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Biomedical subjects

N H Neff

Publications and source records attributed to N H Neff.

At least 109 records · Page 6Linked to original sources
PubMed1984

The muscarinic receptor adenylate cyclase complex of rat striatum: desensitization following chronic inhibition of acetylcholinesterase activity.

Chronic inhibition of acetylcholinesterase activity by treatment with diisopropylfluorophosphate (DFP) decreased the capacity of acetylcholine (ACh) acting at a muscarinic receptor to inhibit basal adenylate cyclase activity in homogenates from rat striatum. There was also a loss of the capacity of ACh to inhibit the activation of adenylate cyclase by dopamine. The desensitization of the muscarinic receptor adenylate cyclase complex was associated with a marked attenuation of the capacity of ACh to stimulate a high-affinity GTPase activity present in striatal membranes. The EC50 value of ACh for inhibiting adenylate cyclase and for stimulating GTPase activity increased following treatment with DFP, while the Hill coefficient for both responses was unaltered.

Acetylcholinesterase↗
PubMed1984

Measurement of acetylcholine turnover rate in brain: an adjunct to a simple HPLC method for choline and acetylcholine.

An existing method for measuring acetylcholine (ACh) and choline (Ch) is shown to be useful for measuring the turnover rate of ACh in mouse brain. Methyl-[3H]Ch is injected into mice. They are killed at different times by microwave irradiation and Ch and ACh extracted and separated by reverse-phase HPLC. Ch and ACh are converted to hydrogen peroxide by a post-column enzyme reaction. Hydrogen peroxide, which is directly related to the tissue content of Ch or ACh, is determined electrochemically. The fractions that correspond to the detector response for Ch and ACh are collected for the measurement of radioactivity. In this way specific radioactivities of endogenous Ch and ACh are estimated in the same sample. We used the specific radioactivity values determined by this procedure to estimate the turnover of ACh for striatum, cerebral cortex, and hippocampus of the mouse.

Acetylcholine↗
PubMed1984

gamma-aminobutyric acid B receptors are negatively coupled to adenylate cyclase in brain, and in the cerebellum these receptors may be associated with granule cells.

Baclofen and gamma-aminobutyric acid (GABA) are shown to inhibit basal adenylate cyclase activity in brain of rat. The response is mediated through the GABAB receptor, and the rank order of potency for agonists is (-)-baclofen (EC50 = 4 microM) greater than GABA (EC50 = 17 microM) greater than muscimol greater than (+)-baclofen. GABAA agonists are not effective inhibitors of cyclase activity. The response is bicuculline-insensitive, and diazepam does not modify the GABA or (-)-baclofen inhibition of adenylate cyclase. Studies with neurologically mutant mice correlated a loss in GABAB receptor-mediated inhibition of cyclase with a loss in cerebellar granule cells. Thus, the GABAB receptor is negatively coupled to adenylate cyclase in various brain areas, and, in the cerebellum, data suggest a granule cell localization of this activity.

Adenylyl Cyclases↗
PubMed1984

An endogenous ligand modulates dopamine-containing neurons of retina via alpha-2 adrenoceptors.

Environmental light induces the activation of dopamine (DA)-containing neurons of rat retina and as a consequence DA turnover increases. The state of DA metabolism is directly related to the content of 3,4-dihydroxyphenylacetic acid in retina. Alpha-2 adrenoceptors are present in the retina and their activation diminishes the retinal content of 3,4-dihydroxyphenylacetic acid of rats placed in the light, but not of rats placed in the dark. When alpha-2 antagonists are administered, they increase retinal DA metabolism of rats in the light as well as of rats in the dark. These results are consistent with the notion that an endogenous agonist fully occupies the alpha-2 receptor in the dark and only partially occupies the receptors in the light. The most likely endogenous agonist for these receptors is epinephrine released from a newly identified population of epinephrine-containing amacrine cells.

Animals↗
PubMed1983

Differential location of adenosine A1 and A2 receptors in striatum.

Stimulation of either adenosine A1 or A2 receptors results in a decrease or an increase in the adenylate cyclase activity, respectively. With various concentrations of the adenosine agonist N6-phenylisopropyladenosine, both responses on cyclase are observed in a crude membrane preparation from rat striatum. The A2 receptors appeared to be associated primarily with intrinsic striatal neurons, as a kainic acid injection into the striatum resulted in about a 70% loss of receptor responsiveness to cyclase. The A1 receptors were more diffuse, being associated with intrinsic neurons and with cortical-striatal nerve terminals. From studies with 6-hydroxydopamine, we were unable to associate either receptor with dopaminergic nerve terminals within the striatum.

Animals↗
PubMed1983

Location of adenosine release and adenosine A2 receptors to rat striatal neurons.

Three types of striatal lesions were performed to determine the site of adenosine synthesis and release and the location of adenosine A2 receptors: decortication; injection of 6-hydroxydopamine (6-OHDA) into the median forebrain bundle; and injection of kainic acid into the striatum. The parameters measured in the striatum were content of adenosine, activation of adenylate cyclase by N6-(L-phenylisopropyl) adenosine (PIA) and release of endogenous adenosine from a perfused slice. Decortication and 6-OHDA had only minimal affects on the parameters measured. In contrast, kainic acid injection into the striatum decreased the content of adenosine, the release of adenosine from a slice preparation and diminished the ability of PIA to activate adenylate cyclase. We postulate that neurons which synthesize and release adenosine, originate in the striatum. The adenosine receptors appear to be of the adenosine A2 type and they may be located on adjacent neurons or on the adenosine releasing neurons themselves.

Adenosine↗
PubMed1983

Minireview. Evidence that dopamine is a neurotransmitter in peripheral tissues.

In the CNS, dopamine (DA) is a recognized neurotransmitter as well as a precursor for norepinephrine (NE) and epinephrine (EPI). In contrast to the CNS, DA has been assumed to be only a precursor in peripheral tissues. There is now, however, considerable evidence to support the hypothesis that it may function as a neurotransmitter and/or cotransmitter in peripheral tissues in addition to being a precursor. In this minireview we summarize evidence supporting the view that DA plays a role of its own in peripheral neurotransmission.

Animals↗
PubMed1983

Activation of dopamine-containing amacrine cells of retina: light-induced increase of acidic dopamine metabolites.

The acidic metabolites of dopamine, homovanillic acid (HVA) and 3,4-dihydroxyphenylacetic acid (DOPAC), are present in rat retina. DOPAC is the most abundant metabolite. Both metabolites increase in parallel when rats are taken from a dark to a lighted environment. Haloperidol treatment also increases the metabolites in both dark and light while apomorphine decreases both metabolites in dark and light and partially antagonizes the increase induced by haloperidol.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1983

Inhibition of dopamine-activated adenylate cyclase and dopamine binding by opiate receptors in rat striatum.

Low-affinity (micromolar) 3H-dopamine binding was measured under conditions which permitted dopamine activation and opiate inhibition of adenylate cyclase in rat striatal membranes. Opiate drugs and peptides inhibited the dopamine binding in the presence of both GTP and Gpp(NH)p. Opiate inhibition of adenylate cyclase was, however, observed only in the presence of GTP. It is suggested that the dopamine D1 receptor in striatum may be modulated by the opiate delta receptor through a shared guanine nucleotide binding subunit.

Adenylyl Cyclase Inhibitors↗
PubMed1983

Muscarinic receptors modulate dopamine-activated adenylate cyclase of rat striatum.

We investigated the effect of acetylcholine (ACh) on the activation of adenylate cyclase by dopamine (DA) in a lysed synaptosomal preparation from rat striatum. ACh reduced both basal and the DA-activated adenylate cyclase with an apparent IC50 of approximately 1 microM. From a kinetic analysis it appeared that ACh reduced the Vmax for activation by DA but not the activation constant for DA. For most preparations the Vmax was reduced by 30-40%. The presence of atropine did not affect the activation of the enzyme by DA but it blocked the inhibition by ACh. Following 6-hydroxydopamine lesion of the nigrostriatal pathway, the enzyme became supersensitive to activation by DA and also more sensitive to inhibition by ACh. Inhibition of adenylate cyclase by ACh appeared to be rather specific for activation by DA, as ACh had no effect on activation of adenylate cyclase by the adenosine analogue N6-(L-2-phenylisopropyl)adenosine. These results indicate that some striatal muscarinic and dopaminergic receptors are probably coupled to the same adenylate cyclase domain. Moreover, they suggest a biochemical model for the dynamic balance of cholinergic and dopaminergic neurons that innervate the striatum.

Acetylcholine↗
PubMed1983

Epinephrine: a potential neurotransmitter in retina.

Dopamine (DA), norepinephrine (NE), and epinephrine (EPI) are present in rat retina. DA is the major catecholamine, whereas NE and EPI represent approximately 5% of the DA content. DA is contained in a subpopulation of amacrine cells and has been the subject of numerous studies. We investigated the origin and properties of NE and EPI in retina. Following superior cervical ganglionectomy, there was a decrease in NE content, but no decrease in EPI or phenylethanolamine-N-methyltransferase (PNMT) activity. PNMT in retina has many of the substrate-specificity and inhibitor-sensitivity characteristics of other tissues. Enzyme activity is enhanced in newborn rats by treatment with dexamethasone. Exposure to a lighted environment increases retinal EPI in normal and superior cervical ganglionectomized rats. EPI content increased for more than 2 h in a lighted environment. We conclude that most of the NE is contained within the sympathetic neurons that innervate the eye from the superior cervical ganglion, whereas EPI is contained in retinal elements that are responsive to photic stimulation.

Animals↗
PubMed1983

Adenosine A1 receptors are associated with cerebellar granule cells.

The cerebellum of mouse appears to have only the adenosine A1 receptor, which decreases adenylate cyclase activity, and not the A2 receptor, which increases adenylate cyclase activity. The adenosine analog N6-(L-phenylisopropyl)adenosine (PIA), stimulates the A1 receptor in a membrane preparation and decreases basal adenylate cyclase activity by 40%. The EC50 for PIA is approximately 50 nM. To associate the A1 receptor with a cerebellar cell type, three different neurological mutant mouse strains were studied: staggerer (Purkinje and granule cell defect), nervous (Purkinje cell defect), and weaver (granule cell defect). PIA was unable to effect a maximal decrease in adenylate cyclase activity of membranes prepared from cerebella of the staggerer and weaver mice in comparison with the respective littermate control mice. In contrast, membranes from nervous mice and their littermates showed similar PIA dose-response curves. Moreover, the diminished PIA response observed in the weaver cerebellum, when compared with the control littermate, was not detected in the striatum. This suggests no overall brain defect in the adenosine A1 receptors coupled to adenylate cyclase of the weaver mouse. We conclude that a loss of granule cells coincides with an attenuated response to PIA, implying that the A1 receptors are associated with the granule cells of the cerebellum.

1-Methyl-3-isobutylxanthine↗
PubMed1983

Acetylcholine and choline in neuronal tissue measured by HPLC with electrochemical detection.

A simple, rapid method is presented for the determination of acetylcholine (ACh) and choline (Ch) in neuronal tissue using HPLC with electrochemical detection. The method is based on the separation of ACh and Ch by reverse-phase HPLC and mixing the effluent as it emerges from the column with acetylcholinesterase and Ch oxidase, which converts endogenous Ch and Ch produced by the hydrolysis of ACh to betaine and hydrogen peroxide. Production of hydrogen peroxide is continuously monitored electrochemically. The sensitivity of the procedure is 1 pmol for Ch and 2 pmol for ACh. Specificity of the method is based on HPLC, two specific enzymatic reactions, and the detection of hydrogen peroxide.

Acetylcholine↗
PubMed1983

Dopamine-containing small intensely fluorescent cells and sympathetic ganglion function.

This article reviews some of the neuropharmacology of the dopamine (DA)-containing small intensely fluorescent cells of sympathetic ganglia. The major metabolite of DA found in the ganglia is 3,4-dihydroxyphenylacetic acid (DOPAC). DOPAC content appears to be a direct reflection of DA synthesis. DA synthesis can be enhanced by muscarinic agonists and diminished by muscarinic antagonists. Neuroleptic drugs stimulate DA synthesis in the ganglion, which suggests that a local negative neuronal feedback loop might operate within the ganglion. There may be a correlation between deficient DA synthesis in spontaneous hypertensive rats and the development of hypertension. It is possible that some of the peripheral side effects of drugs that act on dopaminergic neurons in the brain might originate from the drugs' action on peripheral dopaminergic neuronal systems such as the sympathetic ganglion.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1983

Adenylate cyclase activity of synaptic membranes from rat striatum. Inhibition by muscarinic receptor agonists.

Acetylcholine inhibits, by 30-40%, the basal adenylate cyclase activity of purified synaptic plasma membranes prepared from rat striatum (EC50 = 3 microM). Cholinergic receptor agonists inhibit this cyclase activity with the following rank order of potency: oxtremorine greater than acetylcholine greater than arecoline greater than methacholine greater than or equal to muscarine greater than or equal to carbachol greater than bethanechol. Nicotine fails to inhibit the cyclase, and d-tubocurarine fails to inhibit the action of cholinergic drugs. In contrast, atropine and scopolamine antagonize the effect of acetylcholine. The enzyme inhibition elicited by acetylcholine requires the presence of GTP, and disappears after intrastriatal injection of kainic acid. From these results, we infer that striatal adenylate cyclase can be modulated by muscarinic receptors.

1-Methyl-3-isobutylxanthine↗
PubMed1982

Evidence for the presence of dopaminergic receptors in vas deferens.

Specific dopaminergic recognition sites were identified in membranes prepared from rat vas deferens with the ligand (3H)-haloperidol. Specific binding, defined as the difference of (3H)-haloperidol binding in the presence or absence of an excess of unlabelled haloperidol (100 microM), was saturable and a Scatchard analysis of the data revealed a Kd = 21 nM and a Bmax = 74 fmol/mg prot. (+)-Butaclamol was several times more active in displacing (3H)-haloperidol from binding sites than its pharmacologically inactive enantiomer, (-)-butaclamol, demonstrating stereospecificity of binding. Dopamine displaced 50% of (3H)-haloperidol binding at a concentration of approximately 10 microM, while norepinephrine, epinephrine and serotonin were practically ineffective at this concentration. Our results support the notion that there are dopaminergic receptors in the rat vas deferens. We speculate that some of the known effects of dopamine and dopaminergic drugs on sexual behavior may be mediated peripherally and not solely via the CNS as is usually assumed.

Animals↗