Anxiolytic-like activity of the non-selective galanin receptor agonist, galnon.

Galanin's influence on monoaminergic neurotransmission, together with its discrete CNS distribution in corticolimbic brain areas, points to a potential role for this neuropeptide in mediating anxiety- and depression-like responses. To evaluate this hypothesis, the non-selective galanin receptor agonist, galnon, was tested in multiple preclinical models of anxiolytic- and antidepressive-like activity. Acute administration of galnon (0.03-1mg/kg, i.p.) dose-dependently increased punished crossings in the four plate test, with magnitude similar to the effects of the endogenous ligand, galanin (0.1-1.0 microg, i.c.v.). Moreover, the effects of galnon and galanin were blocked by central administration of the non-selective galanin receptor antagonist, M35 (10 microg, i.c.v.). Interestingly, the benzodiazepine receptor antagonist, flumazenil (1mg/kg, i.p.), reversed galnon's effect in the four plate test, implicating GABAergic neurotransmission as a potential mechanism underlying this anxiolytic-like response. In the elevated zero maze, galnon (0.3-3.0mg/kg, i.p.) and galanin (0.03-0.3 microg, i.c.v.) increased the time spent in the open arms, while in the stress-induced hyperthermia model, galnon (0.3-30 mg/kg, i.p.) attenuated stress-induced changes in body temperature. Consistent with these anxiolytic-like effects, in vivo microdialysis showed that acute galnon (3mg/kg, i.p.) treatment preferentially elevated levels of GABA in the rat amygdala, a brain area linked to fear and anxiety behaviors. In contrast to the effects in anxiety models, neither galnon (1-5.6 mg/kg, i.p.) nor galanin (0.3-3.0 microg, i.c.v.) demonstrated antidepressant-like effects in the mouse tail suspension test. Galnon (1-10mg/kg, i.p.) also failed to reduce immobility time in the rat forced swim test. In vitro, galnon and galanin showed affinity for human galanin receptors expressed in Bowes melanoma cells (K(i)=5.5 microM and 0.2 nM, respectively). Galanin displayed high affinity and functional potency for membranes expressing rat GALR1 receptors (K(i)=0.85 nM; EC(50)=0.6 nM), while galnon (10 microM) failed to displace radiolabeled galanin or inhibit cAMP production in the same GALR1 cell line. Galnon (10 microM) showed affinity for NPY1, NK2, M5, and somatostatin receptors but no affinity for galanin receptors expressed in rat hippocampal membranes. Taken together, the present series of studies demonstrate novel effects of galnon in various preclinical models of anxiety and highlight the galaninergic system as a novel therapeutic target for the treatment of anxiety-related disorders. Moreover, these data indicate rodent GALR1 receptors do not mediate galnon's in vivo activity.

Synthesis and biological evaluation of benzodioxanylpiperazine derivatives as potent serotonin 5-HT(1A) antagonists: the discovery of Lecozotan.

A series of benzodioxanylpiperazine derivatives possessing a 4-aryl amide substituent was prepared and evaluated for 5-HT(1A) affinity and functional antagonist activity in vitro and in vivo. All of the compounds in this series possessed high affinity for the human 5-HT(1A) receptor and many displayed potent antagonist activity in vitro and varying degrees of intrinsic activity in vivo. Compound 11c (Lecozotan) was selected for further development and is currently in clinical trials.

Effects of the N-methyl-D-aspartate receptor antagonist perzinfotel [EAA-090; [2-(8,9-dioxo-2,6-diazabicyclo[5.2.0]non-1(7)-en-2-yl)-ethyl]phosphonic acid] on chemically induced thermal hypersensitivity.

Perzinfotel [EAA-090; [2-(8,9-dioxo-2,6-diazabicyclo[5.2.0]non-1(7)-en-2-yl)-ethyl]phosphonic acid] is a selective, competitive N-methyl-D-aspartate (NMDA) receptor antagonist with high affinity for the glutamate site. The current study evaluated whether perzinfotel would have antinociceptive effects or block thermal hypersensitivity associated with the administration of chemical irritants in rats. Perzinfotel lacked antinociceptive effects but dose- and time-dependently blocked prostaglandin E(2) (PGE(2))- and capsaicin-induced thermal hypersensitivity in a warm-water tail-withdrawal assay in rats. Doses of 10 mg/kg intraperitoneal or 100 mg/kg oral blocked PGE(2)-induced hypersensitivity by 60 to 80%. The magnitude of reversal was greater than other negative modulators of the NMDA receptor studied, such as uncompetitive channel blockers (e.g., memantine, dizocilpine, and ketamine), a NR2B selective antagonist (e.g., ifenprodil), and other glutamate antagonists [e.g., selfotel, 3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP), D,L-(E)-2-amino-4-propyl-5-phosphono-3-pentenoic acid (CGP-39653)], up to doses that suppressed operant rates of responding. In contrast to other negative modulators of the NMDA receptor studied, which typically decreased operant rates of responding at doses that lacked antinociceptive effects, perzinfotel did not modify response rates at doses that blocked irritant-induced thermal hypersensitivity. Collectively, these studies demonstrate that perzinfotel has therapeutic ratios for effectiveness versus adverse effects superior to those seen with other competitive and uncompetitive NMDA receptor antagonists studied.

The acoustic startle reflex in Sprague-Dawley rats is altered by permanent middle cerebral artery occlusion.

The startle reflex is an unconditioned, quantifiable behavior used to study sensory modalities. We examined whether the acoustic startle reflex (ASR) was sensitive to lesions induced by focal cerebral ischemia. Sprague-Dawley rats were pre-screened for startle reflex responses 3-6 days prior to surgery and there were no differences in mean startle amplitude across groups. Animals were subjected to permanent middle cerebral artery occlusion (pMCAo) or a sham surgical procedure. Twenty-four hours later rats were evaluated for ASR prior to sacrifice. Infarct volumes were subsequently determined by quantitative image analysis of 2,3,5-triphenyltetrazolium chloride-stained brain sections. Infarct volumes of rats undergoing pMCAO ranged from 0 to 48%. Data were divided into three groups based upon percent infarction: mild (0-20%), moderate (21-35%), and severe (>35%). A within-subject analysis revealed a significant decrease in mean startle amplitude of only severely infarcted rats relative to their pre-surgery startle responses. Furthermore, the lesioned brain areas observed in these animals provide an anatomical basis for these results. Our findings demonstrate that ASR is affected in a model of stroke. Further work is needed to characterize this behavioral test and to determine whether it may have application as a surrogate endpoint for clinical stroke studies.

Anxiolytic-like activity of the mGluR5 antagonist MPEP: a comparison with diazepam and buspirone.

The selective and systemically active antagonist for the metabotropic glutamate receptor subtype 5 (mGluR5), 2-methyl-6-(phenylethynyl)pyridine (MPEP) was shown to display anxiolytic-like activity in a number of unconditioned assays of stress and anxiety (elevated plus maze, shock probe burying, marble burying, social interaction, and stress-induced hyperthermia) in rodents. In this report, we extend these observations found using unconditioned models of anxiety to include three models of conditioned anxiety, comparing the activity of MPEP to the clinically used anxiolytics, diazepam, and buspirone. MPEP and diazepam, but not buspirone, showed anxiolytic-like activity in the fear-potentiated startle (FPS) model. In a conditioned ultrasonic vocalization (USV) procedure, MPEP, diazepam, and buspirone reduced vocalizations to a similar degree. In the modified Geller-Seifter procedure, MPEP, diazepam, and buspirone displayed statistically significant anxiolytic-like activity, increasing the number of punished responses. Thus, these findings confirm and extend previous reports that MPEP exhibits anxiolytic-like activity in rats, and suggests that development of mGluR5 antagonists may provide a novel approach to treating anxiety disorders.