Functional and pharmacological differences between recombinant N-methyl-D-aspartate receptors

N-methyl-D-aspartic acid (NMDA) receptors transiently transfected into mammalian HEK-293 cells were characterized with subunit-specific antibodies and electrophysiological recordings. Deactivation time course recorded in response to fast-glutamate pulses were studied in isolated and lifted cells, as well as in outside-out membrane patches excised from cells expressing recombinant NR1 subunits in combination with the NR2A, NR2B, NR2C, or NR2D NMDA receptor subunits. Transfected cells were preidentified by the fluorescence emitted from the coexpressed Aequorea victoria jellyfish Green Lantern protein. Currents generated by NR1/NR2A channels displayed double exponential deactivation time course being faster than that in NR1/NR2B or NR1/NR2C channels. However, a large decay variability was observed within each cotransfection, suggesting that mechanisms additional to subunit composition may also regulate deactivation time course. NR1/NR2D channels displayed slowly deactivating currents. Channel deactivation was fast and comparable among receptors obtained by cotransfecting five distinct spliced variants of the NR1 subunit, each with the NR2A subunit. Additionally, recovery from desensitization was slower for NR1/NR2B than for NR1/NR2A channels. The average deactivation time course of responses to brief L-glutamate applications in cells where NR1/NR2A/NR2B cDNAs were cotransfected at variable ratio was intermediate between those of the NR1/NR2A and NR1/NR2B channels. Although immunocytochemical evidence indicates that the majority of cells are cotransfected by all plasmids in triple transfection, our experimental condition did not allow for a tight control of the expression of NMDA receptor subunits. This produced the result that many cells were characterized by deactivation time course and haloperidol sensitivities of separate NR1/NR2A and NR1/NR2B subunit heteromers. We also speculate on the possible formation of channels resulting from the coassembly in the same receptor of NR1/NR2A/NR2B subunits from a minority of cells that gave responses to brief application of L-glutamate characterized by slow deactivation time course and decreased haloperidol sensitivity.

The majority of N-methyl-D-aspartate receptor complexes in adult rat cerebral cortex contain at least three different subunits (NR1/NR2A/NR2B)

A monoclonal antibody (R1JHL) against the NR1 subunit of the N-methyl-D-aspartate (NMDA) receptor has been developed that recognizes an epitope in the region of the amino-terminal amino acids 341-561 (a region common to all splice variants of NR1). This monoclonal antibody identifies a broad band at 115 kDa in immunoblots using membranes from NR1-transfected cells and from rat brain tissue. No cross-reactivity with any NR2 subunit is seen. With the goal to determine quantitatively the subunit composition of cortical NMDA receptors, we used the monoclonal antibody to NR1 and polyclonal antibodies against the NR2A and NR2B subunits to perform immunoprecipitations of receptor subunits from solubilized adult rat cortical membranes. Solubilization of the receptor subunits was accomplished under both nondenaturing (native) conditions, under which the subunits seem to remain associated with one another, and denaturing conditions, under which the subunits are associated from each other. Although each of these antibodies selectively immunoprecipitates only its corresponding (cognate) subunit when the subunits have been solubilized under denaturing conditions, each of the antibodies immunoprecipitates a sizable fraction of the other two NMDA receptor subunits when membranes are solubilized under nondenaturing conditions, indicating an interaction in situ. Using quantitative immunoblot analysis of the three subunits in both the pellets and supernatants from the immunoprecipitations, we found 1) the dominant NMDA receptor complex in adult rat cortex contains at least three subunits, NR1/NR2A/NR2B; 2) a smaller fraction of NMDA receptors are composed of only two subunits, NR1/NR2B or NR1/NR2A; 3) there are no complexes that contain NR2A/NR2B that do not contain NR1; 4) only a small fraction of each subunit is not associated with any other NMDA receptor subunit; 5) no coimmunoprecipitation of noncognate subunits occurs unless the subunits are assembled with each other in situ; and 6) there is no physical interaction between these NMDA receptor subunits and the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor GluR2 or GluR3 subunits. These results suggest that functional studies with recombinant receptors composed of at least three subunits may be the most physiologically meaningful.

Quantitative autoradiography of beta 1- and beta 2-adrenergic receptors in rat brain

We have used quantitative autoradiography to localize in rat brain beta 1- and beta 2-adrenergic receptors. These receptors were labeled in vitro with 125I-labeled pindolol, an antagonist of beta-adrenergic receptors that binds nonselectively to both beta 1 and beta 2 subtypes. The selective inhibition of 125I-labeled pindolol binding with specific antagonists of beta 1 and beta 2 receptors allowed the visualization of beta-adrenergic receptor subtypes. High levels of beta 1 receptors were observed in the cingulate cortex, layers I and II of the cerebral cortex, the hippocampus, the Islands of Calleja, and the gelatinosus, mediodorsal, and ventral nuclei of the thalamus. High levels of beta 2 receptors were found in the molecular layer of the cerebellum, over pia mater, and in the central, paraventricular, and caudal lateral posterior thalamic nuclei. Approximately equal levels of beta 1 and beta 2 receptors occurred in the substantia nigra, the olfactory tubercle, layer IV of the cerebral cortex, the medial preoptic nucleus, and all nuclei of the medulla. The pronounced differences in the ratio of beta 1 to beta 2 receptors among brain regions suggests that the subtypes of beta-adrenergic receptors may play different roles in neuronal function.

beta1- and beta2-Adrenergic receptors in rat cerebral cortex are independently regulated

Repeated administration of the tricyclic antidepressant desmethylimipramine to adult rats for 10 days caused a 40% decrease in the density of beta1-adrenergic receptors in the cerebral cortex but had no effect on the density of beta2-adrenergic receptors. Conversely, destruction of noradrenergic neurons by administration of 6-hydroxydopamine to neonatal rats caused a 64% increase in the density of beta1-adrenergic receptors in adult cerebral cortex with no change in the density of beta2-adrenergic receptors. These results suggest that the beta-adrenergic receptors in rat cortex involved in neuronal function are primarily of the beta1 subtype.

beta-Adrenergic receptor involvement in 6-hydroxydopamine-induced supersensitivity in rat cerebral cortex

The intraventricular administration of 6-hydroxydopamine, a procedure which destroys noradrenergic nerve terminals in the central nervous system, caused an increase in the density of beta-adrenergic receptors in rat cerebral cortex, without affecting their affinity for isoproterenol. The results suggest that changes in the density of adrenergic receptors are involved in 6-hydroxydopamine-induced supersensitivity at central noradrenergic synapses.

Developmental changes in localization of NMDA receptor subunits in primary cultures of cortical neurons

Immunoblot analysis, using antibodies against distinct N-methyl-D-aspartic acid (NMDA) receptor subunits, illustrated that the NR2A and NR2B subunit proteins have developmental profiles in cultured cortical neurons similar to those seen in vivo. NR1 and NR2B subunits display high levels of expression within the first week. In contrast, the NR2A subunit is barely detectable at 7 days in vitro (DIV) and then gradually increased to mature levels at DIV21. Immunocytochemical analysis indicated that NMDA receptor subunits cluster in the dendrites and soma of cortical neurons. Clusters of NR1 and NR2B subunits were observed as early as DIV3, while NR2A clusters were rarely observed before DIV10. At DIV18, NR2B clusters partially co-localize with those of NR2A subunits, but NR2B clusters always co-localize with those of NR1 subunits. Synapse formation, as indicated by the presence of presynaptic synaptophysin staining, was observed as early as 48-72 h after plating. However, in several neurons at ages less than DIV5 where synapses were scarce, NR2B and NR1 clusters were abundant. Furthermore, while NR2B subunit clusters were seen both at synaptic and extrasynaptic sites, NR2A clusters occurred almost exclusively in front of synaptophysin-labelled boutons. This result was supported by electrophysiological recording of NMDA-mediated synaptic activity [NMDA-excitatory postsynaptic currents (EPSCs)] in developing neurons. At DIV6, but not at DIV12, CP101, 606, a NR1/NR2B receptor antagonist, antagonized spontaneously occurring NMDA-EPSCs. Our data indicate that excitatory synapse formation occurs when NMDA receptors comprise NR1 and NR2B subunits, and that NR2A subunits cluster preferentially at synaptic sites.

Muscarinic regulation of Alzheimer's disease amyloid precursor protein secretion and amyloid beta-protein production in human neuronal NT2N cells

The Alzheimer amyloid precursor protein (APP) undergoes complex processing resulting in the production of a 4-kDa amyloid peptide (A beta) which has been implicated in the pathogenesis of Alzheimer's disease. Recent studies have shown that cells can secrete carboxyl terminus truncated APP derivatives (APP-S) in response to physiological stimulus. We have used human central nervous system neurons (NT2N) derived from a teratocarcinoma cell line (NT2) to study the signal transduction pathways involved in APP-S secretion and A beta production. Muscarinic receptors (m2 and m3) as well as the heterotrimeric GTP-binding protein Gq and the beta 1 isoform of phospholipase C were present in NT2N neurons. Stimulation of the muscarinic receptor with carbachol resulted in phospholipase C activation as shown by a transient increase in the second messengers 1,2-diacyl-sn-glycerol and inositol 1,4,5-trisphosphate. Carbachol also caused an increase in intracellular Ca2+ levels measured in single NT2N neurons. Under these conditions, carbachol caused a time-dependent 2-fold increase in APP-S secretion into the medium. In contrast, prolonged treatment with carbachol caused a decrease in A beta production into the medium. These results suggest that APP-S secretion and A beta production in NT2N neurons are regulated by the muscarinic/phospholipase C signal transduction pathway. Furthermore, activation of this pathway results in dissociation of APP-S secretion and A beta production.

Dopamine receptor changes following destruction of the nigrostriatal pathway: lack of a relationship to rotational behavior

Phenomena consistent with postsynaptic supersensitivity developed in the rat neostriatum following the destruction of dopaminergic afferent neurons. A gradual increase in the density of binding sites for [3H]spiperone occurred over a 2-3 week period. This increase was apparent only after the almost complete loss of dopamine-containing nerve terminals as measured by the depletion of endogenous dopamine. The properties of the receptor labeled by [3H]spiperone were not altered by denervation. Elimination of dopamine-containing nerve endings in the neostriatum was accompanied by the gradual development of an increase in dopamine-sensitive adenylate cyclase activity in homogenates of the caudate ipsilateral to the lesion as compared to the contralateral side. The administration of apomorphine led to pronounced circling behavior. This effect occurred rapidly and was maximal within 3 days following destruction of dopaminergic neurons. The increase in the density of dopamine receptors and in a receptor-mediated function may partially account for the development of enhanced electrophysiological responses to dopamine agonists in the neostriatum. However, the results do not explain the drug-induced rotational behavior which develops after destruction of the dopamine-containing nigrostriatal pathway. This behavioral phenomenon clearly preceded the appearance of receptor alterations in the corpus striatum.

Characterization of NMDA receptor subunit-specific antibodies: distribution of NR2A and NR2B receptor subunits in rat brain and ontogenic profile in the cerebellum

Selective antisera for NMDA receptor subunits NR2A and NR2B have been developed. Each antiserum identifies a single band on an immunoblot at approximately 175 kDa that appears to be the appropriate subunit of the NMDA receptor. Using these antisera the relative densities of the subunits in eight areas of adult rat brain have been determined. The NR2A subunit was found to be at its highest level in hippocampus and cerebral cortex, to be at intermediate levels in striatum, olfactory tubercle, mid-brain, olfactory bulb, and cerebellum, and to be at lowest levels in the pons-medulla. The NR2B subunit was found to be expressed at its highest levels in the olfactory tubercle, hippocampus, olfactory bulb, and cerebral cortex. Intermediate levels were expressed in striatum and mid-brain, and low levels were detected in the pons-medulla. No signal for NR2B was found in the cerebellum. These regional distributions were compared with that for [3H]MK-801 binding sites. It was found that although the distribution of the NR2A subunit corresponds well with radioligand binding, the distribution of the NR2B subunit does not. The ontogenic profiles of NR2A and NR2B subunits in the rat cerebellum were also determined. Just following birth [postnatal day (P) 2] NR2A subunits are undetectable, whereas NR2B subunits are expressed at amounts easily measurable. Beginning at about P12 the levels of NR2A rise rapidly to reach adult levels by P22. At the same time (P12), levels of NR2B protein begin to decline rapidly to reach undetectable levels by 22 days after birth.(ABSTRACT TRUNCATED AT 250 WORDS)

Ontogeny of beta-adrenergic receptors in rat cerebral cortex

The ontogeny of beta-adrenergic receptors in rat cerebral cortex has been studied using [125I]iodohydroxybenzylpindolol as a ligand in an in vitro binding assay. The concentration of beta-adrenergic receptors was very low during the first week after birth. Between days 7 and 14 there was a rapid increase in the density of receptors. Adult levels were reached by the end of the second week. The affinities of 1-isoproterenol and iodohydroxybenzylpindolol for beta-adrenergic receptors did not vary with the age of the animal. Fluoride stimulated adenylate cyclase activity in the cerebral cortex was 40% of the adult level at birth and gradually increased to maximal levels over the next two weeks. On the other hand, catecholamine stimulated cyclic-3',5'-adenosine monophosphate accumulation was barely detectable during the first week after birth, but it increased rapidly to adult levels between days 7 and 14. The results suggest that it is the development of beta-adrenergic receptors that permits the expression of catecholamine sensitive adenylate cyclase activity. Norepinephrine stores in the cerebral cortex developed slowly reaching adult levels approximately two months after birth. There is therefore little correlation between the ontogeny of presynaptic adrenergic nerve terminals and the postsynaptic development of beta-adrenergic receptors.

Multicenter prospective evaluation of laparoscopic antireflux surgery. Preliminary report

BACKGROUND

A prospective study of 116 patients undergoing laparoscopic antireflux surgery was undertaken in four centers in the United Kingdom and the United States.

METHODS

Patients with a hiatal hernia (n = 80) underwent total Rosetti-Hell fundoplication, whereas those without a hiatal defect (n = 36) were treated by a partial fundoplication (Toupet). The follow-up period ranged from 3 to 24 months; median was 13 months.

RESULTS

The median duration of the operations was 2.5 h. Intraoperative complications were encountered in 16 patients (14.0%) and conversion to laparotomy was necessary for esophageal perforation in one. The postoperative recovery of gastrointestinal function was rapid and the median hospital stay from the time of the operation to discharge was 2 days, range 1-10. A good symptomatic result (> 70% reduction of preoperative symptom score) was observed in 106 patients (91%). There were no postoperative deaths but 15 patients (13.0%) developed complications in the immediate postoperative period. At 3 months, complete endoscopic healing of the esophagitis was observed in 65/92 patients (71%) and improvement by at least one grade was seen in 19 patients (21%). Twenty-four-hour pH monitoring, which was abnormal preoperatively in 93% of patients, was normal after surgery in 95%. There were 10 symptomatic failures (persistent reflux symptoms) and 14 patients (12%) developed adverse symptoms related to the procedure (gas-bloat 8, dysphagia 9, gastroparesis 1, explosive diarrhoea 1). Readmission to hospital within 3 months was necessary in 9 patients.

CONCLUSIONS

Laparoscopic antireflux surgery can be performed with a low morbidity. In the short term, 83% of patients were rendered symptom free. These results are similar to those reported after the equivalent open operations.

Regional and ontogenic expression of the NMDA receptor subunit NR2D protein in rat brain using a subunit-specific antibody

A polyclonal antibody for the NMDA receptor subunit NR2D has been developed that identifies an approximately 160-kDa band on immunoblots from NR2D transfected cells and CNS tissues. No cross-reactivity is seen with other NMDA receptor subunits. The NR2D receptor subunit is N-glycosylated in both brain and transfected cells. Transfected cells expressing NR2D are immunofluorescently labeled, whereas untransfected cells or cells transfected with other NMDA receptor subunit cDNAs are not. Similarly, the NR2D subunit is selectively and quantitatively immunoprecipitated, whereas the NR1, NR2A, or NR2B subunit is not. The relative densities of the NR2D subunit in nine areas of postnatal day 7 and adult rat brains have been determined by quantitative immunoblotting. NR2D was expressed at highest levels in the thalamus, midbrain, medulla, and spinal cord, whereas intermediate levels of this subunit were found in the cortex and hippocampus. Low or undetectable levels were seen in the olfactory bulb, striatum, and cerebellum. Following a peak after the first week of birth, NR2D protein levels decreased by about twofold in adulthood in all rat brain regions examined. More complete ontogenic profiles were determined for the diencephalon, telencephalon, and spinal cord where similar ontogenic patterns were seen. NR2D protein is present at high levels at embryonic stages of development, rises to a peak at postnatal day 7, and decreases but remains measurable during late postnatal life. This study demonstrates the generation and characterization of an antibody selective for the NR2D NMDA receptor subunit as well as a determination of the distribution and ontogenic profile of this subunit in rat brain. The results suggest that native NMDA receptors containing the NR2D subunit may have functional roles not only in the young brain but also in adult brain.

beta-adrenergic receptors in rat liver: effects of adrenalectomy

The response of rat liver adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] to catecholamines is enhanced after adrenalectomy. To investigate this phenomenon, we developed an in vitro assay for beta-adrenergic receptors of plasma membranes derived from livers of control and adrenalectomized rats, using [125I]iodohydroxybenzylpindolol (IHYP), a potent beta-adrenergic receptor antagonist. Binding of IHYP reached equilibrium within 30 min and dissociation occurred with a half-time of approximately 60 min. The l-isomers of isoproterenol and propranolol were at least 50 times more potent as inhibitors of IHYP binding than were the corresponding d-isomers. Adrenalectomy did not affect the rates of association or dissociation of IHYP or the dissociation constants of several ligands that are active at beta-adrenergic receptors. The number of binding sites for IHYP was determined in homogenates and in purified membranes of livers from control and adrenalectomized rats. The number of sites increased 3- to 5-fold after adrenalectomy. A similar increase in hormone stimulation of adenylate cyclase was observed. These changes were reversed by the administration of cortisone. The increase in the number of binding sites for IHYP may be a compensatory response to the impairments in gluconeogenesis and glycogenolysis which occur after adrenalectomy.

Subunit composition of N-methyl-D-aspartate receptors in the central nervous system that contain the NR2D subunit

The N-methyl-D-aspartate (NMDA) receptor is assembled using proteins from two gene families, NR1 and NR2. Although a few studies have examined the composition of NMDA receptors containing NR1, NR2A, and NR2B, the composition of native NMDA receptors that incorporate the NR2D subunit is not known. The goal of the current study was to examine the subunit composition of native NMDA receptors that contain the NR2D subunit in the rat central nervous system by immunoprecipitation of assembled NMDA receptors from rat brain tissues using specific antibodies against NR1, NR2A, NR2B, and NR2D subunits. NMDA receptors were solubilized using either nondenaturing (native) conditions, in which the subunits remain assembled in complexes, or denaturing conditions, in which the NMDA subunits are dissociated from one another. Each of the antibodies selectively and quantitatively immunoprecipitated only the corresponding subunit when the subunits were solubilized using denaturing conditions. In contrast, when NMDA receptors were solubilized under nondenaturing conditions, immunoprecipitation followed by quantitative immunoblot analysis of the resulting pellets show that the majority of the NR2D protein is associated with the NR1 subunit. In addition, the NR2D subunit forms a heteromeric assembly with NR1, as well as with NR2A and/or NR2B subunits, reflecting ternary complex formation. Finally, a binary complex composed of only NR1/NR2D subunits was found in the thalamus but not in the midbrain, where the complexes always contained either NR2A or NR2B, demonstrating that in the central nervous system, different subtypes of NR2D-containing NMDA receptors are present that vary in spatial expression, perhaps indicating distinct physiological and behavioral roles.

Evidence that M3 muscarinic receptors in rat parotid gland couple to two second messenger systems

The binding affinities of muscarinic antagonists were compared with their abilities to block carbachol (CCh)-mediated stimulation of Ca2+ mobilization and inhibition of isoproterenol-elicited adenosine 3',5'-cyclic monophosphate (cAMP) accumulation in rat parotid cells. The binding of [3H]quinuclidinyl benzilate (QNB) to membranes was inhibited by antagonists with the following potencies (dissociation constant, nM): atropine (1.1) approximately 4-diphenylacetoxy-N-methylpiperidine methbromide (4-DAMP) (1.6) much greater than pirenzepine (136) greater than 11-[[2-[(diethylamino)methyl-1-piperidinyl]-acetyl]acetyl]-5,11- dihydro-6H-pyrido[2,3-b][1,4]-benzodiazepine-6-one (AF-DX 116) (5,293). AF-DX 116 blocked Ca2+ mobilization and inhibition of cAMP accumulation with low affinities [inhibitory concentration at 50% (IC50) = 3150 and 6,528 nM, respectively], whereas 4-DAMP blocked these responses with considerably higher affinities (IC50 = 4.3 and 11.4 nM, respectively). Schild plots of 4-DAMP and AF-DX 116 antagonism of CCh-stimulated inositol trisphosphate accumulation showed inhibitor constant (Ki) values of 0.85 and 1,585 nM, respectively, whereas Schild plots of 4-DAMP, AF-DX 116, and methoctramine antagonism of CCh-induced inhibition of cAMP accumulation showed Ki values of 1.3, 1,585, and 2,754 nM, respectively. Preincubation of cells with 0.1 mM 3-isobutyl-1-methylxanthine did not prevent the capacity of CCh to inhibit cAMP accumulation. Pertussis toxin blocked the CCh-elicited and Gi-mediated inhibition of cAMP formation. Northern blot analysis showed the presence of mRNA for the M3, but not for the M2, subtype in parotid gland. An immunochemical procedure using m1-m5 specific antibodies was performed in parotid membranes and showed that the m3 receptor accounts for 93% of precipitable receptors. These data suggest that M3 receptors in the rat parotid are coupled to both the stimulation of Ca2+ mobilization and the inhibition of cAMP accumulation.

Ophthalmologic safety of long-term hydroxychloroquine treatment

Ocular toxicity of long-term hydroxychloroquine treatment was assessed by regular ophthalmologic examinations in 99 patients. No patient developed significant loss of vision or visual field constriction to a white test object. Three patients had evidence of toxicity, but the medication had to be permanently discontinued in only one who subsequently had regression of all abnormalities except visual field constriction to a red test object. Neither duration of treatment nor the diagnosis of systemic lupus erythematosus predisposed patients to toxicity.

Hippocampal dependent learning ability correlates with N-methyl-D-aspartate (NMDA) receptor levels in CA3 neurons of young and aged rats

Hippocampal N-methyl-D-Aspartate (NMDA) receptors mediate mechanisms of cellular plasticity critical for spatial learning in rats. The present study examined the relationship between spatial learning and NMDA receptor expression in discrete neuronal populations, as well as the degree to which putative age-related changes in NMDA receptors are coupled to the effects of normal aging on spatial learning. Young and aged Long-Evans rats were tested in a Morris water maze task that depends on the integrity of the hippocampus. Levels of NR1, the obligatory subunit for a functional NMDA receptor, were subsequently quantified both biochemically by Western blot in whole homogenized hippocampus, and immunocytochemically by using a high-resolution confocal laser scanning microscopy method. The latter approach allowed comprehensive, regional analysis of discrete elements of excitatory hippocampal circuitry. Neither method revealed global changes, nor were there region-specific differences in hippocampal NR1 levels between young and aged animals. However, across all subjects, individual differences in spatial learning ability correlated with NR1 immunofluorescence levels selectively in CA3 neurons of the hippocampus. Parallel confocal microscopic analysis of the GluR2 subunit of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole proprionic acid (AMPA) receptor failed to reveal reliable differences as a function of age or spatial learning ability. This analysis linking age, performance, and NR1 levels demonstrates that although dendritic NR1 is generally preserved in the aged rat hippocampus, levels of this receptor subunit in selective elements of hippocampal circuitry are linked to spatial learning. These findings suggest that NMDA receptor abundance in CA3 bears a critical relationship to learning mediated by the hippocampus throughout the life span.

Changes in NMDA receptor subunit expression in response to contusive spinal cord injury

Differential assembly of N-methyl-D-aspartate (NMDA) receptor subunits determines their functional characteristics. Using in situ hybridization, we found a selective increase of the subunits NR1 and NR2A mRNA at 24 h in ventral motor neurons (VMN) caudal to a standardized spinal cord contusion injury (SCI). Other neuronal cell populations and VMN rostral to the injury site appeared unaffected. Significant up-regulation of NR2A mRNA also was seen 1 month after SCI in thoracic and lumbar VMN. The selective effects on VMN caudal to the injury site suggest that the loss of descending innervation leads to increased NMDA receptor subunit expression in these cells after SCI, which may alter their responses to glutamate. In contrast, protein levels determined by western blot analysis show decreased levels of NR2A 1 month after SCI in whole thoracic segments of spinal cord that included the injury sites. No effects of injury were seen on subunit levels in cervical or lumbar segments. Taken together with our previous study showing alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptor subunit down-regulation after injury, our data suggest that glutamate receptor composition is significantly altered after SCI. These changes need to be taken into account to properly understand the function of, and potential pharmacotherapy for, the chronically injured spinal cord.

Reduction of AMPA-selective glutamate receptor subunits in the entorhinal cortex of patients with Alzheimer's disease pathology: a biochemical study

Using biochemical techniques we determined concentrations of the AMPA-selective glutamate receptor subunits GluR1 and GluR2/3 in the entorhinal cortex of patients with Alzheimer's disease pathology and age-matched controls. Tangle density was also determined in anatomically matched samples and correlated with GluR1 and GluR2/3 receptor concentration. In Alzheimer's disease brain, Western blot analysis revealed average reductions of 43% and 38% for GluR1 and GluR2/3, respectively. Based on previous immunohistochemical studies, we infer that the majority of protein reduction was due to decreases in GluR1 and GluR2/3 immunolabeled elements in the more superficial layers of the entorhinal cortex (layers II and III). These layers of the entorhinal cortex contained numerous neurofibrillary tangles in Alzheimer's disease, but neither GluR1 nor GluR2/3 protein concentration correlated significantly with tangle density. We hypothesize that the decrease in specific glutamate receptor subunits, particularly GluR2/3, may contribute to the vulnerability of neurons in the entorhinal cortex via mechanisms involving calcium conductance through AMPA-selective channels.

Selective increases in the density of cerebellar beta-1-adrenergic receptors

Destruction of noradrenergic neurons by 6-hydroxydopamine or chronic blockade of beta-adrenergic receptors with propranolol increased the density of beta 1-adrenergic receptors two-fold in rat cerebellum but had no effect on the density of beta 2-adrenergic receptors. The results suggest that even through beta 1 receptors comprise only 5-10% of the total number of Beta-adrenergic receptors in the cerebellum they are the receptors specifically innervated by noradrenergic neurons and they may thus be the physiologically important receptors.