Ketamine enhances structural plasticity in mouse mesencephalic and human iPSC-derived dopaminergic neurons via AMPAR-driven BDNF and mTOR signaling.

Among neurobiological mechanisms underlying antidepressant properties of ketamine, structural remodeling of prefrontal and hippocampal neurons has been proposed as critical. The suggested mechanism involves downstream activation of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, which trigger mammalian target of rapamycin (mTOR)-dependent structural plasticity via brain-derived neurotrophic factor (BDNF) and protein neo-synthesis. We evaluated whether ketamine elicits similar molecular events in dopaminergic (DA) neurons, known to be affected in mood disorders, using a novel, translational strategy that involved mouse mesencephalic and human induced pluripotent stem cells-derived DA neurons. Sixty minutes exposure to ketamine elicited concentration-dependent increases of dendritic arborization and soma size in both mouse and human cultures as measured 72 hours after application. These structural effects were blocked by mTOR complex/signaling inhibitors like rapamycin. Direct evidence of mTOR activation by ketamine was revealed by its induction of p70S6 kinase. All effects of ketamine were abolished by AMPA receptor antagonists and mimicked by the AMPA-positive allosteric modulator CX614. Inhibition of BDNF signaling prevented induction of structural plasticity by ketamine or CX614. Furthermore, the actions of ketamine required functionally intact dopamine D3 receptors (D3R), as its effects were abolished by selective D3R antagonists and absent in D3R knockout preparations. Finally, the ketamine metabolite (2R,6R)-hydroxynorketamine mimicked ketamine effects at sub-micromolar concentrations. These data indicate that ketamine elicits structural plasticity by recruitment of AMPAR, mTOR and BDNF signaling in both mouse mesencephalic and human induced pluripotent stem cells-derived DA neurons. These observations are of likely relevance to the influence of ketamine upon mood and its other functional actions in vivo.

Neural response to the observable self in social anxiety disorder.

BACKGROUND: Distorted images of the observable self are considered crucial in the development and maintenance of social anxiety. We generated an experimental situation in which participants viewed themselves from an observer's perspective when exposed to scrutiny and evaluation by others. Method Twenty patients with social anxiety disorder (SAD) and 20 control subjects were assessed using functional magnetic resonance imaging (fMRI) during the public exposure of pre-recorded videos in which they were each shown performing a verbal task. The examiners acted as the audience in the experiment and rated performance. Whole-brain functional maps were computed using Statistical Parametric Mapping. RESULTS: Robust activation was observed in regions related to self-face recognition, emotional response and general arousal in both study groups. Patients showed significantly greater activation only in the primary visual cortex. By contrast, they showed significant deactivation or smaller activation in dorsal frontoparietal and anterior cingulate cortices relevant to the cognitive control of negative emotion. Task-related anxiety ratings revealed a pattern of negative correlation with activation in this frontoparietal/cingulate network. Importantly, the relationship between social anxiety scores and neural response showed an inverted-U function with positive correlations in the lower score range and negative correlations in the higher range. CONCLUSIONS: Our findings suggest that exposure to scrutiny and evaluation in SAD may be associated with changes in cortical systems mediating the cognitive components of anxiety. Disorder severity seems to be relevant in shaping the neural response pattern, which is distinctively characterized by a reduced cortical response in the most severe cases.

Appetite-suppressing effects of urocortin, a CRF-related neuropeptide.

The neuropeptide corticotropin-releasing factor (CRF) is well known to act on the central nervous system in ways that mimic stress and result in decreases in exploration, increases in sympathetic activity, decreases in parasympathetic outflow, and decreases in appetitive behavior. Urocortin, a neuropeptide related to CRF, binds with high affinity to the CRF2 receptor, is more potent than CRF in suppressing appetite, but is less potent than CRF in producing anxiety-like effects and activation. Doses as low as 10 nanograms injected intracerebroventricularly were effective in decreasing food intake in food-deprived and free-feeding rats. These results suggest that urocortin may be an endogenous CRF-like factor in the brain responsible for the effects of stress on appetite.

Pharmacokinetics and time-course of D(2) receptor occupancy induced by atypical antipsychotics in stabilized schizophrenic patients.

The (123)I-IBZM SPECT measured D(2) receptor occupancy (D(2)RO) in chronically dosed, stabilized schizophrenic patients and its relationship with antipsychotic (AP) pharmacokinetics (PK) over time is still unclear. The aims of this study were: 1) To define the relationship between striatal D(2) receptor occupancy (D( 2)RO) and plasma concentration (C(P)) in stabilized schizophrenic patients on clinically relevant doses using (123)I-IBZM SPECT; 2) To investigate the time course of AP-induced D(2)RO and corresponding C(P). Forty-six schizophrenic patients on their clinically required doses of risperidone, olanzapine, clozapine or quetiapine were included. D( 2)RO and C(P) were measured over time following a sparse-sampling experimental design, and individual PK and D(2)RO-time profiles were estimated using a population approach. Observed striatal D(2)RO and C(P) ranges were 28-75% and 9.4-60.5 ng/mL for risperidone, 22-84% and 8.6-89.5 ng/mL for olanzapine, 5-53% and 41.6-818.2 ng/mL for clozapine and 0-64% and 37.9-719.6 ng/mL for quetiapine. A PK-D(2)RO relationship was found for the four APs. D(2)RO pattern over time was stable for risperidone, olanzapine and clozapine but fluctuating for quetiapine. Stabilized schizophrenic patients show a wide range of both D(2)RO and C(P) at clinically effective doses of the four AP, suggesting that clinical response to these AP may be maintained with D(2)RO below 65%. D(2)RO patterns over time differ between AP. These results should be considered for accurate interpretation of D(2)RO measurements, proper design of studies and optimization of drug regimens for patients on AP treatment.

Altered neuroadaptation in opiate dependence and neurogenic inflammatory nociception in alpha CGRP-deficient mice.

The neuropeptide alpha CGRP (calcitonin gene-related peptide) is involved in the complex process of pain signaling, but the precise contribution of alpha CGRP remains unclear. Here we show that mice lacking alpha CGRP display an attenuated response to chemical pain and inflammation. Furthermore, alpha CGRP(-/-) mice do not show changes in heroin self-administration or morphine tolerance, but display a marked decrease in morphine withdrawal signs, suggesting an important contribution of alpha CGRP to opiate withdrawal.

Behavioral effects of central administration of the novel CRF antagonist astressin in rats.

Astressin, a novel corticotropin releasing factor (CRF) antagonist, has been found to be particularly potent at inhibiting the hypothalamo-pituitary-adrenal axis. The aim of the present study was to determine the effects in rats of astressin in attenuating the anxiogenic-like response produced by social stress and intracerebroventricular (ICV) CRF administration on the elevated plus-maze, and ICV CRF-induced locomotor activation in the rat. Astressin significantly reversed the anxiogenic-like response induced by both social stress and ICV rat/humanCRF (r/hCRF) on the elevated plus-maze, but failed to block the effects of r/hCRF-induced locomotor activity in a familiar environment. When these results were compared to previous studies performed with the same paradigms using other CRF antagonists, astressin showed effects similar to those of D-PheCRF(12-41) on plus-maze performance. However, contrary to alpha-helicalCRF(9-41) and D-PheCRF(12-41), astressin had no effect on CRF-induced locomotor activity. These results suggest that astressin may have a unique anti-CRF profile compared to previously tested antagonists.

Mechanisms of hypertension in patients with chronic obstructive pulmonary disease and acute respiratory failure.

PURPOSE: To investigate the effects of hypoxemia, hypercapnia, and cardiovascular hormones (norepinephrine, endothelin-1, and atrial natriuretic factor) on blood pressure during acute respiratory failure. PATIENTS AND METHODS: Patients with chronic obstructive pulmonary disease and acute respiratory failure were divided into four groups of 10 patients each: hypoxemia-normocapnia, hypoxemia-hypercapnia, hypoxemia-hypocapnia, and normoxemia-hypercapnia. Plasma norepinephrine levels were determined by high-performance liquid chromatography with electrochemical detection. Plasma endothelin-1 and atrial natriuretic factor levels were radioimmunoassayed after chromatographic preextraction. RESULTS: Systolic blood pressure and cardiovascular hormone levels were greater in patients with hypercapnia (whether or not they also had hypoxemia) than in those with normocapnia and hypoxemia. For example, in patients with hypercapnia and normoxemia, the mean (+/- SD) systolic blood pressure was 183+/-31 mm Hg and the mean norepinephrine level was 494+/-107 pg/mL, as compared with 150+/- 6 mm Hg and 243+/-58 pg/mL in those with normocapnia and hypoxemia (both P<0.05). Similar results were seen for endothelin-1 and atrial natriuretic factor levels, and for the comparisons of hypoxemic patients who were hypercapnic with those who were normocapnic. CONCLUSIONS: These results suggest that blood carbon dioxide levels, rather than oxygen levels, are responsible for hypertension during acute respiratory failure, perhaps as a result of enhanced sympatho-adrenergic activity.

Endogenous opioid system and atrial natriuretic factor in normotensive offspring of hypertensive parents at rest and during exercise test.

OBJECTIVE: To investigate the effects of the endogenous opioid system on plasma atrial natriuretic factor (ANF) levels during sympathetic hyperactivity. DESIGN: We studied the young normotensive offspring of parents who both had essential hypertension, who are characterized by a hyperactive sympathetic nervous system. METHODS: We assessed plasma beta-endorphin, met-enkephalin, dynorphin B, ANF and noradrenaline levels, blood pressure and heart rate values in eight normotensive offspring and in 10 young normotensive subjects with no family history of hypertension (controls) at rest and during two exercise tests: the first test performed with the infusion of placebo (1.5 ml/min saline) and the second test with the infusion of an opioid antagonist (9.5 micrograms/kg per min naloxone hydrochloride). ANF and opioids were radioimmunoassayed after chromatographic pre-extraction. RESULTS: At rest plasma met-enkephalin, dynorphin B, ANF and noradrenaline values in the normotensive offspring were significantly higher than in the controls. Exercise with placebo significantly raised all hormonal and haemodynamic parameters in the two groups. This increase was significantly higher in the normotensive offspring than in the controls. Naloxone did not modify any parameter in either group at rest, but it enhanced further the rise in plasma noradrenaline levels induced by exercise in both groups. A similar effect of naloxone during exercise was observed for plasma ANF levels in the normotensive offspring. CONCLUSIONS: Our findings show that plasma met-enkephalin, dynorphin B, ANF and noradrenaline levels at rest and during exercise are higher in normotensive offspring than in controls. The effects of naloxone indicate that in normotensive offspring at rest the opioid system does not affect ANF release, whereas during exercise it attenuates ANF hypersecretion, possibly by reducing noradrenaline release.

Distribution of the messenger RNA for the small conductance calcium-activated potassium channel SK3 in the adult rat brain and correlation with immunoreactivity.

Small conductance calcium-activated potassium channels are voltage independent potassium channels which modulate the firing patterns of neurons by activating the slow component of the afterhyperpolarization. The genes encoding a family of small conductance calcium-activated potassium channels have been cloned and up to now three known members have been described and named small conductance calcium-activated potassium channel type 1, small conductance calcium-activated potassium channel type 2 and small conductance calcium-activated potassium channel type 3; the distribution of their messenger RNA in the rat CNS has already been performed but only in a limited detail. The present study represents the first detailed analysis of small conductance calcium-activated potassium channel type 3 mRNA distribution in the adult rat brain and resulted in a strong to moderate expression of signal in medial habenular nucleus, substantia nigra compact part, suprachiasmatic nucleus, ventral tegmental area, lateral septum, dorsal raphe and locus coeruleus. Immunohistological experiments were also performed and confirmed the presence of small conductance calcium-activated potassium channel type 3 protein in medial habenular nucleus, locus coeruleus and dorsal raphe. Given the importance of dorsal raphe, locus coeruleus and substantia nigra/ventral tegmental area for serotonergic, noradrenergic and dopaminergic transmission respectively, our results pose the morphological basis for further studies on the action of small conductance calcium-activated potassium channel type 3 in serotonergic, noradrenergic and dopaminergic transmission.

Morphometrical and microdensitometrical studies on phenylethanolamine-N-methyltransferase- and neuropeptide Y-immunoreactive nerve terminals and on glucocorticoid receptor-immunoreactive nerve cell nuclei in the paraventricular hypothalamic nucleus in adult and old male rats.

The phenylethanolamine-N-methyltransferase- and neuropeptide Y-immunoreactive nerve terminal profiles and the glucocorticoid receptor-immunoreactive nuclear profiles have been characterized in the parvocellular part of the paraventricular hypothalamic nucleus of the adult (3 month) and the old (24 month) male rat. The phenylethanolamine-N-methyltransferase-, neuropeptide Y- and glucocorticoid receptor-immunoreactive structures have been demonstrated by means of the indirect immunoperoxidase procedure and analysed in a quantitative way by means of morphometrical and microdensitometrical approaches using both semiautomatic and automatic image analysis. During aging there is (a) a marked reduction in the number of neuropeptide Y-immunoreactive profiles, a moderate reduction of phenylethanolamine-N-methyltransferase-immunoreactive profiles and a small reduction in the number of glucocorticoid receptor-immunoreactive profiles without a significant change in the evenness of distribution of such profiles as evaluated by means of Gini's index; (b) a loss of the significant correlation in the distribution of the glucocorticoid receptor- and phenylethanolamine-N-methyltransferase-immunoreactive profiles at the two most caudal levels analysed (A5150 and A5270 micron) while a significant correlation developed between these two distributions at a more rostral level (A5400 micron); (c) a substantial decline in the overlap area of the glucocorticoid receptor- and phenylethanolamine-N-methyltransferase-immunoreactive profiles at four out of five rostrocaudal levels analysed; (d) a marked reduction in the density-intensity of the neuropeptide Y-immunoreactive profiles and a small significant reduction in the density-intensity of the phenylethanolamine-N-methyltransferase-immunoreactive profiles without any associated changes in the intensity of the glucocorticoid receptor-immunoreactive profiles. Furthermore, three-dimensional reconstructions of the overall distribution of the glucocorticoid receptor-, phenylethanolamine-N-methyltransferase- and neuropeptide Y-immunoreactive structures have been made in the paraventricular hypothalamic nucleus of the adult male rat. The present results indicate a reduction of neuropeptide Y- and phenylethanolamine-N-methyltransferase-immunoreactive nerve terminal profiles in the parvocellular part of the paraventricular hypothalamic nucleus during aging. These results may in part reflect a loss of neuropeptide Y-like peptides in phenylethanolamine-N-methyltransferase-immunoreactive nerve terminals of the paraventricular hypothalamic nucleus, favouring our view that during aging the modulatory peptides may be lost, leading to a loss of

Time-dependent induction of anxiogenic-like effects after central infusion of urocortin or corticotropin-releasing factor in the rat.

RATIONALE: Corticotropin-releasing factor (CRF) and urocortin (Ucn) belong to the CRF-related family, share a high degree of structural homology and bind to CRF receptors. However, compared with CRF, Ucn was shown to display either weaker or similar anxiogenic-like effects in vivo. OBJECTIVE: To compare the anxiogenic-like responses of rats injected intracerebroventricularly (ICV) with different doses of either rat/human CRF (r/hCRF) or rat Ucn (rUcn) at different intervals after injection. METHODS: Rats were tested on three validated paradigms of emotional behavior [i.e. elevated plus-maze (EPM), defensive withdrawal (DW) and conflict test (CT)] 5 and 30 min after treatment. RESULTS: In the EPM test only r/hCRF, but not rUcn, produced anxiogenic-like effects at the dose of 1.0 microg, when the peptides were injected 5 min before testing. At 30 min after injection, both peptides caused a significant reduction of open arms exploration, rUcn being effective at 0.01 microg. In the DW test both peptides were equally potent in decreasing the exploratory behavior and increasing the time spent in the chamber at the dose of 1.0 microg when tested 30 min after injection. In the CT both rUcn (0.25-1.0 microg) and r/hCRF (0.75-1.0 microg) decreased significantly the responding in the punished component. However, rUcn reduced food responding also in the unpunished component possibly due to its powerful anorectic activity. CONCLUSIONS: Comparison of anxiogenic-like activities of r/hCRF and rUcn at doses up to 1.0 microg revealed striking differential effects that depended on the time of testing after ICV peptide injection, and on the paradigm of anxiety used. These results suggest that the onset of r/hCRF and rUcn actions related to behavioral responses to anxiety is likely to depend on brain peptide-specific mechanisms including binding properties to CRF-receptors, differential distribution to specific functional brain sites and the distribution and effectiveness of binding-protein interactions.

Indole-pyruvic acid treatment reduces damage in striatum but not in hippocampus after transient forebrain ischemia in the rat.

The effects of treatment with indole-pyruvic acid, an endogenous metabolite of tryptophan converted into kynurenic acid in the brain, were studied in rats after transient forebrain ischemia induced by the 4-vessel occlusion procedure. The histological analysis showed a significant protective effect of indole-pyruvic acid treatment on striatal ischemic lesions assessed by the extent of regional atrophy and the area of neuronal disappearance 14 days after ischemia. Striatal neurons were labelled by dopamine and adenosine 3':5' monophosphate regulated phosphoprotein-32 immunoreactivity. Conversely, increased neuronal loss, regional atrophy and glial fibrillary acidic protein immunoreactivity, an index of post-injury astroglial activation, were observed in the hippocampal formation, especially the CA3 field, of indole-pyruvic acid-treated rats when compared with vehicle-treated ischemic rats. The treatment with indole-pyruvic acid did not produce any improving effects in a test assessing short-term impairments after transient ischemia (motor test score at 24 h and 48 h post-ischemia). Furthermore, no significant effects of indole-pyruvic acid treatment were found on performance in water T-maze studied at 7 and 14 days post-ischemia. The opposite effects of indole-pyruvic acid on ischemic lesion in different brain regions may be related to its multiple neurochemical actions in the brain. The protective effect of indole-pyruvic acid on ischemic damage in striatum may be due to its conversion into kynurenic acid, a broad spectrum glutamate receptor antagonist. At hippocampal level, where glutamate receptor antagonists have been proved ineffective in the present lesion model, indole-pyruvic acid-induced changes in monamine availability may lead to a worsening of neuronal damage.

Effects of chronic treatment with uridine on striatal dopamine release and dopamine related behaviours in the absence or the presence of chronic treatment with haloperidol.

Uridine (15mg/kg/day, i.p.), haloperidol (1mg/kg/day, i.p.), uridine (15mg/kg/day, i.p.) plus haloperidol (1mg/kg/day, i.p.) or saline have been chronically administered to Sprague-Dawley male rats. Following 1 week of wash-out, the effects of these treatments on basal striatal dopamine (DA) release as well as on the DA release induced by an acute haloperidol challenge (2mg/kg, i.p.) were studied by means of intracerebral microdialysis. Behavioural tests such as haloperidol-induced catalepsy or apomorphine-induced stereotypics were also performed 4-7 days after drug withdrawal. The chronic treatment with uridine alone or associated with haloperidol markedly reduced DA release induced by an acute haloperidol challenge. The behavioural studies also indicated a change in DA-related behaviours in these conditions. The animals chronically treated with uridine showed significant increases in the stereotypy scores and in the catalepsy induced by an acute haloperidol challenge with respect to saline treated rats. The present results indicate that a chronic uridine treatment is able to potentiate the reduction of the striatal DA transmission induced by acute and chronic haloperidol treatment. This finding suggests the possibility to reduce the neuroleptic dose in the treatment of schizophrenia by combining neuroleptic and uridine treatments, thus making it possible to relieve some of the side effects of neuroleptic therapy.

The role of CRF in behavioral aspects of stress.

CRF in the central nervous system appears to hve activating properties on behavior and to coordinate behavioral responses to stressors. These behavioral effects of CRF appear to be independent of the pituitary-adrenal axis and can be reversed by CRF antagonists. CRF antagonist administration reverses not only decreases in behavior associated with stress, but also increases in behavior associated with stress, thus suggesting that the role of CRF is stress dependent and not intrinsic to a given behavioral response. Further, microinjection of alpha-helical CRF 9-41 and immunotargeting of CRF neurons in separate brain compartments reveal a link between the anatomical sites that contain CRF and the nature of the behavioral response to stressors that can be modified by suppression of endogenous CRF activity therein. These actions of CRF in coordinating coping responses to stress at several bodily levels are consistent with a role for CRF similar to the dual role of other hypothalamic releasing factors in integrating hormonal and neural mechanisms by acting both as secretagogues for anterior pituitary hormones and as extrapituitary peptide neurotransmitters. Moreover, dysfunction in such a fundamental homeostatic system may be the key to a variety of pathophysiological conditions including mental disorders.

On the role of neuropeptide Y in information handling in the central nervous system in normal and physiopathological states. Focus on volume transmission and neuropeptide Y/alpha 2 receptor interactions.

The NPY neurons play an important role in information handling in the CNS by their ability to interact in both wiring and volume transmission at the network, local circuit and synaptic level. The importance of NPY/alpha 2 receptor-receptor interactions in cardiovascular, neuroendocrine and vigilance control is emphasized. Alterations in these receptor-receptor interactions take place in the spontaneously hypertensive rats as well as in the ischemic brain, which may have profound consequences for the information handling and contribute to the functional alterations found in these pathophysiological states. Finally, in the aging brain there appears to exist a marked reduction in NPY transmission line, which may affect higher brain functions, such as learning and memory retrieval. The most impressive result is, however, the indications of a role for NPY in volume transmission, where NPY appears to produce syndromic actions via its conversion into biologically active fragments, which may have preferential actions at Y2 NPY receptors. These syndromic pathways may be altered in the spontaneously hypertensive rat and may be controlled by gonadal steroids and glucocorticoids. Glucocorticoid receptors have been demonstrated in all arcuate NPY neurons and all NA/NPY and A/NPY costoring neurons.

Intramembrane interactions between neurotensin receptors and dopamine D2 receptors as a major mechanism for the neuroleptic-like action of neurotensin.

Evidence has been presented that behavioral actions of NT, inducing its neuroleptic-like action, can be explained on the basis of NT-D2 intramembrane receptor-receptor interactions in the basal ganglia, unrelated to the coexistence phenomenon, leading to reduced affinity and transduction of the D2 agonist binding site. By reducing selectively D2 receptor transduction at the pre- and postsynaptic level, the NT receptor appears capable of switching the DA synapses towards a D1 receptor-mediated transduction, illustrating how receptor-receptor interactions can increase the functional plasticity of central synapses (FIG. 12).

Involvement of alpha6 nicotinic receptor subunit in nicotine-elicited locomotion, demonstrated by in vivo antisense oligonucleotide infusion.

Enhanced locomotion in a habituated environment is a well documented effect of nicotine mediated by the mesotelencephalic dopaminergic system. The nicotinic receptor subunit alpha6 is, among other subunits, strongly expressed in the dopaminergic neurons of the mesencephalon. To examine the functional role of this subunit, we inhibited its expression in vivo using antisense oligonucleotides. In vitro treatments of embryonic mesencephalic neuron cultures demonstrated that the alpha6 antisense oligonucleotides caused a marked decrease in the level of alpha6 subunit protein. In vivo, 1 week infusion of alpha6 antisense oligonucleotides by osmotic mini-pump reduced the effect of nicotine on locomotor activity in habituated environment by 70%. These data support the notion that the effects of nicotine on the dopaminergic system involve alpha6 subunit containing nAChRs.

Opioid peptides in response to mental stress in asymptomatic dilated cardiomyopathy.

Fourteen asymptomatic dilated cardiomyopathy patients showing normal plasma levels of beta-endorphin, Met-enkephalin, dynorphin B, norepinephrine and endothelin-1 but elevated atrial natriuretic factor (ANF) levels underwent two Mental Arithmetic Tests (MAT), with placebo and naloxone hydrochloride infusion, respectively. MAT significantly (p < 0.01) increased blood pressure, heart rate, opioid peptides, norepinephrine, ANF, but not endothelin-1. Naloxone infusion significantly (p < 0.05) attenuated the increments produced by MAT in all measured parameters during placebo infusion. These results indicate that in asymptomatic dilated cardiomyopathy the endogenous opioid system, activated by stress-induced sympathoadrenergic hyperactivity, may further increase the sympathetic tone in a positive feedback that is interrupted by naloxone.

Chronic nicotine treatment decreases neurofilament immunoreactivity in the rat ventral tegmental area.

Region-specific decreases of neurofilament proteins have been described in the ventral tegmental area of rats chronically treated with either morphine or cocaine. The aim of the present study was to assess if the levels of neurofilament proteins are changed in the ventral tegmental area by chronic treatment with nicotine. Immunoreactivity for NF-68, NF-160 and NF-200 was determined using NR4, BF10 and RT97 antibodies, respectively. Measurements were performed using computer-assisted microdensitometry of brain sections from rats exposed to chronic nicotine treatment (0.4 mg/kg/dayx6 days) or to saline. Chronic nicotine treatment reduced NF-160 and NF-200 immunoreactivity by 44.5% (P<0.01) and 22.5% (P<0. 05), respectively, in the ventral tegmental area but not in the substantia nigra. A trend towards reduction was observed for NF-68 immunoreactivity in the ventral tegmental area. These preliminary results suggest that nicotine shares the same properties with cocaine and morphine to reduce neurofilament proteins in the ventral tegmental area, a key brain structure of the reward system.