Pharmacologic reversal of acute changes in diffusion-weighted magnetic resonance imaging in focal cerebral ischemia.

Recently, diffusion-weighted magnetic resonance imaging (DWI) has been shown to visualize acute ischemic lesions in the brain before changes are observable with conventional magnetic resonance imaging. However, the underlying mechanisms of these acute DWI changes are unclear and may include both reversible and irreversible damage. In this study, we demonstrate that acute DWI lesions may be reversed with MK801 therapy postischemia. Sprague-Dawley rats (n = 12) were subjected to middle cerebral artery occlusion and DWI scans were obtained beginning 60 min postocclusion. Distinct regions of hyperintensity were observed in the basal ganglia and cortex, corresponding with the expected distribution of ischemia in this model. After the first scan, animals were treated with MK801 (0.5 mg/kg i.v.) or normal saline and subsequently scanned again 30 and 60 min after treatment. In the control group, the area of hyperintense lesions continued to increase, by 55% in the cortex and 57% in the basal ganglia. MK801 therapy significantly (p < 0.01) reduced the area of damage by the third DWI scan at 60 min posttreatment (-50% cortex, -22% basal ganglia, -41% total hemisphere) compared to pretreatment scans. Tetrazolium (TTC) stains at 24 h confirmed that MK801 significantly reduced the volumes of infarction (p < 0.05). These results demonstrate that significant portions of the acute ischemic lesion on DWI are reversible with pharmacologic intervention.

WIN 63480, a hydrophilic TCP-site ligand, has reduced agonist-independent NMDA ion channel access compared to MK-801 and phencyclidine.

NMDA channel blockers are potentially advantageous therapeutic agents for the treatment of ischemia and head trauma, which greatly elevate extracellular glutamate, because they should most effectively inhibit high levels of receptor activation. A novel high affinity TCP site ligand, WIN 63480, does not produce MK-801- or PCP-like behavioral activation at anti-ischemic doses. While WIN 63480, MK-801 and PCP were all observed to be effective blockers of open NMDA channels, WIN 63480 had much less access to closed NMDA channels. This difference may be due to the fact that WIN 63480 is hydrophilic (logD = -4.1) while MK-801 and PCP are lipophilic (logD = +1.8). In vivo, closed channel access may result in a non-competitive profile of antagonism for MK-801 and PCP compared to a more uncompetitive profile for WIN 63480. Release of glutamate, and depolarization, are likely to produce a high level of NMDA receptor activation in ischemic areas compared to normal tissue. Consequently, at anti-ischemic doses, WIN 63480 may produce less inhibition of physiological NMDA-mediated processes in neural systems involved in behavioral regulation than MK-801 or PCP, leading to an improved side effect profile.

Alpha 2-adrenergic agonists/antagonists: the synthesis and structure-activity relationships of a series of indolin-2-yl and tetrahydroquinolin-2-yl imidazolines.

The synthesis and alpha 2-adrenergic activity of a series of indolin-2-yl and tetrahydroquinolin-2-yl imidazolines are described. The indolin-2-yl imidazoline 4b was found to possess potent alpha 2-adrenergic agonist and antagonist activity. The modification of the substituents on the indoline ring of 4b has led to the separation of these activities. Substitution on the aromatic ring of 4b with halogen or increasing the size of the N-alkyl substituent of 4b gave alpha 2-adrenergic antagonists without agonist activity. The N-allylindoline 4d is more potent than idazoxan in vitro and is equipotent in vivo, but is less receptor selective (alpha 2 vs. alpha 1) than idazoxan. The cis-1,3-dimethylindolin-2-yl imidazoline 6a is an alpha 2-adrenergic agonist equal in potency to clonidine in vitro, while the trans-1,3-dimethylindolin-2-yl imidazoline 6b is a moderately potent alpha 2-adrenergic antagonist.

Synthesis and antidepressant properties of novel 2-substituted 4,5-dihydro-1H-imidazole derivatives.

A unique combination of alpha 2-adrenoreceptor antagonist and serotonin-selective reuptake inhibitory activities has been identified in a series of 2-substituted 4,5-dihydro-1H-imidazole derivatives. This combination of blocking activities has provided one of these derivatives, napamezole hydrochloride (2), with potential as an antidepressant. A discussion of the syntheses of these compounds includes a convenient method for the conversion of nitriles to imidazolines with ethylenediamine and trimethylaluminum.

Discovery of 6,11-ethano-12,12-diaryl-6,11-dihydrobenzo[b]quinolizinium cations, a novel class of N-methyl-D-aspartate antagonists.

6,11-Ethano-12,12-diaryl-6,11-dihydrobenzo[b]quinolizinium cations 8, a novel class of N-methyl-D-aspartate (NMDA) antagonists acting at the phencyclidine site, have been identified. Structure-activity relationship studies around the lead compound 8a led to the identification of 12g (WIN 67870-2), one of the most potent compounds in this series. Compound 12g has a Ki = 1.8 +/- 0.2 nM vs [3H]TCP binding, has 700-fold selectivity for binding to the open state of the NMDA receptor-ionophore, and was devoid of MK-801- and PCP-like behavioral effects in rats. Compound 12g was neuroprotective in cultured mouse cortical neurons and exhibited antiischemic activity in a rat middle cerebral artery occlusion/reperfusion model of focal ischemia.

Two tests in rats for antianxiety effect of clinically anxiety attenuating antidepressants.

The effects of mianserin, trazodone, amoxapine, maprotiline, and doxepin were assessed in punishment and pentylenetetrazol drug discrimination paradigms. These two procedures are used to identify antianxiety activity in rats. In the punishment procedure, misanserin produced an inverse dose-related increase in punished responding. The magnitude of the increase in punished responding with mianserin was comparable to that observed with the anxiolytic, buspirone. This effect was not observed with any of the other antidepressants tested. None of the antidepressants were found to be active in antagonizing the discriminative stimulus effects of pentylenetetrazol. In fact, at high doses there was a suggestion that the antidepressants may generalize to the pentylenetetrazol discriminative stimulus. Therefore, several antidepressants with purported clinical antianxiety activity, were not active in two procedures that detect antianxiety activity in rats.

The effects of chronic morphine treatment on neurotensin-induced antinociception.

Previous studies have shown that the opioid antagonist naloxone does not alter neurotensin (NT)-induced antinociception. In the present studies, tolerance to morphine in mice significantly attenuated NT-induced antinociception, but not NT-induced hypothermia. In addition, centrally administered NT inhibited naloxone-precipitated jumping in morphine-dependent mice. These results indicate complex interactions between NT-induced antinociception and opioid systems.

The effects of neurotensin, beta-endorphin, and bombesin on ethanol-induced behaviors in mice.

The effects of the three peptides neurotensin, beta-endorphin, and bombesin on ethanol-induced behaviors were studied in mice. Intracisternal administration of these peptides to mice prolonged the duration of sleep induced by ethanol (5.2 g/kg). Neurotensin and beta-endorphin also enhanced ethanol-induced hypothermia. None of the peptides, when administered alone, produced sleep. However, all three compounds impaired the aerial righting reflex and induced sleep when followed by an IP dose of ethanol (3.5 g/kg), which alone did not induce sleep. These results, taken together with previous findings, suggest that neuropeptides may be involved in the complex mechanisms of action of ethanol on the CNS.

Modification of the actions of ethanol by centrally active peptides.

Ethanol (2.0-5.0 g/kg, IP) caused a dose-related impairment of the aerial righting reflex of mice 60 min after injection. Ethanol (3.5 g/kg, IP) given simultaneously with neurotensin (30 micrograms, IC), bombesin (30 micrograms, IC) or beta-endorphin (20 micrograms, IC) caused a greater impairment of the reflex than ethanol alone. Simultaneous treatment with ethanol (4.0 g/kg, IP) and thyrotropin-releasing hormone (TRH, 3.0-30 micrograms, IC) caused less impairment of this measure than ethanol alone. None of the peptides altered the height of aerial righting when administered alone, or when administered with ethanol no peptide altered blood or brain ethanol content. Unexpectedly, TRH (20 and 40 mg/kg, IP) potentiated the action of ethanol by increasing punished licking in water-deprived rats, rather than antagonizing this acute action of ethanol. Like ethanol (1.0 and 2.0 g/kg, IP), beta-endorphin (100 micrograms, IC) suppressed ethanol-withdrawal tremor and audiogenic-seizure susceptibility in ethanol-dependent rats. beta-Endorphin (1 microgram) and bombesin (10 and 30 micrograms, IC) reduced only audiogenic-seizure susceptibility. TRH (10-100 micrograms, IC, or 1-40 mg/kg, IV) and neurotensin (10-100 micrograms, IC) had no effect on these ethanol-withdrawal signs. These findings suggest that centrally active peptides may play a role in certain acute and chronic actions of ethanol. Because TRH, neurotensin, bombesin and beta-endorphin do not alter all actions of ethanol in the same way, an interaction of ethanol with many functionally independent neuronal circuits is suggested.

Increased hypothalamic norepinephrine metabolism after water deprivation in the rat.

Rat brain catecholamine metabolism was changed over a period of several days by limited access to water (10 min/day). One or two weeks limited access to water caused an increase in hypothalamic norepinephrine metabolism as measured with alpha-methyl-para-tyrosine. Brain stem and telencephalon norepinephrine was not affected by the limited access to water regimen. Dopamine metabolism in the corpus striatum and the hypothalamus was not altered by limited access to water. If the limited access to water was continued for 3 or more weeks, hypothalamic norepinephrine metabolism then returned to normal. The increase in hypothalamic norepinephrine metabolism was confirmed by a second method measuring in vivo tyrosine hydroxylase activity. Additional experiments demonstrate that this affect is specific for water deficits. Limited access to food had no effect on the metabolism of norepinephrine in the hypothalamus. Water deficits produced by replacing water with a 2% NaCl solution caused a similar increase in hypothalamic norepinephrine metabolism to that observed after one week limited access to water. Furthermore, 10 min access to water stopped the increased hypothalamic metabolism of norepinephrine seen after one week of limited access to water. The regional specificity (effect seen in hypothalamus but not the telencephalon and brain stem), and the stimulus specificity (water and not food deficits) suggest hypothalamic norepinephrine involvement in thirst or hormonal control of water regulation.

The effects of neuropeptides on discrete-trial conditioned avoidance responding.

The effects of intracerebroventricular administration of several peptides on discrete-trial, conditioned avoidance responding were assessed in the rat. Three peptides (neurotensin, bombesin and beta-endorphin) produced a neuroleptic-like effect (i.e. a decrease in avoidance responding with no effect on escape responding). A low dose (0.6 nmol) of each peptide elicited a significant effect. Neurotensin and bombesin produced a significant but partial decrease in avoidance responding; larger doses of these peptides did not produce a greater effect. beta-Endorphin elicited dose-related decrements in avoidance responding. In addition, the effect of neurotensin, but not bombesin or beta-endorphin, was antagonized by simultaneous administration of an equimolar dose of thyrotropin-releasing hormone. Hence, the 3 peptides do not appear to produce decreases in avoidance responding by the same mechanism. Thyrotropin-releasing hormone, luteinizing hormone-releasing hormone, bradykinin, substance P, des-Tyr1-gamma-endorphin and melanotropin inhibiting factor did not significantly affect avoidance responding. These findings, taken together with previous findings, suggest that intracerebroventricular administration of certain endogenous peptides (neurotensin, bombesin and beta-endorphin) may exert neuroleptic-like effects.

Adaptation to cold antagonizes neurotensin-induced hypothermia in mice.

Intracerebrally-administered neurotensin produces a marked hypothermia in a variety of mammals. In this study, prior adaptation to a cold environment was found to significantly antagonize the hypothermia produced by intracisternally-administered neurotensin in mice. This antagonism required both previous exposure to cold ambient temperatures and cold exposure immediately prior to, or simultaneously with, neurotensin administration. The antagonism of neurotensin-induced hypothermia by prior cold-adaptation was blocked by indomethacin, but not by acetylsalicylic acid, suggesting that brain prostaglandin synthesis may be essential for this newly-discovered phenomenon.

Evaluation of adenosine agonists as potential analgesics.

Adenosine agonists, N6-cyclohexyladenosine (CHA), N6-cyclopentyladenosine (CPA), N6-phenylisopropyladenosine (PIA), 5'-N-ethylcarboxamidoadenosine (NECA), 5'-N-methylcarboxamidoadenosine (MECA) and 2-chloroadenosine (CADO), produced a dose-related inhibition of acetylcholine (ACh)-induced writhing in mice. The antinociceptive potency of adenosine agonists was comparable to that of morphine. Adenosine agonists were 10-1000 times more potent when given i.c.v. than p.o., suggesting a central site of action. Theophylline antagonized the antinociceptive activity of R-PIA in the writhing assay, suggestive of an adenosine receptor-mediated event. The sedative/ataxic properties of adenosine agonists were evaluated using a rotorod assay. Adenosine agonists impaired performance on the rotorod in doses comparable to and in some cases lower than those active in the ACh writhing assay. The results of the present study suggest that adenosine agonists attenuate nociceptive responding to a chemical stimulus through a central purinergic mechanism. The ability of adenosine agonists to inhibit ACh-induced writhing may be secondary to their sedative/ataxic properties.

Behavioral effects of neurotensin: operant responding and assessment of 'anhedonia'.

Neurotensin and antipsychotic drugs share certain properties. This study investigates whether neurotensin and neuroleptics share the ability to produce 'anhedonia'. A dose-response curve for the effect of neurotensin on continuously reinforced behavior was obtained in Experiment 1. Centrally administered neurotensin reduced food-reinforced responding. Based on the results of Experiment 1, a dose of neurotensin (0.95 micrograms) was chosen which had minimal effects on food-reinforced operant responding. To test for anhedonia, repeated presentations of this dose were given. Because response rates did not decrease over repeated testing, no evidence for anhedonia was found.

The effects of serotonin antagonists in a behavioral despair procedure in mice.

Six serotonin antagonists (pizotifen, mianserin, cyproheptadine, ketanserin, trazodone and methysergide) were tested in mice in a behavioral despair procedure. The behavioral despair procedure detects most antidepressant compounds. Pizotifen, mianserin and cyproheptadine were found to be active and the others were inactive. The serotonin binding potency at serotonin1 or serotonin2 receptors, or the ratio of potency at these receptors did not correlate with activity in the behavioral despair procedure. However, the serotonin antagonists that were active in the behavioral despair procedure were all found to be potent antagonists at histamine1 receptors. It is suggested that the activity of some serotonin antagonists in the behavioral despair procedure is best explained by their antihistaminergic potency.

Sigma receptor binding affinity and inhibition of apomorphine-induced climbing.

Several relatively selective compounds with affinity for the sigma binding site were assessed for their ability to inhibit apomorphine-induced climbing in the mouse. Although, the majority of compounds inhibited apomorphine-induced climbing, there was no correlation between the ability to inhibit climbing and potency in sigma binding assays using [3H]1,3-di-o-tolylguanidine (DTG) or [3H](+)-pentazocine as ligands. The potency of the compounds to inhibit binding to muscarinic M1 or M2 receptors correlated with the potency to inhibit apomorphine-induced climbing. However, several of the compounds that inhibit climbing had microM affinity at muscarinic receptors. Whether these concentrations were achieved in vivo is unclear. Our data suggest that sigma activity per se is not responsible for inhibition of apomorphine-induced climbing.

The effect of neurotensin on food consumption in the rat.

The effect of neurotensin on feeding behavior were studied in rats. Intracerebroventricular administration of neurotensin (3.3-30 micrograms) produced a dose-related decrease in food intake in 24 h food deprived rats. Acute intracerebroventricular injection of neurotensin (30 micrograms) shortly after the ingestion of a novel flavor did not produce a flavor aversion during testing 48 h later, suggesting that reduction of food intake by low doses of centrally administered neurotensin is not related to a conditioned taste aversion. Intracerebroventricularly administered thyrotropin-releasing hormone (2.2 micrograms) also inhibited food intake and appeared to attenuate slightly the inhibition of food intake induced by 10 micrograms neurotensin.

Alpha 2-adrenergic antagonists effect on amphetamine-induced behaviors.

The effects of alpha 2-adrenergic antagonists on amphetamine-induced locomotion and stereotypy were studied in mice. Six alpha 2-antagonists (i.e., yohimbine, rauwolscine, piperoxan, tolazoline, RX781094, and RS21361) selectively attenuated amphetamine-induced increases in locomotion at doses which did not effect amphetamine-induced stereotypies. Higher doses of the antagonists which attenuated baseline stereotypies also attenuated amphetamine-induced increases in stereotypies. The effect of the alpha 2-antagonists was qualitatively similar to that observed with the atypical antipsychotic clozapine. Furthermore, the in vivo relative potency of the alpha 2-antagonists in the present study was comparable to that reported in other studies. These results suggest that alpha 2-adrenergic receptors may modulate the effects of amphetamine on locomotion in mice.