Chen, Long, Mark Muhlhauser, and Charles R. Yang. Glycine tranporter-1 blockade potentiates NMDA-mediated responses in rat prefrontal cortical neurons in vitro and in vivo. J Neurophysiol 89: 691-703, 2003. First published October 30, 2002 10.1152/jn.00680. 2002 receptor (NMDA-R) has pivotal roles in neural development, learning, memory, and synaptic plasticity. Functional impairment of NMDA-R has been implicated in schizophrenia. NMDA-R activation requires glycine to act on the glycine-B (GlyB) site of the NMDA-R as an obligatory co-agonist with glutamate. Extracellular glycine near NMDA-R is regulated effectively by a glial glycine transporter (GlyT1). Using whole-cell voltage-clamp recordings in prefrontal cortex (PFC) slices, we have shown that exogenous GlyB site agonists glycine and D-serine, or a specific GlyT1 inhibitor N[3-(4Ј-fluorophenyl)-3-(4Ј-phenylphenoxy)-propyl]sarcosine (NFPS) in the presence of exogenous glycine (10 M), potentiated synaptically evoked NMDA excitatory postsynaptic currents (EPSCs) in vitro. Furthermore, in urethan-anesthetized rats, microiontophoretic NMDA pulses excite single PFC neurons. When these responses were blocked by approximately 50% to approximately 90% on continuous iontophoretic application of the GlyB site, antagonist (ϩ)HA-966, intravenous NFPS (5 mg/kg), or a GlyB site agonist D-serine (50 mg/kg iv) reversed this (ϩ)HA-966 block. NFPS may elevate endogenous glycine levels sufficiently to displace (ϩ)HA-966 from the GlyB sites of the NMDA-R, thus enabling reactivation of the NMDA-Rs by iontophoretic NMDA applications. D-Serine (50 -100 mg/kg iv) or NFPS (1-2 mg/kg iv) alone also augmented NMDAevoked excitatory responses. These data suggest that direct GlyB site stimulation by D-serine, or blockade of GLYT1 to elevate endogenous glycine to act on unsaturated GlyB sites on NMDA-Rs, potentiated NMDA-R-mediated firing responses in rat PFC. Hence, blockade of GlyT1 to elevate glycine near the NMDA-R may activate hypofunctional NMDA-R, which has been implicated to play a critical role in the pathophysiology of schizophrenia.

Irritation of the urinary bladder causes activation of normally "silent" nociceptive primary afferent fibers. In the present study, it is reported that irritation of the urinary bladder or urethra with infusion of 0.5% acetic acid robustly activates motoneurons that innervate the striated muscle of the external anal sphincter via spinal reflex mechanisms. The activation of anal motoneurons following irritation of the bladder and urethra are termed vesicoanal and urethroanal reflexes, respectively. The reflexes can be mimicked by acute application of capsaicin to the bladder and urethra, and they show desensitization following prolonged topical application of capsaicin or following chronic systemic pretreatment with capsaicin. The reflexes can be demonstrated in chronic spinal cord-transected animals, indicating that the reflex pathways are organized within the spinal cord. The urethroanal reflex is also physiologically activated by urethral distension and/or increases in intraluminal pressure. In addition to activation of anal sphincter activity, slight distension, pressure increases, or instillation of 0.5% acetic acid into the urethra inhibited bladder contractions through activation of an inhibitory urethrovesical reflex. These reflexes are discussed in terms of clinical characteristics of urethritis and prostatitis. Anecdotally, it was discovered that the bladder can buffer acetic acid.

Following oral administration of the prodrug LY2969822, the mGlu receptor agonist LY2934747 was formed and this attenuated pain behaviours across a broad range of preclinical pain models.

No abstract

The objective of the described research effort was to identify a novel serotonin and norepinephrine reuptake inhibitor (SNRI) with improved norepinephrine transporter activity and acceptable metabolic stability and exhibiting minimal drug−drug interaction. We describe herein the discovery of a series of 3-substituted pyrrolidines, exemplified by compound 1. Compound 1 is a selective SNRI in vitro and in vivo, has favorable ADME properties, and retains inhibitory activity in the formalin model of pain behavior. Compound 1 thus represents a potential new probe to explore utility of SNRIs in central nervous system disorders, including chronic pain conditions. KEYWORDS: SERT, NET, dual, reuptake inhibitor, SNRI, SERT RO, α-MMT, pain M anipulation of central nervous system (CNS) levels of the neurotransmitters serotonin (5-HT) and norepinephrine (NE), through inhibition of the corresponding reuptake transporters SERT (serotonin transporter) and NET (norepinephrine transporter), has been a successful strategy for treating several CNS disorders including depression, generalized anxiety disorder, and several chronic pain conditions. 1−6 Several compounds that selectively inhibit these transporters (known as serotonin norepinephrine reuptake inhibitors or SNRIs) are available on the market (compounds 5−8, see Figure 1) and have proven to be safe and effective drugs for the treatment of pain and/or mood disorders. However, these molecules often show more potent inhibition of SERT than NET in vitro (Table 1). Published studies have demonstrated that selective SERT and NET inhibitors can show additive or synergistic analgesic efficacy. 7,8 For our targeted indication of pain, we hypothesized that a SNRI that inhibited SERT and NET with comparable potency would lead to a compound with a superior efficacy and safety profile. Therefore, we undertook to develop a new SNRI that, in a single molecule, improved NET activity versus current SNRIs, retained potent and balanced in vivo activity at both transporters, had good brain exposure, was metabolically stable, and provided minimal drug−drug interaction (DDI) risk to patients on other therapies.Our search for a balanced SNRI led to the discovery of a series of 3-substituted pyrrolidines, exemplified by compound 1. Amine containing compounds have long been a fertile source of reuptake inhibitors with a variety of profiles. 9 SNRIs 5−8 all show a similar pharmacophore, with an amine and an aryl group separated by 2−4 sp 3 hybridized atoms. The pyrrolidines we synthesized and tested represent a conformationally constrained version of this general pharmacophore that maintains potent transporter inhibition. 10 Compound 1 contains several innovative features that make it an improvement over earlier scaffolds. The pyrrolidine ring provided the secondary amine that is common to many reuptake inhibitors, but in a novel constrained geometry. Introduction of the pyridine ring, in place of a phenyl ring, was a key change that delivered both our desired pharmacological profile and...