Patricia C. Contreras

D-serine antagonized phencyclidine- and MK-801-induced stereotyped behavior and ataxia

D-Serine, a selective agonist at the strychnine-insensitive glycine binding site, antagonized PCP-induction of stereotyped behavior and ataxia in a dose-dependent manner. At intraventricular doses of 0.1, 0.5 and 1 mumol/rat, D-serine significantly attenuated PCP-induction of stereotyped behavior in rats. Only doses of 0.5 and 1.0 mumol/rat of D-serine antagonized PCP-induction of ataxia. D-Serine (0.5 mumol/rat) also antagonized MK-801 induced stereotyped behavior and ataxia. These results suggest that agonists at the strychnine-insensitive glycine site may be clinically useful as a novel class of atypical antipsychotic agents.

Sigma receptors modulate both A9 and A10 dopaminergic neurons in the rat brain: functional interaction with NMDA receptors

The sigma receptor ligands, (+)-pentazocine and (+)-SKF 10,047, were found to increase dopamine metabolism (DOPAC, HVA) and release (3-MT) in both the striatum and olfactory tubercle of the rat, in a dose-dependent manner, after central as well as peripheral administration. The effect of (+)-SKF 10,047 was stereospecific. The increase in dopamine metabolism was not blocked by naloxone pretreatment, excluding an action via opioid receptors. More interestingly, this modulation was blocked by pretreatment with the NMDA receptor antagonist, CPP. Neither sigma ligand exhibited any affinity for D1 or D2 dopamine receptors or for NMDA, PCP or NMDA-associated glycine receptors. Sigma receptors thus appear to modulate dopaminergic function in both A9 and A10 projections. This modulation appears to involve a functional interaction with NMDA receptors or an NMDA-utilizing synapse downstream to neurons modulated by sigma receptors.

Selective memory impairment by phencyclidine in rats

Phencyclidine (PCP) users sometimes report lack of recall of events occurring while they are under the influence of the drug. The present experiment was designed to test whether rats remember information learned after PCP administration. Rats were trained to choose one arm of a T-maze to obtain a food reward. The following day they were injected with either PCP (1 mg/kg) or vehicle and trained to choose the opposite arm for a reward (reversal learning). A third group of rats received neither injections nor training on the second day. On the third day, all rats were tested for their preference of maze arms. Rats who had been injected with saline before reversal learning chose the arm rewarded during the reversal, while rats receiving PCP on the second day chose randomly. The rats which did not learn the reversal chose the arm learned on day 1. These results indicate that while PCP did not interfere with the rats ability to learn, it interfered with long-term storage of information.

A Review of the In Vitro and In Vivo Neurochemical Characterization of the NMDA/PCP/Glycine/Ion Channel Receptor Macrocomplex*

ConclusionsCurrent neurochemical studies of the NMDA receptor macromolecular complex are yielding new insights into the interactions of the subunits of this complex and the associated potential clinical benefits of selective modulation of these subnits. Such studies offer the great potential for a new generation of pharmacotherapies for a wide range of CNS disorders, including stroke, a condition for which there is currently no effective pharmacological treatment. However, it is essential to understand that the first generation products in this area may not be optimal pharmacotherapies, such that haracterization of possible receptor subtypes and understanding the molecular biology of the component proteins of the receptor complex will be crucial in the design of the optimal pharmacological modulators of the NMDA receptor complex.

Clozapine attenuates N-methyl-d-aspartate receptor complex-mediated responses in vivo: tentative evidence for a functional modulation by a noradrenergic mechanism

Recent studies revealed a role for dopamine and noradrenaline in the etiology of ischemia-induced neuronal cell death. In the present investigation, the modulation by clozapine, an atypical antipsychotic agent that interacts with adrenergic receptors, of N-methyl-D-aspartate (NMDA) receptor complex-mediated events were studied by examining its effects on levels of cGMP in the cerebellum. Clozapine decreased basal levels of cGMP in the cerebellum and antagonized harmaline-, methamphetamine-, pentylenetetrazol- and D-serine-induced increases in levels of cGMP with ED50 values of 3.9, 2.36, 2.13 and 2.1 mg/kg (i.p.). However, clozapine (1.25-25 mg/kg) did not attenuate the quisqualate-induced increases in levels of cGMP, indicating a specific modulation of events modulated by the NMDA receptor complex. Antagonists of dopamine (D2), serotonin (5-HT)-5-HT1, 5-HT2 and 5-HT3 [haloperidol, propranolol, ritanserin, ICS 205-930 [(3-tropanyl-indole-3-carboxylate methiodide)] respectively], did not reverse the response to harmaline. However, WB-4101 [(2,6-dimethoxy-phenoxyethyl)aminomethyl-1,4-benzodioxane HCl], and alpha 1-adrenergic antagonist, reversed harmaline-, D-serine-, PTZ- and MA-induced increases in levels of cGMP, indicating an adrenergic modulation of the events mediated by the NMDA receptor complex. Intracerebellar and intracerebroventricular administration of clozapine and intracerebellar administration of WB-4101 reversed the D-serine-induced response, indicating a central locus of action. These results indicated that clozapine modulates levels of cGMP predominantly through its interactions with central adrenergic receptors.

Glycine modulation of the phencyclidine binding site in mammalian brain.

Neurophysiological studies have shown that glycine potentiates the NMDA response in cultured neurons by a strychnine-insensitive mechanism. Autoradiographic data have demonstrated a correspondence between strychnine-insensitive [3H]glycine binding sites and NMDA-sensitive [3H]glutamate binding sites. Here we report that in synaptic plasma membranes from rat brain, the binding of a PCP analog, [3H]TCP, was enhanced more than 5-fold by 1 microM glycine. This glycine stimulation of binding of [3H]TCP was blocked by the competitive NMDA-receptor antagonist, D-AP7. These data provide support for the hypothesis that a unique amino acid recognition site is associated with the proposed NMDA/PCP receptor complex in brain.

Region-Specific Targets of p42/p44MAPK Signaling in Rat Brain

Abstract: In vitro studies indicate that p42/p44MAPK phosphorylate both nuclear and cytoplasmic proteins. However, the functional targets of p42/p44MAPK activation in vivo remain unclear. To address this question, we localized activated p42/p44MAPK in hippocampus and cortex and determined their signaling effects after electroconvulsive shock treatment (ECT) in rats. Phosphorylated p42/p44MAPK content increased in the cytoplasm of hippocampal neurons in response to ECT. Consistent with this cytoplasmic localization, inhibition of ECT‐induced p42/p44MAPK activation by the extracellular signal‐regulated kinase kinase inhibitor PD098059 blocked phosphorylation of the cytoplasmic protein microtubule‐associated protein 2c (MAP2c), but failed to inhibit the induction of the nuclear protein c‐Fos in response to ECT. In contrast to hippocampal neurons, cortical neurons exhibited an increase in amount of phosphorylated p42/p44MAPK in both the nucleus and cytoplasm after ECT. Accordingly, PD098059 blocked the induction of Fos‐like immunoreactivity in the nuclei of cortical neurons as well as MAP2c phosphorylation in the cytoplasm. Our data indicate that both nuclear and cytoplasmic substrates can be activated by p42/p44MAPK in vivo. However, the functional targets of p42/p44MAPK signaling depend on the precise location of p42/p44MAPK within different subcellular compartments of brain regions. These results indicate unique functional pathways of p42/p44MAPK‐mediated signal transduction within different brain regions in vivo.

Ifenprodil and SL 82.0715 potently inhibit binding of [3H](+)-3-PPP to σ binding sites in rat brain

Abstract SL 82.0715 and ifenprodil are potent anti-ischemic agents, which are believed to be due to non-competitive antagonism of N- methyl- d -aspartate (NMDA). It has been proposed that SL 82.0715 and ifenprodil non-competitively antagonize the actions of NMDA by interacting as antagonists with a polyamine site associated with the NMDA/phencyclidine (PCP)/glycine complex. The present study demonstrates that the actions of SL 82.0715 and ifenprodil may also be due in part to an interaction with sigma binding sites, a property that is not shared with polyamines.

Evaluation of U-50,488H analogs for neuroprotective activity in the gerbil

U-50,488H, a kappa (kappa) opioid ligand with moderate potency at sigma (sigma) receptors, protects against mechanical and ischemia-induced injury. The purpose of this study was to evaluate the possibility that sigma-receptors may be involved in mediating the neuroprotective actions of U-50,488H. This possibility was examined by testing the potential of a series of U-50,488H analogs, which are potent sigma-ligands with minimal activity at kappa-opioid receptors, to protect against ischemia-induced neuronal damage in the gerbil. Like U-50,488H, BD-449 (20 mg/kg), the cis-diastereomer of U-50,4888H, protected against ischemia-induced neuronal damage as did BD-737 (50 and 30 mg/kg) and BD-738 (50 mg/kg). All 3 compounds interacted selectively with sigma-receptors. In contrast, BD-601 (50 mg/kg), did not protect against ischemia-induced neuronal damage, although it also interacted potently with sigma-receptors. One difference between the compounds that were neuroprotective and BD-601 is that only BD-601 produced sigma-like behavioral effects in the rat. Thus, it is possible that BD-601 may interact differently or at a different sigma-subtype than BD-449, BD-737 and BD-738 with sigma-receptors. However, these results clearly indicate that an interaction with kappa-opioid receptors is not required for anti-ischemic activity, and that sigma-receptors may play a role in neuroprotection.

[3H]MK-801 binding in Alzheimer's disease

The density of [3H]MK-801 binding sites was studied in homogenates prepared from different cortical regions of postmortem brains of Alzheimer patients and age matched controls. Highest number of binding sites for this noncompetitive antagonist of the N-methyl-D-aspartate (NMDA) receptor was in temporal pole (Brodmann area A-38) in both groups. There were no consistent differences between patients and controls in either binding density or affinity constant in any of the areas studied. Involvement of glutamatergic neurotransmission in Alzheimers disease does not seem to be at the level of the MK-801 recognition site on the NMDA receptor complex.