Katsuya Iwatsubo

EFFECTS OF NARCOTIC ANALGESIC DRUGS ON THE CYCLIC ADENOSINE 3′, 5′‐MONOPHOSPHATE‐ADENYLATE CYCLASE SYSTEM IN RAT BRAIN

1 The concentrations of cyclic adenosine 3′, 5′‐monophosphate (cyclic AMP), measured in discrete brain areas removed from rats killed by microwave irradiation, rose transiently in most areas after the administration of morphine. The most pronounced changes, however, were found 2 h after doses of either 10 or 60 mg/kg morphine when cyclic AMP levels declined significantly in the hypothalamus, medulla and cerebellum. In morphine‐tolerant rat brains there were no decreases in cyclic AMP levels. 2 Basal adenylate cyclase activity in crude nerve‐ending fractions from discrete areas of rat brain was unaffected by the addition of active analgesic agonists, antagonists or inactive isomers to the assay medium in vitro, except for a nonspecific inhibition at drug concentrations of 1 mM. 3 The acute administration of morphine or levorphanol, but not dextrorphan produced transient increases in basal cyclase activity of crude nerve‐ending preparations from midbrain and striatum. In morphine‐tolerant rats, these changes in basal adenylate cyclase activity were no longer seen.

Dopamine-sensitive adenylate cyclase of the caudate nucleus of rats treated with morphine.

Abstract The addition of narcotic analgesics in vitro to nerve ending preparations from rat caudate nucleus in an assay of adenylate cyclase activity (AC) resulted in an inhibition of basal AC only at drug concentrations of 10− 4 M or higher, and no inhibition of dopamine-stimulated (DA) AC at these drug concentrations. The acute administration of morphine at a moderately high dose (60 mg/kg) produced an increase in striatal cAMP levels, and increases in basal and DA-AC in caudate nerve-endings. In morphine-tolerant rats, striatal cAMP levels and basal AC were similar to control values, while DA-AC was elevated. These results suggest: (1) that opiates do not act directly on DA-AC, the ‘dopamine receptor’, and (2) that the observed behavioural DA sensitivity in tolerant animals may be produced by the DA-AC supersensitivity.

Penetration of nicotine-14C into several rat tissues in vivo and in vitro

Abstract The penetration of nicotine-14C into several rat tissues in vivo and in vitro was studied. When 5 mg/kg of nicotine-14C was injected intraperitoneally, the following maximum tissue-to-blood ( T B ) ratios were obtained after 10–20 minutes: kidney, 8.7; liver, 6.7; submaxillary gland, 6.2; brain cortex, 3.5; brain stem, 2.4; and heart, 1.8. Pretreatment with hexamethonium decreased the T B ratio of kidney, but there was no influence on the nicotine level of the other tissues. Tissue levels were not influenced by pretreatment with hexobarbital. After incubating the tissue slices with 10−4 M nicotine-14C for 30 minutes at 37°, the following slice-to-medium ratios ( S M ) were obtained: brain cortex, 2.0; submaxillary gland, 2.1; liver, 2.1; and kidney cortex, 2.6. When oxidative phosphorylation was uncoupled or metabolic pathways were blocked, the penetration of nicotine-14C into the above slices was not affected. Alteration of pH of the medium from 6.0 to 9.0 increased the S M ratios of the four tissues over 2 times. The penetration of nicotine-14C seemed to reach a maximum at pH 8.0–9.0.

Neuronal activity of the substantia nigra (pars compacta) after injection of kainic acid into the caudate nucleus

Abstract In rats the caudate nucleus (Cd) of one side was injected with 2.5 μg kainic acid (KA) in 1 μl saline and that of the other side with saline of the same volume. Three to sixty days later, neuronal activities of the substantia nigra were examined by stimulating the caudate nucleus on each side. Two major types of activity were distinguished: pure inhibition and antidromic excitation followed by inhibition. With 65 substantia nigra units sampled from the side of saline injection, the frequency of incidence for the pure inhibition was 58.5% and that for the antidromic excitation followed by inhibition was 21.5%. In five units (7.7%), caudate stimulation remained ineffective. A total of 97 substantia nigra units was recorded from the side of KA injection and characterized as follows: (i) 42.3% had no effect of caudate stimulation, this being much higher than the control. Pure inhibition was encountered at a reduced frequency (29.9%) and its duration was markedly shortened. These findings are interpreted to mean that GABAergic strionigral inhibitory neurons were killed or damaged by locally injected KA. (ii) Antidromic excitation was seen as frequently as in the control side (19.6%). Inhibition following it was not reduced in duration. The antidromic inhibition of substantia nigra neurons from the caudate nuclei was suggested to be due to dopaminergic self-inhibition as proposed by Groves and his co-workers.

A Possible involvement of the central endorphin system in the autoanalgesia induced by chronic administration of freund's adjuvant solution in rats

Abstract Chronic pain was induced in rats by daily injections of complete Freunds adjuvant into hind paws. Daily changes of pain threshold and endorphin (ED) content and their receptors in 4 divided parts: cortex, diencephalon‐mesencephalon containing striatum (D‐M), pons‐medulla (P‐M) and spinal cord, were measured. Decrease in pain responsiveness was observed in the adjuvant‐injected group with concomitant increase of ED content in P‐M and spinal cord. This decrease in pain responsiveness in the adjuvant‐injected group was significantly different from that in the non‐treated control group being partially reversed by naloxone. Furthermore, [3H]met‐enkephalin binding sites increase in number in P‐M of the adjuvant‐injected group when maximal decrease of pain responsiveness was observed, returning to control level thereafter. Scatchard analysis revealed the increase of the low affinity binding site in P‐M of the adjuvant‐injected group. In cortex and D‐M, on the other hand, ED content tended to decrease and no change was observed in number of [3H]met‐enkephalin binding sites. These results indicate that the ED system in P‐M and spinal cord may be more substantially involved in autoanalgesia than in cortex and D‐M.

Effects of dopaminergic agonists and antagonists on [3H]apomorphine binding to striatal membranes: sulpiride lack of interactions with positive cooperative [3H]apomorphine binding

Effects of dopaminergic agonists and antagonists on [3H]apomorphine binding to striatal membranes of rat brain was examined. Haloperidol and spiroperidol exhibited biphasic inhibition of [3H]apomorphine binding; one of which had the Hill coefficient of 0.9, whereas the other had that of 0.4. The former accounted for 65% of [3H]apomorphine binding while the latter consisted of 35% of the binding. Furthermore, the latter disappeared after kainic acid lesions. On the other hand, sulpiride and metoclopramide reduced [3H]apomorphine binding to 31% with the Hill coefficient of 0.9. The inhibition of [3H]apomorphine binding with the Hill coefficient of 0.4 which was shown by haloperidol and spiroperidol was not observed for sulpiride and metoclopramide. Previously, we demonstrated non- and positive-cooperative [3H]apomorphine binding to stiatal membranes. In the present study, it has been also shown that sulpiride inhibits non-cooperative [3H]apomorphine binding leaving that with allosteric properties unaffected. No inhibition of dopamine-sensitive adenylate cyclase was observed by 10(-4) M sulpiride while 90% inhibition was obtained with 10(-5) M haloperidol. From those results, it is suggested that non-cooperative [3H]spomorphine binding is not coupled with dopamine-sensitive adenylate cyclase.

Narcotic analgesics and nigrostriatal dopaminergic neurons

Abstract Administration of opiates and antipsychotic elicits various biochemical and electrophysiological events in the nigrostriatal dopaminergic system. How do these two classes of drugs produce enhancement of the turnover rate of dopamine and an increase in the firing rate of the dopaminergic neurons? This article summarizes recent data which are casting some light on this problem.

Nechanism of Substance P-Induced Salivary Secretion in Rats

Leeman and Hammerschlag (1,2) found a potent sialogogic substance in the rough extract from bovine or rat hypothalamus. This sialogogue has been known to be substance P itself. Although substance P (SP), one of tachykinins, has been recognized as a neurotransmitter (3,4) or a modulator (5,6) of the primary sensory neurone, mechanism of sialogogic action of this substance still remained undissolved.

ENDORPHIN LEVELS IN THE RAT BRAIN AFTER THE TOOTH PULP STIMULATION

Summary Various types of electrical stimulation of tooth pulp and inhibitors of degradation and synthesis of opioid peptides were tested in order to find possible changes in endorphin content of three areas of brain, pons-4. diencephalon-mesencephalon-striaturm (D-M) and cortex, in rats. It was found that stimulation with short trains produced a significant increase in pons-C4. In the animals treated with D-phenylalanine, a weak inhibitor of carboxypeptidase, tooth pulp stimulation failed to cause any further changes. In the animals treated with cycloheximide which inhibits the peptide synthesis in the brain, tooth pulp stimulation produced a significant decrease in endorphin content in D-M. Thus, noxious stimulation may cause changes in endorphin levels in opposite directions depending on areas of the brain.