Chronic phencyclidine treatment induces long-lasting glutamatergic activation of VTA dopamine neurons.

Use of phencyclidine (PCP) can mimic some aspects of schizophrenia. However, the underlying mechanism is unclear. Administration of PCP is known to activate mesolimbic dopamine pathway. In this study, we focused on ventral tegmental area (VTA) of mesolimbic dopamine pathway as target of PCP for inducing schizophrenia-like symptoms. Single VTA neuron was isolated and its neural activity was monitored by measuring cytosolic Ca(2+) concentration ([Ca(2+)]i) followed by immunocytochemical identification of dopamine neurons. Administration of glutamate increased [Ca(2+)]i in dopamine neurons from control rats, and the [Ca(2+)]i increase was inhibited in the presence of PCP. In contrast, in VTA dopamine neurons from rats chronically treated with PCP for 7 days, administration of glutamate was able to induce [Ca(2+)]i increase in the presence of PCP. Furthermore, this glutamate-induced [Ca(2+)]i increase in the presence of PCP continued even after washout of glutamate and this effect lasted as long as PCP was present. This long-lasting glutamate-induced [Ca(2+)]i increase in the presence of PCP was not observed or significantly attenuated under Ca(2+) free condition and by N-type Ca(2+) channel blocker ω-conotoxin. The results indicate that chronic treatment with PCP reverses the acute PCP effect on VTA dopamine neurons from inhibitory to stimulatory tone, and consequently induces long-lasting activation of dopamine neurons by glutamate.

Nonlinear dynamical analysis of the effect by six stimuli on electroencephalogram.

The present study investigated the search by correlation dimension (D2) for the effect of six stimuli (sucrose, spearmint, gum-base chewing as a voluntary movement, and three combinations of these stimuli) on EEG findings. Twenty normal adult subjects received sucrose, spearmint oil, gum-base alone, and three combinations of these stimuli. EEG recordings were obtained while the subjects rested quietly with their eyes closed, as the following procedure: section I, 1 minute at rest; section II, first 5-minute recording (control record); session III, each stimulus affecting for 3 minutes; session IV, 1 minute at rest; session V, 5-minute recording (poststimulus record). The EEG activity was filtered with a 0.5 Hz high pass and a 30 Hz low pass filter. The final data (epoch) for analysis were selected from all data by our epoch inducing system, and D2 was calculated using a novel analytical program. D2 was found to increase after subjects inhaled spearmint. In contrast, D2 decreased after subject's chewed gum-base and after the combination stimuli with chewing. Furthermore, the D2 change observed after each stimulus was similar to the observed D2 changes in the theta band. These findings suggest that D2 expressed the change in EEG as a brain response after each stimulus. It was also demonstrated that the change of EEG complexity as a brain response to stimulation is related to theta rhythm that might be able to produce at the cortical limbic area. We confirmed that the change observed in the complexity in response to which the chewing stimulus relates in our present study is the model that best fits that theory of the change on complexity suggested by Stam CJ.

Brain region-specific effects of short-term treatment with duloxetine, venlafaxine, milnacipran and sertraline on monoamine metabolism in rats.

We examined brain region-specific changes in monoamines and metabolites, and their ratios, after short-term administration of antidepressants to rats. Serotonin noradrenaline reuptake inhibitors (SNRIs; duloxetine, venlafaxine, milnacipran) and a serotonin-selective reuptake inhibitor (SSRI; sertraline) elevated serotonin (5-HT) levels in the midbrain (MB). Duloxetine and venlafaxine increased 5-HT levels in the brainstem and 5-HT terminal areas, whereas milnacipran and sertraline increased levels in the brainstem only. Significant reductions in 5-HT turnover were observed in various forebrain regions, including the hippocampus and hypothalamus, after treatment with all of the tested drugs except for milnacipran. In addition, there was reduced 5-HT turnover in the dorsolateral frontal cortex (dlFC), the medial prefrontal cortex (mPFC), and both the dlFC and the mPFC after treatment with duloxetine, sertraline, and venlafaxine, respectively. Venlafaxine significantly increased dopamine (DA) levels in the nucleus accumbens (NAc) and the substantia nigra and decreased DA turnover in the NAc. Similar changes were observed after treatment with duloxetine and sertraline in the NAc, whereas milnacipran increased DA levels in the mPFC. Limited increases in noradrenaline levels were detected after treatment with duloxetine, venlafaxine, or sertraline, but not after treatment with milnacipran. These results show that SNRIs and SSRIs induced region-specific monoaminergic changes after short-term treatment.

Dopamine transporter density and behavioral response to methylphenidate in a hyperlocomotor rat model.

Rats exposed prenatally to 5-bromo-2'-deoxyuridine (BrdU-rats) display hyperlocomotive activity, making them a possibly useful animal model for the study of attention deficit hyperactivity disorder (ADHD). Using this model, we investigated dopamine transporter (DAT) density and behavioral outcomes in BrdU-rats, some of which were also administered methylphenidate, a psychostimulant that is widely used for the treatment of ADHD. Pregnant rats were exposed to BrdU from gestational day 9 through 15. In male offspring, DAT densities in different regions of the striatum were quantified at three weeks of age. At seven weeks of age, locomotor, rearing and grooming behaviors were evaluated in an open-field setting, with or without methylphenidate treatment (1 mg/kg or 4 mg/kg). The results revealed no significant changes in striatal DAT densities in BrdU-rats compared with controls. Extreme hyperlocomotion of BrdU-rats was detected in the open-field environment, an effect that was exacerbated following treatment with the lower and higher dose of methylphenidate. Such increase in locomotor activity was observed only with the higher dose in control animals. In summary, degeneration of dopaminergic neurons in the terminal field was not detected in juvenile BrdU-rats, although adult animals displayed hyperactive behavior in a mildly stressful environment as well as hypersensitivity to a psychostimulant that facilitates dopaminergic neurotransmission.

Repetitive transcranial magnetic stimulation induces kf-1 expression in the rat brain.

Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive approach used for stimulating the brain, and has proven effective in the treatment of depression, however the mechanism of its antidepressant action is unknown. Recently, we have reported the induction of kf-1 in rat frontal cortex and hippocampus after chronic antidepressant treatment and repeated electroconvulsive treatment (ECT). In this study, we demonstrated the induction of kf-1 after rTMS in the rat frontal cortex and hippocampus, but not in hypothalamus. Our data suggest that kf-1 may be a common functional molecule that is increased after antidepressant treatment, ECT and rTMS. In conclusion, it is proposed that induction of kf-1 may be associated with the treatment induced adaptive neural plasticity in the brain, which is a long-term target for their antidepressant action.

Locomotor hyperactivity following prenatal exposure to 5-bromo-2'-deoxyuridine: neurochemical and behavioral evidence of dopaminergic and serotonergic alterations.

Prenatal exposure to 5-bromo-2'-deoxyuridine (BrdU) has been reported to induce abnormal behaviors in offspring, including marked hyperactivity. In this study, the contribution of the serotonin (5-HT) and dopamine (DA) systems to BrdU-induced developmental neurotoxicity was investigated. Sprague-Dawley rats were treated with BrdU on gestational days 9 through 15 (50mg/kg, i.p.) and male offspring (BrdU-rats) were examined. The BrdU-rats exhibited a 3.5-fold increase in locomotor activity. The dopamine D2 receptor antagonist sulpiride increased locomotor activity in the BrdU-rats, but decreased it in control rats. The BrdU-rats responded to the 5-HT1A receptor antagonist NAN190 much more than the controls. The measurement of monoamines revealed significant decreases in DA, dihydroxyphenylacetic acid, and homovanilic acid, and significant increases in 5-HT and 5-hydroxy-3-indolacetic acid, with a decrease in the 5-HT turnover ratio in the striatum of BrdU-rats. Thus, prenatal exposure to BrdU induced alterations in both the DA and 5-HT systems.

Orexins (hypocretins) directly interact with neuropeptide Y, POMC and glucose-responsive neurons to regulate Ca 2+ signaling in a reciprocal manner to leptin: orexigenic neuronal pathways in the mediobasal hypothalamus.

Orexin-A and -B (hypocretin-1 and -2) have been implicated in the stimulation of feeding. Here we show the effector neurons and signaling mechanisms for the orexigenic action of orexins in rats. Immunohistochemical methods showed that orexin axon terminals contact with neuropeptide Y (NPY)- and proopiomelanocortin (POMC)-positive neurons in the arcuate nucleus (ARC) of the rats. Microinjection of orexins into the ARC markedly increased food intake. Orexins increased cytosolic Ca(2+) concentration ([Ca(2+)](i)) in the isolated neurons from the ARC, which were subsequently shown to be immunoreactive for NPY. The increases in [Ca(2+)](i) were inhibited by blockers of phospholipase C (PLC), protein kinase C (PKC) and Ca(2+) uptake into endoplasmic reticulum. The stimulation of food intake and increases in [Ca(2+)](i) in NPY neurons were greater with orexin-A than with orexin-B, indicative of involvement of the orexin-1 receptor (OX(1)R). In contrast, orexin-A and -B equipotently attenuated [Ca(2+)](i) oscillations and decreased [Ca(2+)](i) levels in POMC-containing neurons. These effects were counteracted by pertussis toxin, suggesting involvement of the orexin-2 receptor and Gi/Go subtypes of GTP-binding proteins. Orexins also decreased [Ca(2+)](i) levels in glucose-responsive neurons in the ventromedial hypothalamus (VMH), a satiety center. Leptin exerted opposite effects on these three classes of neurons. These results demonstrate that orexins directly regulate NPY, POMC and glucose-responsive neurons in the ARC and VMH, in a manner reciprocal to leptin. Orexin-A evokes Ca(2+) signaling in NPY neurons via OX(1)R-PLC-PKC and IP(3) pathways. These neural pathways and intracellular signaling mechanisms may play key roles in the orexigenic action of orexins.

The blockade by phencyclidine of glutamate-induced intracellular calcium increase in cultured neocortical neurons.

A calcium imaging technique combined with a confocal laser scanning microscope (CLSM) was applied to investigate the effects of phencyclidine (PCP) on glutamate-induced calcium increases in same group of primary cultured neocortical neurons. Non-N-methyl-D-aspartate (NMDA) receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) alone did not significantly alter glutamate-induced changes of fluorescence (89.6%), while addition of PCP greatly blocked increases in fluorescence to 32.6% of the glutamate response. Competitive NMDA receptor antagonist DL-2-amino-5-phosphonovaleric acid (APV) alone and the addition of PCP reduced glutamate responses to 30.5% and 21.2%, respectively. These data clearly demonstrate that the neuropharmacological properties of PCP may function through its blockade of the NMDA receptor.

5-Hydroxytryptamine7 (5-HT7) receptor immunoreactivity-positive 'stigmoid body'-like structure in developing rat brains.

We examined the expression of 5-hydroxytryptamine(7) (5-HT(7)) receptor protein in developing and adult rats with immunohistochemical technique. In adult male rats, 5-HT(7) receptor immunoreactivity was detected in the septum, striatum, indusium griseum, tenia tecta, thalamus, hippocampus and hypothalamus in the forebrain as well as the pons and cerebellum. In brains of 1, 7, 15 and 21 days old male rats but not of adult ones, 5-HT(7) receptor immunoreactivity-positive dot-like structures were detected. The dot-like structures were visualized in hypothalamus, hippocampus, frontal cortex, brainstem and cerebellum at 1 day old male rats. In 7 days old male rats, the dot-like structures were found in the hypothalamus, medial preoptic area (MPA), bed nucleus of the stria terminalis (BST), amygdaloid nucleus and brainstem reticular formation. In 15 and 21 days old male and female rats, 5-HT(7) receptor immunoreactive dots were most clearly detected in MPA, hypothalamus, raphe pallidus, raphe magnus and brainstem reticular formation. The 5-HT(7) receptor immunoreactivity-positive dot-like structures were shown in the cytoplasm and they were less than 1 microm in diameter in 1 and 7 days old rats and became larger to 1-3 microm in 15 and 21 days old rats. From the distribution and morphologic features, the 5-HT(7) receptor immunoreactivity-positive dot-like structure found in developing rat brains is considered to be identical to a cytoplasmic inclusion named 'stigmoid body'.

Effects of a neurosteroid, pregnenolone, during the neonatal period on adenosine A1 receptor, dopamine metabolites in the fronto-parietal cortex and behavioral response in the open field.

Neuronal dysfunction in the frontal cortex has been reported in the etiology of mental disorders, including schizophrenia. The adenosine A(1) receptor system, as well as the dopaminergic system, are important in the control of cortical neuronal activity. We hypothesize that neuroexcitability in early life is critical to the normal development of the brain, and neurosteroids are factors that modulate neuroexcitability during the development period. In this study, we treated neonatal rats with a neurosteroid, pregnenolone (10 microg/g) from postnatal day (PD) 3 until PD 7. In pregnenolone-treated male and female rats, adenosine A(1) receptor density, the amount of dopamine (DA), serotonin (5-HT) and their metabolites in the fronto-parietal cortex and behavioral responses in the open field were examined pre- and post-puberty. A decrease in K(d) values for the adenosine A(1) receptor binding assay using [(3)H]1,3-dipropyl-8-cyclopentylxanthine (DPCPX), increased formation of DA metabolites and hyper-locomotor activity in the open field were found in pregnenolone-treated rats compared with controls in pre- and post-puberty. An increase in 5-HT metabolites was found in the pregnenolone-treated rats in pre-puberty, but not post-puberty. These effects of pregnenolone were not different between males and females. However, correlations between horizontal and vertical activities in the open field were disrupted only in pregnenolone-treated females. The present results indicate that pregnenolone treatment during the neonatal period influences the cortical dopaminergic and adenosinergic systems as well as behavioral responses in the open field.

The selective sigma ligand MS-377 attenuates the blockade by phencyclidine of NMDA-induced intracellular calcium.

The role of MS-377, a novel selective sigma1 ligand currently being developed for the treatment of schizophrenia, in modulating the activities of phencyclidine (PCP) on NMDA-induced calcium increase was examined in primary cultured neocortical neurons using calcium-imaging technique combined with a confocal laser scanning microscope. PCP significantly blocked NMDA-induced increases in intracellular calcium. The blockade by PCP of NMDA response was attenuated by both MS-377 and another highly selective sigma1 ligand, 3-PPP. The results agree with the interpretation that sigma ligands may directly or indirectly modulate NMDA receptor complex functions, and may suggest that MS-377 might be therapeutically useful in cases of PCP-induced psychosis or schizophrenia.

Perirhinal cortical lesion suppresses the secondary generalization in kainic acid-induced limbic seizure.

To elucidate the role of the perirhinal cortex (PRC) in experimental epilepsy, the effects of the lesion of the PRC on kainic acid (KA)-induced limbic seizure were investigated. The PRC lesion was made by means of ibotenic acid (IBO) microinjection. The electroencephalogram in the PRC-lesioned rats demonstrated suppression of the propagation of epileptic discharges from the limbic structures to the sensorimotor cortex. Behaviorally, motor manifestations such as mastication, facial twitching and forelimb clonus were attenuated. These results indicate that the PRC seems to be a potent relay station of the secondary generalization from the limbic structures to the sensorimotor cortex.

Eye movements during the Rorschach test in schizophrenia.

In order to understand relationships between scanning behaviors, characteristics of visual stimuli and the clinical symptoms in schizophrenia, eye movements of 37 schizophrenic patients and 36 controls were recorded using an eye-mark recorder during a free-response period in a Rorschach test. Four cards (I, II, V and VIII) were used. Data were analyzed during 15 s from the presentation of each card. For all cards, the number of eye fixations and the number of eye fixation areas were fewer, and total scanning length and mean scanning length were shorter for schizophrenic patients than for controls. For card II, in the non-popular response group, eye fixation frequency upon area 5 + 6 (red) was higher for schizophrenic patients. For card VIII, in the popular response group, eye fixation frequency upon area 5 + 6 (pink) was lower for schizophrenic patients. For cards II and VIII, the number of eye fixations was inversely correlated with negative symptoms. For card II, total scanning length tended to be inversely correlated with negative symptoms, and mean eye fixation time was correlated with negative symptoms. The number of eye fixation areas was inversely correlated with positive symptoms. For card VIII, eye fixation frequency in a stimulative area tended to be correlated with positive symptoms. Scanning behaviors in schizophrenic patients are affected by characteristics of visual stimuli, and partially by clinical symptoms.

Relationship of nonlinear analysis, MRI and SPECT in the lateralization of temporal lobe epilepsy.

OBJECTIVES: The purpose of this study was to investigate the correlation of lateralization by nonlinear analysis, magnetic resonance imaging (MRI) and interictal single-photon emission computed tomography (SPECT) in patients with temporal lobe epilepsy. METHODS: Twenty-three patients (7 males, 16 females) were examined by MRI, interictal SPECT and EEG. Nonlinear dynamic properties of neuronal networks were estimated by calculating correlation dimensions on interictal EEG signals and corresponding surrogate data. Lateralization was detected based on the criteria introduced in this study. Concordance rates of the results among the three methods were compared. RESULTS: Epileptogenic foci were shown in the temporal areas in 21 patients using the nonlinear method (8 left, 2 right, 11 both), while 20 patients showed abnormalities in temporal lobes on MR images (13 left, 5 right, 2 both). Low cerebral blood flows of the temporal lobes were detected in all patients (11 left, 8 right, 4 both). Completely concordant lateralization was observed in 8 patients (35%) for the nonlinear method and MRI, in 9 patients (39%) for the nonlinear method and SPECT, and in 10 patients (43%) for MRI and SPECT. There were no significant differences among the concordance rates for these different methods. CONCLUSIONS: Our results revealed that correlation dimension is useful for differentiating dynamic properties of neuronal networks in the interictal state, and can provide informative data for localizing epileptogenic foci in epileptic patients. Therefore, the present nonlinear method is recommended for use with patients during presurgical evaluation.

A neuroactive steroid, pregnenolone, alters the striatal dopaminergic tone before and after puberty.

Neuroactive steroids are known to modulate excitability in neurons. Neuronal activity during early development is critical to normal development of the brain. A neuroactive steroid, pregnenolone, was administered (10 microg/g) to rats from postnatal day 3 (PD 3) through PD 7. Dopamine (DA), serotonin (5-HT) and their metabolites were measured in the striatum. The results showed that neonatal treatment with pregnenolone increases DA and 5-HT turnover in the striatum at 3 weeks of age. The increased 5-HT turnover in the pregnenolone-treated animals was normalized at 14 weeks of age whereas the DA turnover in the pregnenolone-treated group was lower than in the control group. The present study indicated that pregnenolone treatment during the neonatal period induced abnormal development of the striatal dopaminergic function in adulthood.

A shift in information flow between prefrontal cortex and the ventral tegmental area in methamphetamine-sensitized rats.

We examined the effects of long-term methamphetamine (MAP) administration to rats on locomotor traces and reward-seeking behavior that was evaluated through ventral tegmental intracranial self-stimulation (ICSS). Furthermore, using the directed coherence (DCOH) EEG analysis method, correlation of prefrontal cortical and ventral tegmental EEGs was investigated in terms of the direction of information transmission. The results showed a transition from 'mixed type' behavior to 'fixed type' behavior during long-term MAP treatment, accompanied by a gradually diminished rate of ICSS and increased reward threshold. Correlating to these changes, a dominant information flow from ventral tegmental area (VTA) to prefrontal cortex (PFC) was observed after long-term MAP administration. Together with our previously reported finding of reciprocal information flow between PFC and VTA in MAP-induced hyperactive and stereotyped behavior, the present results indicate that information flow and its direction may be useful in explaining the neuronal substrates mediating development of behavioral sensitization. The predominant information flow from the VTA to PFC that occurs with sensitization supports recent speculations concerning impulsivity in drug addiction.

Nonlinear analysis of EEG after repetitive transcranial magnetic stimulation.

The purpose of this study was to investigate whether repetitive transcranial magnetic stimulation (rTMS) can change nonlinear dynamic properties of the cerebral cortex. Two rTMS trains (10 Hz, 3 seconds, 100% of motor threshold) were administered to the left frontal area in healthy subjects. EEG signals were collected at 14 electrode sites before and after stimulation, and were filtered digitally into delta, theta, alpha, beta, and gamma bands. Basing on an improved algorithm introduced in the authors' recent study, dimension estimates were calculated on these signals as well as on the corresponding surrogate data. Sham treatment was designed into this study. The data showed that EEG signals obviously exhibited lower dimension estimates than the surrogate data, whereas the theta and alpha rhythms presented the lowest values among the frequency components. rTMS increased the dimension estimates of EEG signals during the first 2 minutes. Similar findings were also obtained on the delta and beta components. This study revealed that EEG signals in the normal state can be described by a nonlinear dynamic process. This process can be affected temporarily by rTMS. Neuronal networks revealed by EEG signals show more complicated properties after stimulation.