine receptors of the rat striatum or nucleus accumbens in vitro. At low doses (< or = 10 mg/kg) amisulpride preferentially blocks presynaptic dopamine autoreceptors that control dopamine synthesis and release in the rat, whereas at higher doses (40-80 mg/kg) postsynaptic dopamine D2 receptor occupancy and antagonism is apparent. In contrast, haloperidol is active in all of these paradigms within the same dose range. Amisulpride preferentially inhibits in vivo binding of the D2/D3 antagonist [3H]raclopride to the limbic system (ID50 = 17 mg/kg) in comparison to the striatum (ID50 = 44 mg/kg) of the rat, increases striatal and limbic tissue 3,4-dihydroxyphenylacetic acid levels with similar potency and efficacy, and preferentially increases extracellular 3,4-dihydroxyphenylacetic acid levels in the nucleus accumbens when compared to the striatum. Haloperidol shows similar potency for the displacement of in vivo [3H]raclopride binding in striatal and limbic regions and preferentially increases striatal tissue 3,4-dihydroxyphenylacetic acid levels. The present data characterize amisulpride as a specific dopamine receptor antagonist with high and similar affinity for the dopamine D2 and D3 receptor. In vivo, it displays a degree of limbic selectivity and a preferential effect, at low doses, on dopamine D2/D3 autoreceptors. This atypical profile may explain the therapeutic efficacy of amisulpride in the treatment of both positive and negative symptoms of schizophrenia.

Increased expression of NGFI-A mRNA in the rat striatum following burst stimulation of the medial forebrain bundle.

Using in situ hybridization, we examined the mRNA expression for several immediate early genes in dopamine-innervated brain areas following electrical burst vs. regular stimulation of the medial forebrain bundle in anaesthetized rats. Two hours after 5 Hz burst stimulation, the expression of the nerve growth factor-inducible clone A (NGFI-A) mRNA was increased in the medial part of the striatum. This increase was prevented by pretreatment with the dopamine-D1 receptor antagonist, SCH23390 (0.1 mg/kg i.p.). After 8 Hz burst stimulation, NGFI-A mRNA expression was increased in the medial, central and lateral parts of the striatum. Induction occurred predominantly in cells expressing mRNAs for the dopamine-D1 receptor, substance P and dopamine and cAMP-regulated phosphoprotein (DARP-32). Regular stimulation had no effect on NGFI-A mRNA expression. The induction of NGFI-A was related to the levels of dopamine released by burst or regular stimulation as demonstrated with in vivo amperometry. Two hours after stimulation, the expression of none of the other genes studied was altered. One hour after 8 Hz burst stimulation, the expression of NGFI-A, NGFI-B and jun-B mRNAs was increased in the striatum and that of NGFI-A, NGFI-B, c-fos, fos-B and jun-B mRNAs was variably increased in the nucleus accumbens and lateral septum. These results provide additional support for the physiological importance of burst firing activity in midbrain dopamine neurons for the activation of their target cells. They demonstrate a spatial and temporal specificity as regards the brain region, the gene activated, the receptor involved and the phenotype of the cells affected.

Excitatory effects of dopamine released by impulse flow in the rat nucleus accumbens in vivo.

Dopamine is generally considered to be an inhibitory neurotransmitter in the central nervous system. Dopamine release in the nucleus accumbens can be evoked by chemical stimulation of the afferent cell bodies using N-methyl-D-aspartate microinjection in the ventral tegmental area. We report here that following such injections most neurons of the nucleus accumbens were excited. This excitation was abolished if dopaminergic neurons were lesioned and was blocked by antagonists of the D1 dopamine receptors. Finally, excitatory responses to electrical stimulation of the hippocampus were strongly facilitated by endogenously released dopamine. We suggest, therefore, that under physiological conditions, dopamine acting on D1 receptors is actually an excitatory neurotransmitter.