Acute intrathecal administration of quipazine elicits air-stepping behavior.

Serotonin plays a pivotal role in the initiation and modulation of locomotor behavior in the intact animal, as well as following spinal cord injury. Quipazine, a serotonin 2 receptor agonist, has been used successfully to initiate and restore motor behavior in rodents. Although evidence suggests that the effects of quipazine are spinally mediated, it is unclear whether intrathecal (IT) quipazine administration alone is enough to activate locomotor-like activity or whether additional stimulation is needed. Thus, the current study examined the effects of IT administration of quipazine in postnatal day 1 rats in two separate experiments. In experiment 1, quipazine (0.1, 0.3, or 1.0 mg/kg) was dissolved in saline and administered via IT injection to the thoracolumbar cord. There was no significant effect of drug on hindlimb alternating stepping. In experiment 2, quipazine (0.3 or 1.0 mg/kg) was dissolved in a polysorbate 80-saline solution (Tween 80) and administered via IT injection. Polysorbate 80 was used to disrupt the blood-brain barrier to facilitate absorption of quipazine. The injection was followed by tail pinch 5 minutes post-injection. A significant increase in the percentage of hindlimb alternating steps was found in subjects treated with 0.3 mg/kg quipazine, suggesting that IT quipazine when combined with sensory stimulation to the spinal cord, facilitates locomotor-like behavior. These findings indicate that dissolving the drug in polysorbate 80 rather than saline may heighten the effects of IT quipazine. Collectively, this study provides clarification on the role of quipazine in evoking spinally-mediated locomotor behavior.

Synthesis and biological evaluation of one novel technetium-99m-labeled nitroquipazine derivative as an imaging agent for serotonin transporter.

Imaging of serotonin transporter (SERT) by positron emission tomography (PET) or single-photon emission-computed tomography (SPECT) in humans would provide useful information in diagnosis and therapy of several neurodegenerative and neuropsychiatric disorders. 6-Nitroquipazine is a highly potent and selective inhibitor of the SERT. For the development of new (99m)Tc-labeled 6-nitroquipazine derivatives as SERT imaging agents, novel [N-[2-((3-(4-(6-nitroquinolin-2-yl)piperazin-1-yl)propyl)(2-mercaptoethyl)amino]-acetyl-2-aminoethanethiolato] [(99m)Tc]technetium (V) oxide ((99m)Tc-MAMA-3-PQ) and its rhenium analog were synthesized and characterized. (99m)Tc-MAMA-3-PQ displayed high initial brain uptake (0.52% ID/organ at 2 min post-injection (pi)) and relatively fast washout in mice (0.09% ID/organ at 60 min pi). The regional brain distribution studies in rats showed high-specific binding ratios at 60 min pi. Maximum regional contrast ratio observed for thalamus/cerebellum was 2.94, followed by 2.62 for hypothalamus/cerebellum. These encouraging results lead us to further explore its derivatives as new imaging agents for the SERT in the brain.

PET examination of [(11)C]5-methyl-6-nitroquipazine, a radioligand for visualization of the serotonin transporter.

Radiohalogenated 5-halo-6-nitroquipazine analogues have been shown to be potential radioligands for visualization of the serotonin transporter (5-HTT) with PET and SPECT. In the present study a methylated analogue, 5-methyl-6-nitroquipazine (MNQP), was radiolabeled with carbon-11 in a two step reaction via a palladium catalyzed cross coupling reaction between N-t-BOC-protected 5-tributylstannyl-6-nitroquipazine and [(11)C]methyl iodide as key step. [(11)C]MNQP was examined in the cynomolgus monkey brain with positron emission tomography (PET) and the appearance of labeled metabolites in monkey plasma was measured with gradient HPLC. Radioactivity increased continuously in all brain regions during the 90 minutes acquisition time. Highest accumulation of radioactivity was observed in the thalamus and brainstem, regions with a known high density of 5-HTT. The calculated ratios between the thalamus and brainstem to the 5-HTT poor cerebellum were 1.5 and 1.3-1.4, respectively, 80 minutes after radioligand injection. Pretreatment with citalopram prior to the PET measurement markedly reduced the binding in the thalamus and the brainstem. At 15 and 30 minutes after injection of [(11)C]MNQP approximately 90% and 60%, respectively, of radioactivity in plasma represented unchanged radioligand. The slow kinetics and moderate ratios recorded however, may limit its use as a PET radioligand for quantitative studies of the serotonin transporter with PET.

Synthesis of a fluorine-18-labelled derivative of 6-nitroquipazine, as a radioligand for the in vivo serotonin transporter imaging with PET.

Considerable efforts have been engaged in the design, synthesis and pharmacological characterization of radioligands for imaging the serotonin transporter, based on its implication in several neuropsychiatric diseases, such as depression, anxiety and schizophrenia. In the 5-halo-6-nitroquipazine series, the fluoro derivative has been designed for positron emission tomography (PET). The corresponding 5-iodo-, 5-bromo- and 5-chloro N-Boc-protected quipazines as labelling precursors, as well as 5-fluoro-6-nitroquipazine as a reference compound have been synthesized. 5-[(18)F]Fluoro-6-nitroquipazine has been radiolabelled with fluorine-18 (positron-emitting isotope, 109.8 min half-life) by nucleophilic aromatic substitution from the corresponding N-Boc protected 5-bromo- and 5-chloro-precursors using K[(18)F]F-K(222) complex in DMSO by conventional heating (145 degrees C, 2 min) or microwave activation (50 W, 30-45 s), followed by removal of the protective group with TFA. Typically, 15-25 mCi (5.5-9.2 GBq) of 5-[(18)F]fluoro-6-nitroquipazine (1-2 Ci/micromol or 37-72 GBq/micromol) could be obtained in 70-80 min starting from a 550-650 mCi (20.3-24.0 GBq) aliquot of a cyclotron [(18)F]F(-) production batch (2.7-3.8% non decay-corrected yield based on the starting [(18)F]fluoride). Ex vivo studies (biodistribution in rat), as well as PET imaging (in monkey) demonstrated that 5-[(18)F]fluoro-6-nitroquipazine ([(18)F]-1d) readily crossed the blood brain barrier and accumulated in the regions rich in 5-HT transporter (frontal- and posterial cortex, striata). However, the low accumulation of the tracer in the thalamus (rat and monkey) as well as the comparable displacement of the tracer observed with both citalopram, a -HT re-uptake inhibitor and maprotiline, a norepinephrine re-uptake inhibitor (rat), indicate that 5-[(18)F]fluoro-6-nitroquipazine ([(18)F]-1d) does not have the suggested potential for PET imaging of the serotin transporter (SERT).

Syntheses and binding affinities of 6-nitroquipazine analogues for serotonin transporter. Part 1.

6-Nitroquipazine has been known as one of the most potent and selective inhibitors of serotonin transporter in vitro and in vivo. Nine derivatives of 6-nitroquipazine were synthesized and tested for their potential abilities to displace [3H]citalopram binding to the rat cortical membranes.

Characterization of bromine-76-labelled 5-bromo-6-nitroquipazine for PET studies of the serotonin transporter.

The development of suitable radioligands for brain imaging of the serotonin transporter is of great importance for the study of depression and other affective disorders. The potent and selective serotonin transporter ligand, 5-iodo-6-nitro-2-piperazinylquinoline, has been labelled with iodine-123 and used as a radioligand for single photon emission computerized tomography. To evaluate the potential of the bromine-76-labelled analogue, 5-bromo-6-nitroquipazine, as a radioligand for positron emission tomography (PET), its brain distribution and binding characteristics were examined in rats. In vivo brain distribution and ex vivo autoradiography demonstrated that [76Br]5-bromo-6-nitroquipazine enters the brain rapidly. The regional brain distribution of [76Br]5-bromo-6-nitroquipazine was consistent with the known distribution of serotonin transporters in the midbrain, pons, thalamus, striatum, and neocortex. Specific binding was inhibited by the selective serotonin reuptake inhibitor citalopram. The peripheral metabolism in plasma was rapid, but more than 90% of the radioactivity in brain represented unchanged radioligand 2 h postinjection (p.i.). A preliminary PET study was also performed in a baboon. Following the intravenous injection of [76Br]5-bromo-6-nitroquipazine in a baboon, there was a conspicuous accumulation of radioactivity in thalamus, striatum, and pons. The radioactivity in these brain regions was 1.5 times higher than in the cerebellum at 3 h and 2.5-4 times higher at 24 h. A rapid metabolism of the radioligand in plasma was observed (38% unchanged after 5 min). The results indicate that [76Br]5-bromo-6-nitroquipazine has potential for PET imaging of the serotonin transporter.

N-methylquipazine: carbon-11 labelling of the 5-HT3 agonist and in vivo evaluation of its biodistribution using PET.

N-Methylquipazine (2-[1-(4-methyl)-piperazinyl)quinoline)) was labelled with carbon-11 by reacting [11C]methyl iodide with the nor-compound, quipazine. Radiochemical conversions were 79 +/- 7%, based on the alkylating agent. The total synthesis time including purification was 40 to 45 min. N-[Methyl-11C]methylquipazine thus synthesized was >99% radiochemically pure, and the specific activity ranged between 12-37 GBq/mumol. Dynamic imaging with PET was used to examine in vivo its distribution in rat and monkey. In rat the organ uptake at intermediate times was: liver > heart > whole brain > or = lung > extracerebral tissue. Brain uptake and wash-out were rapid: A maximum was reached in 2 to 3 min with subsequent decrease to approximately equal to 50% the peak value by 13 min. In monkey the tracer uptake was heterogeneous and high in regions known to contain 5-HT3 receptors but also in regions devoid of these receptors. Tissue kinetics were similar for all regions (initial rapid accumulation with tmax < or = 7 min, followed by slow decrease with all regions approaching the level of the cerebellum at 30 to 35 min). Pretreating with quipazine significantly decreased only the ratio of uptake in the medulla oblongata compared to the cerebellum. Although the nonspecificity of its binding limits the usefulness of N-[methyl-11C]methylquipazine, both its kinetic behavior and the blocking results indicate that a more selective arylpiperazine might prove to be a more attractive tracer for PET studies of 5-HT3 receptors.

El droperidol interactúa con receptores serotonérgicos y adrenoceptores Ó- cardiovasculares / Droperidol interactions with serotonergic and cardiovascular Ó adrenoceptors

En este trabajo se investigó si los receptores cardiovasculares de la serotonina (5-HT) son antagonizados por el droperidol. Los efectos de este fármaco sobre la vasopresión y el cronotropismo positivo obtenidos con la infusión intravenosa de noradrenalina (NA; 1 µg.kg-1.min-1), angiotensina II (1 µg.kg-1.min-1) y quipazina (100 µg.kg-1.min-1) se estudiaron en ratas desmeduladas. El droperidol (0.01 - 1 mg.kg-1,i.v.) revirtió los efectos presores de la NA y la quipazina en forma dependiente de la dosis. El pretratamiento con propranolol, bromefeniramina o atropina (1 mg.kg-1, i.v.; cada uno), no previno los efectos del neuroléptico. Por otra parte, el droperidol no modificó la respuesta presora de la angiotensina II, ni el cronotropismo de las drogas estudiadas. Se observó que los efectos inhibitorios del droperidol (DI50 141 µg/kg; LC 105-191) y de la ketanserina (Di50 110 µg/kg; LC 91-132) sobre la vasopresión de la quipazina, son similares; sin embargo, esta última no fue modificada por la prazosina. Estos resultados indican una interacción del droperidol con los reeptores vasculares 5-HT y confirman su capacidad para bloquear Ó-adrenoceptores

[125I]5-iodo-6-nitroquipazine: a potent and selective ligand for the 5-hydroxytryptamine uptake complex. II. In vivo studies in rats.

The in vivo regional distribution and pharmacological profile of [125I]5-iodo-6-nitroquipazine in the rat brain were studied to evaluate this compound as a potential in vivo imaging agent of the 5-hydroxytryptamine (serotonin or 5-HT) uptake complex. This radioligand penetrated the blood-brain barrier quickly and efficiently, with 1.9% of injected dose found in the whole brain at 5 min post i.v. injection. The regional brain distribution of radioactivity at time points later than 2 h was highly correlated with the known distribution of serotonin uptake sites and terminals. Coadministration of 2 mg/kg paroxetine inhibited > 90% of the total in vivo binding of [125I]5-iodo-6-nitroquipazine. Other serotonin uptake inhibitors, such as fluoxetine and sertraline, were also effective inhibitors of [125I]5-iodo-6-nitroquipazine brain binding in vivo. Non-serotonergic uptake blockers (desipramine, nomifensine, and GBR-12909) and the postsynaptic serotonin receptor agent LSD had no effect on [125I]5-iodo-6-nitroquipazine binding in vivo even at high doses. Lesioning of the serotonergic system by p-chloramphetamine produced approximately 90% decrease in specific in vivo binding. Extraction and analysis of brain radioactivity indicated that approximately 95% of the extractable radioactivity was unmetabolized [125I]5-iodo-6-nitroquipazine. These results indicate that [125I]5-iodo-6-nitroquipazine is a specific, useful radioligand for studying serotonergic uptake sites and terminals in animals, and an 123I-radiolabeled form of the drug would be an excellent candidate for non-invasive single photon emission computed tomography (SPECT) imaging of these sites in the living human brain.

High-affinity [3H]6-nitroquipazine binding sites in rat brain.

6-Nitroquipazine is a very potent and selective inhibitor of neuronal 5-hydroxytryptamine (5-HT; serotonin) uptake. We have characterized the specific binding of [3H]6-nitroquipazine to rat brain membranes at 22 degrees C. The present results indicate the presence of a single saturable high-affinity binding component for [3H]6-nitroquipazine. Scatchard analysis revealed an apparent equilibrium dissociation constant (Kd) of 93.0 +/- 2.23 pM, and a maximal number of binding sites (Bmax) of 831.7 +/- 18.7 fmol/mg protein (mean +/- S.D., n = 4). The kinetically derived dissociation constant was 74.5 pM. [3H]6-Nitroquipazine binding was inhibited selectively by 5-HT uptake inhibitors, and a good correlation was demonstrated between the potency of various drugs to inhibit [3H]6-nitroquipazine binding and [3H]5-HT uptake. The highest densities of [3H]6-nitroquipazine binding were obtained in the hypothalamus and midbrain, intermediate binding was observed in the striatum, hippocampus, medulla oblongata and cortex, and the lowest binding was observed in the cerebellum. Lesioning of 5-HT neurons with p-chloroamphetamine resulted in a 72% reduction in [3H]6-nitroquipazine binding compared to controls. These results indicate that the binding site specifically labelled by [3H]6-nitroquipazine is associated with the neuronal 5-HT transporter complex. [3H]6-Nitroquipazine is an excellent radioligand for the study of the 5-HT uptake system.

Similarity of 5-HT2 receptor sites in dominant and subordinate vervet monkeys.

Pharmacological studies using serotonergic agents have revealed status-linked behavioral effects in dominant and subordinate vervet monkeys. A possible explanation for the greater drug response observed in dominant animals is that there is a CNS difference between dominant and subordinate animals. Such differences could exist at the level of serotonin receptor sites, membrane responsiveness, or interaction with other neurotransmitters. We have examined the specific 3H-ketanserin binding in various regions of vervet monkey brain to evaluate the hypothesis that dominant and subordinate vervet monkeys differ in CNS 5-HT2 receptor sites. No differences were found in the number or affinity of 3H-ketanserin binding sites between dominant and subordinate animals. Further, no differences were found in the displacement of 3H-ketanserin binding by the serotonin agonist quipazine. These results suggest the conclusion that differences at 5-HT2 binding sites do not account for status-linked differences in behavioral drug response in vervet monkeys and that other or additional mechanisms must underlie status-related drug response differences.