Ultradian rhythm of pontomesencephalic opiate receptor: modification by chloramphenicol

Chloramphenicol prevents carbachol-induced REM sleep in cats

Twenty-four cats were implanted for chronic sleep recordings. One week after the surgery, cats were divided into four groups. Two groups were treated with three i.p. injections of 150 mg/kg chloramphenicol (CAP) separated by 12 h. Carbachol (8 micrograms/1 microliter) or saline (1 microliter) was injected into the pontine reticular formation (PRF) 1 h after the last injection of CAP. The other two groups received saline or carbachol into the PRF without CAP pre-treatment. Polygraphic recordings were started immediately after the microinjection and lasted 11 h. Carbachol increased REM sleep (P < 0.001) and reduced SWS2 (P < 0.05). In contrast, chloramphenicol reduced REM sleep (P < 0.001) and increased SWS2 (P < 0.01). The combination of these drugs increased wakefulness (P < 0.01) and reduced both SWS2 and REM sleep (P < 0.001). This data shows that chloramphenicol prevents carbachol induced REM sleep. Results are discussed in terms of an interaction between brain proteins and the cholinergic system to induce REM.

Chloramphenicol modifies benzodiazepine receptor rhythm in the pontomesencephalic formation of the rat

Pontomesencephalic benzodiazepine (BZ) receptors were measured at 4 h intervals throughout a 24 h day, and compared with those in frontal cortex, using [3H]diazepam binding. Animals were treated with saline, chloramphenicol (CAP) or thiamphenicol (TAP). An ultradian rhythm of receptors was observed in both cases, which was abolished by CAP but not by TAP. Saturation curves and Scatchard analysis indicated decreased binding was due to a decrease in the number of receptors. CAP effect on REM sleep, could be mediated by a general decrease of neurotransmitter receptors at precise periods of the wake-sleep rhythm.

Daily modifications of 3H-naloxone binding sites in the rat brain: a quantitative autoradiographic study

The endogenous opioid peptides, the opiate receptors and several related behaviours, like opioid-mediated analgesia, show daily variations in different animal species including rats. The attempt to correlate the daily rhythm of opiate receptors in the central nervous system (CNS) to opiate related rhythmic phenomena requires an experimental approach with a high anatomical resolution, as the opioid distribution is very heterogeneous. In this paper we present the study of daily variations of 3H-naloxone binding sites in the different regions of the adult male rat brain, performed by means of quantitative autoradiography. Five rats are sacrificed at each investigated time of the day (0200, 0600, 1000, 1400, 1800 and 2200). The ligant is 3H-naloxone (4 nM), the quantification is performed by means of densitometric procedures (image analyzer Tesak VDC 501, computer Digital PDP 11, 3H-microscale). The statistical analysis is performed according to the single Cosinor method and the one-way analysis of variance followed by the multiple range test of Duncan. We analysed 33 different regions of the rat CNS, and the daily variations of opiate receptors are regionally selective. A circadian rhythm is found in the anterior cingulate cortex, hippocampal cortex, periventricular, medial, ventral, reticular and posterior nuclei of the thalamus, rhomboid, gelatinosus and rheuniens nuclei, lateral hypothalamus, locus coeruleus, grey substance of the pons, reticular formation of medulla oblongata, inferior olivary complex, medial part of the nucleus of the solitary tract and nucleus of the spinal tract of the trigeminal nerve. An ultradian rhythm is found in the medial and lateral preoptic areas, in the medial hypothalamus, in the medial and in the lateral nuclei of habenula. No significant variations during 24 hr according to the Cosinor analysis are found in the dorsal and lateral cerebral cortex, striatum, globus pallidus, bed nucleus of the stria terminalis, septal nuclei, lateral nucleus of the thalamus, cochlear nuclei, nucleus of the solitary tract, lateral and caudal parts, dorsal motor nucleus of the vagal nerve, XII and IX nerve nuclei. The amplitude of the daily variations observed ranges from 10 to 40%. Our results demonstrate the high anatomical selectivity of the daily modifications of 3H-naloxone binding sites in the rat CNS. They also indicate that quantitative autoradiography is a suitable and sensitive technique for these studies.

Circadian rhythms in mammalian neurotransmitter receptors

At the present time, the following summary statements can be made as to 24-hour changes in receptor binding. In all receptors studied in homogenates from whole rat forebrain (alpha 1, alpha 2, beta-adrenergic, muscarinic cholinergic, dopaminergic, 5HT-1, 5HT-2, adenosine, opiate, benzodiazepine, GABA, imipramine), significant variations over 24 hours have been documented. The receptor rhythms measured change in wave form, amplitude, and phase throughout the year, even though the animals have been kept on a defined and constant LD cycle. Whether these rhythms are truly seasonal requires further investigation. The rhythms are circadian: i.e. they persist in the absence of time cues, and the unimodal rhythms do not persist after lesion of the putative circadian pacemaker in the suprachiasmatic nuclei. The rhythms can be uni- or bimodal, and each brain region shows a particular pattern. The pattern can be different for the same ligand in different nuclei of a given brain region (e.g. hypothalamus). Nearly all studies of receptor rhythms have been carried out in rats; the results vary according to strain and even within the same strain from different breeding lines. Receptor rhythm characteristics are modified by age: e.g. the amplitude, phase, as well as the 24-hour mean of binding to a given ligand in a defined brain region. The changes in number of binding sites over 24 hours can be correlated with amine turnover, second messenger, or function of that brain region; however these relationships, although consistent within a region, do not hold for all regions. If gradual changes in CNS neurotransmitter receptor function are considered important in the pathogenesis of schizophrenia and affective disorders and the mode of action of psychopharmacological agents, then consideration of the short term rapid change over 24 hours is equally necessary. Chronic treatment with a number of psychoactive drugs known to induce up- or down-regulation of receptor number, also induces marked changes in circadian rhythm parameters of wave form, amplitude, phase and 24-hour mean. This is of methodological importance for single time-point studies, since the interpretation of the results will depend on time of day. Preliminary evidence supports the assumption that the significant variation in receptor binding throughout the day may underlie the well-known circadian rhythms of susceptibility to many CNS drugs. New findings of circadian rhythms in receptors on blood cells indicate the relevance of these changes also in human physiology.