News and Publications

Sleep and Cytokine Research

D.F. Darko, A. Dawson, M. Erman, R. Hayduk, M.M. Mitler, J.S. Poceta

HORMONAL REGULATION OF SLEEP

Because of our interest in the hormonal regulation of sleep, we hypothesized that an aspect of coordination between secretion of human growth hormone (hGH) and slow wave sleep, defined as the strength of the delta wave on electroencephalograms (EEGs), is affected by HIV infection. Data were collected on 11 control subjects who were seronegative for HIV and on 12 subjects who were seropositive for the virus. Plasma samples were obtained every 15 minutes throughout the night while the EEG was recorded. Plasma samples were assayed for hGH. The delta activity on the EEG was extracted by using fast Fourier transform. The data were divided into 4 sleep cycles by using polysomnography. The time base was adjusted so that each subject received equal representation within each sleep cycle, although lengths of the sleep cycles differed.

Our results suggested that sleep cycles were not affected strongly by HIV infection. We found similar delta activities in the 2 groups of subjects, an orderly pattern of peak plasma levels of hGH in the first, second, and fourth sleep cycles of the night in the control subjects, and a degradation of this orderly pattern of hGH peak plasma levels in the subjects seropositive for HIV. The association between hGH and sleep cycle in healthy human subjects was again confirmed. The degradation suggests that nocturnal, sleep cycle-related protein anabolism or secretion may have been modified in the subjects with HIV infection.

NARCOLEPSY

Narcolepsy is a CNS disorder characterized by disabling dysregulation of sleep and wakefulness. Narcolepsy is not rare; it affects about 1 of every 1000-2000 North Americans. A 5-year research project funded by the National Institute of Neurological Disorders and Stroke on the human genetics of narcolepsy is under way. This multisite project involves work with M. Anne Spence, University of California, Irvine, and L. Field, University of Calgary, Alberta.

Although the inheritance of narcolepsy is not known, the disorder is strongly, but not always, associated with subtypes of the HLA region on chromosome 6: HLA-DR15(DRB1*1501) and HLA-DQ6(DQB1*0602). Thus, the presence of HLA-associated and non-HLA-associated forms indicates that narcolepsy is at least 2 disorders. Further, both the HLA-associated (H+) form and the non-HLA-associated (H-) form occur as sporadic isolated cases (F-) and in persons with a family history of narcolepsy (F+). Possibly, each of the 4 types, (H+F-), (H+F+), (H-F-), and (H-F+), represents a different etiology.

Since April 2000, we have identified 19 new probands for our study. Workups (e.g., medical examinations, HLA typing, sleep recordings) of these persons and their blood relatives are progressing. We started a pilot project to expand on the now-famous study by Nishino et al. at Stanford University, who found that 7 of 9 patients with narcolepsy had nondetectable levels of hypocretin-1 in the cerebrospinal fluid (CSF) whereas all 8 control subjects without narcolepsy had detectable levels. The hypocretins are found in synaptic secretory vesicles of fibers that project to several areas implicated in the sleep-wake cycle.

In the study by Nishino et al., the CSF samples were collected at various times through the usual workday, between 9:30 a.m. and 3:45 p.m. We plan to collect samples of CSF through a 24-hour period to determine if a diurnal change occurs in the levels of hypocretin-1 and hypocretin-2 in control subjects and if patients with narcolepsy have detectable levels at times other than 9 a.m. to 4 p.m. Among the 2 patients with narcolepsy in the study by Nishino et al. who had detectable levels of hypocretin-1, the level was in the normal range in one and twice the normal level in the other.

We are also collaborating with S.G. Potkin and J. Christian Gillin, University of California, Irvine, on positron emission tomography studies in patients with narcolepsy. The first scans were scheduled for mid-March 2001.

TNF-a AND THE CNS

The function of TNF-a in sleep is widely studied. TNF-a is somnogenic; it promotes sleep and increases the time spent in slow wave sleep. The somnogenicity of TNF-a raised the question of its possible influence in patients with narcolepsy or HIV infection. In a pilot study, 4 patients with narcolepsy who had the HLA-DR15(DRB1*1501) and HLA-DQ6(DQB1*0602) markers, and 4 control subjects (healthy, unaffected first-degree blood relatives of the patients with narcolepsy) were evaluated. In another study, 24 patients who were seropositive for HIV were evaluated. Blood samples were collected hourly through a 24-hour period for the control subjects and the patients with narcolepsy and every 2 hours for the HIV patients.

In all 3 groups, plasma concentrations of TNF-a varied during the 24-hour period. Patients with narcolepsy and the control subjects had a consistent pattern of change in TNF-a levels through the 24 hours. This pattern did not occur in the HIV patients. Analysis of the data indicated a significant difference between the minimum and maximum plasma levels of TNF-a for the 4 control subjects and for the 24 patients who were seropositive for HIV but not for the 4 patients with narcolepsy. These data represent the first systematic examination of TNF-a levels in patients with narcolepsy or HIV infection. Because the pattern of changes during the 24-hour period was similar in the control subjects and the patients with narcolepsy, this sequence may be the normal configuration. The patients had lower plasma concentrations of TNF-a than the control subjects did. We estimated that the addition of one more pair of subjects who differed by as little as 10% in the same direction would have produced a significant difference between the 2 groups in the TNF-a levels. Further research should include examination of large samples of patients with the sporadic form or the familial form of narcolepsy to determine if these groups differ in the patterns or levels of TNF-a.

SLEEP AND BREATHING

In a project on sleep and breathing, we assessed total upper airway resistance, nasal resistance, hypoxic drive, and hypercapnic drive during wakefulness and sleep in young male smokers before and after smoking cessation. Upper airway resistance is the resistance to airflow through the nose, mouth, and throat during inspiration; increased upper airway resistance causes snoring and sleep apnea. Nasal resistance is the resistance to airflow through the nose only. Hypoxic drive and hypercapnic drive are the increases in the effort to breathe that occur with decreases in the amount of oxygen or increases in the amount of carbon dioxide in the air.

We are testing the following hypotheses: (1) Nicotine, through its respiratory stimulant effect, increases hypercapnic and hypoxic respiratory responses. (2) The irritants contained in cigarette smoke increase upper airway resistance. (3) The combination of increased inspiratory drive and increased upper airway resistance due to tobacco smoke containing nicotine causes instability of the upper airway and leads to more snoring and more obstructive respiratory events (sleep apnea) during sleep.

We have begun a systematic analysis of the data. Preliminary inspection of data for each of the study nights indicated several findings. First, our earlier observation that resistance increases during non-REM sleep, especially slow wave sleep, and that it is relatively low during REM sleep is supported by the new data. Second, resistance tends to be greater in the presence of nicotine during non-REM sleep but not during waking or REM sleep. This finding does not support our main hypothesis, and we will analyze this finding further. Nasal resistance appears to be higher during sleep than during waking and higher before smoking cessation than after cessation. A final analysis of all data and publication of the results are pending.

PUBLICATIONS
Erman, M.K., Erwin, C.W., Gengo, F.M., Jamieson, A.O., Lemmi, H., Mahowald, M.W., Regestein, Q.R., Roth, T., Roth-Schechter, B., Scharf, M.B., Vogel, G.W., Walsh, J.K., Ware, J.C. Comparative efficacy of zolpidem and temazepam in transient insomnia. Hum. Psychopharmacol. 16:169, 2001.

Mitler, M.M. Narcolepsy. In: UpToDate Clinical Reference Library. Rose, B.D. (Ed.). UpToDate, Wellesley, MA, 2001. Available at: www.uptodateinc.com.

Mitler, M.M., Doghramji, K., Shapiro, C. The Maintenance of Wakefulness Test: Normative data by age. J. Psychosom. Res. 49:363, 2000.

Philip, P., Mitler, M. Sleepiness at the wheel: Symptom or behavior? Sleep 23(Suppl. 4):S119, 2000.

Polich, J., Ilan, A., Poceta, J.S., Mitler, M.M., Darko, D.F. Neuroelectric assessment of HIV: EEG, ERP, and viral load. Int. J. Psychophysiol. 38:97, 2000.