Haloperidol and clozapine increase neural activity in the rat prefrontal cortex

Transgenic autoinhibition of p21-activated kinase exacerbates synaptic impairments and fronto-dependent behavioral deficits in an animal model of Alzheimer's disease

Defects in p21-activated kinase (PAK) lead to dendritic spine abnormalities and are sufficient to cause cognition impairment. The decrease in PAK in the brain of Alzheimer's disease (AD) patients is suspected to underlie synaptic and dendritic disturbances associated with its clinical expression, particularly with symptoms related to frontal cortex dysfunction. To investigate the role of PAK combined with Aβ and tau pathologies (3xTg-AD mice) in the frontal cortex, we generated a transgenic model of AD with a deficit in PAK activity (3xTg-AD-dnPAK mice). PAK inactivation had no effect on Aβ40 and Aβ42 levels, but increased the phosphorylation ratio of tau in detergent-insoluble protein fractions in the frontal cortex of 18-month-old heterozygous 3xTg-AD mice. Morphometric analyses of layer II/III pyramidal neurons in the frontal cortex showed that 3xTg-AD-dnPAK neurons exhibited significant dendritic attrition, lower spine density and longer spines compared to NonTg and 3xTg-AD mice. Finally, behavioral assessments revealed that 3xTg-AD-dnPAK mice exhibited pronounced anxious traits and disturbances in social behaviors, reminiscent of fronto-dependent symptoms observed in AD. Our results substantiate a critical role for PAK in the genesis of neuronal abnormalities in the frontal cortex underlying the emergence of psychiatric-like symptoms in AD.

Effects of methamphetamine on single unit activity in rat medial prefrontal cortex in vivo

To investigate how neuronal activity in the prefrontal cortex changes in an animal model of schizophrenia, we recorded single unit activity in the medial prefrontal cortex of urethane-anesthetized and awake rats following methamphetamine (MA) administration. Systemic MA injection (4 mg/kg, IP) induced inconsistent changes, that is, both enhancement and reduction, in unit discharge rate, with a subset of neurons transiently (<30 min) elevating their activities. The direction of firing rate change was poorly predicted by the mean firing rate or the degree of burst firing during the baseline period. Also, simultaneously recorded units showed opposite directions of firing rate change, indicating that recording location is a poor predictor of the direction of firing rate change. These results raise the possibility that systemic MA injection induces random bidirectional changes in prefrontal cortical unit activity, which may underlie some of MA-induced psychotic symptoms.

Early life stress causes FG-7142-induced corticolimbic dysfunction in adulthood

Maternal separation (MS) during the neonatal period enhances stress responsivity in adulthood. The medial prefrontal cortex (mPFC) and the basolateral amygdala (BLA) are involved in coordinating various stress responses. Evidence indicates that MS reduces benzodiazepine and GABA(A) receptor expression in these regions, although their effects on neuronal function in the mPFC and the BLA remain unknown. The present study was conducted to assess the effects of MS on neuronal activity in the mPFC and BLA in response to the benzodiazepine receptor partial inverse agonist N-methyl-beta-carboline-3-carboxamide (FG-7142). Rat pups were subjected to MS (360 min), brief handling (H; 15 min) or standard animal facility rearing (AFR) on postnatal days 2-14. In adult males, in vivo electrophysiology under isoflurane anesthesia was used to conduct acute recordings of extracellular unit activity in response to systemic FG-7142 administration. Animals subjected to H showed significantly increased basal mPFC activity compared to MS and AFR animals. There were no differences in basal BLA activity between the early rearing groups. In response to FG-7142, MS animals showed significantly attenuated mPFC activity compared to H animals and a nonsignificant trend towards attenuated mPFC activity compared to AFR animals. In contrast to mPFC, MS animals showed significantly potentiated FG-7142-induced activity in the BLA, compared to both H and AFR animals. These findings indicate that MS induces functionally relevant alterations in corticolimbic GABA(A) receptor signaling. Given that FG-7142 mimics several behavioral and physiological effects of stress, these results may also model stress-induced corticolimbic dysfunction caused by early life stress.

Systemic administration of the benzodiazepine receptor partial inverse agonist FG-7142 disrupts corticolimbic network interactions

The medial prefrontal cortex (mPFC) and basolateral amygdala (BLA) coordinate various stress responses. Although the effects of stressors on mPFC and BLA activity have been previously examined, it remains unclear to what extent stressors affect functional interactions between these regions. In vivo electrophysiology in the anesthetized rat was used to examine mPFC and BLA activity simultaneously in response to FG-7142, a benzodiazepine receptor partial inverse agonist that mimics various stress responses, in an attempt to model the effects of stressors on corticolimbic functional connectivity. Extracellular unit and local field potential (LFP) recordings, using multielectrode arrays positioned in mPFC and BLA, were conducted under basal conditions and in response to systemic FG-7142 administration. This drug increased mPFC and BLA unit firing at the lowest dose tested, whereas higher doses of FG-7142 decreased various burst firing parameters in both regions. Moreover, LFP power was attenuated at lower (<1 Hz) and potentiated at higher frequencies in mPFC (1-12 Hz) and BLA (4-8 Hz). Interestingly, FG-7142 diminished synchronized unit firing, both within and between mPFC and BLA. Finally, FG-7142 decreased LFP synchronization between these regions. In a separate group of animals, pretreatment with the selective benzodiazepine receptor antagonist flumazenil blocked the changes in burst firing, LFP power and synchronized activity induced by FG-7142, confirming direct benzodiazepine receptor-mediated effects. These results indicate that FG-7142 disrupts corticolimbic network interactions via benzodiazepine receptor partial inverse agonism. Perturbation of mPFC-BLA functional connectivity induced by FG-7142 may provide a useful model of corticolimbic dysfunction induced by stressors.

Clozapine but not haloperidol treatment reverses sub-chronic phencyclidine-induced disruption of conditional discrimination performance

Abusers of phencyclidine (PCP) often present with a symptom profile similar to that exhibited by schizophrenic patients. Animal models utilising such psychotomimetics are currently informing research into the condition. Accumulating evidence suggests that a central cognitive deficit in schizophrenia is the inability to use task-setting cues to guide goal directed behaviour and that this ability is mediated by prefrontal dopamine (DA). The current study used the non-competitive NMDA antagonist phencyclidine (PCP) and Haloperidol (typical antipsychotic) and Clozapine (atypical antipsychotic) in order to further investigate the influence of DAergic manipulation on a task that requires the use of conditional information to inform goal-directed performance. An instrumental conditional discrimination task was employed in which rats learn to respond appropriately according to the presence of specific auditory conditional stimuli. Probe test 1 showed impaired conditional discrimination performance following sub-chronic PCP administration (seven twice-daily injection protocol) compared to control which was reversed by acute treatment with clozapine (5 mg/kg) but not haloperidol (0.1 mg/kg) both administered 60 min pre-test. Probe test 2 (8 days post-treatment) showed enduring deficits to conditional discrimination performance that were again reversed by clozapine but not haloperidol (injection procedures as above). These results show that tasks dependent upon conditional relationships are particularly sensitive to manipulation of DAergic systems as prolonged treatment with PCP has been shown to selectively reduce prefrontal cortex (PFC) DA activity and treatment with clozapine (known to ameliorate cognitive deficits) but not haloperidol has been shown to selectively restore PFC DA levels.

Electrophysiological effects of acute and chronic olanzapine and fluoxetine in the rat prefrontal cortex

Since the prefrontal cortex (PFC) is thought to play an important role in depression and schizophrenia, we studied the effects of fluoxetine and olanzapine on PFC neurons in rats using extracellular, in vivo recordings. Acute or 5-day administration of olanzapine (1-10 mg/kg, iv or 20 mg/kg, sc) did not change the firing rate of PFC neurons. However, a 21-day treatment with olanzapine (20 mg/kg per day, sc) significantly increased the firing rate of PFC neurons and increased their responsiveness to the iontophoretic administration of the GABA(A) antagonist bicuculline. Acute administration of fluoxetine (10 mg/kg, iv) also did not change the firing rate of PFC neurons. However, a 21-day treatment with fluoxetine (10 mg/kg per day) significantly decreased the firing rate of PFC neurons and decreased their responsiveness to the iontophoretic administration of bicuculline. Co-administration of olanzapine (10 mg/kg per day, sc) during the last 5 days of a 21-day fluoxetine treatment (10 mg/kg per day) prevented the suppression of firing and decreased responsiveness to the iontophoretic administration of bicuculline of PFC neurons. In conclusion, chronic, but not acute, olanzapine treatment significantly enhanced the firing and excitability of PFC neurons. In addition, chronic, but not acute, fluoxetine treatment significantly suppressed the firing and excitability of PFC neurons. Further, short-term olanzapine treatment attenuated the suppression of firing and excitability of PFC neurons induced by chronic fluoxetine treatment. These effects of olanzapine, fluoxetine, and the olanzapine/fluoxetine combination in the PFC may play an important role in the beneficial therapeutic effect of these compounds in schizophrenia and depression and may have implications for the treatment of treatment-resistant depression.

Comparative analysis of acute and chronic administration of haloperidol and clozapine using [3H] 2-deoxyglucose metabolic mapping

In an effort to compare and contrast the mechanisms of action of typical and atypical antipsychotic drugs, [3H] 2-deoxyglucose metabolic mapping was employed following acute and chronic administration of haloperidol (1 mg/kg i.p. acute and 0.5 mg/kg i.p. chronic) and clozapine (20 mg/kg i.p., both acute and chronic). Optical density ratios (ODR) were measured in 62 brain structures. An overall decrease in ODR was observed in many of the regions analyzed. Acute haloperidol elicited significant decreases, particularly in the thalamus and hippocampus. Acute clozapine decreased glucose uptake in the caudate putamen, hippocampus, central gray, locus coreleus, and the thalamus. In both chronically treated haloperidol and clozapine animals, significant decreases in ODR were seen in the thalamus and hippocampal areas most dramatically, with other changes in the superior colliculus, retrospenial cortex, and the cerebellum. Clozapine caused significant effects in 32 nuclei acutely and only 19 nuclei chronically. Haloperidol caused significant effects in 23 nuclei acutely and 15 nuclei chronically. The pattern of change induced by haloperidol and clozapine were remarkably similar when considering their pharmacology is somewhat different. Both antipsychotics elicited fewer significant changes upon chronic administration.