The relative abilities of MPTP and MPP+ to compete with [3H]dopamine for the rat and marmoset striatal dopamine uptake site.
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1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
Biomedical subjects
N M Barnes
Publications and source records attributed to N M Barnes.
Angiotensin II inhibits acetylcholine release from human temporal cortex: implications for cognition.
Angiotensin II was shown to inhibit potassium-stimulated release of [3H]acetylcholine from slices of fresh human temporal cortex, obtained at surgery, and subsequently loaded with [3H]choline for the biochemical analyses. The inhibitory effect of angiotensin II was antagonised by the specific angiotensin II receptor antagonist [1-sarcosine, 8-threonine]-angiotensin II. High affinity binding sites were identified in the human temporal cortex using [125I]angiotensin II, and may provide the functional site of action of angiotensin II to modify [3H]acetylcholine release.
Acetylcholine↗
Topographical distribution of 5-HT3 receptor recognition sites in the ferret brain stem.
The distribution of [3H]zacopride (1.0 nM) to putative 5-HT3 receptor recognition sites in the ferret hindbrain was assessed using autoradiography. Specific binding (defined by the inclusion of granisetron, 1.0 microM) was heterogeneously distributed with highest density within the dorsal vagal complex (area postrema, nucleus tractus solitarius and dorsal motor nucleus of the vagus nerve). Lower densities were detected in the spinal trigeminal nerve complex whilst no other significant specific binding was detected ventral to the dorsal vagal complex. The location of 5-HT3 receptor recognition sites within the dorsal vagal complex may provide sites of action for zacopride and other 5-HT3 receptor antagonists to inhibit the emesis induced by cancer chemotherapeutic agents and x-radiation.
Animals↗
The actions of (-)N-n-propylnorapomorphine and selective dopamine D1 and D2 receptor agonists to modify the release of [3H]dopamine from the rat nucleus accumbens.
The ability of (-)N-n-propylnorapomorphine and selective D1 and D2 dopamine receptor agonists and antagonists to modify the release of [3H]dopamine, induced by potassium from the nucleus accumbens, was studied using an in vitro superfusion technique. (-)N-n-Propylnorapomorphine, in picomolar concentrations, inhibited the release of [3H]dopamine, the inhibition being antagonised by fluphenazine and the selective D2 receptor antagonist sulpiride; the selective D1 receptor antagonist SCH 23390 was ineffective. The selective D1 receptor agonist SKF 38393 and the selective D2 agonist quinpirole, both inhibited the potassium-induced release of [3H]dopamine; no synergistic effect was observed to a combined treatment with SKF 38393 and quinpirole. The effects of SKF 38393 and quinpirole were selectively antagonised by SCH 23390 and sulpiride, respectively, although both antagonists failed to modify the release of [3H]dopamine when administered alone. Receptor antagonists for other transmitter sites, e.g. noradrenaline, 5-hydroxytryptamine and acetylcholine, failed to modify potassium-induced release of [3H]dopamine, when administered alone or to prevent the inhibition of the release caused by (-)N-n-propylnorapomorphine. It is concluded that the action of dopamine agonists on both dopamine D1 and D2 receptors in the nucleus accumbens can reduce the release of [3H]dopamine in the in vitro system. Comparable actions in vivo may contribute to the ability of dopamine agonists to moderate locomotor responding.
2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
Characterisation and autoradiographic localisation of 5-HT3 receptor recognition sites identified with [3H]-(S)-zacopride in the forebrain of the rat.
The pharmacological characterisation and topographical distribution of [3H]-(S)-zacopride recognition sites in the forebrain of the rat was studied using homogenate and autoradiographic radioligand binding techniques. [3H]-(S)-Zacopride labelled a single, saturable, specific binding site (defined by 10.0 microM granisetron) in homogenates prepared from the entorhinal cortex of the rat (pKD = 9.51 +/- 0.08; Bmax = 104 +/- 7 fmol mg-1 protein; mean +/- SEM, n = 8). Pharmacological characterisation of the recognition site, within the entorhinal cortex, suggested that [3H]-(S)-zacopride selectively labelled the recognition site of the 5-HT3 receptor. Specific binding of [3H]-(S)-zacopride (defined by 1.0 microM granisetron) was differentially distributed throughout the forebrain of the rat; highest densities were located within sub-nuclei of the amygdala (cortical amygdaloid nucleus, amygdalohippocampal area, posterior medial cortical amygdaloid nucleus, posterior lateral amygdaloid nucleus), cortical areas (primary olfactory cortex, entorhinal cortex) and hippocampus. Non-specific binding was distributed homogeneously, although lower in myelinated structures. It is concluded that [3H]-(S)-zacopride selectively labels 5-HT3 receptor recognition sites within the forebrain of the rat; the topographical distribution of these sites, within the limbic nuclei, is consistent with the behavioural actions in animal models of the selective 5-HT3 receptor antagonists.
Animals↗
The differential activities of R (+)- and S(-)-zacopride as 5-HT3 receptor antagonists.
R(+)- and S(-)-zacopride were assessed as potential 5-HT3 receptor antagonists in behavioural and biochemical tests. The S(-)isomer was more potent than the R(+)isomer to antagonise the hyperactivity induced by the injection of amphetamine or the infusion of dopamine into the nucleus accumbens in the rat. In contrast, the R(+)isomer was more potent to reduce the aversive behaviour of mice to a brightly illuminated environment and in a marmoset human threat test, to facilitate social interaction in rats, to increase performance in a mouse habituation test and prevent a scopolamine-induced impairment, and to antagonise the inhibitory effect of 2-methyl-5-hydroxytryptamine to reduce [3H]acetylcholine release in slices of the rat entorhinal cortex. In binding assays, [3H]S(-)-zacopride and [3H]R(+)-zacopride labelled homogenous populations of high-affinity binding sites in the rat entorhinal cortex, R(+)-zacopride compete for a further 10 to 20% of the binding of [3H]R(+)/S(-)-zacopride or [3H]R(+)-zacopride in excess of that competed for by (S)(-)-zacopride. It is concluded that both isomers of zacopride have potent but different pharmacological activities, with the possibility of different recognition sites to mediate their effects.
Animals↗
Ketotifen and its analogues reduce aversive responding in the rodent.
The abilities of ketotifen and other 4-piperidylidene derivatives (HF200-184, HE36-953, SDZ209-321 and SDZ206-703) to inhibit aversive responding were compared in the mouse light/dark test box and in the rat social interaction test. Ketotifen and HF200-184 reduced aversive responding of the mouse to the brightly illuminated area of the test box and facilitated rat social interaction; HF200-184 was approximately 100 times more potent than ketotifen. The chronic administration and withdrawal from treatment with diazepam, ethanol, nicotine and cocaine in the mouse was associated with increased behavioural suppression which was prevented by the administration of ketotifen and HF200-184 during the period of withdrawal. HE36-953 also prevented the behavioural consequences of withdrawal from diazepam and cocaine. The relative potencies of ketotifen and its analogues to inhibit aversive responding did not correlate with their affinities for the 5-HT3 recognition site. It is concluded that compounds within the 4-piperidylidene series can reduce behavioural suppression in rodent models of anxiety and attenuate the behavioural consequences of withdrawing from treatment with drugs of abuse.
Animals↗
Neurochemical consequences following injection of the substance P analogue, DiMe-C7, into the rat ventral tegmental area.
The effect on forebrain catecholamine- and indoleamine-related neurochemical levels was investigated following stimulation of the rat ventral tegmental area with the substance P analogue, DiMe-C7. DiMe-C7 (6.0 micrograms) induced a marked hyperactivity in rats with maximal response between 15 and 30 min following the injection. Fifteen min following the DiMe-C7 injection levels of dopamine and/or its metabolites (3,4-dihydroxyphenylacetic acid, homovanillic acid) were significantly increased in the nucleus accumbens, amygdala, entorhinal cortex and striatum relative to vehicle-injected animals. Although the increase in dopamine metabolism in the nucleus accumbens is consistent with the behavioural hyperactivity, it is concluded that other forebrain nuclei may also be involved in the mediation of the hyperactivity response.
Animals↗
Consensus meeting agrees distribution of 5-HT3 receptors in mammalian hindbrain.
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Animals↗
The ACE inhibitor [3H]SQ29,852 identifies a high affinity recognition site located in the human temporal cortex.
The angiotensin converting enzyme (ACE) inhibitor [3H]SQ29,852 identified a single high affinity recognition site (defined by 10.0 microM captopril) in the human temporal cortex (pKD 8.62 +/- 0.03; Bmax 248 +/- 24 fmol mg-1 protein, mean +/- S.E.M., n = 4). ACE inhibitors and thiorphan competed to a similar level for the [3H]SQ29,852 binding site in the human temporal cortex with a rank order of affinity (pKi values mean +/- S.E.M., n = 3), lisinopril (9.49 +/- 0.02), captopril (9.16 +/- 0.08), SQ29,852 (8.58 +/- 0.04), epicaptopril (7.09 +/- 0.08), fosinopril (7.08 +/- 0.05) and thiorphan (6.40 +/- 0.04). Since this rank order of affinity is similar to the affinity of these compounds to inhibit brain ACE activity it is concluded that [3H]SQ29,852 selectively labels the inhibitor recognition site of ACE in the human temporal cortex.
Adult↗
Cisplatin induced emesis: preliminary results indicative of changes in plasma levels of 5-hydroxytryptamine.
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Adult↗
Anxiolytic-like action of DuP753, a non-peptide angiotensin II receptor antagonist.
The potential of DuP753, an angiotensin II receptor antagonist, to inhibit the suppressed behaviour of mice in a light/dark aversion test was investigated. The aversive response to the light compartment of the apparatus was reduced (increase in latency to move from the light to the dark compartment and decreases in rears, line crossings and percentage of time spent in the dark compartment) following treatment with DuP753 (0.1-1000 micrograms kg-1 p.o., 45 min before the test). These results further implicate the modulation of mental function by angiotensin II.
Angiotensin II↗
Angiotensin II inhibits cortical cholinergic function: implications for cognition.
In the present studies we have shown that angiotensin II (AT II), in a concentration-dependent manner in rat tissue (10(-9)-10(-5) M) or at a single concentration in human tissue (10(-6) M), can inhibit potassium-stimulated release of [3H]acetylcholine ( [3H]Ach) from slices of rat entorhinal cortex and human temporal cortex preloaded with [3H]choline for the biochemical analyses. The inhibitory effects of AT II (10(-6) M) were antagonised by the specific AT II receptor antagonist [1-sarcosine, 8-threonine]AT II in a concentration-dependent manner in rat tissue (10(-11)-10(-8) M) and at the single concentration employed in the human studies (10(-7) M). Also demonstrated were other components of the angiotensin system in the human temporal cortex; ACE activity was present (1.03 nmol min-1 mg-1 protein), as were AT II recognition sites (Bmax = 8.6 fmol mg-1 protein). It is hypothesised that the potential cognitive enhancing properties of ACE inhibitors may reflect their action to prevent the formation of AT II and so remove an inhibitory modulator of cholinergic function.
Acetylcholine↗
Angiotensin II inhibits the release of [3H]acetylcholine from rat entorhinal cortex in vitro.
The effects of angiotensin I and II on basal potassium-induced release of [3H]acetylcholine were investigated in slices of rat entorhinal cortex. Potassium (10-25 mM) produced a concentration-dependent increase in the release of [3H]acetylcholine in the presence of extracellular calcium. Angiotensin II (10(-9)-10(-5) M) (but not angiotensin I) reduced the potassium-induced release of [3H]acetylcholine in a concentration-related manner to 60% of control levels, but did not effect basal tritium release. The effect of angiotensin II was antagonised by [1-sarcosine, 8-threonine] angiotensin II, an angiotensin II receptor antagonist, but not by agents acting on alpha- and beta-adrenoceptors, muscarinic, nicotinic, histamine or 5-hydroxytryptamine receptors nor by the angiotensin converting enzyme (ACE) inhibitor SQ 29852. The results indicate that angiotensin II acting via an angiotensin II receptor can inhibit the release of [3H]acetylcholine in slices of the rat entorhinal cortex. It is hypothesised that the ability of ACE inhibitors to facilitate cognitive processes may be related to a reduced availability of angiotensin II.
Acetylcholine↗
5-HT3 receptors mediate inhibition of acetylcholine release in cortical tissue.
The release of cerebral acetylcholine from terminals in the cerebral cortex has been shown to be regulated by 5-hydroxytryptamine (5-HT) but it is not known which subtype of the 5-HT receptor is involved. 5-HT receptor agonists increase acetylcholine levels in vivo, indicating a reduced turnover, and reduce release of acetylcholine from striatal slices in vitro. Depleting 5-HT by inhibiting synthesis or by destroying the neurons containing 5-HT potentiates acetylcholine release, and increases acetylcholine turnover in the cerebral cortex and hippocampus. Selective antagonists for the 5-HT3 receptor subtypes which seem to have effects on mood and activity may exert their effect through the regulation of acetylcholine release in the cortex and limbic system. Radioligand binding studies show a high density of 5-HT3 receptors in the cholinergic-rich entorhinal cortex and we provide evidence that a reduction in cortical cholinergic function can be effected in vitro by 5-HT3 receptors.
Acetylcholine↗
Identification and characterisation of 5-hydroxytryptamine 3 recognition sites in human brain tissue.
[3H]Zacopride displayed regional saturable specific binding to homogenates of human brain tissues, as defined by the inclusion of BRL43694 [endo-N-(9-methyl-9-azabicyclo[3.3.1]non-3-yl)-1-methylindazole-3- carboxamide] in the incubation media. Scatchard analysis of the saturation data obtained from amygdaloid and hippocampal tissues identified the binding as being of high affinity and to a homogeneous population of binding sites (KD = 2.64 +/- 0.75 and 2.93 +/- 0.41 nmol/L and Bmax = 55 +/- 7 and 44 +/- 9 fmol/mg of protein in the amygdala and hippocampus, respectively). 5-Hydroxytryptamine 3 (5-HT3) receptor agonists and antagonists competed for the [3H]zacopride binding site, competing with up to 40% of total binding with a similar rank order of affinity in both tissues; agents acting on various other neurotransmitter receptors failed to inhibit binding. Kinetic data revealed a fast association that was fully reversible (k+1 = 6.61 X 10(5) and 7.65 X 10(5)/mol/L/s and k-1 = 3.68 X 10(-3) and 3.45 X 10(-3)/s in the amygdala and hippocampus, respectively). It is concluded that [3H]zacopride selectively labels with high affinity 5-HT3 recognition sites in human amygdala and hippocampus and, if these binding domains represent 5-HT3 receptors, may provide the opportunity for 5-HT3 receptor antagonists to modify 5-HT function in the human brain.
Adult↗
Reserpine, para-chlorophenylalanine and fenfluramine antagonise cisplatin-induced emesis in the ferret.
The involvement of 5-hydroxytryptamine (5-HT) with cisplatin-induced emesis in the ferret was investigated using reserpine, para-chlorophenylalanine and fenfluramine. Pretreatment with reserpine (5 mg/kg, 24 hr), fenfluramine (5 mg/kg, 4 days) or para-chlorophenylalanine (100 or 400 mg/kg, 4 days) antagonised cisplatin-induced emesis. All treatments reduced the levels of 5-HT in the area postrema and at other cerebral sites, but whilst this action was relatively selective for small doses of para-chlorophenylalanine [only modest effects on noradrenaline (NA) and no change in the content of dopamine (DA) in the area postrema], other treatments reduced levels of dopamine and noradrenaline. Data are discussed in terms of an involvement of 5-HT/catecholamines in the area postrema with the mediation of emesis induced by cisplatin.
Animals↗
[3H]zacopride: ligand for the identification of 5-HT3 recognition sites.
[3H]Zacopride displayed saturable binding to homogenates of the rat entorhinal cortex as measured by the inclusion of the 5-HT3 receptor antagonist BRL43694 in the incubation media. Scatchard analysis indicated a single high affinity binding site (KD 0.76 +/- 0.08 nM, Bmax 77.5 +/- 6.5 fmol (mg protein)-1) with a Hill slope close to unity. Other 5-HT3 receptor antagonists (zacopride, ICS 205-930, GR38032F, GR65630, metoclopramide and cocaine) also competed for the binding site displacing 60% of the total [3H]zacopride binding. 5-HT and 2-methyl-5-HT also were competitive antagonists for [3H]zacopride binding whereas 5-HT1/5-HT2 agonists and antagonists, and agents acting on other neurotransmitter receptors had Ki values greater than 10(-5) M. It is concluded that [3H]zacopride may prove a useful ligand for the study of 5-HT3 recognition sites.
Animals↗