Thomas Francis Seeger

Immunohistochemical localization of PDE10A in the rat brain

PDE10A is a newly identified cAMP/cGMP phosphodiesterase for which mRNA is highly expressed in the mammalian striatum. In the present study, PDE10A protein and mRNA expression throughout the rat brain were determined, using a monoclonal antibody (24F3.F11) for Western blot and immunohistochemical analyses and an antisense riboprobe for in situ hybridization. High levels of mRNA are observed in most of the neuronal cell bodies of striatal complex (caudate n, n. accumbens and olfactory tubercle), indicating that PDE10A is expressed by the striatal medium spiny neurons. PDE10A-like immunoreactivity is dense throughout the striatal neuropil, as well as in the internal capsule, globus pallidus, and substantia nigra. These latter regions lack significant expression of PDE10A mRNA. Thus, PDE10A is transported throughout the dendritic tree and down the axons to the terminals of the medium spiny neurons. These data suggest a role for PDE10A in regulating activity within both the striatonigral and striatopallidal pathways. In addition, PDE10A immunoreactivity and mRNA are found at lower levels in the hippocampal pyramidal cell layer, dentate granule cell layer and throughout the cortex and cerebellar granule cell layer. Immunoreactivity is detected only in cell bodies in these latter regions. This more restricted subcellular localization of PDE10A outside the striatum suggests a second, distinct function for the enzyme in these regions.

Alterations in gene regulation following inhibition of the striatum-enriched phosphodiesterase, PDE10A

PDE10A is a member of the phosphodiesterase superfamily highly enriched within medium spiny neurons (MSN) in mammalian striatum. We have used inhibitors of PDE10A and quantitative measures of mRNA to demonstrate that PDE10A controls striatal gene expression by regulating MSN cyclic nucleotide signaling pathways. Acute treatment with PDE10A inhibitors produces rapid and transient transcription of the immediate early gene cfos in rat striatum. Although inhibition of PDE10A causes accumulation of both cAMP and cGMP, the increase in striatal cfos expression appears to depend on changes in cAMP, since the increase is present in mice deficient in nNOS which fail to increase cGMP in response to PDE10A inhibition. Consistent with its expression in a majority of striatal MSN, PDE10A inhibition significantly induces expression of both substance P and enkephalin, neuropeptide markers for the direct and indirect striatal output pathways, respectively. These findings support the hypothesis that PDE10A modulates signal transduction in both striatal output pathways and suggest that PDE10A inhibitors may offer a unique approach to the treatment of schizophrenia.

Synthesis and SAR of 2-aryloxy-4-alkoxy-pyridines as potent orally active corticotropin-releasing factor 1 receptor antagonists.

A series of 2-aryloxy-4-alkoxy-pyridines ( 1) was identified as novel, selective, and orally active antagonists of the corticotropin-releasing factor 1 (CRF 1) receptor. Among these, compound 2 (CP-316311) is a potent and selective CRF 1 receptor antagonist with an IC 50 value of 6.8 nM in receptor binding and demonstrates oral efficacy in central nervous system (CNS) in vivo models. The regiochemistry of compounds in this series was determined by an X-ray structural analysis. A method to control regioselectivity via pyridine- N-oxides was developed. The synthesis of compounds in series 1 (Figure ) and [ (3)H]- 2 as well as the structure-activity relationship (SAR) are discussed. The in vitro, ex vivo, and in vivo properties of representative compounds are described herein. Compound 2 was advanced to phase II depression trials to test the hypothesis that CRF 1 antagonists could be used clinically as antidepressant drugs.

Chapter 5. Novel Antipsychotics

Publisher Summary This chapter describes the novel atypical anti-psychotic agents that are used in treating schizophrenia. Use of such agents is also popular because of their reduced side effects compared to other similar agents. Newly identified dopamine receptors (D3, D4, D5), which were further characterized, has included the first autoradiographic visualization of D3 receptors in rat and human brain. The D4 receptor has been found to exist as several polymorphic variants that may explain the genetic range of susceptibility to schizophrenia and/or varied individual response to anti-psychotics. Researchers have measured the levels of messenger RNA (mRNA) for D1, D2, D3, and D5 receptors in the rat brain after neuroleptic treatment. Clinical trials with roxindole, a D2 autoreceptor agonist, showed efficacy in a group of schizophrenic patients with primary negative symptoms, whereas, results with SDZ-HDZ912 have been less conclusive. The virtues of this atypical anti-psychotic continue to be extolled. Debate on the novel mechanisrn(s) of action of clozapine continues: its superior efficacy has been attributed to interactions with a variety of receptor sites in the CNS and this list has been expanded to include 5HT 1c , D 4 , and glutamate. The chapter also discusses the role of serotonine antagonists, sigma receptors, neurokinin, and others. Several additional receptors have been proposed as having a potential role in the alleviation of psychotic symptoms. The genetic factor in the development of schizophrenia has been further emphasized as has the incidence of the disease because of prior exposure to viral pathogens. Other biological findings like the interaction of neuroleptics with the CNS receptors utilizing positron emission tomography (PET) and magnetic resonance imaging (MRI) techniques, and molecular modeling studies have also got their significance.