Effects of mood stabilizers on the inhibition of adenylate cyclase via dopamine D(2)-like receptors.

OBJECTIVE: The mood stabilizing drugs lithium, carbamazepine and valproate modulate brain adenosine monophosphate (cAMP) levels, which are assumed to be elevated in bipolar disorder patients. The aim of this work was to investigate how these three mood stabilizing agents affect the regulation of cAMP levels by dopamine D(2)-like receptors in vitro in rat cortical neurons in culture and in vivo in the rat prefrontal cortex. METHODS: The production of cAMP was measured in the cultured cortical neurons or in microdialysis samples collected from the prefrontal cortex of freely moving rats using the [8-(3)H] and [(125)I] radioimmunoassay kits. RESULTS: In vitro and in vivo data showed that the treatment with the mood stabilizing drugs had no effect on basal cAMP levels in vitro, but had differential effects in vivo. Direct stimulation of adenylate cyclase (AC) with forskolin increased cAMP levels both in vitro and in vivo, and this effect was significantly inhibited by all three mood stabilizers. Activation of dopamine D(2)-like receptors with quinpirole partially inhibited forskolin-induced increase in cAMP in untreated cultures, but no effect was observed in cortical neuron cultures treated with the mood stabilizing drugs. Similar results were obtained by chronic treatment with lithium and valproate in the prefrontal cortex in vivo. However, surprisingly, in carbamazepine-treated rats the activation of dopamine D(2)-like receptors enhanced the responsiveness of AC to subsequent activation by forskolin, possibly as a consequence of chronic inhibition of the activity of the enzyme. CONCLUSIONS: It was shown that each of these drugs affects basal- and forskolin-evoked cAMP levels in a distinct way, resulting in differential responses to dopamine D(2)-like receptors activation.

The interaction between dopamine D2-like and beta-adrenergic receptors in the prefrontal cortex is altered by mood-stabilizing agents.

Several studies have suggested the involvement of biogenic monoaminergic neurotransmission in bipolar disorder and in the therapy for this disease. In this study, the effects of the mood-stabilizing drugs lithium, carbamazepine or valproate on the dopaminergic and adrenergic systems, particularly on D2-like and beta-adrenergic receptors, were studied both in cultured rat cortical neurones and in rat prefrontal cortex. In vitro and in vivo data showed that stimulation of beta-adrenergic receptors with isoproterenol increased cyclic adenosine monophosphate (cAMP) levels and this effect was significantly inhibited by lithium, carbamazepine or valproate. The activation of dopamine D2-like receptors with quinpirole decreased the isoproterenol-induced rise in cAMP in control conditions. This inhibition was observed in vivo after chronic treatment of the rats with carbamazepine or valproate, but not after treatment with lithium or in cultured rat cortical neurones after 48 h exposure to the three mood stabilizers. Dopamine D2 and beta1-adrenergic receptors were found to be co-localized in prefrontal cortical cells, as determined by immunohistochemistry, but western blot experiments revealed that receptor levels were differentially affected by treatment with the three mood stabilizers. These data show that mood stabilizers affect D2 receptor-mediated regulation of beta-adrenergic signalling and that each drug acts by a unique mechanism.

Decrease in parvalbumin-expressing neurons in the hippocampus and increased phencyclidine-induced locomotor activity in the rat methylazoxymethanol (MAM) model of schizophrenia.

Treatment of rats with methylazoxymethanol (MAM) on gestational day (GD)17 disrupts corticolimbic development in the offspring (MAM-GD17 rats) and leads to abnormalities in adult MAM-GD17 rats resembling those described in schizophrenic patients. The underlying changes in specific cortical and limbic cell populations remain to be characterised. In schizophrenia, decreases in inhibitory gamma-aminobutyric acid (GABA)-containing interneurons that express the calcium-binding protein parvalbumin have been reported in the prefrontal cortex and hippocampus. In this study we analysed the expression of parvalbumin (PV), calretinin (CR) and calbindin (CB) in the prefrontal cortex and hippocampus of MAM-GD17 rats. Exposure in utero to MAM led to a significant decrease in the number of neurons expressing PV in the hippocampus, but not the prefrontal cortex. Neurons expressing CR or CB were not affected in either structure. The neurochemical changes in MAM-GD17 rats were accompagnied by increased hyperlocomotion after administration of phencyclidine (PCP), analogous to the hypersensitivity of schizophrenic patients to PCP. Therefore, the developmental MAM-GD17 model reproduces key neurochemical and behavioural features that reflect cortical and subcortical dysfunction in schizophrenia, and could be a useful tool in the development of new antipsychotic drugs.

Changes in KCNQ2 immunoreactivity in the amygdala in two rat models of temporal lobe epilepsy.

Potassium channels containing the KCNQ2 subunit play an important role in the regulation of neuronal excitability and therefore have been implicated in epilepsy. This study describes the expression of KCNQ2 subunit immunoreactivity in the basolateral amygdala in two rat models of temporal lobe epilepsy, (1) amygdala kindling and (2) spontaneously epileptic rats after status epilepticus induced by hippocampal electrical stimulation. KCNQ2 subunit immunoreactivity was assessed with a commercial antibody raised against a C-terminal part of the KCNQ2 protein. We show that KCNQ2 subunit immunoreactivity is upregulated in the basolateral amygdala in both models and that generalized seizures are required to induce this upregulation. We hypothesize that the upregulation of potassium channels containing the KCNQ2 subunit might represent a mechanism to counteract seizures in experimental temporal lobe epilepsy.

Spontaneous epileptic rats show changes in sleep architecture and hypothalamic pathology.

PURPOSE: The goal of the present study was to investigate the relationship between sleep, hypothalamic pathology, and seizures in spontaneous epileptic rats. METHODS: Rats were implanted with radiotelemetry transmitters for measuring electrocorticogram (ECoG) and stimulation electrodes in the hippocampus. Epileptogenesis was triggered by 2 h of electical stimulation-induced self-sustained status epilepticus (SSSE). After SSSE, ECoGs were monitored over a 15-week period for the occurrence of interictal high-amplitude low-frequency (HALF) acitvity and spontaneous reoccurring seizures (SRSs). RESULTS: Spontaneous epileptic rats showed clinical features of temporal lobe epilepsy (TLE), such as spontaneous seizures, interictal activity and neuronal cell loss in the dorsomedial hypothalamus, a region important for normal sleep regulation. Interestingly, epileptic rats showed disturbances in sleep architecture, with a high percentage of the seizures occurring during sleep. CONCLUSIONS: Therefore we conclude that a close association exists between epileptiform activity and alterations in sleep architecture that may be related to hypothalamic pathology.

PKN3 is required for malignant prostate cell growth downstream of activated PI 3-kinase.

Chronic activation of the phosphoinositide 3-kinase (PI3K)/PTEN signal transduction pathway contributes to metastatic cell growth, but up to now effectors mediating this response are poorly defined. By simulating chronic activation of PI3K signaling experimentally, combined with three-dimensional (3D) culture conditions and gene expression profiling, we aimed to identify novel effectors that contribute to malignant cell growth. Using this approach we identified and validated PKN3, a barely characterized protein kinase C-related molecule, as a novel effector mediating malignant cell growth downstream of activated PI3K. PKN3 is required for invasive prostate cell growth as assessed by 3D cell culture assays and in an orthotopic mouse tumor model by inducible expression of short hairpin RNA (shRNA). We demonstrate that PKN3 is regulated by PI3K at both the expression level and the catalytic activity level. Therefore, PKN3 might represent a preferred target for therapeutic intervention in cancers that lack tumor suppressor PTEN function or depend on chronic activation of PI3K.

Basal forebrain cholinergic system is involved in rapid nerve growth factor (NGF)-induced plasticity in the barrel cortex of adult rats.

We have previously reported that topical application of nerve growth factor (NGF) to the barrel cortex of an adult rat rapidly augmented a whisker functional representation (WFR) by increasing its area and height within minutes after NGF application. In addition, we found that TrkA, the high-affinity NGF receptor, was only found on fibers projecting into the barrel cortex. Here we use a combination of techniques including chronic intrinsic signal optical imaging, neuronal fiber tracking and immunohistological techniques, to test the hypothesis that NGF-induced rapid cortical plasticity is mediated by the cortical projections of the basal forebrain cholinergic system (BFCS). Our studies localize the source of the cells in the BFCS that project to a single WFR and also demonstrate that TrkA-immunoreactive fibers in the cortex are also cholinergic and likely arise from the BFCS. In addition, by selectively lesioning the BFCS cortical fibers with the immunotoxin 192 IgG-saporin, we show that NGF-induced WFR-cortical plasticity is eliminated. These results, taken together with our previously reported imaging results that demonstrated that agonists of the cholinergic system (particularly nicotine) showed transient NGF-like augmentations of a WFR, implicate the BFCS cortical projections as necessary for NGF's rapid plasticity in the adult rat somatosensory cortex.

In vivo modulation of a cortical functional sensory representation shortly after topical cholinergic agent application.

The aim of the present study was to determine whether cholinergic increase in the size of a functional representation (collective evoked response from a large population of neurons) can be observed shortly (within an hour) after treatment onset and whether nicotinic receptors can participate in this type of modulation. Cholinergic agonist application has been found previously to increase the response of a single cortical neuron to a stimulus. Also, pairing cholinergic basal forebrain stimulation with delivery of a tone has been reported to increase the size of that tone's functional representation. Whereas the increase in a single cortical neuron response can occur within seconds after cholinergic agonist application, to date the increase in the size of a functional representation has only been investigated within one to several weeks after the onset of pairing basal forebrain stimulation with tone delivery. Furthermore, primarily muscarinic receptors have been implicated in these types of changes in cortical activity. By using optical imaging of intrinsic signals in vivo, we found that the size of a whisker's functional representation in the primary somatosensory cortex of the rat increases substantially within 69 or 46 minutes after topical application of either a muscarinic or nicotinic agonist to the exposed cortex, respectively, and decreases within 23 minutes after topical application of a muscarinic antagonist. For each cholinergic agent, we verified that delivery of a cholinergic agent by means of topical application can lead to the agent's successful penetration through the cortical layers in the time allotted to complete an imaging experiment. Furthermore, the time course of penetration for each agent was characterized. Based on the combined imaging/penetration results, we speculate on potential sites of cholinergic action in the cortex. Irrespective of the exact mechanism of action, we demonstrate here that an increase in the size of a functional sensory representation can occur shortly by means of activation of either nicotinic or muscarinic receptors.