Normalization of auditory physiology by cigarette smoking in schizophrenic patients.

OBJECTIVE: Because many schizophrenic patients are heavy smokers, it has been suggested that nicotine normalizes some neuronal deficit involved in their illness. Schizophrenic subjects have various difficulties with maintenance of attention and selective processing of sensory information. One defect in sensory gating in schizophrenia has been characterized by recording auditory evoked potentials. Most normal subjects have a decrease in the evoked response to the second of two closely paired stimuli, whereas most schizophrenic subjects do not. The aim of this study was to determine whether smoking normalizes this deficit in auditory sensory gating in schizophrenia. METHOD: Changes in auditory sensory gating in response to smoking cigarettes were studied in 10 smokers without psychiatric illness and 10 schizophrenic smokers. Both groups were asked to abstain from smoking from 11:00 p.m. until 8:00 a.m. the next morning, when their auditory evoked responses to pairs of clicks were recorded. The ability to gate sensory information is reflected in a decrease in the P50 wave amplitude in response to the second of the two stimuli. After baseline recordings, the subjects smoked as much as they wished, and then two postsmoking recordings were performed. RESULTS: The schizophrenic patients had a marked but brief improvement in P50 auditory gating immediately after smoking, whereas P50 gating for the normal smokers was slightly impaired. CONCLUSIONS: This study suggests that cigarette smoking can transiently normalize the impairment of auditory sensory gating in schizophrenic patients.

Replication of a P50 auditory gating deficit in Australian patients with schizophrenia.

Schizophrenic patients reportedly have a deficit in the control of sensitivity to auditory stimuli as shown by the P50 auditory evoked potential wave in a conditioning-testing paradigm that measures suppression of response to a repeated stimulus. Although this finding has been replicated by several US laboratories, one European group has not found differences between schizophrenic patients and normal control subjects. In the present study, investigators in the Schizophrenia Research Center at the Prince of Wales Hospital in Sydney, Australia, selected 22 normal control subjects, 11 acutely ill schizophrenic inpatients, and 11 clinically stable schizophrenic outpatients. Both schizophrenic groups were treated with similar doses of classical neuroleptic medications. Evoked potentials were recorded by an investigator from the US laboratory that initially reported the difference; five averages, each the response to 32 stimulus pairs, were recorded from each subject. The normal control subjects demonstrated significantly more suppression of the P50 response to the repeated stimuli than the schizophrenic groups, as previously reported. There were no significant changes in the suppression measure over the five trials. The suppression of the P50 wave by schizophrenic outpatients was somewhat greater than that by schizophrenic inpatients, but both schizophrenic groups had decreased suppression, compared with the normal subjects. The mean P50 suppression for five averages was successfully used in a logistic regression to classify subjects as normal or schizophrenic. This method was more accurate than attempts to classify subjects with only one average. The mean amplitude of the initial conditioning response did not differ between groups. Schizophrenic patients had slightly shorter mean latencies. There was no direct relationship of P50 suppression to measures of clinical psychopathology.

Effects of sound intensity on a midlatency evoked response to repeated auditory stimuli in schizophrenic and normal subjects.

Inhibitory gating of response to repeated stimuli is demonstrated by several event-related potentials, including the auditory P50 wave. The present study examined the effects of variation in sound intensity on this phenomenon in schizophrenics and normal subjects. Paired clicks, 500 ms apart, were presented 50 dB above threshold to 10 normal subjects and 10 schizophrenics. The normal subjects demonstrated significantly more decrement of response to the second stimulus than did the schizophrenics. When the sounds were noticeably louder(70 dB above threshold), no such difference was observed. Rather, both groups had similarly diminished gating of response. A significant difference between schizophrenics and normal subjects was also observed when the sounds were 30 dB above threshold, but the difference was smaller than that at 50 dB. At any stimulus intensity, concomitant eye movements led to loss of gating of P50 in the normal subjects.

HIV-1 transmission in injection paraphernalia: heating drug solutions may inactivate HIV-1.

In response to recent concerns about risk of HIV-1 transmission from drug injection paraphernalia such as cookers, ethnographic methods were used to develop a descriptive typology of the paraphernalia and practices used to prepare and inject illegal drugs. Observational data were then applied in laboratory studies in which a quantitative HIV-1 microculture assay was used to measure the recovery of infectious HIV-1 in cookers. HIV-1 survival inside cookers was a function of the temperature achieved during preparation of drug solutions; HIV-1 was inactivated once temperature exceeded, on average, 65 degrees C. Although different types of cookers, volumes, and heat sources affected survival times, heating cookers 15 seconds or longer reduced viable HIV-1 below detectable levels.