Amino-alkyl-cyclohexanes are novel uncompetitive NMDA receptor antagonists with strong voltage-dependency and fast blocking kinetics: in vitro and in vivo characterization

The present study characterized the in vitro NMDA receptor antagonistic properties of novel amino-alkyl-cyclohexane derivatives and compared these effects with their ability to block excitotoxicity in vitro and MES-induced convulsions in vivo. The 36 amino-alkyl-cyclohexanes tested displaced [3H]-(+)-MK-801 binding to rat cortical membranes with K(i)s between 1.5 and 143 microM. Current responses of cultured hippocampal neurones to NMDA were antagonized by the same compounds with a wide range of potencies (IC50s of 1.3-245 microM, at -70 mV) in a use- and strongly voltage-dependent manner (delta 0.55-0.87). The offset kinetics of NMDA receptor blockade was correlated with equilibrium affinity (Corr Coeff. 0.87 P < 0.0001). As an example, MRZ 2/579 (1-amino-1,3,3,5,5-pentamethyl-cyclohexane HCl) had similar blocking kinetics to those previously reported for memantine (K(on) 10.67 +/- 0.09 x 10(4) M(-1) s(-1), K(off) 0.199 +/- 0.02 s(-1), K(d) = K(off)/K(on) = 1.87 microM c.f. IC50 of 1.29 microM). Most amino-alkyl-cyclohexanes were protective against glutamate toxicity in cultured cortical neurones (e.g. MRZ 2/579 IC50 2.16 +/- 0.03 microM). Potencies in the three in vitro assays showed a relatively strong cross correlation (all corr. coeffs. > 0.72, P < 0.0001). MRZ 2/579 was also effective in protecting hippocampal slices against 7 min. hypoxia/hypoglycaemia-induced reduction of fEPSP amplitude in CA1 with an EC50 of 7.01 +/- 0.24 microM. MRZ 2/579 showed no selectivity between NMDA receptor subtypes expressed in Xenopus oocytes but was somewhat more potent than in patch clamp experiments-IC50s of 0.49 +/- 0.11, 0.56 +/- 0.01 microM, 0.42 +/- 0.04 and 0.49 +/- 0.06 microM on NR1a/2A /2B, /2C and 2/D, respectively. In contrast, memantine and amantadine were both 3-fold more potent at NR1a/2C and NR1a/2D than NR1a/2A receptors. All Merz amino-alkyl-cyclohexane derivatives inhibited MES-induced convulsions in mice with ED50s ranging from 3.6 to 130 mg/kg i.p. The in vivo and in vitro potencies correlated indicating similar access of most compounds to the CNS. MRZ 2/579 administered at 10 mg/kg resulted in peak plasma concentrations of 5.3 and 1.4 microM following i.v. and p.o. administration respectively, which then declined with a half life of around 170-210 min. Analysis of A.U.C. concentrations indicates a p.o./i.v. bioavailability ratio for MRZ 2/579 of 60%. MRZ 2/579 injected i.p. at a dose of 5 mg/kg resulted in peak brain extracellular fluid (ECF) concentrations of 0.78 microM (brain microdialysates). Of the compounds tested MRZ 2/579, 2/615, 2/632, 2/633, 2/639 and 2/640 had affinities, kinetics and voltage-dependency most similar to those of memantine and had good therapeutic indices against MES-induced convulsions. We predict that these amino-alkyl-cyclohexanes, which all had methyl substitutions at R1, R2, and R5, at least one methyl or ethyl at R3 or R4 and a charged amino-containing substitution at R6, could be useful therapeutics in a wide range of CNS disorders proposed to involve disturbances of glutamatergic transmission.     

Plasma dopa concentrations after different preparations of levodopa in normal subjects

1 The concurrent administration of levodopa with a decarboxylase inhibitor produced a plasma concentration/time curve comparable with 1/4 to 1/5 of the dose of levodopa given alone.

2 There was no evidence to suggest that the decarboxylase inhibitor slowed the rate of elimination of levodopa from plasma.

3 Metoclopramide (Maxolon) increased the rate of levodopa absorption. Higher plasma concentrations of levodopa during the first 2 h after dosing were followed by lower plasma concentrations during the third and fourth hours. The amount of levodopa absorbed after Larodopa as indicated by the AUC was not altered by adding metoclopramide.

4 None of the current preparations of levodopa produced sustained plasma concentrations.

5 In vitro testing confirmed that Brocadopa Temtabs tablets disintegrate and dissolve slowly. In vivo, Brocadopa Temtabs behaved as a slow release preparation but it did not produce sustained plasma concentrations of levodopa.

     

Association of aggressive behavior with altered serotonergic function in patients who are not suicidal

OBJECTIVE: The purpose of this study was to determine whether aggression and serotonergic dysfunction are related in the absence of a history of suicidal behavior. Although serotonergic dysfunction has been implicated in aggressive and impulsive behavior, most studies of such behavior have included individuals with a history of suicide attempts. Low concentrations of CSF 5-hydroxyindoleacetic acid (5-HIAA) have been consistently associated with suicidal behavior, presenting a potential confound in the link between aggression and serotonergic dysfunction. METHOD: The authors examined the association between aggression and CSF 5-HIAA concentrations in a group of 64 patients who had different DSM-III-R axis I diagnoses and no past suicidal behavior. Aggressive (N=35) and nonaggressive (N=29) groups were defined by a median split on a six-item history of adulthood aggressive behavior. RESULTS: The aggressive group had significantly lower CSF 5-HIAA concentrations than the nonaggressive group. Aggressive individuals also scored significantly higher on self-report measures of hostility, impulsiveness, and sensation seeking. CSF 5-HIAA concentrations, however, did not correlate with self-reported hostility and impulsivity. CONCLUSIONS: There is an association between aggressive behavior and serotonergic dysfunction independent of suicidal behavior in patients with axis I disorders who exhibit relatively milder forms of aggressive behavior. Analogous to findings with suicidal behavior, a low concentration of CSF 5-HIAA is related to aggressive behavior but does not show the same relationship to the continuum of aggressive feelings and thoughts.     

Neuroprotective and symptomatological action of memantine relevant for alzheimer’s disease — a unified glutamatergic hypothesis on the mechanism of action

The involvement of glutamate mediated neurotoxicity in the pathogenesis of Alzheimer's disease is finding increasingly more acceptance in the scientific community. Central to this hypothesis is the assumption that in particular glutamate receptors of the N-methyl-D-aspartate (NMDA) type are overactivated in a tonic rather than a phasic manner. Such continuous mild activation leads under chronic conditions to neuronal damage. Moreover, one should consider that impairment of plasticity (learning) may result not only from neuronal damage per se but also from continuous activation of NMDA receptors. To investigate this possibility we tested whether overactivation of NMDA receptors using either non-toxic doses/concentrations of a direct NMDA agonist or through an indirect approach--decrease in magnesium concentration--produces deficits in plasticity. In fact NMDA both in vivo (passive avoidance test) and in vitro (LTP in CA1 region) impaired learning and synaptic plasticity. Under these conditions memantine which is an uncompetitive NMDA receptor antagonist with features of "improved magnesium" (voltage dependence, affinity) attenuated the deficit. The more direct proof that memantine can act as a surrogate for magnesium was obtained in LTP experiments under low magnesium conditions. In this case as well, impaired LTP was restored in the presence of therapeutically relevant concentrations of memantine (1 microM). In vivo, doses leading to similar brain/serum levels produce neuroprotection in animal models relevant for neurodegeneration in Alzheimer's disease such as neurotoxicity produced by inflammation in the NBM or beta-amyloid injection to the hippocampus. Hence, we postulate that if in Alzheimer's disease overactivation of NMDA receptors occurs indeed, memantine would be expected to improve both symptoms (cognition) and slow down disease progression because it takes over the physiological function of magnesium.     

REACT: Rapid Evaluation Assessment of Clinical Reasoning Tool

IntroductionClinical reasoning encompasses the process of data collection, synthesis, and interpretation to generate a working diagnosis and make management decisions. Situated cognition theory suggests that knowledge is relative to contextual factors, and clinical reasoning in urgent situations is framed by pressure of consequential, time-sensitive decision-making for diagnosis and management. These unique aspects of urgent clinical care may limit the effectiveness of traditional tools to assess, teach, and remediate clinical reasoning.MethodsUsing two validated frameworks, a multidisciplinary group of clinicians trained to remediate clinical reasoning and with experience in urgent clinical care encounters designed the novel Rapid Evaluation Assessment of Clinical Reasoning Tool (REACT). REACT is a behaviorally anchored assessment tool scoring five domains used to provide formative feedback to learners evaluating patients during urgent clinical situations. A pilot study was performed to assess fourth-year medical students during simulated urgent clinical scenarios. Learners were scored using REACT by a separate, multidisciplinary group of clinician educators with no additional training in the clinical reasoning process. REACT scores were analyzed for internal consistency across raters and observations.ResultsOverall internal consistency for the 41 patient simulations as measured by Cronbach’s alpha was 0.86. A weighted kappa statistic was used to assess the overall score inter-rater reliability. Moderate reliability was observed at 0.56.DiscussionTo our knowledge, REACT is the first tool designed specifically for formative assessment of a learner’s clinical reasoning performance during simulated urgent clinical situations. With evidence of reliability and content validity, this tool guides feedback to learners during high-risk urgent clinical scenarios, with the goal of reducing diagnostic and management errors to limit patient harm.Supplementary InformationThe online version contains supplementary material available at 10.1007/s11606-022-07513-5.