[Dreaming and schizophrenia: a common neurobiological background?]

Comment les neurosciences recherchent la clé des songes

Le sommeil est une succession de deux phases : le sommeil profond d’une part et le sommeil paradoxal d’autre part, qui possède des caractères propres à la veille et au sommeil, ce qui a conduit à proposer que cette phase hébergerait les rêves. Cette hypothèse est maintenant considérée comme simplificatrice, le sommeil profond abritant aussi des rêves aux caractéristiques différentes. Dans ces conditions, déterminer les structures cérébrales associées au rêve est difficile. Le rêve et la veille impliquent les mêmes mécanismes. L’origine des stimulations du cortex, en l’absence de stimulation externe, reste débattue et la fonction du rêve incomprise. Pour certains, le rêve pourrait être un épiphénomène provoqué par le bruit de fond de la transmission synaptique.

Cacna1c (Cav1.2) Modulates Electroencephalographic Rhythm and Rapid Eye Movement Sleep Recovery

STUDY OBJECTIVES

The CACNA1C gene encodes the alpha 1C (α1C) subunit of the Cav1.2 voltage-dependent L-type calcium channel (LTCC). Some of the other voltage-dependent calcium channels, e.g., P-/Q-type, Cav2.1; N-type, Cav2.2; E-/R-type, Cav2.3; and T-type, Cav3.3 have been implicated in sleep modulation. However, the contribution of LTCCs to sleep remains largely unknown. Based on recent genome-wide association studies, CACNA1C emerged as one of potential candidate genes associated with both sleep and psychiatric disorders. Indeed, most patients with mental illnesses have sleep problems and vice versa.

DESIGN

To investigate an impact of Cav1.2 on sleep-wake behavior and electroencephalogram (EEG) activity, polysomnography was performed in heterozygous Cacna1c (HET) knockout mice and their wild-type (WT) littermates under baseline and challenging conditions (acute sleep deprivation and restraint stress).

MEASUREMENTS AND RESULTS

HET mice displayed significantly lower EEG spectral power than WT mice across high frequency ranges (beta to gamma) during wake and rapid eye movement (REM) sleep. Although HET mice spent slightly more time asleep in the dark period, daily amounts of sleep did not differ between the two genotypes. However, recovery sleep after exposure to both types of challenging stress conditions differed markedly; HET mice exhibited reduced REM sleep recovery responses compared to WT mice.

CONCLUSIONS

These results suggest the involvement of Cacna1c (Cav1.2) in fast electroencephalogram oscillations and REM sleep regulatory processes. Lower spectral gamma activity, slightly increased sleep demands, and altered REM sleep responses found in heterozygous Cacna1c knockout mice may rather resemble a sleep phenotype observed in schizophrenia patients.

Association of Per3 length polymorphism with bipolar I disorder and schizophrenia

BACKGROUND

Sleep-wake disturbances have frequently been reported in bipolar disorder and schizophrenia, and are considered to be caused by an underlying circadian rhythm disorder. The study presented here was designed to investigate the existence of Per3 polymorphism in bipolar disorder type I (BD-I) and schizophrenic patients in South India.

METHODS

Blood samples were collected from 311 BD-I patients, 293 schizophrenia patients, and 346 age- and sex-matched normal controls. Per3 genotyping was performed on DNA by polymerase chain reaction using specific primers.

RESULTS

An increased prevalence of five repeat homozygotes was seen in BD-I patients as compared with healthy controls (odds ratio =1.72 [95% confidence interval: 1.08-2.76, P=0.02]). In BD-I patients, the frequency of the five repeat allele was higher (allele frequency =0.41), and that of the four repeat allele lower (allele frequency =0.36) (χ (2)=4.634; P<0.03) than in the control group. No significant association was observed in the allele frequencies of four and five repeat alleles in schizophrenia patients when compared with controls.

CONCLUSION

The occurrence of the five repeat allele of Per3 may be a risk factor for BD-I onset in this ethnic group.