Neuronal aspects of opiate dependence and tolerance in comparison to central depressants

Some acute and chronic effects of opiates and of central depressants have been reviewed, in order that a comparison can be made between the actions of these drugs. Special emphasis has been given to opiate-induced changes at the neuronal level, which have been studied either by the direct microelectrophoretic application of drugs to single neurones or by application of drugs to the myenteric plexus/longitudinal muscle preparation of the guinea pig ileum. Available evidence suggests that chronic exposure of nervous tissue to opiates as well as to central depressants causes changes in neuronal excitability, which become apparent upon withdrawal of the drug. Although opiates and central depressants cause similar changes they appear to do so by different mechanisms. Such differences between the mode of action of opiates and central depressants may provide an explanation for the differing chronic effects of these drugs.

Actions of opiates upon single unit activity in the cortex of naive and tolerant rats

The effect of microelectrophoretically and systemically applied opiates on neuronal discharge activity in the sensorimotor cortex of naive and morphine tolerant/dependent rats has been studied. In naive rats depression of spontaneous discharge activity was the predominant effect of low doses of phoretically applied morphine. Higher doses and repeated application frequently converted this effect into excitation. Only the depressant effect was antagonised by naloxone. Naloxone itself had no effect on spontaneous discharge activity when applied at dose-levels sufficient to antagonise the depressant effect of morphine. Levorphanol mimicked the action of morphine whereas dextrorphan was inactive. Morphine depressed the excitatory action of L-glutamate and of acetylcholine by a naloxone-antagonisable mechanism. Systemic application of Fentanyl mimicked the inhibitory effect of phoretically applied morphine upon transcallosally evoked discharge activity. The late response was markedly depressed whereas the primary response was little affected. Phoretically applied naloxone antagonised the effects of systemically applied Fentanyl. In chronically morphinised rats the depressant effect of microelectrophoretically administered morphine was almost lacking and a naloxone-resistant excitation became the predominant effect. In these animals the excitant effect of naloxone was also increased and the anti-glutamate effect and the anti-acetylcholine effect of morphine was abolished. The present data speak in favour of a postsynaptically located stereospecific receptor which mediates the inhibitory effects of opiates and which may be involved in the development of acute and chronic tolerance to these drugs.

Inhibition of thalamic and hypothalamic somatosensory evoked potentials by stimulation of substantia nigra and its modification by morphine and methotrimeprazine (levomepromazine)

A brief electrical stimulation of the substantia nigra induced a marked and long lasting inhibition of the somatosensory evoked potentials recorded from the centrum medianum of the thalamus (CM) and posterior hypothalamic area (PHA) following sciatic stimulation in unanesthetized rabbits. The nigral inhibitory effect on CM was prolonged by the administration of morphine (4 mg/kg i.v.) but not influenced by that of methotrimeprazine (2-4 mg/kg i.v.). In contrast, the nigral inhibitory effect on PHA was enhanced by the injection of methotrimeprazine (2 mg/kg i.v.), but not changed by that of morphine (4 mg/kg i.v.). These results indicate that the inhibitory system originating from the substantia nigra operates on the somatosensory transmissions from the peripheral nerve to the thalamus and hypothalamus, and that morphine or methotrimeprazine in small doses induced a selective potentiation of the nigral inhibitory influence on the thalamus or hypothalamus, respectively.

Effects of indomethacin and the other anti-inflammatory agents on activation of dorsal horn cell in the spinal cord induced by intra-arterial injection of bradykinin

Bradykinin (1-2 mug) injected into the femoral artery of the rabbit induced a marked increase in the firing rates of the dorsal horn cells (lamina V cells). This response was markedly inhibited by intravenous administration of indomethacin (1.0 mg/kg), acetylsalicyclic acid (20 mg/kg), aminopyrine (50 mg/kg) and oxyphenbutazone (20 mg/kg) in both intact and spinal preparations. Moreover, the intra-arterial injection of these agents depressed the response in lower doses. With these same low doses, no significant suppression occurred when the intravenous route was used. These results indicate that indomethacin and other anti-inflammatory agents tested suppress the bradykinin-induced response of the dorsal horn cell at the periphery, probably at the paravascular sensory nerve.

Indirect and direct depressive effects of morphine on activation of lamina V cell of the spinal dorsal horn induced by intra-arterial injection of bradykinin

Small doses of morphine (0.3-2.0 mg/kg i.v.) inhibited, in the majority of intact rabbits, the unitary activities of the lumbar lamina V dorsal horn neurons induced by intra-arterial injection of bradykinin, a potent pain producing substance, but not in spinal rabbits. A large dose of morphine (5.0 mg/kg), however, inhibited the bradykinin-induced response even in spinal rabbits. These results suggest that morphine, in small doses, inhibits the sensory transmission of bradykinin-induced pain at the dorsal horn of the spinal cord, through its facilitatory action on the descending inhibitory mechanism; in large doses the level of dorsal horn is directly inhibited.

[Dense material observed in pericapillary space of the thyroid of Hashimoto's disease]

An electron microscopic observation was performed on the follicular capillary of thyroid of Hashimoto's disease. Material was the thyroid obtained from a 41-years-old female showing typical features of this disease both clinically and histologically. Some remarkable findings were the presence of multi-layered basement membrane like structure, and the accumulation of dense minute granular materials concerning with long processes of lymphcyte in the widened pericapillary space. From the above-mentioned findings, it was postulated that there was abnormal transport on follicular basement membrane-pericapillary space-endothelial basement membrane system.

Ultrastructure of the giant cell in de Quervain's subacute thyroiditis

The author made an electron microscopic observation on multinucleated giant cells which appear in the thyroid gland in subacute thyroiditis (de Quervain). Numerous typical desmosomes, which intermingled with myriad of mitochondria and small electron dense granules, were found in the cytoplasm of giant cell. Desmosome is one peculiar to the intercellular junction of follicular epithelium of the thyroid gland, and the fact that many desmosomes were found in the cytoplasm is one of the proofs showing this giant cell to be possibly derived from the follicular epithelium.

Supersensitivity of cortical neurones of the rat to acetylcholine and L-glutamate following chronic morphine treatment

the effect of microelectrophoretically applied L-glutamate and acetylcholine on discharge activity of cortical neurones was studied in naive and in morphine-tolerant/dependent rats. The thresholds for increase in discharge activity elicited by these 2 putative neurotransmitters were 3 times lower in the tolerant/dependent rats than in the naive rats, indicating the development of supersensitivity.

Prognostic significance of serum albumin urea ratio in suture line leakage of the alimentary tract

Prognostic significance of postoperative changes in serum albumin and urea concentrations as well as their ratio was statistically evaluated in 73 patients with suture line leakage of the abdominal alimentary tract. Increase in serum urea was associated with poor prognosis regardless of the site of leakage. Although the serum albumin concentration was poorly correlated to prognosis, its ratio to serum urea was of more prognostic significance than the urea value alone. When the ratio of the serum albumin nitrogen to the urea nitrogen fell below 10, there was a sharp rise in mortality as well as in morbidity, associated with poor local defense reaction, high incidence of spreading peritonitis, severe systemic complications, and decreased tolerance to tube feeding as well as parenteral hyperalimentation. A special therapeutic policy was suggested for the management of leakage in patients with critically low albumin/urea ratios.