Altered functional brain network connectivity and glutamate system function in transgenic mice expressing truncated Disrupted-in-Schizophrenia 1.

Considerable evidence implicates DISC1 as a susceptibility gene for multiple psychiatric diseases. DISC1 has been intensively studied at the molecular, cellular and behavioral level, but its role in regulating brain connectivity and brain network function remains unknown. Here, we utilize a set of complementary approaches to assess the functional brain network abnormalities present in mice expressing a truncated Disc1 gene (Disc1tr Hemi mice). Disc1tr Hemi mice exhibited hypometabolism in the prefrontal cortex (PFC) and reticular thalamus along with a reorganization of functional brain network connectivity that included compromised hippocampal-PFC connectivity. Altered hippocampal-PFC connectivity in Disc1tr Hemi mice was confirmed by electrophysiological analysis, with Disc1tr Hemi mice showing a reduced probability of presynaptic neurotransmitter release in the monosynaptic glutamatergic hippocampal CA1-PFC projection. Glutamate system dysfunction in Disc1tr Hemi mice was further supported by the attenuated cerebral metabolic response to the NMDA receptor (NMDAR) antagonist ketamine and decreased hippocampal expression of NMDAR subunits 2A and 2B in these animals. These data show that the Disc1 truncation in Disc1tr Hemi mice induces a range of translationally relevant endophenotypes underpinned by glutamate system dysfunction and altered brain connectivity.

Preclinical characterization of selective phosphodiesterase 10A inhibitors: a new therapeutic approach to the treatment of schizophrenia.

We have recently proposed the hypothesis that inhibition of the cyclic nucleotide phosphodiesterase (PDE) 10A may represent a new pharmacological approach to the treatment of schizophrenia (Curr Opin Invest Drug 8:54-59, 2007). PDE10A is highly expressed in the medium spiny neurons of the mammalian striatum (Brain Res 985:113-126, 2003; J Histochem Cytochem 54:1205-1213, 2006; Neuroscience 139:597-607, 2006), where the enzyme is hypothesized to regulate both cAMP and cGMP signaling cascades to impact early signal processing in the corticostriatothalamic circuit (Neuropharmacology 51:374-385, 2006; Neuropharmacology 51:386-396, 2006). Our current understanding of the physiological role of PDE10A and the therapeutic utility of PDE10A inhibitors derives in part from studies with papaverine, the only pharmacological tool for this target extensively profiled to date. However, this agent has significant limitations in this regard, namely, relatively poor potency and selectivity and a very short exposure half-life after systemic administration. In the present report, we describe the discovery of a new class of PDE10A inhibitors exemplified by TP-10 (2-{4-[-pyridin-4-yl-1-(2,2,2-trifluoro-ethyl)-1H-pyrazol-3-yl]-phenoxymethyl}-quinoline succinic acid), an agent with greatly improved potency, selectivity, and pharmaceutical properties. These new pharmacological tools enabled studies that provide further evidence that inhibition of PDE10A represents an important new target for the treatment of schizophrenia and related disorders of basal ganglia function.

Dose-specific effects of scopolamine on canine cognition: impairment of visuospatial memory, but not visuospatial discrimination.

RATIONALE: The cholinergic system is linked extensively to memory, but its exact role remains controversial. In particular, scopolamine-induced impairment in rodents is not task specific, which may be due to difficulty in developing rodent protocols to assess deficits in recent memory, in which the remembered event is brief and distinct, and/or to non-specific behavioral impairment. OBJECTIVES: The present study sought to determine whether scopolamine-induced deficits in recent memory, using a working memory task, could be dose-specifically dissociated from deficits in associative memory in dogs. METHODS: A Latin-square design was used to determine the effect of scopolamine (5, 10 and 15 microg/kg; SC) on a variable delayed-non-matching-to-position (DNMP) task, which assesses visuospatial working memory. Subsequently, the minimal effective dose (15 microg/kg; SC) was administered prior to testing on a landmark discrimination task, which provides a measure of allocentric spatial ability, a black-white discrimination task, an oddity discrimination task and tests of exploratory behavior. We also investigated the effects of a 30 microg/kg dose (SC) on tests of oddity discrimination and behavioral activity. RESULTS: A 15 microg/kg dose produced significant impairment on the DNMP task, but did not affect performance of any discrimination task and did not alter behavior on tests of open field or curiosity. A 30 microg/kg dose caused disruption on discrimination performance and on open field measures. CONCLUSIONS: Working memory performance is most sensitive to scopolamine-induced impairment and can be dissociated from scopolamine-induced deficits in discrimination performance and non-cognitive behaviors. The present results indicate that scopolamine-induced impairments of working memory in the dog can serve as a model of age-related cholinergic dysfunction.

Atropisomeric quinazolin-4-one derivatives are potent noncompetitive alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonists.

Piriqualone (1) was found to be an antagonist of AMPA receptors. Structure activity optimization was conducted on each of the three rings in 1 to afford a series of potent and selective antagonists. The sterically crowded environment surrounding the N-3 aryl group provided sufficient thermal stability for atropisomers to be isolated. Separation of these atropisomers resulted in the identification of (+)-38 (CP-465,022), a compound that binds to the AMPA receptor with high affinity (IC50 = 36 nM) and displays potent anticonvulsant activity.

Hyperphosphorylated tau and neurofilament and cytoskeletal disruptions in mice overexpressing human p25, an activator of cdk5.

Hyperphosphorylation of microtubule-associated proteins such as tau and neurofilament may underlie the cytoskeletal abnormalities and neuronal death seen in several neurodegenerative diseases including Alzheimer's disease. One potential mechanism of microtubule-associated protein hyperphosphorylation is augmented activity of protein kinases known to associate with microtubules, such as cdk5 or GSK3beta. Here we show that tau and neurofilament are hyperphosphorylated in transgenic mice that overexpress human p25, an activator of cdk5. The p25 transgenic mice display silver-positive neurons using the Bielschowsky stain. Disturbances in neuronal cytoskeletal organization are apparent at the ultrastructural level. These changes are localized predominantly to the amygdala, thalamus/hypothalamus, and cortex. The p25 transgenic mice display increased spontaneous locomotor activity and differences from control in the elevated plus-maze test. The overexpression of an activator of cdk5 in transgenic mice results in increased cdk5 activity that is sufficient to produce hyperphosphorylation of tau and neurofilament as well as cytoskeletal disruptions reminiscent of Alzheimer's disease and other neurodegenerative diseases.

Synthesis, SAR and pharmacology of CP-293,019: a potent, selective dopamine D4 receptor antagonist.

A series of novel, potent and selective pyrido[1,2-a]pyrazine dopamine D4 receptor antagonists are reported including CP-293,019 (D4 Ki = 3.4 nM, D2 Ki > 3,310 nM), which also inhibits apomorphine-induced hyperlocomotion in rats after oral dosing.

Characterization of CP-122,721; a nonpeptide antagonist of the neurokinin NK1 receptor.

CP-122,721 [(+)-(2S,3S)-3-(2-methoxy-5-trifluoromethoxybenzyl)amino-2 -phenylpiperidine] interacts with high affinity (pIC50 = 9.8) at the human NK1 receptor expressed in IM-9 cells. In the presence of CP-122,721, there was a reduction in Bmax of [125I]BH-SP binding with no change in affinity suggesting that CP-122,721 does not interact with the NK1 receptor in competitive manner. In an in vitro functional assay. CP-122,721 blocked SP-induced excitation of locus ceruleus cells in guinea pig brain slices with a IC50 value of 7 nM. In vivo, CP-122,721 potently blocked plasma extravasation in guinea pig lung elicited by aerosolized capsaicin (1 mM) with an ID50 = 0.01 mg/kg, p.o. Orally administered CP-122,721 antagonized Sar9, Met (O2)11-SP-induced locomotor activity in guinea pigs with an ID50 = 0.2 mg/kg suggesting good entry into the central nervous system. In addition, consistent with insurmountable blockade observed in vitro, CP-122,721 (0.01, 0.03 0.3 mg/kg, p.o.) produced a rightward shift in the dose response curve for SP-induced hypotension in the awake dog that was accompanied by a decrease in the maximal response. Thus, in vitro and in vivo CP-122,721 appears to behave functionally as a non-competitive antagonist producing an insurmountable blockade of the actions of SP.

3-Benzisothiazolylpiperazine derivatives as potential atypical antipsychotic agents.

A series of substituted phenethyl derivatives of 3-benzisothiazolylpiperazine incorporating potent D2 and 5-HT2A antagonist activity was investigated as an approach to a novel atypical antipsychotic agent. The in vitro profile of 8e from this series is a combination of D2 receptor affinity comparable to the typical antipsychotic agent haloperidol and a 5-HT2A/D2 ratio comparable to the atypical agent clozapine. In vivo 8e possesses activity consistent with an efficacious antipsychotic agent with less tendency to induce extrapyramidal side effects in man.

Ziprasidone (CP-88,059): a new antipsychotic with combined dopamine and serotonin receptor antagonist activity.

Ziprasidone (CP-88,059) is a combined 5-HT (serotonin) and dopamine receptor antagonist which exhibits potent effects in preclinical assays predictive of antipsychotic activity. Whereas the compound is a dopamine antagonist in vitro and in vivo, its most potent action is antagonism of 5-HT2A receptors, where its affinity is an order of magnitude greater than that observed for dopamine D2 sites. Laboratory and clinical findings have led to a hypothesis that antagonism of 5-HT2A receptors in the brain limits the undesirable motor side effects associated with dopamine receptor blockade and improves efficacy against the negative symptoms of schizophrenia. Ziprasidone possesses an in vitro 5-HT2A/dopamine D2 receptor affinity ratio higher than any clinically available antipsychotic agent. In vivo, ziprasidone antagonizes 5-HT2A receptor-induced head twitch with 6-fold higher potency than for blockade of d-amphetamine-induced hyperactivity, a measure of central dopamine D2 receptor antagonism. Ziprasidone also has high affinity for the 5-HT1A, 5-HT1D and 5-HT2C receptor subtypes, which may further enhance its therapeutic potential. The prediction of antipsychotic efficacy without severe motor side effects is supported by the relatively weak potency of ziprasidone to produce catalepsy in animals, contrasted with its potent antagonism of conditioned avoidance responding and dopamine agonist-induced locomotor activation and stereotypy. The compound is well tolerated in animals at doses producing effective dopamine antagonism in the brain. Ziprasidone should be a valuable addition to the treatment of psychotic disorders.

Pharmacology of CP-99,994; a nonpeptide antagonist of the tachykinin neurokinin-1 receptor.

(+)-(2S,3S)-3-(2-methoxybenzylamino)-2-phenylpiperidine (CP-99,994) binds selectively and with high affinity (Ki = 0.25 nM) to neurokinin (NK)-1 tachykinin receptors in a human cell line and in guinea pigs where it acts as an antagonist as evidenced by its blockade of substance P-induced excitation of locus coeruleus neurons in vitro. Subcutaneously administered CP-99,994 antagonized locomotor activity in guinea pigs induced by intraventricular infusion of [Sar9,Met(O2)11]-substance P (50 micrograms) with an ID50 = 0.59 mg/kg, indicating that CP-99,994 penetrates into the central nervous system. Orally administered CP-99,994 potently blocked (ID50 = 4 mg/kg) the leakage of Evans blue dye into trachea and bronchi elicited by exposure of guinea pigs to aerosol capsaicin (1 mM). CP-99,994 has reduced affinity (IC50 = 3 microM) for the L-type calcium channel in contrast to CP-96,345 (IC50 = 27 nM) an earlier nonpeptide antagonist. Thus, CP-99,994 represents an important pharmacological tool for investigating the physiological role of substance P and a potentially novel therapeutic agent for treating a variety of diseases.

Role of prostaglandins in the behavioral changes induced by murine interleukin 1 alpha in the rat.

Continuous infusion of murine recombinant interleukin 1 alpha (rIL-1 alpha) produces weight loss, appetite suppression, reduction in horizontal locomotor activity (crossovers) and vertical locomotor activity (rears), and an increase in drinking behavior in the rat. The role of prostaglandins (PG) in the elicitation of these effects was studied. Infusion of rIL-1 alpha produced a transient increase in serum (PGs) which peaked at 24 to 48 h. This increase was completely inhibited by piroxicam. However, inhibition of circulating PG by piroxicam did not block the reductions in appetite, crossover, and rears induced by rIL-1 alpha; it restored normal drinking behavior and only partially restored body weight. Continuous intraperitoneal infusion of PGE2 at 24 micrograms/day exposed the animals to serum levels of PGE2 comparable to those produced by infusion with rIL-1 alpha. Yet, at the point of maximum weight loss induced by rIL-1 alpha (72 h), PGE2 infusion resulted in only a quarter of the weight loss. Compared with rIL-1 alpha, continuously infused PGE2 produced significantly smaller reductions in appetite, crossovers, and rears, and had no effect on drinking behavior. From these observations, we conclude that the rIL-1 alpha-induced increase in drinking behavior was fully dependent on products of the cyclooxygenase pathway, but not necessarily PGE2. However, because of the failure of piroxicam to fully reverse rIL-1 alpha effects on eating, mobility, and weight loss, there must also be a significant PG-independent component to account for the full range of rIL-1 alpha effects.

1-Naphthylpiperazine derivatives as potential atypical antipsychotic agents.

The design and synthesis of a series of potential atypical antipsychotic agents based on the structure of 1-naphthylpiperazine are described. The incorporation of dopamine antagonist activity into the parent structure was achieved with heterocyclic surrogates for the catechol moiety of dopamine. Compound 4b from this series showed a biochemical profile that translated to behavioral activity in the rat predictive of an antipsychotic agent with a low propensity to cause extrapyramidal side effects in man.

4-Amino[1,2,4]triazolo[4,3-a]quinoxalines. A novel class of potent adenosine receptor antagonists and potential rapid-onset antidepressants.

A series of 4-amino[1,2,4]triazolo[4,3-a]quinoxalines has been prepared. Many compounds from this class reduce immobility in Porsolt's behavioral despair model in rats upon acute administration and may therefore have therapeutic potential as novel and rapid acting antidepressant agents. Optimal activity in this test is associated with hydrogen, CF3, or small alkyl groups in the 1-position, with NH2, NH-acetyl, or amines substituted with small alkyl groups in the 4-position, and with hydrogen or 8-halogen substituents in the aromatic ring. Furthermore, many of these 4-amino[1,2,4]triazolo[4,3-a]quinoxalines bind avidly, and in some cases very selectively, to adenosine A1 and A2 receptors. A1 affinity of these compounds was measured by their inhibition of tritiated CHA (N6-cyclohexyladenosine) binding in rat cerebral cortex membranes and A2 affinity by their inhibition of tritiated NECA (5'-(N-ethylcarbamoyl)adenosine) binding to rat striatal homogenate in the presence of cold N6-cyclopentyladenosine. Structure-activity relationship (SAR) studies show that best A1 affinity is associated with ethyl, CF3, or C2F5 in the 1-position, NH-iPr or NH-cycloalkyl in the 4-position, and with an 8-chloro substituent. Affinity at the A2 receptor is mostly dependent on the presence of an NH2 group in the 4-position and is enhanced by phenyl, CF3, or ethyl in the 1-position. The most selective A1 ligand by a factor of greater than 3000 is 121 (CP-68,247; 8-chloro-4-(cyclohexyl-amino)-1- (trifluoromethyl)[1,2,4]triazolo[4,3-a]quinoxaline) with an IC50 of 28 nM at the A1 receptor. The most potent A2 ligand is 128 (CP-66,713; 4-amino-8-chloro-1- phenyl[1,2,4]triazolo[4,3-a]quinoxaline) with an IC50 of 21 nM at the A2 receptor and a 13-fold selectivity for this receptor. Representatives from this series appear to act as antagonists at both A1 and A2 receptors since they antagonize the inhibiting action of CHA on norepinephrine-stimulated cAMP formation in fat cells and they decrease cAMP accumulation induced by adenosine in limbic forebrain slices. Thus certain members of this 4-amino[1,2,4]triazolo[4,3-a]quinoxaline series are among the most potent and A1 or A2 selective non-xanthine adenosine antagonists known.

Effects of continuously administered murine interleukin-1 alpha: tolerance development and granuloma formation.

Continuous infusion of murine recombinant interleukin-1 alpha (rIL-1 alpha) into rats by using intraperitoneally implanted osmotic pumps led to marked decreases in body weight, liver enzymes (serum glutamic oxalacetic transaminase, serum glutamic pyruvic transaminase, and sorbitol dehydrogenase), appetite, and mobility and increases in drinking, blood urea nitrogen, and total peripheral blood leukocytes within 3 days. Granuloma formation was found in the local area of rIL-1 alpha release. As early as day 3, a focal infiltrate of polymorphonuclear leukocytes, mononuclear leukocytes, and plasma cells filled the area; by day 6, extensive fibrosis was found. A loss of rIL-1 alpha-induced changes, with the exception of granuloma formation, occurred by day 10. A marked decrease in the response to rIL-1 alpha was also observed when animals were challenged by implantation of new pumps containing rIL-1 alpha, with monitoring of body weight, or by subcutaneous injection of rIL-1 alpha, with monitoring of serum colony-stimulating factor production. We propose that, even in the continuous presence of interleukin-1, replacement of the acute responses to interleukin-1 by restoration of more normal physiology may be advantageous upon acquisition of specific immunity.

The effects of continuous administration of murine interleukin-1 alpha in the rat.

Recombinant murine IL-1 alpha was administered continuously to rats by means of osmotic pumps implanted intraperitoneally. Continuous infusion of rIL-1 alpha in a range between 0.12 and 12.0 micrograms/day for four days was found to produce concentration-dependent weight loss. Behavioral parameters were continuously monitored and recorded at the 3.0 micrograms/day concentration in electronically-monitored activity cages during Days 2 through 5 of rIL-1 alpha administration. Parameters were separated into those affected during the dark phase (active period) or the light phase (resting period). Eating activity was found to be significantly reduced during each dark period through day 5, when compared with either untreated or PBS vehicle-infused animals. During the fourth and fifth days of infusion, however, eating behavior in animals infused with rIL-1 alpha began to increase toward control level in the latter, but not the earlier, half of the dark period. In contrast, drinking behavior was found to be significantly elevated only during the light periods. Continuous infusion of rIL-1 alpha also produced significant reductions in both horizontal locomotor activity (crossovers) and vertical locomotor activity (rears). However, in contrast to the trend toward a return of normal eating behavior, locomotor activity remained decreased through the fifth day of rIL-1 alpha infusion. These results suggest changes that could be produced by IL-1 in chronic inflammatory disease and infection.