Gregory E. Martin

Increase in brain 125I-cholecystokinin (CCK) receptor binding following chronic haloperidol treatment, intracisternal 6-hydroxydopamine or ventral tegmental lesions

Specific 125I-CCK receptor binding was significantly increased in brain tissue taken from guinea pig or mouse following chronic (2-3 week) daily administration of haloperidol (2-3 mg/kg/day). Scatchard analysis indicated the increase in CCK binding was due to an increased receptor number (B max) with no change in affinity (Kd). In guinea pigs, the increased CCK binding was observed in the mesolimbic regions and frontal cortex, but not in striatum, hippocampus nor posterior cortex. In mice, however, the increases occurred in both pooled cerebral cortical-hippocampal tissue, and in the remainder of the brain. Enhanced CCK receptor binding was also observed in membranes prepared from whole brain of mice one month following intracisternal injection of 6-hydroxydopamine. Additionally, an increase in CCK binding was observed in mesolimbic regions and frontal cortex, but not striatum or hippocampus, of guinea pigs 3 weeks after an unilateral radiofrequency lesions of the ipsilateral ventral tegmentum. The present studies demonstrate that three different procedures which reduce dopaminergic function in the brain enhance CCK receptor binding. The data provide further support for a functional interrelationship between dopaminergic systems and CCK in some brain regions and raise the possibility that CCK may play a role in the antipsychotic action of neuroleptics.

Pharmacological profiles of the putative dopamine autoreceptor agonists 3-PPP and TL-99

The putative dopamine (DA) autoreceptor agonists, N-n-propyl-3-(3-hydroxyphenyl)-piperidine (3-PPP) and 6, 7-dihydroxy-2-dimethylaminotetralin (TL-99) were compared with apomorphine in a series of tests indicative of DA receptor activation. All three agents displaced [3H] apomorphine and [3H] spiroperidol from DA recognition sites in rat brain and caused contralateral turning in the 6-hydroxydopamine lesioned rat. Apomorphine and TL-99 were generally more potent than 3-PPP. All three agents were also active at the DA autoreceptor that controls the synthesis of dopamine as indicated in vivo using the gamma-butyrolactone (GBL) procedure and in vitro using a synaptosomal preparation. In addition, all agents produced emesis in beagles. clear differences in the drugs actions were observed in other test procedures. In the rat, apomorphine was the only compound which caused stereotypy or rotation following a reversible KCI-induced lesion of the striatum. Conversely, TL-99 and 3-PPP lacked activity in these procedures. Presumably, activity in these two tests indicates postsynaptic DA receptor activation. Each of the putative autoreceptor agonists produced a monotonic dose-related decrease in the mouse locomotor activity as opposed to the biphasic effect exerted by apomorphine. This action on the mouse locomotor activity, coupled with the results for the GBL test, provides an index of autoreceptor activation. In contrast to 3-PPP, both apomorphine and TL-99 increased locomotor activity in animals pretreated with reserpine and alpha-methyl-p-tyrosine and caused rotation in unilaterally caudectomized mice. In these test procedures thought to reflect activity at the postsynaptic DA receptor, TL-99 differed in its action from 3-PPP in a manner which suggests 3-PPP may be a more selective DA autoreceptor agonist.

Antinociceptive and hypothermic actions of neurotensin administered centrally in the rat

Abstract Dose-response curves for hypothermia and antinociception were derived following the administration of neurotensin via 3 routes in the rat. The peptide was given intracisternally (ICI), intraventricularly (IVT) or within the thecum of the spinal subarachnoid space to the rat maintained in a thermoneutral environment. Hypothermia and increased latency to respond to a hot plate (55°C) were evoked following ICI and IVT injections, whereas only a hypothermia was observed after the intrathecal injections. Furthermore, the dose required to produce significant hypothermia or antinociception was lower following ICI (0.25 and 1 nmole) than IVT (9.0 and 12.0) or intrathecal (24, > 48) injections. Via each route of administration, a significant fall in rectal temperature was induced at doses lower than required to produce antinociception.

ANTINOCISPONSIVE EFFECTS OF NEUROTENSIN AND NEUROTENSIN‐RELATED PEPTIDES

A naloxone-insensitive antinocisponsive action. and a decrease in body temperature? are two prominent effects in rodents of neurotensin (NT) given by the intracerebroventricular or intracisternal (i.c.) route of administration. Various experimental findings described herein indicate that these two actions are separable and independent, that is, the antinocisponsive effect of NT does not result secondarily as a consequence of the substances hypothermic action. This report also summarizes previousi- and recently obtained results dealing with the sites in the central nervous system responsible for the hypothermic and antinocisponsive effects of NT. Finally, we describe results on the initial biological testing of recently synthesized cyclic octapeptides related structurally to NT. As shown below along with the equivalent cyclic form of NT. I:, the other two substances have a similar make-up, with D-Lysine in place of L-Lysine at position 6. They differ only in the amino acids at positions 8 and 9.

Electrophysiological, biochemical and behavioral assessment of dopamine autoreceptor activation by a series of dopamine agonists.

The rank order of potency to activate central dopamine autoreceptors of seven compounds known to possess central nervous system dopamine agonist activity were assessed with the following techniques: (1) inhibition of dopaminergic neuronal firing in anesthetized rats, (2) inhibition of dopamine synthesis in rats pretreated with gamma-butyrolactone, and (3) inhibition of mouse locomotor activity. The compounds were also examined for their ability to induce stereotypic behaviors in rats as an index of postsynaptic dopamine receptor activation. The compounds under investigation were apomorphine, N-n-propyl-norapomorphine, lergotrile, bromocriptine, RU 24926 and 6-ethyl-9-oxaergoline (EOE). There was a high degree of correlation between the rank order of potency of the compounds in all three of the presumptive autoreceptor tests and with minor variations the following rank order of potency was found: N-n-propylnorapomorphine greater than or equal to EOE greater than apomorphine greater than lergotrile greater than or equal to RU 24926 greater than bromocriptine. However, in the induction of stereotypies, the rank order of potency was considerably different: N-n-propylnorapomorphine greater than apomorphine greater than EOE greater than RU 24926 greater than lergotrile greater than bromocriptine. There was a poor and statistically significant degree of correlation between the rank order of potency of the test compounds to induce stereotyped behaviors and any of the other three test procedures. Altogether, these data confirm and extend the suspected dopaminergic agonist properties of the compounds under investigation and additionally lend credence to the assumption that the three putative autoreceptor assays employed do in fact reflect dopaminergic autoreceptor activation.

Differences in the pharmacological actions of intrathecally administered neurotensin and morphine

Neurotensin or morphine can each cause hypothermia and an antinocisponsive effect when administered into the liquor spaces of the rat brain. These actions of neurotensin are not blocked by naloxone whereas those of morphine are. The present experiments were carried out to examine the action of each substance following its injection into the subarachnoid space of the spinal cord. Given intrathecally, neurotensin evoked a dose-related fall in the rectal temperature of the rat without exerting an antinocisponsive action. Morphine on the other hand evoked hyperthermia and a dose-related antinocisponsive action. Since neurotensin exerted an effect on rectal temperature opposite to that of morphine and failed to exert an antinocisponsive effect, the data provide further evidence to suggest that neurotensin and morphine exert their effect via different mechanisms. Furthermore, the results also suggest that neurotensin exerts its antinocisponsive action via a supraspinal site.

Selectivity of cyproheptadine as assessed by radioligand binding

Brodde, 0.-E., Gross, G. (1980) Naunyn-Schmiedebergs Arch. Pharmacol. 31 1 : 249-254 Brodde, 0.-E., Freistuhler, J., Meyer, F.-J. (1981a) J . Cardiovasc. Pharmacol. 3: 828-837 Brodde, 0.-E., Meyer, F.-J., Schemuth, W., Freistuhler, J. (1981b) Naunyn-Schmiedebergs Arch. Pharmacol. 3 16 : 24-30 Doxey, J. C., Roach, A. G. (1980) J. Auton. Pharmacol. 1: 73-99 Drew, G. M. (1978) Br. J. Pharrnacol. 64: 293-300 Listinsky, J. J., Kohli, J. D., Goldberg, L. I. (1980) J .

L-654,284 a new potent and selective α2-adrenoceptor antagonist

SummaryL-654,284 ((2R, 12bS)-N-(1,3,4,6,7,12b-hexahydro-2H-benzo[b]-furo[2,3-a] quinolizine-2-yl)-N-methyl-2-hydroxyethanesulfonamide) was tested in several in vitro and in vivo models for α2-adrenoceptor antagonist activity and compared to several reference agents. In vitro L-654,284 competed for the binding of 3H-clonidine or 3H-rauwolscine (Kis 0.8 nM, 1.1 nM) and blocked the presynaptic effects of clonidine in the rat isolated vas deferens (pA2, 9.1). L-654,284 exhibited marked α2- vs. α1-adrenoceptor selectivity in vitro, inhibiting 3H-prazosin binding with a Ki of 110 nM and blocking the effects of methoxamine on the vas deferens with a pA2 of 7.5. In vivo L-654,284 at 22 nmoles/kg i.v. doubled the ED50 of clonidine to produce mydriasis in rats. Given orally, the potency of L-654,284 in this test was reduced by a factor of 5.5. L-654,284 also potently increased cerebrocortical NE turnover in the rat, another in vivo index of α2-adrenoceptor blockade in the central nervous system. In the periphery, L-654,284 demonstrated α2-adrenoceptor selectivity by preferentially blocking the pressor effects of UK 14304 versus those of methoxamine in the pithed rat. Overall, L-654,284 was generally a more potent α2-adrenoceptor antagonist than RX 781094 with comparable α2/α1 selectivity and was several times more potent and α2-selective than WY 26703 or yohimbine. In addition, L-654,284 had better (5–6 times) oral bioavailability than RX 781094 or WY 26703.

Potent dopamine agonist activity of a novel ergoline, 6-Ethyl-9-oxaergoline (EOE)

6-Ethyl-9-oxaergoline (EOE) and its enantiomers were compared with apomorphine in a number of tests designed to measure dopamine (DA) agonist activity within the central nervous system. In rats, the tests were: interaction with DA receptors labeled with 3H-apomorphine or 3H-spiroperidol; the effects on DA synthesis as assessed by the gamma-butyrolactone procedure; turning in 6-OHDA lesioned animals; stereotypy; and, slowing of DA cell firing rates. In the mouse, locomotor activity, hypothermia and postural asymmetry in caudectomized animals were studied. Emesis in the beagle was also examined. The (-)-enantiomer of EOE was more potent than either the (+)-enantiomer or the racemate in all tests. With the exception of inducing stereotypy and the displacement of 3H-apomorphine from rat striatal membranes, (-)-EOE was equi- or more potent than apomorphine in all test procedures. (-)-EOE was effective following oral administration and exhibited a longer duration of action than apomorphine. The results indicate EOE is a potent DA agonist.

Catecholamine Release within the Striatum of the Freely Moving Rat

The push-pull method was used in conscious rats in two different types of experiments. In the first, intranigral application of GABAergic agonists was shown to produce both contralateral circling and [3H]dopamine efflux from the ipsilateral striatum. In the second experiment, MK-801, a novel experimental compound, was found to be dissimilar from amphetamine insofar as it does not produce the release of [3H]dopamine from the striatum during its local application. This novel agent presents an intriguing profile of activity whose mechanism of action remains to be fully elucidated. The usefulness of the push-pull method in helping to resolve a complicated behavioral-neurochemical question as well as a tool for studying neuropharmacological effects of novel agents is clear. The development of new and more sensitive HPLC assay techniques should soon alleviate the need for radiolabeling endogenous catecholamine stores and should greatly further advance the usefulness of this technique.