Genetic studies of daily variations of first-step enzymes of monoamines metabolism in the brain of inbred strains of mice and hybrids. II. Daily variations of tyrosine hydroxylase activity in the locus coeruleus

Circadian functioning of Locus Cœruleus of the nocturnal rat and diurnal rodent Arvicanthis

The noradrenergic Locus Cœruleus is one of the major arousal structures involved in inducing wakefulness. While brain noradrenaline (NA) amounts display 24-h variations, the origin of NA rhythm is currently unknown. In this study, we tested the hypothesis that NA rhythm could result from its rhythmic synthesis. Therefore, we investigated the 24-h expression profile of NA rate-limiting enzyme, tyrosine hydroxylase (th), in the Locus Cœruleus (LC) of the nocturnal rat and the diurnal rodent Arvicanthis, under 12 h:12 h light/dark (LD) and constant darkness (DD) conditions. In both species, th mRNA levels vary significantly over 24-h. In nocturnal rats, th mRNA profiles show a unimodal rhythm, with peak values in late day in LD, and in the middle of the subjective day in DD. In contrast, th mRNA rhythm in Arvicanthis is characterized by a bimodal profile, with higher levels at the beginning of the day and of the night in LD, and in the middle of the subjective day and night in DD. The rhythmic pattern of th expression may be dependent on a LC clock machinery. Therefore, we investigated the expression of three clock genes, namely bmal1, per1, and per2, and found that their mRNAs display significant variations between day and nighttime points in both species, but in opposite directions. These data show that NA rhythm may be related to circadian expression of th gene in both species, but differs between nocturnal and diurnal rodents. Furthermore, the phase opposition of clock gene expression in the rat compared to Arvicanthis suggests that the clock machinery might be one of the mechanisms involved in th rhythmic expression.

Circadian rhythms and pain

The goal of this review is to provide a perspective on the nature and importance of the relationship between the circadian and pain systems. We provide: 1) An overview of the circadian and pain systems, 2) a review of direct and correlative evidence that demonstrates diurnal and circadian rhythms within the pain system; 3) a perspective highlighting the need to consider the role of a proposed feedback loop of circadian rhythm disruption and maladaptive pain; 4) a perspective on the nature of the relationship between circadian rhythms and pain. In summary, we propose that there is no single locus responsible for producing the circadian rhythms of the pain system. Instead, circadian rhythms of pain are a complex result of the distributed rhythms present throughout the pain system, especially those of the descending pain modulatory system, and the rhythms of the systems with which it interacts, including the opioid, endocrine, and immune systems.

Brain tyrosine hydroxylase in the catfish Heteropneustes fossilis: annual and circadian variations, and sex and regional differences in enzyme activity and some kinetic properties

Dynamics of tyrosine hydroxylase (TH) was studied in various brain regions and pituitary in relation to annual/seasonal and circadian variations in either sex of the catfish Heteropneustes fossilis. alpha-Methylparatyrosine inhibited TH activity significantly in a time-(in vivo study) and concentration-(in vitro study) dependent manner. The inhibition was higher in resting phase than preparatory phase and in females than males (time-course study). The apparent kinetic constant of inhibition (K(i)) varied both seasonally and regionally. The values were higher in resting phase and in the forebrain regions (telencephalon and hypothalamus) than medulla oblongata. No significant sex difference was noticed in the K(i) values in the same season. TH activity showed significant annual/seasonal variations with telencephalon and hypothalamus showing higher activity than medulla oblongata. The females showed significantly higher enzyme activity than males with a distinct activity peak in June (prespawning phase). Such an activity peak was apparently absent in males. TH activity showed significant circadian/diurnal variations, the highest activity was noticed at 12 h and the lowest at 24 h. The apparent Michaelis-Menten constant (K(m)) values (hypothalamic TH) for substrate (L-tyrosine) and cofactor (DMPH(4)) showed seasonal variations with the highest values in the resting phase, decreasing through preparatory and prespawning phases, to the lowest values in spawning phase. V(max) was the lowest in the resting phase and highest in the spawning phase. TH activity was low in the pituitary and could be detected in pooled samples from March (preparatory phase) to July (spawning phase). Activity showed significant variations, which could be correlated with the gonadosomatic index. The results show that TH activity could be positively correlated with the annual reproductive cycle. The enzyme activity could be also correlated with seasonal, sex, and regional variations in the apparent K(m) and V(max) values suggesting apparent differences in the affinity of the enzyme towards substrate and cofactor.

Influences of biological rhythms on the effects of psychotropic drugs

The efficacy of psychotropic drugs varies depending on the time of administration. This phenomenon is observed with antipsychotics, antidepressants, mood stabilizers, benzodiazepines, barbiturates, and psychostimulants. The presence or absence of this phenomenon and the rhythm phase in the efficacy of each drug varies depending on the drug, dose, parameter measured, animal species, and strain. A recent study demonstrating circannual changes in the phases of circadian rhythm of drug efficacy suggests that discrepancies between studies may be considerably explained by the presence of a circannual rhythm. The rhythms in drug effects are suggested not to be due to rhythmic changes in the pharmacokinetics of the drugs but rather to an endogenous rhythm in drug susceptibility resulting from a circadian rhythm in the intracerebral neurotransmission system. The presence of this phenomenon and its law have been demonstrated to a considerable extent in animals, but corresponding clinical reports in humans remain insufficient despite its clinical importance. Further study in humans is certainly warranted.

Tyrosine hydroxylase expression within Balb/C and C57black/6 mouse locus coeruleus. I. Topological organization and phenotypic plasticity of the enzyme-containing cell population

Tyrosine hydroxylase phenotype expression was investigated in the catecholaminergic population of the locus coeruleus neurons of two pure inbred mouse strains, Balb/C and C57Black/6. Therefore, we have characterized the precise organization of tyrosine hydroxylase-expressing perikarya population, in control animals and following RU24722 treatment, which is known to induce tyrosine hydroxylase expression. Serial coronal sections were selected along the caudo-rostral extent of the structure and were processed for tyrosine hydroxylase immunocytochemistry. Three days after the treatment, an increase in the number of cells which expressed tyrosine hydroxylase was observed all along the locus coeruleus in the Balb/C strain only. This increase equalized the catecholaminergic neuron populations of the two strains. In the caudal subdivision of the structure, these newly detected perikarya were intermingled with the perikarya which expressed tyrosine hydroxylase in control conditions. In the rostral half, the additional immunoreactive perikarya enlarged the mean coerulean space, defined as the area delimited by the tyrosine hydroxylase-containing perikarya. These results demonstrate a plasticity of the tyrosine hydroxylase phenotype expression, topologically organized and specific to the Balb/C strain.

Tyrosine hydroxylase expression within Balb/C and C57black/6 mouse locus coeruleus. II. Quantitative study of the enzyme level

The tyrosine hydroxylase phenotype expression was further investigated in the perikarya and pericoerulean areas of the locus coeruleus of two pure inbred mouse strains, Balb/C and C57Black/6, which the topological organization and phenotypic plasticity of the enzyme-containing cell population were previously studied. The tyrosine hydroxylase level and the mean protein quantity provided by each cell were significantly higher within the spaces delimited by the enzyme containing perikarya in the C57Black/6 strain as compared to the Balb/C strain. Three days after RU24722 administration, tyrosine hydroxylase tissue concentration and quantity were significantly increased in both strains. Two strain-dependant mechanisms of this pharmacologically induced protein modulation were demonstrated: the mean tyrosine hydroxylase quantity provided by each cell was increased in the C57Black/6 strain whereas the increase was obviously explained by the subset of additional tyrosine hydroxylase expressing cells previously reported in Balb/C strain. A comparable volume of pericoerulean immunolabeled neuropile, which contains a similar tyrosine hydroxylase level, was measured between the two strains. Within this tissue compartment, an undissociated RU24722 responsiveness was observed between the two strains: a significant increase in the protein level was measured principally resulting from a significant increase in the volume. These results revealed a strain-dependent difference in the response to the RU24722 treatment which may result from a genetic separation of two kinds of tyrosine hydroxylase phenotypic regulations within the perikarya area of the locus coeruleus; whereas the surrounding neuropile seemed to have a different mechanism of the phenotypic protein expression and modulation.

Effects of the antidepressant drugs clomipramine and mianserin on tryptophan hydroxylase activity in the rat brain, measured at two points in the light/dark cycle

Tryptophan hydroxylase activity has been measured in synaptosomal preparations from rat brain. A significant circadian variation in enzyme activity was apparent in corpus striatum, (p < 0.001), brainstem and cortex (p < 0.01). A single dose of clomipramine or mianserin (20 mg/kg) had no effect on brainstem enzyme activity measured at mid-light or mid-dark. Chronic administration (7.5 mg/kg i.p. twice daily for 2 weeks) of either clomipramine or mianserin significantly increased enzyme activity. There was no significant difference between the drug effects measured at mid-light or mid-dark.

Chronopharmacology of psychotropic drugs: circadian rhythms in drug effects and its implications to rhythms in the brain

The effects of many kinds of psychotropic drugs have been shown in animal studies to follow a circadian rhythm. Trials for the clinical application of this circadian rhythm have already been undertaken. Although the mechanisms underlying this phenomenon are still unclear, chronological changes in the levels of drugs in the blood and brain suggest that it is primarily due to rhythms in the brain's susceptibility to drugs. Rhythms are present in the level of intracerebral neurotransmitters, receptors and second messengers. Each of these rhythms may cause other rhythms within each system of neurotransmitters, which in turn induces a rhythm in the susceptibility to drugs.

Diurnal changes in actin mRNA levels and incorporation of 35S-methionine into actin in the rat hypothalamus

1. The in vitro incorporation of 35S-methionine into actin and total soluble proteins, as well as the levels of actin mRNA, were studied in the hypothalamus and frontal cerebral cortex of adult male rats killed at six different time intervals during a 24-hr cycle. 2. The specific activity of total soluble proteins after labeled methionine incubations did not vary as a function of time of day in any of the examined brain regions. 3. The incorporation of 35S-methionine into a 43-kDa protein, corresponding to the electrophoretic mobility of actin, varied diurnally in the hypothalamus, exhibiting a maximum at 1200 hr. Such a diurnal variation was not found in frontal cerebral cortex. 4. Similar results were obtained when labeled methionine incorporation into actin was assessed in hypothalamus and cerebral cortex by an immunoprecipitation procedure. 5. An increase in actin hypothalamic mRNA levels, quantitated by dot-blot analysis, was found at 0800, 4 hr in advance to the maximum in 35S-methionine incorporation to actin. 6. The levels of actin mRNA did not vary significantly as a function of time of day in the frontal cerebral cortex.

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.

Distribution and quantification of 5-HT nerve cell bodies in the nucleus raphe dorsalis area of C57BL and BALBc mice. Relationship between anatomy and biochemistry

BALBc and C57BL mice have been shown to have a different 5-HT metabolism. The present study compares the number and the distribution of 5-HT cell bodies in the nucleus raphe dorsalis area (B7 + B6) of these strains. By using 5-HT immunohistochemistry, we found a higher number of 5-HT neurons in the most caudal part of NRD (B6) of BALBc mice compared to C57BL. This difference may be correlated with a higher level of endogenous 5-HT, a higher uptake capacity toward exogenous [3H]5-HT, and a lower release of the amine in this same area of BALBc mice compared to C57BL. It could also imply a significant participation of the nerve cell bodies in the regulation of 5-HT transmission inside 5-HT nuclei.

Early postnatal development of EEG and sleep-waking cycle in two inbred mouse strains

The postnatal maturation of brain electrical activity and sleep-waking cycle were studied in two inbred mouse strains (C57BL and BALBc), previously differentiated in their sleep patterns at adult age. Genetic differences are evident during the first postnatal period (until day 12) in the maturation of electrical activity which is both earlier and slower in C57BL than in BALBc. On the other hand, from day 12 onwards, as soon as the sleep-waking cycle can be defined by using EEG morphology to select quiet sleep (QS) and active sleep (AS) C57BL is characterized by a higher amount of AS and a lower amount of waking (W) than BALBc, as found in juvenile and adult mice. These differences appear a little later when the recordings are performed on animals which are isolated instead of being left with the rest of the litter.

Genetic differences in daily rhythms of pain sensitivity in mice

A dark phase increase in pain sensitivity was evident in C57BL/6 inbred mice. On the contrary Swiss mice are characterized by decreased nocturnal pain sensitivity. The latter finding is in agreement with a number of previous studies based on albino mice. However, our findings indicate that (1) nocturnal decreased pain sensitivity is not the rule in the mouse and (2) large differences are evident when the onset in peak nocturnal analgesia is considered.

Determination of daily variations of brain 5-hydroxytryptamine and dopamine turnovers and of the clearance of their acidic metabolites in conscious rats by repeated sampling of cerebrospinal fluid

Central 5-hydroxytryptamine (5-HT) and dopamine (DA) turnovers were estimated simultaneously in conscious freely moving rats kept on a 12-h dark/12-h light cycle by sampling cisternal CSF of each animal before and after giving probenecid and determining the accumulation of the acidic metabolites of the two amines. The turnovers of both transmitters and the clearances of their acid metabolites from the brain were shown to be significantly greater during the dark (red light) period than during the white light period.

The staircase test in mice: a simple and efficient procedure for primary screening of anxiolytic agents

The staircase test consists of placing a naive mouse in an enclosed staircase with five steps and observing the number of steps climbed and rearings made in a 3-min period. All the clinically active anxiolytics tested (chlordiazepoxide, clorazepate, diazepam, lorazepam, meprobamate, phenobarbital) reduce rearing at doses which did not reduce the number of steps climbed. The majority of non-anxiolytic substances tested (haloperidol, chlorpromazine, imipramine, amitriptyline, amphetamine, morphine and carbamazepine) produced a parallel reduction of both behavioural variables. Ethosuximide had no effect on behaviour. The anticonvulsant sodium valproate produced an anxiolytic profile in this test, since it reduced rearing, while increasing step climbing. This result confirms the anxiolytic properties of valproate observed in other behavioural models. Our results indicate that the staircase test in mice is simple, rapid and selective for anxiolytics. The test is well suited for use as a primary screening method.

The locus coeruleus: a quantitative and genetic study in mice

A fluorescence histochemical study of the pontine catecholaminergic (CA) neurons of two inbred strains of mice, BALB/c (C) and C57BL/6 (B6) and their F1 hybrids revealed that the total number of the fluorescent cells in the C strain was 38% lower than that of the B6 strain. In F1 hybrids, the total number of neurons was not statistically different from that of the B6 parent. During the development from birth to adulthood, the same quantitative differences between strains were observed.

Endogenous serotonin (5-HT) and 5-hydroxyindole acetic acid (5-HIAA) levels in large regions and in discrete brain areas of C57BL and BALBc mice at three times of the day

The serotoninergic system has been analysed in the brainstem and the forebrain of adult C57BL and BALBc mice. Endogenous 5-HT and 5-HIAA levels have also been measured in the different raphe nuclei and in the caudate nucleus and the hippocampus of these strains, using the micropunch technique and the radioenzymatic method (for 5-HT) and a new radioimmunoassay (for 5-HIAA). This investigation was performed at three times of the day: 9:00 hr; 14:00 hr; 20:00 hr to underline the differences between the strains. Most of the time, higher 5-HT and 5-HIAA levels are found in the brainstem and the raphe nuclei of the BALBc strain compared to C57BL. In the forebrain the differences are reversed, except in the caudate nucleus and the hippocampus where the levels of 5-HT are identical in the two strains. Moreover the 5-HIAA/5-HT ratio shows a higher turn-over of the amine in the C57BL strain.

Uptake of [3H]serotonin and [3H]noradrenaline in the raphe nuclei and the locus coeruleus of C57BL/6 Rholco and BALB/c Cenlco mice at three times of the day

Uptake of [3H]serotonin (5-HT) and [3H]noradrenaline (NA) in the raphe nuclei and the locus coeruleus of C57BL/6 and BALB/c mice has been analysed at 3 times of the day. Daily mean results clearly show a higher uptake of [3H]5-HT and [3H]NA in the raphe dorsalis of the BALB/c strain than in C57BL/6. A higher uptake of [3H]NA is also found in the locus coeruleus of BALB/c mice than in C57BL/6. However, differences between the strains are neither visible at all times of the day nor simultaneously in the different structures.

Circadian variations of noradrenaline, 5-hydroxytryptamine and dopamine in specific brain areas of C57Bl/6 and BALB/c mice

Daily variations in noradrenaline, 5-hydroxytryptamine and dopamine turnover were evident in two strains of mice (C57Bl/6 and BALB/c) subjected to 12-12 h light-dark cycles. These fluctuations were also evident under continuous light (L-L) in C57Bl/6 mice only, a strain which is characterized by clear-cut circadian wheel running activity in the absence of external synchronizers.

Circadian variations in the activity of tyrosine hydroxylase, tyrosine aminotransferase, and tryptophan hydroxylase: relationship to catecholamine metabolism

Circadian variations in the activity of tyrosine hydroxylase, tyrosine aminotransferase, and tryptophan hydroxylase were observed in the rat brain stem. Tyrosine hydroxylase exhibited a bimodal pattern with peaks occurring during both the light and dark phases of the circadian cycle. Tyrosine aminotransferase had one daily peak of activity occurring late in the light phase, whereas tryptophan hydroxylase activity was maximal late in the dark phase. Circadian fluctuations in tyrosine hydroxylase activity did not correlate well with circadian variations in the turnover rates of norepinephrine or dopamine nor with levels of these catecholamines. This supports the idea that although tyrosine hydroxylase is the rate-limiting enzyme in the synthesis of catecholamines, other factors must also be involved in the in vivo regulation of this process. Administration of alpha-methyl-p-tyrosine (AMT) methyl ester HCl (100 mg/kg) had no effect on the activity of tryptophan hydroxylase, but effectively eliminated the peak of tyrosine hydroxylase activity that occurred during the light phase. AMT also lowered levels of tyrosine aminotransferase, but only at times near the daily light to dark transition. These chronotypic effects of AMT emphasize the importance of "time of day" as a factor that must be taken into account in evaluating the biochemical as well as the pharmacological and toxicological effects of drugs.

Variations in brain cortical polysome translation products among rats of the same strain

Studies were undertaken to determine whether there exist variations among the translation products of polysomes from different brains of animals of the same strain. Polysomes were prepared from individual rat cortices and translated in a reticulocyte protein-synthesizing system containing rabbit reticulocyte factors and L-[35S]methionine; he resulting radioactive proteins were analyzed by two-dimensional polyacrylamide gel electrophoresis autoradiography. Comparison of the autoradiographs revealed that two acidic proteins, A and B, of apparent 54,000 M. W. occur as three phenotype: A only, B only, or A plus B. These proteins were not detectable by Coomassie brilliant blue staining of two-dimensional electrophoretograms of brain protein preparations. Messenger RNA was extracted from pooled cortices and translated in a wheat germ extract, and both A and B proteins were detected among the products of translation. Cyclic AMP affinity chromatography of the translation products of cortical polysomes showed that both A and B proteins bind to cyclic AMP. Our data are consistent with the conclusion that there are qualitative differences in the polysome translation products that bind to cyclic AMP among individual cortices of rats of the same strain.

Strain differences in amphetamine sensitivity in mice. I. A diallel analysis of open field activity

Experiments are reported which show that 1 mg/kg of d-methylamphetamine HCl induced hyperactivity in pigmented strains (C57BR, C57BL/6, and SEC) and hypoactivity or no change in albino strains (BALB/c, A, and AKR) of mice. In F1 hybrids, the B6 genotype was partially dominant over BR and C, and BR over C. In animals back-crossed to C parents widespread distributions with two peaks were obtained in control experiments, and amphetamine induced hyperactivity in 38% of the albino population, and hypoactivity or no significant change in 45% of the pigmented one. This genetic study indicates that genes influencing locomotor activity are independent from those influencing amphetamine sensitivity. From results obtained in back-crosses and C57BL/6-c2J mice, the albino gene does not seem to be involved in the hypoactive effect of amphetamine.

Strain differences in amphetamine sensitivity in mice. II. Overcompensation of paradoxical sleep after deprivation in two C57 strains

d-Methylamphetamine (1--4 mg/kg) induced wakefulness for 3--5 h followed by paradoxical sleep (PS) rebound in C57BR, C57BL/6, and BALB/c mice. Slow-wave sleep (SWS) and PS suppression time were proportional to the given dose and different among strains. It was also dependent on the time of injection. Later PS rebound was significant in C57 strains, and in certain cases greater than PS loss, whereas rebound was small in BALB/c mice and PS loss was not completely compensated.