Monoamine oxidase inhibition by L-deprenyl depends on both sex and route of administration in the rat

The monoamine oxidase B (MAO-B) inhibitor L-deprenyl, widely used to treat Parkinson's disease, has frequently been studied in animal models. We have examined the effects of several variables on activity levels of MAO-A and B in rat brain and liver following chronic (3 wks) treatment with L-deprenyl. Significant effects were observed for sex (females showed lower overall MAO-B activity in the liver), dose (MAO-A and B inhibition increased with dose, with females exhibiting greater sensitivity), route of administration (subcutaneous injection was more efficient than oral dosing), and dosing interval (MAO-B was significantly inhibited when dosing interval was increased to as long as 168 hours). Our results thus indicate that the effectiveness of L-deprenyl in vivo is dependent on several factors and that these must be taken into account in studies involving the benefits or risks of this drug.

The effect of L-deprenyl on behavior, cognitive function, and biogenic amines in the dog

Behavioral and pharmacological effects of oral administration of L-deprenyl in the dog are described. Spontaneous behavior is unaffected at doses below 3 mg/kg while at higher doses there was stereotypical responding. There was evidence of improved cognitive function in animals chronically treated with a 1 mg/kg dose but the effectiveness varied considerably between subjects. Chronic administration produced a dose dependent inhibition in brain, kidney and liver monoamine oxidase B, and had no effect on monoamine oxidase A. There were also dose dependent increases in brain phenylethylamine and in plasma levels of amphetamine. Dog platelets did not have significant levels of MAO-B. Brain dopamine and serotonin metabolism were unaffected by L-deprenyl at doses up to 1 mg/kg. It appears that for the dog, deamination of catecholamines is controlled by MAO-A. Nevertheless, it is suggested that L-deprenyl serves as a dopaminergic agonist, and there is also evidence that it affects adrenergic transmission. These catecholaminergic actions may account for the effects of L-deprenyl on behavior and cognitive function.

GABA and pentobarbital potentiation of chloride influx into microsacs is influenced by incubation time

GABA-mediated chloride influx into rat cerebral cortical microsacs, and its potentiation by pentobarbital (PB), was studied in incubations lasting 50 or 3000 ms. The 3000 ms assays were carried out manually, while the 50 ms assays were performed in a quench flow machine. The EC50 of the GABA effect and the Hill coefficient were both lower at the longer incubation times. Percent increase of the effect of GABA (at EC30 concentration) by pentobarbital was greater in the 3000 ms than in the 50 ms incubations. Preincubation of microsacs with PB for 5 s before the 50 ms incubation with GABA, did not increase the effect of PB beyond that obtained by adding PB into the incubation only. This finding is consistent with earlier ones cited, which imply that only PB binding that occurs after GABA has bound can potentiate the effect of GABA, and suggests that the concentrations of PB and GABA required to enhance chloride influx in vivo may be higher than those commonly reported in the literature.

An Alu sequence interrupts a human 5-hydroxytryptamine1D receptor pseudogene

Molecular cloning studies have now identified six HTR genes encoding the biosynthesis of the structurally homologous human serotonin (5-hydroxytryptamine; 5-HT) receptors, namely 5-HTR1A, 5-HTR1B, 5-HTR1C, 5-HTR1D, 5-HTR2 and 5-HTRS31. Several of these receptors are encoded by intronless genes, and we now report the cloning of another intronless serotonergic HTR gene. This gene was cloned by a method using the polymerase chain reaction. The nucleotide sequence of this gene is most closely homologous to the 5-HTR1D gene; however, several stop codons, frame shifts and deletions are present in the coding region suggesting that this is a pseudogene which could not encode a functional receptor. Sequence analysis also revealed that the coding sequence of this pseudogene is disrupted by insertion of a 283-bp Alu repeat sequence.

Blockade of chronic tolerance to ethanol by the NMDA antagonist, (+)-MK-801

Previous studies indicated that learning and memory play important roles in the development of tolerance to ethanol. (+)-MK-801 has been shown to impair learning and might thus also block the development of tolerance to ethanol. To test this possibility, rats were trained to criterion on the moving belt, a complex motor coordination test. Acute i.p. injection of (+)-MK-801 (a non-competitive NMDA channel blocker) produced dose-related impairment on this test. A dose of 0.1 mg/kg, that had negligible effect by itself, potentiated the acute effects of ethanol. In a chronic experiment with different animals, half of the rats received (+)-MK-801 or saline daily, followed 30 min later by ethanol (1.8 g/kg i.p.) and three practice runs on the belt, and 1 h later a second dose of (+)-MK-801 or saline. The other half received the same drugs but ethanol followed the practice. (+)-MK-801 blocked the functional tolerance to ethanol in both groups when the pre-ethanol dose was 0.25 mg/kg, but not when it was 0.1 mg/kg. Tolerance to the effects of (+)-MK-801 itself did not occur over 2 weeks of treatment. These results suggest that NMDA receptors are involved in development of chronic tolerance to ethanol as shown previously with rapid tolerance.

Effect of NMDA receptor antagonists on rapid tolerance to ethanol

Hypothermia and motor impairment (tilt-plane test) were used to assess whether N-methyl-D-aspartate (NMDA) receptors play a role in the development of rapid tolerance to ethanol, i.e., tolerance to a second dose of ethanol given 24 h after the effect of the first dose of ethanol had disappeared. Results showed that (+)-MK-801 and ketamine blocked the development of rapid tolerance to ethanol on both tests. Since these drugs did not modify blood or brain alcohol levels in any of the groups, the blockade of ethanol rapid tolerance cannot be attributed to changes in pharmacokinetics of ethanol. These data suggest that the role of NMDA receptors in ethanol tolerance may be similar to their role in memory and learning, involving a facilitation of transmission in certain synapses.

Effects of sedatives on GABA-mediated chloride flux into cerebral cortical microsacs prepared from emotional and non-emotional mice

Some strains of rats and mice express increased momentary fear or emotionality when exposed to a novel environment. Previous studies have found significantly fewer diazepam binding sites in the brains of Balb/cJ mice compared to C57BL and AKR/J mice and this has been suggested to contribute to the increased emotionally of the 'nervous' Balb strain. The influx of 36Cl into cerebral cortical microsacs was used to functionally assess the effects of GABA, diazepam and pentobarbital in the Balb mice compared to nonemotional animals (C57 and ICR mice). Slight differences in the ability of GABA to increase chloride influx were found among the three strains. Pentobarbital potentiation of GABA-mediated chloride flux was slightly higher in the ICR mice compared to Balb and C57. Diazepam potentiation of the effects of GABA, however, was significantly decreased in the Balb mice, strengthening the hypothesis that the benzodiazepine receptor is involved in mediating animal emotionality.

Role of the gamma-aminobutyric acid receptor/chloride channel complex in tolerance to ethanol and cross-tolerance to diazepam and pentobarbital

The role of the gamma-aminobutyric acid (GABA) receptor/chloride channel complex in the development of tolerance to ethanol and cross-tolerance to diazepam and pentobarbital was assessed. Rats given a low (1.8 g/kg) dose of ethanol before daily practice on the moving belt test of motor incoordination, and those given a high daily dose (3.6 g/kg) not paired with practice, showed tolerance to ethanol and cross-tolerance to diazepam and pentobarbital, whereas rats receiving 1.8 g/kg of ethanol after practice did not. Control rats were trained on the moving belt, but received no ethanol treatment. No differences were seen among the treatment groups in the abilities of GABA or ethanol to increase 36Cl uptake into cerebral cortical microsacs. However, diazepam potentiation of GABA-mediated chloride flux was significantly lower in rats receiving daily intoxicated practice, but only if they received an i.p. injection of ethanol 1 hr before sacrifice. The degree of pentobarbital potentiation of the effect of GABA did not correlate with the behavioral cross-tolerance observed. The results indicate that behaviorally augmented cross-tolerance from ethanol to diazepam correlates incompletely with changes on the biochemical level.

Differential inhibition by NMDA antagonists of rapid tolerance to, and cross-tolerance between, ethanol and chlordiazepoxide

We have recently found that the non-competitive N-methyl-D-aspartate (NMDA) antagonists, (+)MK-801 and ketamine, block the development of rapid tolerance to ethanol. In the present report we show that they also block rapid cross-tolerance from chlordiazepoxide to ethanol as well as ethanol to chlordiazepoxide. However, NMDA antagonists fail to block the development of rapid tolerance to chlordiazepoxide. Our results suggest that NMDA antagonists may affect not only the acquisition of rapid tolerance or cross-tolerance to sedatives but also the ability to express that tolerance or cross-tolerance, depending on the drugs used. It is also possible that the phenomena of rapid tolerance and rapid cross-tolerance have basic differences not previously reported in the literature.

Potentiation of gamma-aminobutyric acid-mediated chloride flux by pentobarbital and diazepam but not ethanol

The influx of 36Cl- into cerebral cortical and cerebellar microsacs from ICR mice and Sprague-Dawley rats was studied in incubations lasting 3 s, 500 ms, or 21 ms. In the 3-s assay, 10-40 mM ethanol did not affect either basal or gamma-aminobutyric acid (GABA)-mediated Cl- flux, at any GABA concentration tested. Only at a concentration of 600 mM did ethanol potentiate Cl- flux in both mouse and rat preparations. Ethanol (20 mM) also did not affect the significant potentiation of GABA-mediated flux produced by 50 microM pentobarbital or 2 microM diazepam in ICR mouse microsacs. In 21- and 500-ms incubations (quench-flow method), 50 microM pentobarbital significantly potentiated GABA-mediated Cl- flux in rat cortical microsacs, but 10-50 mM ethanol did not. These studies suggest that some as yet unrecognized factor is essential for ethanol enhancement of GABA-mediated Cl- flux, as reported by others in brain homogenates and in tissue culture.

Arginine-8-vasopressin potentiates acute ethanol intoxication

AVP maintains ethanol (EtOH) tolerance after cessation of chronic EtOH treatment. However, the acute interaction of AVP and EtOH has not been well characterized. Rats were trained on a moving belt and the EtOH dose-response relationship (range 1.0-2.0 g/kg) was determined after pretreatment with saline, AVP (2.5-40 micrograms SC or 10 ng ICV), the AVP-V1 receptor antagonist [Des-Gly9,d(CH2)5(1),O-Et-Tyr2, Val4,Arg8]-vasopressin (10 ng ICV), or AVP in combination with the V1 antagonist. AVP produced a 16% decrease in the EtOH ED50 when given either SC or ICV; this decrease, which appears to represent true potentiation rather than additivity, was prevented by the preadministration of the V1 antagonist. Other rats were made EtOH-tolerant by 7 daily injections of either EtOH alone (1.8 g/kg IP) or EtOH (1.5 g/kg IP) + AVP (10 micrograms SC), followed by a practice session on the moving belt. In both sets of tolerant animals, AVP potentiation of acute EtOH effects was still seen on day 6. The mechanism of AVP potentiation of EtOH-induced impairment is unknown, but the failure of the V1 antagonist alone to alter the effect of EtOH suggests that endogenous AVP is not involved directly in modulating EtOH intoxication.

MRI-T2 values in the differentiation of recurrence and fibrosis after radiation of nasopharyngeal carcinoma

The possibility of T2 values in the differentiation of local recurrence and irradiation fibrosis was studied prospectively in 36 patients with nasopharyngeal carcinoma (NPC) after radiotherapy. All the patients had a soft-tissue mass in the nasopharynx demonstrated by CT. Fourteen patients had tumor recurrence, 20 radiation fibrosis, 1 postradiation edema, and 1 inflammatory change. The control group consisted of 8 patients with untreated NPC. It was found that T2 was longer in patients with tumor than in patients with radiation fibrosis. We conclude that MRI may be used as a noninvasive method for differentiating radiation fibrosis from local recurrent NPC, but the prolonged T2 value of tumor is not specific and may be seen in radiation edema and infection.

Endogenous substrates of rat heart protein kinase C type I, II, and III isozymic forms in cardiac sarcolemma

The endogenous substrate proteins of rat cardiac protein kinase C type I, II, and III isozymic forms were studied in rat cardiac sarcolemma. The 19-, 21-, 29-, 35-, and 95-kDa proteins were phosphorylated by both types II and III, but not type I. The extent of phosphorylation by individual protein kinase C isozymic forms was additive and equal to the extent of phosphorylation observed when a mixture of isozymic forms was employed. The extent of phosphorylation of the 21-kDa protein by type III was much higher than that by type II. These results suggest that the protein kinase C isozymes have preferences for specific endogenous substrate proteins. The phosphorylation of these endogenous substrate proteins by protein kinase C isozymes probably plays a role in cardiac cell functions.

Arginine8-vasopressin potentiates the motor incoordinating effects of pentobarbital

Arginine8-vasopressin (AVP, 10 micrograms), injected s.c., potentiated the motor-impairing effects of pentobarbital (10-20 mg/kg) injected i.p. in rats 1 h after AVP. Motor incoordination was assessed on the moving belt task. However, AVP (0.1-100 nM) failed to enhance pentobarbital potentiation of GABA-mediated 36Cl- uptake in rat cerebral cortical or cerebellar microsacs. There was also no effect of a 10 micrograms s.c. injection of AVP 1 h before killing, on pentobarbital potentiation of GABA-mediated chloride flux in either cerebral cortical or cerebellar microsacs.

Differences among effects of sedative-hypnotic drugs on GABA-mediated chloride flux: quench flow studies

The effects of 40 microM pentobarbital (PB), 1 microM diazepam (DZ) and 50 mM ethanol (EtOH) on gamma-aminobutyric acid (GABA)-mediated chloride flux into rat cerebral cortical microsacs were studied during 50 ms incubations with 36Cl. A quench-flow machine was used, allowing for preincubations and incubation of precise duration. A 1 s preincubation with PB did not increase the already significant effect of PB on GABA-mediated flux during the 50 ms incubation, but the 1 s preincubation was necessary for showing the effect of diazepam. EtOH had no effect, whether or not it was added in the preincubation. When microsacs were preincubated with 32 microM GABA for 1 s, far greater potentiation of the GABA effect was seen when the PB was also present during the preincubation than when it was only introduced in the incubation. Preincubation with both DZ and GABA also had a greater effect than merely adding DZ into the incubation, after the preincubation with GABA. Ethanol had no effect when added either during or after the 1 s preincubation with GABA. The different effects of these sedatives on GABA-mediated chloride flux are strongly suggestive of different loci or mechanisms of action.

NMDA antagonist inhibits rapid tolerance to ethanol

To test whether N-methyl-D-aspartate (NMDA) receptors have a role in the development of ethanol tolerance, (+)MK-801, an NMDA antagonist, and (-)MK-801, an inactive isomer, were tested in a rapid tolerance paradigm. Results showed that (+)MK-801 blocked the development of rapid tolerance to ethanol in the tilt-plane and hypothermia tests, while (-)MK-801 was ineffective. Neither drug changed the blood ethanol levels in the treated and untreated animals. These data suggest that the known role of NMDA receptors in long-term synaptic facilitation may underlie the effect of learning in the development of tolerance to the motor-impairing and hypothermic effects of ethanol.

Serotonin agonist and antagonist actions in hippocampal CA1 neurons

The actions of serotonin (5-HT) and its putative agonists and antagonists were examined in vitro on hippocampal CA1 neurons using intracellular recordings, demonstrating that the cellular pharmacological effects can not necessarily be predicted from binding characteristics alone. The first response following 5-HT application was often a long-lasting (several minutes) hyperpolarization associated with decreased input resistance. Subsequent 5-HT applications caused only brief hyperpolarizations (30-120 s) and associated decreased input resistance, often followed by membrane depolarization. The post-spike train afterhyperpolarization (AHP) was prolonged for several minutes following the 5-HT induced hyperpolarization. 5-HT1 agonists (8-hydroxy-2-(di-n-propylamino)tetralin, 5-methoxytryptamine, MK-212) caused a prolonged hyperpolarization, decreased input resistance, and enhancement of the AHP. 5-HT applied following agonist application elicited only short-lasting hyperpolarizations. The 5-HT2 antagonists, cyproheptadine and mianserin, and a nonspecific 5-HT antagonist, methysergide, also caused a prolonged hyperpolarization with decreased input resistance. Spiperone, a nonspecific 5-HT antagonist, and ritanserin, a putative specific 5-HT2 receptor antagonist, depolarized CA1 neurons with little or no change in input resistance. The 5-HT-induced short-lasting hyperpolarization was not affected by drop application of 5-HT antagonists, except for methysergide, but perfusion of methysergide, ritanserin, and spiperone attenuated this response. The long-lasting 5-HT hyperpolarization might be mediated by 5-HT1A receptor activation, and the short-lasting hyperpolarization by another serotonergic receptor subtype.

Ethanol tolerance in hippocampal neurons: adaptive changes in cellular responses to ethanol measured in vitro

The passive and synaptic membrane properties of hippocampal CA1 and dentate gyrus granule neurons have been compared in hippocampal slices obtained from control and ethanol-tolerant rats given ethanol up to 24 hr before sacrifice. In addition, the effects of in vitro exposure to a low concentration (20 mM) of ethanol have been examined in neurons obtained from both groups of animals. No differences were observed in the passive or synaptic membrane properties of dentate granule neurons obtained from control and chronically ethanol-exposed rats. Dentate granule neurons obtained from the two groups of animals also showed similar responses to in vitro exposure to 20 mM ethanol. Hippocampal CA1 neurons were also similar, except for the post-spike train afterhyperpolarization which was significantly prolonged in neurons from chronically ethanol-exposed animals. Exposure to 20 mM ethanol in vitro resulted in a significant increase in the amplitude and duration of the afterhyperpolarization in CA1 neurons obtained from control animals, but a significant decrease in CA1 neurons obtained from chronically ethanol-exposed rats. These results suggest that behavioral tolerance to ethanol is accompanied by adaptive changes in the electrophysiological responses of hippocampal CA1 neurons when tested with an acute exposure to ethanol. Chronic treatment with ethanol did not cause such adaptive changes in dentate gyrus granule neurons suggesting that they may be less sensitive to the effects of long-term exposure to ethanol than CA1 neurons.

Actions of arachidonic acid and hepoxilin A3 on mammalian hippocampal CA1 neurons

The effects of arachidonic acid and its lipoxygenase metabolites, the hepoxilins, were investigated in rat hippocampal CA1 neurons in vitro by intracellular electrophysiological recordings. Both arachidonic acid and the hepoxilins cause a hyperpolarization which is sometimes followed by a later depolarization, augment the postspike train long-lasting afterhyperpolarization (AHP) and increase orthodromic inhibitory postsynaptic potentials (IPSPs). These data show that this arachidonic acid metabolic pathway has significant actions on mammalian central neurons, and may represent an important mechanism of neuromodulation.

Computed tomography in the management of nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is one of the common cancers in China. According to mass surveys, the incidence of NPC in some areas of Guangdong is 39.84/100,000. Due to its high contrast resolution CT has the ability to show not only superficial abnormality but also deep infiltration of the fasciae and muscles of the parapharyngeal region. Computed tomography scanning was performed on more than 1000 patients with NPC in the Tumour Hospital in the 2 years from 1984 to 1986. The role of CT scanning in NPC can be summarised as: (1) detection of primary lesions not accessible to pharyngoscopy; (2) determination of the extent of disease; (3) clinical staging; (4) radiotherapy planning; (5) follow up evaluation; (6) the differentiation of recurrence and radiation damage to the brain; and (7) the demonstration of distant metastasis. In contrast to the concept of jugular chain metastasis via the postero-lateral pharyngeal lymph nodes, our material has demonstrated that the lesion most probably spreads to the carotid sheath area directly from the pharyngeal lesion. The tendency of submucosal spread of NPC is emphasised.

Buffer systems variably affect the interaction of norepinephrine with brain Na+-K+ ATPase

The reported effects of norepinephrine (NE) on brain Na+-K+ ATPase are quite variable. Different investigators have reported activation, inhibition, or no effect. An investigation of the importance of reaction conditions on brain Na+-K+ ATPase activity was undertaken to resolve some of these discrepancies. Using porcine cerebral cortical Na+-K+ ATPase and rat brain synaptosomal membrane preparations, it was observed that NE strongly inhibited brain Na+-K+ ATPase in Tris-HCl buffer. This inhibition of the enzyme was reversed by the addition of EDTA. In contrast, NE did not significantly inhibit Na+-K+ ATPase in imidazole-glycylglycine and Krebs-Ringer-phosphate buffers. This buffer dependence of NE inhibition of the enzyme was consistently demonstrated with three different established methods for phosphate measurement. Kinetic analysis indicated that NE, in Tris-HCl buffer, inhibited the enzyme noncompetitively at high affinity, and competitively at low affinity, ATP substrate sites.

Serotonin-1A receptor activation in hippocampal CA1 neurons by 8-hydroxy-2-(di-n-propylamino)tetralin, 5-methoxytryptamine and 5-hydroxytryptamine

Serotonin (5-HT) usually induced a slow hyperpolarization lasting several minutes on first drop-application onto CA1 neurons. Subsequent applications always caused a briefer (less than 2 min) hyperpolarization, usually followed by a depolarization. 8-Hydroxy-2(di-n-propylamino)tetralin, a 5-HT1A receptor agonist, and 5-methoxytryptamine, a 5-HT1 receptor agonist, produced only the long-lasting hyperpolarization. The application of 5-HT agonists caused a persistent prolongation of the post-spike train afterhyperpolarization. These observations suggest that the long-lasting hyperpolarization produced by 5-HT may be mediated by the activation of the 5-HT1A receptor subtype.

Nifedipine delays the acquisition of tolerance to ethanol

Rats were trained to remain on a motor-driven belt until they reached a criterion of not exceeding 1% error (1.2 s off the belt) in a 2 min trial. Upon completion of training, animals were treated with nifedipine and/or ethanol and were tested for degree of impairment after an i.p. injection of 2 g/kg ethanol solution on test days. Chronic nifedipine treatment enhances the acute ethanol effects on motor impairment and delays the acquisition of tolerance to ethanol. Results suggest modification of brain calcium channel activities could delay the development of tolerance to ethanol and may prevent ethanol-induced organic brain damage.

Increase in the brain regional depolarization-dependent Ca2+ uptake in rats preferring ethanol

The depolarization-dependent Ca2+ uptake system has been suggested to be involved in the release of transmitter and synaptic facilitation. It can be employed as an effective probe to study neurotransmission. Although ethanol has been shown to inhibit or facilitate neurotransmission very little is known about the intrinsic activity of neurotransmission in ethanol-preferring rats. Using the depolarization-dependent Ca2+ uptake system, we demonstrated that synaptic neurotransmission is more active in animals with moderate and high preference for ethanol. Results suggest that there are intrinsic differences in the brain regional neurotransmission among rats showing different degrees of preference for ethanol.