Effects of rolipram on the elevated plus-maze test in rats: a preliminary study

Roflumilast protects against spatial memory impairments and exerts anti-inflammatory effects after transient global cerebral ischemia

Phosphodiesterase 4 (PDE4) inhibitors have been shown to present beneficial effects in cerebral ischemic injury because of their ability to improve cognition and target different phases and mechanisms of cerebral ischemia, including apoptosis, neurogenesis, angiogenesis, and inflammation. The present study investigated whether repeated treatment with the PDE4 inhibitor roflumilast rescued memory loss and attenuated neuroinflammation in rats following transient global cerebral ischemia (TGCI). TGCI caused memory impairments, neuronal loss (reflected by Neuronal nuclei (NeuN) immunoreactivity), and compensatory neurogenesis (reflected by doublecortin (DCX) immunoreactivity) in the hippocampus. Also, increases in the protein expression of the phosphorylated response element-binding protein (pCREB) and inflammatory markers such as the glial fibrillary acidic protein (GFAP) and ionized calcium-binding adaptor molecule 1 (Iba-1), were detected in the hippocampus in TGCI rats. Repeated treatment with roflumilast (0.003 and 0.01 mg/kg) prevented spatial memory deficits without promoting hippocampal protection in ischemic animals. Roflumilast increased the levels of pCREB, arginase-1, interleukin (IL) 4, and IL-10 in the hippocampus 21 days after TGCI. These data suggest a protective effect of roflumilast against functional sequelae of cerebral ischemia, which might be related to its anti-inflammatory properties.

Psychopharmacological effects of riparin III from Aniba riparia (Nees) Mez. (Lauraceae) supported by metabolic approach and multivariate data analysis

Background

Currently there is a high prevalence of humor disorders such as anxiety and depression throughout the world, especially concerning advanced age patients. Aniba riparia (Nees) Mez. (Lauraceae), popular known as “louro”, can be found from the Amazon through Guianas until the Andes. Previous studies have already reported the isolation of alkamide-type alkaloids such as riparin III (O-methyl-N-2,6-dyhydroxy-benzoyl tyramine) which has demonstrated anxiolytic and antidepressant-like effects in high doses by intraperitoneal administration.

Methods

Experimental protocol was conducted in order to analyze the anxiolytic-like effect of riparin III at lower doses by intravenous administration to Wistar rats (Rattus norvegicus) (n = 5). The experimental approach was designed to last 15 days, divided in 3 distinct periods of five days: control, anxiogenic and treatment periods. The anxiolytic-like effect was evaluated by experimental behavior tests such as open field and elevated plus-maze test, combined with urine metabolic footprint analysis. The urine was collected daily and analyzed by ¹H NMR. Generated data were statistically treated by Principal Component Analysis in order to detect patterns among the distinct periods evaluated as well as biomarkers responsible for its distinction.

Results

It was observed on treatment group that cortisol, biomarker related to physiological stress was reduced, indicating anxiolytic-like effect of riparin III, probably through activation of 5-HT_2A receptors, which was corroborated by behavioral tests.

Conclusion

¹H NMR urine metabolic footprint combined with multivariate data analysis have demonstrated to be an important diagnostic tool to prove the anxiolytic-like effect of riparin III in a more efficient and pragmatic way.

PDE4B gene polymorphism in Russian patients with panic disorder

Background

Panic disorder is a complex disease of unclear etiology but with an apparent genetic component. PDE4B gene product is involved in many cell processes owing to its function-regulation of the level of a second messenger cAMP. PDE4B gene polymorphism has been shown to be associated with some mental disorders including panic disorder.

Aims

The goal of our study was to evaluate the role of 3 SNPs in the PDE4B gene in the development of panic disorder.

Methods

94 patients diagnosed with panic disorder according to the DSM-IV criteria were enrolled in the study. The population control group included 192 subjects. Genotyping was carried out by real-time PCR with TaqMan probes.

Results

The investigated substitutions are not associated with panic disorder in general and in female/male cohorts (p > 0.05). The analysis of complex genotypes demonstrated two protective complex genotypes (rs1040716:A, T + rs10454453:A + rs502958:A and rs1040716:A, T + rs502958:A) associated with panic disorder in general regardless of the patient's gender (p < 0.05). These genotypes did not correlate with the patient's sex.

Conclusions

We found two complex protective genotypes associated with panic disorder. This can be due to the fact that predisposition to the disease are associated with other genes, while PDE4B gene polymorphism reduces their effect.

The antidepressant- and anxiolytic-like effects of resveratrol: Involvement of phosphodiesterase-4D inhibition

Resveratrol is a natural non-flavonoid polyphenol found in red wine, which has numerous pharmacological properties including anti-stress and antidepressant-like abilities. However, whether the antidepressant- and anxiolytic-like effects of resveratrol are related to the inhibition of phosphodiesterase 4 (PDE4) and its subtypes remains unknown. The same holds true for the subsequent cAMP-dependent pathway. The first set of studies investigated whether resveratrol exhibited neuroprotective effects against corticosterone-induced cell lesion as well as its underlying mechanism. We found that 100 μM corticosterone induced PDE2A, PDE3B, PDE4A, PDE4D, PDE10 and PDE11 expression in HT-22 cells, which results in significant cell lesion. However, treatment with resveratrol increased cell viability in a dose- and time-dependent manner. These effects seem related to the inhibition of PDE4D, as evidenced by resveratrol dose-dependently decreasing PDE4D expression. In addition, the PKA inhibitor H89 reversed resveratrol's effects on cell viability. Resveratrol prevented corticosterone-induced reduction in cAMP, pVASP(s157), pCREB, and BDNF levels, indicating that cAMP signaling is involved in resveratrol-induced neuroprotective effects. Not to mention, PDE4D knockdown by PDE4D siRNA potentiated the effect of low dose of resveratrol on cAMP, pVASP, pCREB, and BDNF expression, while PDE4D overexpression reversed the effect of high dose of resveratrol on the expression of the above proteins. Finally, the subsequent in vivo data supports the in vitro findings, suggesting that resveratrol-induced antidepressant- and anxiolytic-like effects are mediated by PDE4D. Overall, these findings support the hypothesis that PDE4D-mediated cAMP signaling plays an important role in resveratrol's protective effects on stress-induced depression- and anxiety-like behavior.

Attenuation of ethanol abstinence-induced anxiety- and depressive-like behavior by the phosphodiesterase-4 inhibitor rolipram in rodents

RATIONALE

Withdrawal symptoms stand as a core feature of alcohol dependence. Our previous results have shown that inhibition of phosphodiesterase-4 (PDE4) decreased ethanol seeking and drinking in alcohol-preferring rodents. However, little is known about whether PDE4 is involved in ethanol abstinence-related behavior.

OBJECTIVE

The objective of this study was to characterize the role of PDE4 in the development of anxiety- and depressive-like behavior induced by abstinence from ethanol exposure in different animal models.

METHODS

Using three rodent models of ethanol abstinence, we examined the effects of rolipram, a prototypical, selective PDE4 inhibitor, on (1) anxiety-like behavior induced by repeated ethanol abstinence in the elevated plus maze test in fawn-hooded (FH/Wjd) rats, (2) anxiety-like behavior in the open-field test and light-dark transition test following acute ethanol abstinence in C57BL/6J mice, and (3) anxiety- and depressive-like behavior induced by protracted ethanol abstinence in the elevated plus maze, forced-swim, and tail-suspension tests in C57BL/6J mice.

RESULTS

Pretreatment with rolipram (0.1 or 0.2 mg/kg) significantly increased entries and time spent in the open arms of the elevated plus maze test in rats with repeated ethanol abstinence. Similarly, in mice with acute ethanol abstinence, administration of rolipram (0.25 or 0.5 mg/kg) dose-dependently increased the crossings in the central zone of the open-field test and duration and transitions on the light side of the light-dark transition test, suggesting anxiolytic-like effects of rolipram. Consistent with these, chronic treatment with rolipram (0.1, 0.3, or 1.0 mg/kg) increased entries in the open arms of the elevated plus maze test; it also reduced the increased duration of immobility in both the forced-swim and tail-suspension tests in mice after protracted ethanol abstinence, suggesting antidepressant-like effects of rolipram.

CONCLUSIONS

These results provide the first demonstration for that PDE4 plays a role in modulating the development of negative emotional reactions associated with ethanol abstinence, including anxiety and depression. PDE4 inhibitors may be a novel class of drugs for treatment of alcoholism.

Specific Inhibition of Phosphodiesterase-4B Results in Anxiolysis and Facilitates Memory Acquisition

Cognitive dysfunction is a core feature of dementia and a prominent feature in psychiatric disease. As non-redundant regulators of intracellular cAMP gradients, phosphodiesterases (PDE) mediate fundamental aspects of brain function relevant to learning, memory, and higher cognitive functions. Phosphodiesterase-4B (PDE4B) is an important phosphodiesterase in the hippocampal formation, is a major Disrupted in Schizophrenia 1 (DISC1) binding partner and is itself a risk gene for psychiatric illness. To define the effects of specific inhibition of the PDE4B subtype, we generated mice with a catalytic domain mutant form of PDE4B (Y358C) that has decreased ability to hydrolyze cAMP. Structural modeling predictions of decreased function and impaired binding with DISC1 were confirmed in cell assays. Phenotypic characterization of the PDE4B(Y358C) mice revealed facilitated phosphorylation of CREB, decreased binding to DISC1, and upregulation of DISC1 and β-Arrestin in hippocampus and amygdala. In behavioral assays, PDE4B(Y358C) mice displayed decreased anxiety and increased exploration, as well as cognitive enhancement across several tests of learning and memory, consistent with synaptic changes including enhanced long-term potentiation and impaired depotentiation ex vivo. PDE4B(Y358C) mice also demonstrated enhanced neurogenesis. Contextual fear memory, though intact at 24 h, was decreased at 7 days in PDE4B(Y358C) mice, an effect replicated pharmacologically with a non-selective PDE4 inhibitor, implicating cAMP signaling by PDE4B in a very late phase of consolidation. No effect of the PDE4B(Y358C) mutation was observed in the prepulse inhibition and forced swim tests. Our data establish specific inhibition of PDE4B as a promising therapeutic approach for disorders of cognition and anxiety, and a putative target for pathological fear memory.

The Role of Protein Kinase A in Anxiety Behaviors

This review focuses on the genetic and other evidence supporting the notion that the cyclic AMP (cAMP) signaling pathway and its mediator, the protein kinase A (PKA) enzyme, which respond to environmental stressors and regulate stress responses, are central to the pathogenesis of disorders related to anxiety. We describe the PKA pathway and review in vitro animal studies (mouse) and other evidence that support the importance of PKA in regulating behaviors that lead to anxiety. Since cAMP signaling and PKA have been pharmacologically exploited since the 1940s (even before the identification of cAMP as a second messenger with PKA as its mediator) for a number of disorders from asthma to cardiovascular diseases, there is ample opportunity to develop therapies using this new knowledge about cAMP, PKA, and anxiety disorders.

MEK Inhibitors Reverse cAMP-Mediated Anxiety in Zebrafish

Altered phosphodiesterase (PDE)-cyclic AMP (cAMP) activity is frequently associated with anxiety disorders, but current therapies act by reducing neuronal excitability rather than targeting PDE-cAMP-mediated signaling pathways. Here, we report the novel repositioning of anti-cancer MEK inhibitors as anxiolytics in a zebrafish model of anxiety-like behaviors. PDE inhibitors or activators of adenylate cyclase cause behaviors consistent with anxiety in larvae and adult zebrafish. Small-molecule screening identifies MEK inhibitors as potent suppressors of cAMP anxiety behaviors in both larvae and adult zebrafish, while causing no anxiolytic behavioral effects on their own. The mechanism underlying cAMP-induced anxiety is via crosstalk to activation of the RAS-MAPK signaling pathway. We propose that targeting crosstalk signaling pathways can be an effective strategy for mental health disorders, and advance the repositioning of MEK inhibitors as behavior stabilizers in the context of increased cAMP.

The phosphodiesterase-4 inhibitor rolipram attenuates heroin-seeking behavior induced by cues or heroin priming in rats

Inhibition of phosphodiesterase-4 (PDE4), an enzyme that specifically hydrolyzes cyclic adenosine monophosphate (cAMP) increases intracellular cAMP/cAMP-response element binding protein (CREB) signaling. Activation of this signaling is considered as an important compensatory response that decreases motivational properties of drugs of abuse. However, it is not known whether PDE4 is involved in heroin seeking. Self-administration of heroin (50 μg/kg/infusion) was performed under the fixed ratio 1 (FR1) schedule for 14 d and then drug seeking was extinguished for 10 d. The progressive ratio schedule was used to evaluate the relative motivational value of heroin reinforcement. After training, the conditioned cue or heroin priming (250 μg/kg) was introduced for the reinstatement of heroin-seeking behavior. Pretreatment (i.p.) with rolipram (0.03-0.3 mg/kg), a prototypical, selective PDE4 inhibitor, failed to inhibit heroin self-administration under the FR1 schedule, but decreased the reward values under the progressive ratio schedule in a dose-dependent manner. In addition, rolipram decreased the reinstatement of heroin seeking induced by cues or heroin priming even at the lowest dose (0.03 mg/kg); in contrast, the highest dose (0.3 mg/kg) of rolipram was required to decrease sucrose reinforcement. Finally, the effects of rolipram on heroin-seeking behavior were correlated with the increases in expression of phosphorylated CREB in the nucleus accumbens. The study demonstrated that rolipram inhibited heroin reward and heroin-seeking behavior. The results suggest that PDE4 plays an essential role in mediating heroin seeking and that PDE4 inhibitors may be used as a potential pharmacotherapeutic approach for heroin addiction.

Functional testing in animal models of spinal cord injury: not as straight forward as one would think

When exploring potential treatments for spinal cord injury (SCI), functional recovery is deemed the most relevant outcome measure when it comes to translational considerations. Yet, assessing such recovery and potential treatment effects is challenging and the pitfalls are frequently underestimated. The consequences are that in many cases positive results cannot be reliably replicated, and likely treatments that appear to lack effects have been dismissed prematurely. In this article we review the relationships between lesion location/severity and functional outcomes with specific consideration given to floor and ceiling effects. The roles of compensatory strategies, the challenges of distinguishing them from bona fide recovery, and of comparing function to pre-injury levels given the variability inherent in animal testing are discussed. Ultimately, we offer a series of considerations to enhance the power of functional analysis in animal models of SCI.

Learning and memory deficits consequent to reduction of the fragile X mental retardation protein result from metabotropic glutamate receptor-mediated inhibition of cAMP signaling in Drosophila

Loss of the RNA-binding fragile X protein [fragile X mental retardation protein (FMRP)] results in a spectrum of cognitive deficits, the fragile X syndrome (FXS), while aging individuals with decreased protein levels present with a subset of these symptoms and tremor. The broad range of behavioral deficits likely reflects the ubiquitous distribution and multiple functions of the protein. FMRP loss is expected to affect multiple neuronal proteins and intracellular signaling pathways, whose identity and interactions are essential in understanding and ameliorating FXS symptoms. We used heterozygous mutants and targeted RNA interference-mediated abrogation in Drosophila to uncover molecular pathways affected by FMRP reduction. We present evidence that FMRP loss results in excess metabotropic glutamate receptor (mGluR) activity, attributable at least in part to elevation of the protein in affected neurons. Using high-resolution behavioral, genetic, and biochemical analyses, we present evidence that excess mGluR upon FMRP attenuation is linked to the cAMP decrement reported in patients and models, and underlies olfactory associative learning and memory deficits. Furthermore, our data indicate positive transcriptional regulation of the fly fmr1 gene by cAMP, via protein kinase A, likely through the transcription factor CREB. Because the human Fmr1 gene also contains CREB binding sites, the interaction of mGluR excess and cAMP signaling defects we present suggests novel combinatorial pharmaceutical approaches to symptom amelioration upon FMRP attenuation.

Inactivation of Pde8b enhances memory, motor performance, and protects against age-induced motor coordination decay

Phosphodiesterases (PDEs) are critical regulatory enzymes in cyclic nucleotide signaling. PDEs have diverse expression patterns within the central nervous system (CNS), show differing affinities for cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP), and regulate a vast array of behaviors. Here, we investigated the expression profile of the PDE8 gene family members Pde8a and Pde8b in the mouse brain. We find that Pde8a expression is largely absent in the CNS; by contrast, Pde8b is expressed in select regions of the hippocampus, ventral striatum, and cerebellum. Behavioral analysis of mice with Pde8b gene inactivation (PDE8B KO) demonstrate an enhancement in contextual fear, spatial memory, performance in an appetitive instrumental conditioning task, motor-coordination, and have an attenuation of age-induced motor coordination decline. In addition to improvements observed in select behaviors, we find basal anxiety levels to be increased in PDE8B KO mice. These findings indicate that selective antagonism of PDE8B may be an attractive target for enhancement of cognitive and motor functions; however, possible alterations in affective state will need to be weighed against potential therapeutic value.

The phosphodiesterase-4 (PDE4) inhibitor rolipram decreases ethanol seeking and consumption in alcohol-preferring Fawn-Hooded rats

BACKGROUND

Alcohol dependence is a complex psychiatric disorder demanding development of novel pharmacotherapies. Because the cyclic adenosine monophosphate (cAMP) signaling cascade has been implicated in mediating behavioral responses to alcohol, key components in this cascade may serve as potential treatment targets. Phosphodiesterase-4 (PDE4), an enzyme that specifically catalyzes the hydrolysis of cAMP, represents a key point in regulating intracellular cAMP levels. Thus, it was of interest to determine whether PDE4 was involved in the regulation of alcohol use and abuse.

METHODS

Male Fawn-Hooded (FH/Wjd) rats were tested for 5% (v/v) ethanol (EtOH) and 10% (w/v) sucrose operant oral self-administration following treatment with the selective PDE4 inhibitor rolipram (0.0125, 0.025, or 0.05 mg/kg, subcutaneous [s.c.]); rolipram at higher doses (0.05, 0.1, and 0.2 mg/kg, s.c.) was tested to determine its impact on the intake of EtOH, sucrose, or water using the 2-bottle choice drinking paradigm. Subsequent open-field testing was performed to evaluate the influence of higher doses of rolipram on locomotor activity.

RESULTS

Acute administration of rolipram dose-dependently reduced operant self-administration of 5% EtOH, but had no effect on 10% sucrose responding. Time-course assessment revealed significant decreases in EtOH consumption after rolipram (0.1, 0.2 mg/kg) treatment in continuous- and intermittent access to EtOH at 5% or 10%, respectively. Moreover, chronic rolipram treatment time-dependently decreased 5% EtOH consumption and preference during treatment days and after the termination of rolipram administration. Rolipram at the highest doses (0.1 and 0.2 mg/kg) did decrease locomotor activity, but the effect lasted only 10 and 20 minutes, respectively, which did not likely alter long-term EtOH drinking.

CONCLUSIONS

These results suggest that PDE4 plays a role in alcohol seeking and consumption behavior. Drugs interfering with PDE4 may be a potential pharmacotherapy for alcohol dependence.

Regulator of calmodulin signaling knockout mice display anxiety-like behavior and motivational deficits

Regulator of calmodulin (CaM) signaling (RCS), when phosphorylated by protein kinase A (PKA) on Ser55, binds to CaM and inhibits CaM-dependent signaling. RCS expression is high in the dorsal striatum, nucleus accumbens and amygdala, suggesting that the protein is involved in limbic-striatal function. To test this hypothesis, we examined RCS knockout (KO) mice in behavioral models dependent on these brain areas. Mice were tested for food-reinforced instrumental conditioning and responding under a progressive ratio (PR) schedule of reinforcement and in models of anxiety (elevated plus maze and open field). While RCS KO mice showed normal acquisition of a food-motivated instrumental response, they exhibited a lower breakpoint value when tested on responding under a PR schedule of reinforcement. RCS KO mice also displayed decreased exploration in both the open arms of an elevated plus maze and in the center region of an open field, suggesting an enhanced anxiety response. Biochemical studies revealed a reduction in the levels of dopamine and cAMP-regulated phosphoprotein (DARPP-32) in the striatum of RCS KO mice. DARPP-32 is important in reward-mediated behavior, suggestive of a possible role for DARPP-32 in mediating some of the effects of RCS. Together these results implicate a novel PKA-regulated phosphoprotein, RCS, in the etiology of motivational deficits and anxiety.

A new model of Pde4d deficiency: genetic knock-down of PDE4D enzyme in rats produces an antidepressant phenotype without spatial cognitive effects

Phosphodiesterases (PDEs) are a superfamily of intracellular second messenger cyclic nucleotide hydrolyzing enzymes composed of 12 families. The Pde4 family has been implicated in depression and cognition, and PDE4 inhibitors have been evaluated as antidepressants and possible cognitive enhancers. Pde4d(-/-) mice show an antidepressant phenotype and learning enhancement on some tests, but not others as do mice treated with PDE4 inhibitors. Here, we report for the first time the behavioral phenotype of a new Pde4d knock-down (KD) rat model of PDE4D deficiency. Consistent with other data on PDE4D deficiency, Pde4d KD rats showed depression resistance in the Porsolt forced swim test and hyperreactivity of the acoustic startle response with no differential response on prepulse inhibition, suggesting no sensorimotor gating defect. Pde4d KD rats also exhibited a small exploratory activity reduction but no difference following habituation, and no enhanced spatial learning or reference memory in the Morris water maze. A selective improvement in route-based learning in the Cincinnati water maze was seen as well as enhanced contextual and cued fear conditioning and a more rapid rate of cued extinction from their higher freezing level that declined to wild-type (WT) levels only after ∼20 extinction trials. The rat model confirms Pde4d's role in depression but not in spatial learning or memory enhancement and shows for the first time higher fear conditioning and altered extinction compared with controls. The new model provides a tool by which to better understand the role of PDE4D in neuropsychiatric disorders and for the development of alternate treatment approaches.

Postinjury treatment with rolipram increases hemorrhage after traumatic brain injury

The pathology caused by traumatic brain injury (TBI) is exacerbated by the inflammatory response of the injured brain. Two proinflammatory cytokines that contribute to inflammation after TBI are tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β). From previous studies using the parasagittal fluid-percussion brain injury model, we reported that the anti-inflammatory drug rolipram, a phosphodiesterase 4 inhibitor, reduced TNF-α and IL-1β levels and improved histopathological outcome when administered 30 min prior to injury. We now report that treatment with (±)-rolipram given 30 min after injury significantly reduced TNF-α levels in the cortex and hippocampus. However, postinjury administration of (±)-rolipram significantly increased cortical contusion volume and increased atrophy of the cortex compared with vehicle-treated animals at 10 days postinjury. Thus, despite the reduction in proinflammatory cytokine levels, histopathological outcome was worsened with post-TBI (±)-rolipram treatment. Further histological analysis of (±)-rolipram-treated TBI animals revealed significant hemorrhage in the contused brain. Given the well-known role of (±)-rolipram of increasing vasodilation, it is likely that (±)-rolipram worsened outcome after fluid-percussion brain injury by causing increased bleeding.

A biphasic and brain-region selective down-regulation of cyclic adenosine monophosphate concentrations supports object recognition in the rat

BACKGROUND

We aimed to further understand the relationship between cAMP concentration and mnesic performance.

METHODS AND FINDINGS

Rats were injected with milrinone (PDE3 inhibitor, 0.3 mg/kg, i.p.), rolipram (PDE4 inhibitor, 0.3 mg/kg, i.p.) and/or the selective 5-HT4R agonist RS 67333 (1 mg/kg, i.p.) before testing in the object recognition paradigm. Cyclic AMP concentrations were measured in brain structures linked to episodic-like memory (i.e. hippocampus, prefrontal and perirhinal cortices) before or after either the sample or the testing phase. Except in the hippocampus of rolipram treated-rats, all treatment increased cAMP levels in each brain sub-region studied before the sample phase. After the sample phase, cAMP levels were significantly increased in hippocampus (1.8 fold), prefrontal (1.3 fold) and perirhinal (1.3 fold) cortices from controls rat while decreased in prefrontal cortex (∼0.83 to 0.62 fold) from drug-treated rats (except for milrinone+RS 67333 treatment). After the testing phase, cAMP concentrations were still increased in both the hippocampus (2.76 fold) and the perirhinal cortex (2.1 fold) from controls animals. Minor increase were reported in hippocampus and perirhinal cortex from both rolipram (respectively, 1.44 fold and 1.70 fold) and milrinone (respectively 1.46 fold and 1.56 fold)-treated rat. Following the paradigm, cAMP levels were significantly lower in the hippocampus, prefrontal and perirhinal cortices from drug-treated rat when compared to controls animals, however, only drug-treated rats spent longer time exploring the novel object during the testing phase (inter-phase interval of 4 h).

CONCLUSIONS

Our results strongly suggest that a "pre-sample" early increase in cAMP levels followed by a specific lowering of cAMP concentrations in each brain sub-region linked to the object recognition paradigm support learning efficacy after a middle-term delay.

Association study of PDE4B with panic disorder in the Japanese population

BACKGROUND

Panic disorder (PD) is a severe and chronic psychiatric disorder with genetic components underlying in its etiology. The Phosphodiesterase 4B (PDE4B) gene has been reported to be associated with several psychiatric disorders. Several studies indicated that PDE4B may be involved in the regulation of anxiety and depression. Therefore, we investigate the association of PDE4B with PD in the Japanese population.

METHODS

We genotyped 14 single nucleotide polymorphisms (SNPs) of PDE4B in 231 PD cases (85 males and 146 females) and 407 controls (162 males and 245 females). Differences in the genotype, allele and haplotype frequencies between the two groups were compared.

RESULTS

We found a significant association between PDE4B and PD in the haplotype analysis (haplotype C-T-T-A, permutation P=0.031, OR=1.81, 95% CI=1.30-2.51). Sex-specific analyses demonstrated that PDE4B was associated with PD in females in the allele/genotype and haplotype analyses (rs10454453, allele P=0.042, genotype P=0.0034; haplotype C-T-T-A, permutation P=0.028).

CONCLUSION

Our results suggest that PDE4B may play a role in the pathophysiology of PD in the Japanese population. Replication studies using larger samples will be needed for more reliable conclusions.

Mice lacking adenylyl cyclase-5 cope badly with repeated restraint stress

Physiological responses to acute stress proceed with the activation of the hypothalamus-pituitary-adrenal gland (HPA) system. Many brain regions are known to modulate the HPA axis activation in stress responses, but the detailed neural circuits and signaling system in the upstream of the HPA axis have to be explored further. Type 5 adenylyl cyclase (AC5) is highly concentrated in the dorsal striatum and nucleus accumbens, which are implicated in reward and stress-related behavior. AC5(-/-) mice exposed to daily 2-hr restraint stress for only 3-5 days showed poor stress-coping responses, including severe body weight loss, poor coat condition, respiratory difficulties, and freezing behavior. Plasma corticosterone levels during 2-hr stress sessions increased in AC5(-/-) mice compared with those of AC5(+/+) mice. However, neither the corticosterone receptor antagonist RU486 nor the CRH receptor antagonist NBI27914 blocked their poor stress coping, whereas the administration of the GABA(A) receptor allosteric modulator diazepam or the D1 dopamine receptor antagonist SCH23390 prior to restraint stress sessions changed their stress-coping response to the stressed AC5(+/+) mouse level. Stress-triggered c-Fos expression was completely blunted in the dorsal striatum of AC5(-/-). These results suggest that the AC5-associated signal system and neural network are involved in the regulation of anxiety and stress-coping response.

Differential function of phosphodiesterase families in the brain: gaining insights through the use of genetically modified animals

Phosphodiesterases (PDEs) are the only known enzymes to degrade cAMP and cGMP, intracellular signaling molecules key to numerous cellular functions. There are 11 PDE families identified to date, and each is expressed in a unique pattern across brain regions. Here, we review genetic mouse models in which PDEs are either directly manipulated (e.g., genetically deleted) or are changed in a compensatory manner due to the manipulation of another target. We believe these genetic mouse models have contributed to our understanding of how the PDE1, PDE4, and PDE10 families contribute uniquely to overall brain function.

Antidepressant- and anxiolytic-like effects of the phosphodiesterase-4 inhibitor rolipram on behavior depend on cyclic AMP response element binding protein-mediated neurogenesis in the hippocampus

Inhibition of phosphodiesterase-4 (PDE4), an enzyme that catalyzes the hydrolysis of cyclic AMP (cAMP), increases phosphorylation of the cAMP response element binding protein (pCREB) and hippocampal neurogenesis, and produces antidepressant-like effects on behavior; however, causal links among these actions have not been established. In this study, chronic administration of rolipram (0.31-1.25 mg/kg, 16-23 days) produced antidepressant- and anxiolytic-like effects on behavior in mice. It also increased cAMP and pCREB levels in the hippocampus and prefrontal cortex, but increased Sox2, a marker for mitotic progenitor cells, only in the hippocampus. Chronic rolipram treatment also increased hippocampal neurogenesis, as evidenced by increased bromodeoxyuridine (BrdU)-positive cells in the hippocampal dentate gyrus. Methylazoxymethanol (MAM), which is toxic to proliferating cells, reversed rolipram-induced increases in BrdU-positive cells and pCREB in the hippocampus and partially blocked its behavioral effects. Approximately 84% of BrdU-positive cells became newborn neurons, 93% of which co-expressed pCREB; these proportions were not altered by rolipram or MAM, either alone or in combination. Finally, 3 weeks after the end of the MAM treatment, when neurogenesis was no longer inhibited, rolipram again increased hippocampal pCREB and its antidepressant- and anxiolytic-like effects were restored. Overall, these results suggest that rolipram produces its effects on behavior in a manner that at least partially depends on its neurogenic action in the hippocampus, targeting mitotic progenitor cells rather than newborn or mature neurons; cAMP/CREB signaling in hippocampal newborn neurons is critical for neurogenesis and contributes to the behavioral effects of rolipram.

Chronic Galphas signaling in the striatum increases anxiety-related behaviors independent of developmental effects

Current research in the field of anxiety disorders is largely receptor-centric, leaving intracellular pathways largely unexplored. Galphas, the G-protein which stimulates adenylyl cyclase and L-type voltage-gated calcium channels, may be one intracellular molecule regulating anxiety-related behaviors as increased efficacy of Galphas signaling has been noted in patient populations that suffer from anxiety. We report here anxiety-related behaviors in two lines of transgenic mice expressing a constitutively active isoform of Galphas (or Galphas*). The first line expressed Galphas* throughout postnatal forebrain neurons, while the second line of mice conditionally expressed Galphas* selectively in the striatum (Galphas*(str) mice). In the open field, both lines of mice showed a significant preference for the periphery suggesting that expression of Galphas* in the striatum alone was sufficient to produce an anxiogenic phenotype. In the light/dark box, Galphas*(str) mice exhibited longer latencies to enter the light and spent significantly less time in the lit compartment. Similarly, Galphas*(str) mice showed longer latencies to enter the open quadrants and spent less time in the open quadrants of the elevated zero maze. Interestingly, these anxiety-related phenotypes were largely unrelated to developmental effects as mice expressing the Galphas*(str) transgene during development, but not at testing, were normal on most measures. These observations show that chronic Galphas signaling in the striatum is sufficient to trigger anxiety-related behaviors largely independent of developmental effects and suggest the cAMP pathway or L-type voltage-gated calcium channels may be viable targets for future pharmacological intervention in the treatment of anxiety disorders.

Phosphodiesterases in the central nervous system

Phosphodiesterases (PDEs) represent important cornerstones of cGMP signaling in various tissues. Since the discovery of PDE activity in 1962, it has become clear that the functional characteristics of PDEs and their role in cyclic nucleotide signaling are fairly complex. On the one hand, members of the PDE family responsible for the hydrolysis of cGMP affect cellular responses by shaping cGMP signals derived from the activation of soluble cytosolic and/or membrane bound particulate guanylyl cyclases. Conversely, PDEs may function as downstream effectors in the cGMP signaling cascade. To make things even more sophisticated, cGMP modulates the activity of several PDEs either directly, by binding to a regulatory domain, or indirectly, through phosphorylation, and the result can be either inhibition or stimulation of the enzyme, depending on the subtype. Furthermore, cross-talk between cGMP and cAMP signaling is achieved by cGMP-dependent modulation of PDEs hydrolyzing cAMP and vice versa. Mammals possess at least 21 PDE genes and often express a set of PDEs in a tissue- and differentiation-dependent manner. Given these premises, it is still a challenging task to elucidate the physiological function(s) of individual PDE genes. The present chapter focuses on the role of PDEs as regulators of neuronal functions. Useful information regarding this topic has been gained by studying (1) the expression pattern of PDEs in the CNS, (2) the association of PDEs with specific macromolecular signaling complexes and (3) the phenotypes associated with mutations or ablation of PDE genes in man, mice and fruit flies, respectively. PDEs degrading cGMP and/or being regulated by cGMP have been implicated in cognition and learning, Parkinson's disease, attention deficit hyperactivity disorder, psychosis and depression. Correspondingly, modulators of PDEs have become attractive tools for treatment of these disorders of CNS function.

Selective phosphodiesterase inhibitors: a promising target for cognition enhancement

RATIONALE

One of the major complaints most people face during aging is an impairment in cognitive functioning. This has a negative impact on the quality of daily life and is even more prominent in patients suffering from neurodegenerative and psychiatric disorders including Alzheimer's disease, schizophrenia, and depression. So far, the majority of cognition enhancers are generally targeting one particular neurotransmitter system. However, recently phosphodiesterases (PDEs) have gained increased attention as a potential new target for cognition enhancement. Inhibition of PDEs increases the intracellular availability of the second messengers cGMP and/or cAMP.

OBJECTIVE

The aim of this review was to provide an overview of the effects of phosphodiesterase inhibitors (PDE-Is) on cognition, the possible underlying mechanisms, and the relationship to current theories about memory formation.

MATERIALS AND METHODS

Studies of the effects of inhibitors of different PDE families (2, 4, 5, 9, and 10) on cognition were reviewed. In addition, studies related to PDE-Is and blood flow, emotional arousal, and long-term potentiation (LTP) were described.

RESULTS

PDE-Is have a positive effect on several aspects of cognition, including information processing, attention, memory, and executive functioning. At present, these data are likely to be explained in terms of an LTP-related mechanism of action.

CONCLUSION

PDE-Is are a promising target for cognition enhancement; the most suitable candidates appear to be PDE2-Is or PDE9-Is. The future for PDE-Is as cognition enhancers lies in the development of isoform-specific PDE-Is that have limited aversive side effects.

The cyclic AMP phenotype of fragile X and autism

Cyclic AMP (cAMP) is a second messenger involved in many processes including mnemonic processing and anxiety. Memory deficits and anxiety are noted in the phenotype of fragile X (FX), the most common heritable cause of mental retardation and autism. Here we review reported observations of altered cAMP cascade function in FX and autism. Cyclic AMP is a potentially useful biochemical marker to distinguish autism comorbid with FX from autism per se and the cAMP cascade may be a viable therapeutic target for both FX and autism.

Anxiogenic-like behavioral phenotype of mice deficient in phosphodiesterase 4B (PDE4B)

Phosphodiesterase-4 (PDE4), an enzyme that catalyzes the hydrolysis of cyclic AMP and plays a critical role in controlling its intracellular concentration, has been implicated in depression- and anxiety-like behaviors. However, the functions of the four PDE4 subfamilies (PDE4A, PDE4B, PDE4C, and PDE4D) remain largely unknown. In animal tests sensitive to anxiolytics, antidepressants, memory enhancers, or analgesics, we examined the behavioral phenotype of mice deficient in PDE4B (PDE4B-/-). Immunoblot analysis revealed loss of PDE4B expression in the cerebral cortex and amygdala of PDE4B-/- mice. The reduction of PDE4B expression was accompanied by decreases in PDE4 activity in the brain regions of PDE4B-/- mice. Compared to PDE4B+/+ littermates, PDE4B-/- mice displayed anxiogenic-like behavior, as evidenced by decreased head-dips and time spent in head-dipping in the holeboard test, reduced transitions and time on the light side in the light-dark transition test, and decreased initial exploration and rears in the open-field test. Consistent with anxiogenic-like behavior, PDE4B-/- mice displayed increased levels of plasma corticosterone. In addition, these mice also showed a modest increase in the proliferation of neuronal cells in the hippocampal dentate gyrus. In the forced-swim test, PDE4B-/- mice exhibited decreased immobility; however, this was not supported by the results from the tail-suspension test. PDE4B-/- mice did not display changes in memory, locomotor activity, or nociceptive responses. Taken together, these results suggest that the PDE4B subfamily is involved in signaling pathways that contribute to anxiogenic-like effects on behavior.

Phosphodiesterase 10A inhibition is associated with locomotor and cognitive deficits and increased anxiety in mice

Phosphodiesterase 10A (PDE10A) mRNA and protein levels decline in the striatum of R6/1 and R6/2 Huntington's disease (HD) mice prior to motor symptom development. In human HD, PDE10A protein levels are significantly decreased in the caudate-putamen of patients with grade 3 HD compared to age-matched controls. To test whether the loss of PDE10A activity in the striatum was detrimental to normal brain function, we treated wild-type (WT) mice with chronic administration of papaverine, which is a specific inhibitor of PDE10A. At 7 weeks of age, mice were introduced to a weekly battery of motor tests, including assessment of weight, locomotion, gait, and coordination. Beginning at 8 weeks of age, mice received 0, 5, 10 or 20 mg/kg papaverine once daily until the completion of behavioral testing. Following 14 days of papaverine injections, mice were assessed for deficits in cognitive performance as measured in the Morris water maze (MWM). All behavioral tests occurred either immediately prior to or 30 min following a subcutaneous papaverine challenge dose. Twenty-four hours following completion of the 2-3 week MWM protocol, mice were given a dose of papaverine and 30 min later psychological function assessed in the Light-Dark (LD) Test. Chronic administration of papaverine for 42 days was associated with distinct motor perturbations, mild cognitive disturbance and anxiety-like behaviors. Subsequently, we assessed the effect of 14 days papaverine (i.e. sub-chronic) treatment on psychological function of WT and R6/1 HD mice. While sub-chronic papaverine induced anxiety-like behavior in WT mice, it appeared to have little effect on the behavior of R6/1 HD mice. Finally, a separate group of 6-week old WT and R6/2 HD mice were treated for 21 days with saline or 10 mg/kg fluoxetine, an agent with anxiolytic and anti-depressant effects, in order to compare the effects of papaverine and fluoxetine on anxiety-like behavior in the LD test. CREB and PDE10A protein levels in striatum and hippocampus were determined by western blot. While papaverine treatment reduced CREB protein levels in the hippocampus and striatum, fluoxetine increased CREB in the hippocampus. These data suggest that papaverine and fluoxetine may produce quite different effects on behavior; these behaviors may be linked to CREB expression in brain regions associated with motor and cognitive functions. PDE10A protein levels were decreased by both papaverine and fluoxetine. Chronic PDE10A inhibition produced a variety of behavioral and central neurochemical deficits and these effects were exacerbated by stress. The unique localization of PDE10A and its apparent role in basal ganglia function may underlie its role in psychiatric and neurological disorders involving the basal ganglia.

Ethological comparison of the effects of a bovine αs1-casein tryptic hydrolysate and diazepam on the behaviour of rats in two models of anxiety

A bovine alpha s1-casein tryptic hydrolysate was previously demonstrated to display an anxiolytic-like activity in the conditioned defensive burying and in the elevated plus-maze models when i.p. injected. The present study assessed the anxiolytic-like effects of this tryptic hydrolysate after an oral administration in rats faced to the same behavioural situations using diazepam as a reference. In a first experiment, the behavioural effects of the hydrolysate in the conditioned defensive burying test were investigated at doses ranging 5-50 mg/kg. The results showed that the minimal dose required to elicit an anxiolytic-like activity is 15 mg/kg. In a second experiment, the alpha s1-casein tryptic hydrolysate (15 mg/kg, p.o.) was demonstrated to display an anxiolytic-like activity similar to diazepam (3 mg/kg, p.o.) in the conditioned defensive burying test and the elevated plus-maze. However, the ethological analysis of behaviour indicated that this hydrolysate has a different activity compared to diazepam. While diazepam induced a disinhibition state in rats, possibly related to the risk-taking behaviour observed after a benzodiazepine ingestion in humans, the tryptic hydrolysate did not display such a side effect. These results suggest that the mechanism of action of the bovine alpha s1-casein tryptic hydrolysate may differ from that of diazepam.

Subchronic rolipram delivery activates hippocampal CREB and arc, enhances retention and slows down extinction of conditioned fear

Rolipram, a type IV-specific phosphodiesterase inhibitor, is known to improve memory under various learning tasks. Moreover, Rolipram treatments have been shown to increase expression and phosphorylation of a key factor for hippocampal memory consolidation, the cAMP-dependent response element-binding protein, CREB. However, the exact correlation between hippocampal CREB phosphorylation and memory improvement induced by Rolipram has not yet been determined in a CREB-dependent type of hippocampal-related learning in normogenic, intact rodents. Here, we report that subchronic Rolipram delivery by using osmotic minipumps increased the basal rat hippocampal expression and phosphorylation of CREB, as well as the expression of the cAMP-dependent, memory-related protein, Arc. In parallel, the same treatment improved memory consolidation of conditioned fear. Furthermore, the increase of CREB phosphorylation and Arc expression consequent to the learning experience was enhanced in Rolipram-treated rats, compared to controls. By evaluating the time course of memory extinction over 10 days after the initial learning test, we also observed significant slowing down of the memory extinction rate in Rolipram-treated rats. This effect could be attributed to CREB phosphorylation and memory having been initially higher, as osmotic minipumps stopped to release Rolipram the first day after the initial learning test. Our data define the conditions through which the pharmacological manipulation of hippocampal CREB expression and activation result in memory amelioration in normogenic, intact animals. These results are relevant for the study of molecular correlates of memory, and may also be important in view of the efforts to design new pharmacological treatments, targeting the CREB pathway and leading to enhancement of learning and memory, even in the absence of patent neuropathology.

Neurobiology and treatment of anxiety: signal transduction and neural plasticity

The stress-dependence and chronic nature of anxiety disorders along with the anxiolytic effectiveness of antidepressant drugs suggests that neuronal plasticity may play a role in the pathophysiology of anxiety. Intracellular signaling pathways are known in many systems to be critical links in the cascades from surface signals to the molecular alterations that result in functional plasticity. Chronic antidepressant treatments can regulate intracellular signaling pathways and can induce molecular, cellular, and structural changes over time. These changes may be important to the anxiolytic effectiveness of these drugs. In addition, the signaling proteins implicated in the actions of chronic antidepressant action, such as cAMP response element binding protein (CREB), have also been implicated in conditioned fear and in anxiety. The cellular mechanisms underlying conditioned fear indicate roles for additional signaling pathways; however, less is known about such mechanisms in anxiety. The challenge to identify intracellular signaling pathways and related molecular and structural changes that are critical to the etiology and treatment of anxiety will further establish the importance of mechanisms of neuronal plasticity in functional outcome and improve treatment strategies.

Rolipram attenuates MK-801-induced deficits in latent inhibition

Latent inhibition is used to examine attention and study cognitive deficits associated with schizophrenia. Research using MK-801, an N-methyl-D-aspartate (NMDA) open channel blocker, implicates glutamate receptors in acquisition of latent inhibition of cued fear conditioning. Evidence suggests an important relationship between NMDA-induced increases in cyclic adenosine monophosphate (cAMP) and learning and memory. The authors examine whether amplification of the cAMP signaling pathway by rolipram, a selective Type 4 cAMP phosphodiesterase inhibitor, reverses MK-801-induced impairments in latent inhibition. One day before training, mice were injected with MK-801, rolipram, MK-801 and rolipram, or vehicle and received 20 preexposures or no preexposures to an auditory conditioned stimulus (CS). Training consisted of 2 CS-footshock unconditioned stimulus pairings. Rolipram attenuated the disruptive effect of MK-801 on latent inhibition, which suggests a role for the cAMP signaling pathway in the task and implicates phosphodiesterase inhibition as a target for treating cognitive impairments associated with schizophrenia.

Effects of the novel PDE4 inhibitors MEM1018 and MEM1091 on memory in the radial-arm maze and inhibitory avoidance tests in rats

RATIONALE

Inhibition of cyclic AMP (cAMP)-specific phosphodiesterase (PDE4) enhances memory in rodents. MEM1018 and MEM1091 are newly developed PDE4 inhibitors that had not been evaluated as yet for their effects on working and reference memory.

OBJECTIVE

Experiments were carried out to determine whether these two drugs alter memory and if these effects are associated with changes in intracellular cAMP in the brain.

METHODS

The effects of MEM1018 and MEM1091 on memory deficits induced by the N-methyl-D-: aspartate (NMDA) receptor antagonist MK-801 were determined in the eight-arm radial maze and step-through inhibitory avoidance tasks in rats. Their effects on cAMP concentrations in primary cultures of rat cerebral cortical neurons and their potency for inhibiting recombinant PDE4 subtypes were examined.

RESULTS

In the radial-arm maze, MEM1018 and MEM1091 (0.1-2.5 mg/kg, IP) enhanced working and reference memory impaired by MK-801 (0.1 mg/kg). In addition, both drugs antagonized the amnesic effect of MK-801 on passive avoidance behavior. Overall, the behavioral effects of MEM1018 and MEM1091 were similar to the prototypic PDE4 inhibitor rolipram (0.1 mg/kg). Consistent with this, and similar to the effects of rolipram, both MEM1018 (10-30 microM) and MEM1091 (10 microM) enhanced the ability of NMDA (30 microM) to increase cAMP concentrations in rat cerebral cortical neurons, in vitro. MEM1018 and MEM1091 showed greater relative selectivity for PDE4D than rolipram, although the general profiles of the three compounds were similar.

CONCLUSIONS

The novel PDE4 inhibitors MEM1018 and MEM1091 enhance memory in a manner generally similar to rolipram. PDE4D may be the primary target for the PDE4 inhibitors in the mediation of memory.

Phosphodiesterase type 4 isozymes expression in human brain examined by in situ hybridization histochemistry and[3H]rolipram binding autoradiography. Comparison with monkey and rat brain

We have examined the distribution of four different cyclic AMP-specific phosphodiesterase isozyme (PDE4A, PDE4B, PDE4C and PDE4D) mRNAs in the brain of different species by in situ hybridization histochemistry and by autoradiography with [3H]rolipram. We have compared the localization of each isozyme in human brain with that in rat and monkey brain. We have found that the four PDE4 isoforms display a differential expression pattern at both regional and cellular level in the three species. PDE4A, PDE4B and PDE4D are widely distributed in human brain, with the two latter appearing more abundant. In contrast, PDE4C in human brain, presents a more restricted distribution, limited to cortex, some thalamic nuclei and cerebellum. This is at variance with the distribution of PDE4C in rat brain, where it is found exclusively in olfactory bulb. In monkey brain, the highest expression for this isoform is found in the claustrum, and at lower levels in cortical areas and cerebellum. PDE4B presented a broad distribution, being expressed in both neuronal and non neuronal cell populations. In general, the distribution of binding sites visualized with [3H]rolipram correlated well with the expression of each PDE4 isozyme.