Weak prepulses inhibit but do not elicit startle in rats and humans.

BACKGROUND: Inhibition of startle by weak prestimuli is called prepulse inhibition (PPI). It has recently been reported that 10- to 20-dB prepulses trigger eye-blink motor activity and PPI in normal human subjects. Motor activity after prepulses correlated negatively with PPI in four of nine possible conditions. We now report the relationship between prepulse-elicited startle (PPES) and PPI using weak prepulses. METHODS: We assessed PPI and PPES using 1- to 5-dB prepulses in humans and in rats after treatment with vehicle or apomorphine. RESULTS: Prepulses inhibited startle in an intensity-dependent fashion but elicited no startle activity in humans or rats. Apomorphine eliminated PPI in rats and produced a well-documented increase in stimulus-independent motor activity but did not stimulate PPES. CONCLUSIONS: In humans and rats, PPES is not a necessary condition for either the elicitation or the disruption of PPI.     

Barotrauma due to obstruction of the breathing system during a CT-scan examination in a child

A case of pulmonary barotrauma is described in a child undergoing a CT scan in the prone position. Anaesthesia was uneventful until the final exiting movement from the scanner when inadvertent total occlusion of the expiratory limb of a Jackson-Rees modification of the Ayre's T-piece occurred. The rapid rise in intrapulmonary pressure caused bilateral pneumothoraces despite the use of an uncuffed tracheal tube. The unusual demands of anaesthesia in the X-ray department may have contributed to this uncommon complication of the use of an Ayre's T-piece.     

Patient controlled analgesia—assessment of machine feedback to patients

The effect of varying patient-controlled analgesia machine feedback was studied in two groups of patients following a standard surgical procedure using patient controlled analgesia with morphine to control postoperative pain. Analgesic demands, morphine consumption, pain scores and side effects were compared and comments from the patients were noted. There was no significant difference between those whose machines signalled only successful demands compared with those who had every demand acknowledged. The patients in the former group appreciated the extra input and the nursing staff found this machine configuration to be less disturbing to the ward. There was no evidence of a clinically useful placebo effect in the latter group.     

Local anaesthetic: does it really reduce the pain of insertion of all sizes of venous cannula?

A recent study performed in this department showed that a subcutaneous injection of local anaesthetic was significantly less painful than the insertion of a 22-gauge venous cannula. However, our colleagues remained sceptical that local anaesthetic infiltration would eliminate the pain of cannulation. Consequently a further study was undertaken to compare the pain of cannulation with and without the use of local anaesthetic. The results show that pain of cannulation is significantly (p < 0.003) reduced after subcutaneous infiltration with 1% lignocaine when compared to cannulation without local infiltration. Persistent discomfort at the site of cannulation was eliminated by the use of local anaesthetic.     

Morphine induces an increase in extracellular serotonin in the rat diencephalon

The effect of systemic morphine on extracellular serotonin (5-HT) in the diencephalon of unanesthetized, unrestrained rats was investigated by in vivo microdialysis coupled to high performance liquid chromatography with electrochemical detection. Administration of morphine resulted in a dose dependent increase in extracellular 5-HT. Significant increases were first seen at a dose of 5 mg/kg, and a maximal increase occurred at 10 mg/kg. This increase was blocked by pretreatment with naltrexone, indicating that the effect of morphine on 5-HT was mediated by opiate receptors. Morphine also had a significant effect on extracellular 5-hydroxyindoleacetic acid (5-HIAA), leading to a gradual increase across a range of doses. The effect of morphine on 5-HT was compared to effects of morphine on nociception and catalepsy. Increases in 5-HT and 5-HIAA were first detected at doses that were analgesic but too low to elicit catalepsy. Consistent with many reports that opioids cause an increase in synthesis and turnover of 5-HT in the rat forebrain, the present results provide more direct evidence that 5-HT release is increased after morphine administration.