Rat brain amines, blood histamine and glucose levels in relationship to circadian changes in sleep induced by pentobarbitone sodium

The timing of the mouse hind paw incision does not influence postsurgical pain

Chronobiological approaches have emerged as tools to study pain and inflammation. Although time-of-day effects on the expression of pain after injury have been studied, it remains unaddressed whether the timing of the injury itself can alter subsequent pain behaviors. The aim of this study was to assess postsurgical pain behaviors in a mouse hind paw incision assay in a circadian-dependent manner. Incisions were made at one of four equally spaced time points over a 24-hour period, with evoked and spontaneous pain behaviors measured using the von Frey mechanical sensitivity test, Hargreaves' radiant heat paw-withdrawal test, and the Mouse Grimace Scale. Algesiometric testing was performed in C57BL/6 mice prior to and at multiple time points after incision injury, at the same time of day, until pain resolution. No statistically significant differences were observed between groups. This study adds to the literature on circadian rhythms and their influence on pain in the pursuit of more biologically informed pre- and postoperative care.

Circadian Pharmacological Effects of Paeoniflorin on Mice With Urticaria-like Lesions

Paeoniflorin (PF) is a monoterpene glucoside with various biological properties, and it suppresses allergic and inflammatory responses in a rat model of urticaria-like lesions (UL). In the present study, we treated OVA-induced mice presenting UL with PF at four circadian time points (ZT22, ZT04, ZT10, and ZT16) to determine the optimal administration time of PF. The pharmacological effects of PF were assessed by analyzing the scratching behavior; histopathological features; allergic responses such as immunoglobulin E (IgE), leukotriene B4 (LTB4), and histamine (HIS) release; inflammatory cell infiltration [mast cell tryptase (MCT) and eosinophil protein X (EPX)]; and mRNA levels of inflammatory cytokines such as interleukin (IL)-12, IL-6, interferon-γ (IFN-γ), and IL-4. It was demonstrated that PF significantly alleviated scratching behavior and histopathological features, and ZT10 dosing was the most effective time point in remission of the condition among the four circadian time points. Moreover, PF decreased the serum levels of IgE, LTB4, and HIS, and PF administration at ZT10 produced relatively superior effectiveness. PF treatment, especially dosing at ZT10, significantly reduced the number of mast cells and granules and diminished the infiltration of MCT and EPX in the skin tissues of mice with UL. Furthermore, the oral administration of PF effectively decreased the inflammatory cytokine levels of IL-12 mRNA. In conclusion, different administration times of PF affected its efficacy in mice with UL. ZT10 administration demonstrated relatively superior effectiveness, and it might be the optimal administration time for the treatment of urticaria.

Regulation of plasma histamine levels by the mast cell clock and its modulation by stress

At steady state, plasma histamine levels exhibit circadian variations with nocturnal peaks, which is implicated in the nighttime exacerbation of allergic symptoms. However, the regulatory mechanisms are largely unexplored. This study determined how steady-state plasma histamine levels are regulated and affected by environmental factors. We found that plasma histamine levels decreased in mast cell–deficient mice and their circadian variations were lost in mast cell–deficient mice reconstituted with bone marrow–derived mast cells (BMMCs) harboring a mutation in the circadian gene Clock. Clock temporally regulates expression of organic cation transporter 3 (OCT3), which is involved in histamine transport, in mast cells; OCT inhibition abolished circadian variations in plasma histamine levels. Mice housed under aberrant light/dark conditions or suffering from restraint stress exhibited de-synchronization of the mast cell clockwork, concomitant with the loss of circadian variations in OCT3 expression and plasma histamine levels. The degree of compound 48/80–induced plasma extravasation in mice was correlated with plasma histamine levels. Collectively, the mast cell clock mediates circadian regulation of plasma histamine levels at steady state, in part by controlling OCT3 expression, which can be modulated by stress. Additionally, we propose that plasma histamine levels potentiate mast cell–mediated allergic reactions.

Chronopharmacology and Chronotoxicology of CNS Drugs: Interrelationships with Neuromodulators

It has been demonstrated that the effect of a drug, chemical, or poison is diurnal phase dependent. The circadian variation in drug response could be attributed to the diurnal fluctuations of several factors, including absorption, distribution, metabolism, and excretion. Another important factor in determining the response to CNS drugs is the circadian rhythm of brain sensitivity to drugs. The diurnal variability in the concentration of brain neuromodulators could in part explain the circadian rhythm of brain sensitivity. The present paper focuses on the interrelationships between the levels of neuromodulators and the chronopharmacology and chronotoxicology of CNS drugs. Evidence is presented to show that the circadian rhythm of specific brain neuromodulators plays an important role in the pharmacologic or toxicologic action of amphetamine, barbiturates, morphine, and ethanol.

The physiology of brain histamine

Histamine-releasing neurons are located exclusively in the TM of the hypothalamus, from where they project to practically all brain regions, with ventral areas (hypothalamus, basal forebrain, amygdala) receiving a particularly strong innervation. The intrinsic electrophysiological properties of TM neurons (slow spontaneous firing, broad action potentials, deep after hyperpolarisations, etc.) are extremely similar to other aminergic neurons. Their firing rate varies across the sleep-wake cycle, being highest during waking and lowest during rapid-eye movement sleep. In contrast to other aminergic neurons somatodendritic autoreceptors (H3) do not activate an inwardly rectifying potassium channel but instead control firing by inhibiting voltage-dependent calcium channels. Histamine release is enhanced under extreme conditions such as dehydration or hypoglycemia or by a variety of stressors. Histamine activates four types of receptors. H1 receptors are mainly postsynaptically located and are coupled positively to phospholipase C. High densities are found especially in the hypothalamus and other limbic regions. Activation of these receptors causes large depolarisations via blockade of a leak potassium conductance, activation of a non-specific cation channel or activation of a sodium-calcium exchanger. H2 receptors are also mainly postsynaptically located and are coupled positively to adenylyl cyclase. High densities are found in hippocampus, amygdala and basal ganglia. Activation of these receptors also leads to mainly excitatory effects through blockade of calcium-dependent potassium channels and modulation of the hyperpolarisation-activated cation channel. H3 receptors are exclusively presynaptically located and are negatively coupled to adenylyl cyclase. High densities are found in the basal ganglia. These receptors mediated presynaptic inhibition of histamine release and the release of other neurotransmitters, most likely via inhibition of presynaptic calcium channels. Finally, histamine modulates the glutamate NMDA receptor via an action at the polyamine binding site. The central histamine system is involved in many central nervous system functions: arousal; anxiety; activation of the sympathetic nervous system; the stress-related release of hormones from the pituitary and of central aminergic neurotransmitters; antinociception; water retention and suppression of eating. A role for the neuronal histamine system as a danger response system is proposed.

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.

Footshock-induced rise of rat blood histamine depends upon the activation of postganglionic sympathetic neurons

We have previously shown the existence of a novel peripheral reflex inhibitorily modulating the vas deferens sympathetic activity. An interaction between noradrenergic and histamine-containing neurons is involved in this reflex. As an overall mechanism of sympathetic autoregulation, we found that enhanced sympathetic activity in the rat during the stress induced by brief inescapable footshocks caused a marked rise of blood histamine that was seemingly dependent upon sympathetic activity. This rise was prevented by either previous ganglionic blockade with hexamethonium or chronic guanethidine-induced sympathectomy. Previous adrenal demedullation did not impair this rise. Thus, it appears that only the sympathetic postganglionic neuron, interacting with a histamine-containing neuron, is involved in the rise of blood histamine induced by footshocks.

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.

The effects of pre- and postweaning rearing conditions on latent inhibition and partial reinforcement extinction effect in male rats

Male rats were either handled daily or left undisturbed (nonhandled) during the first 21 days of life. At weaning (Day 22) animals in each early treatment condition were assigned to two housing conditions, isolated or grouped, creating four early/late treatment conditions: Handled-Grouped (HG), Handled-Isolated (HI), Nonhandled-Grouped (NHG), and Nonhandled-Isolated (NHI). At maturity, all animals were tested in the latent inhibition (LI, Experiment 1) and the partial reinforcement extinction effect (PREE, Experiment 2) paradigms. In LI, animals receiving prior nonreinforced preexposure to a stimulus (PE) show subsequently retarded conditioning to that stimulus as compared to nonpreexposed (NPE) controls. In the PREE, partially reinforced (PRF) animals exhibit higher resistance to extinction as compared to continuously reinforced (CRF) controls. LI and PREE were obtained in the HG condition, but were impaired in NHG and HI animals. The pattern of impairment was different in the two conditions. The absence of LI in NHG males was due to increased suppression in the PE group, whereas in HI males, was due to decreased suppression in the NPE group. Likewise, the attenuation of the PREE in NHG males stemmed primarily from decreased resistance to extinction in the PRF group, whereas in HI males, it resulted from increased resistance to extinction in the CRF group. The combination of nonhandling and isolation led to the reinstatement of both LI and PREE: normal LI and PREE were obtained in the NHI animals. These results demonstrate that early rearing experience interacts with later experience differentially depending upon the later experience.

Diurnal fluctuation in levels of histamine metabolites in cerebrospinal fluid of rhesus monkey

In samples of ventricular cerebrospinal fluid (CSF) that were collected from a conscious, restrained rhesus monkey at intervals of 30 90 min, levels of the histamine metabolites, tele-methylhistamine (t-MH) and tele-methylimidazoleacetic acid (t-MIAA), were determined by gas chromatography-mass spectrometry. Levels of t-MH and t-MIAA each showed time-related fluctuations. Peak and trough concentrations of t-MIAA, the product of t-MH, paralleled, but lagged about 2 h behind, the levels of t-MH. Within the first 3 h of illumination, metabolite levels increased more than 3-fold; they fell sharply within the first 3 h of darkness. Mean levels of t-MH and t-MIAA were significantly higher during periods of illumination than of darkness. Fluctuations in the levels of pros-methylimidazoleacetic acid (p-MIAA), an endogenous isomer of t-MIAA that is not a histamine metabolite, were markedly different from those of t-MH or t-MIAA; p-MIAA levels peaked only at the middle of the dark period. The time-related fluctuations in levels of t-MH and t-MIAA, but not p-MIAA, are similar to the daily rhythmic changes observed in monkey CSF for the levels of other central neurotransmitters and peptide neurohormones.

Feeding-related circadian variation in tele-methylhistamine levels of mouse and rat brains

Circadian changes in the brain histamine (HA) and tele-methylhistamine (t-MH) levels were studied in mice and rats after adaptation to an alternating 12-h light/dark cycle (lights on at 0600). Although there was no significant circadian fluctuation of the brain HA levels, the levels of t-MH, a major metabolite of brain HA, showed a marked circadian variation. In mice, the t-MH levels were about 80 ng/g from 1200 to 1800 but about two times higher values were obtained from 2400 to 0600 of the next morning. In rats, the t-MH levels ranged from 24 to 28 ng/g at 0600 and 1200, slightly increased at 1800, and reached at 2400 a peak twice as high as the levels seen during the light period. The t-MH levels again rapidly decreased during the subsequent 3 h. In mice fasted from 1200, the t-MH levels did not increase during the period of darkness. When mice were fed at 1200 after a 24-h fast, a significant increase in the t-MH levels was observed at 1800. There was no significant circadian variation of the HA and t-MH levels in the plasma of mice and rats. These results suggest that circadian variation in brain t-MH levels is related to feeding and possible subsequent changes in elimination of t-MH from the brain and/or turnover of HA in the brain. This phenomenon should be given due attention when HA dynamics in the brain are being assessed.

Circadian rhythm of the liver of male rats pre-treated with phenobarbital--II. Hexobarbital sleeping time and lipids content in liver and serum

The circadian rhythm of hexobarbital sleeping time and lipids content in liver and serum were studied in 226 male Sprague-Dawley rats pretreated daily at 0800-0900 with 70 mg/kg (study 1 or 3) or 50 mg/kg (study 2) phenobarbital (PB) orally for 7 days. Thereafter, eight (study 1) or five (study 2 and 3) rats each were studied at 4-hr intervals at 1000, 1400, 1800, 2200, 0200, 0600 and 1000 through the following day. The lighting schedule in the colony was 12:12 +/- light:dark (light from 0600 to 1800). The hexobarbital sleeping times of PB-pretreated rats were generally shortened compared to the controls and no circadian rhythm was observed. PB-treatment increased slightly the liver content of cholesterol, and significantly that of triglycerides and phospholipids. Liver cholesterol and phospholipids showed circadian rhythms with peaks during the dark phase. No circadian rhythm of liver triglycerides existed. In serum, levels of triglycerides and phospholipids were slightly lowered by PB-treatment, while levels of cholesterol and beta-lipoprotein were not influenced. Serum values did not exhibit circadian rhythms.

Mesial prefrontal cortical lesions and timidity in rats. II. Reactivity to novel stimuli

An earlier set of experiments suggested that mesial prefrontal cortical (MFC) lesions in rats enhanced timidity. It was uncertain whether this increased timidity was a general phenomenon, or was restricted to fear of bright, open spaces. The experiments reported here measured behavioral reactivity to a variety of stimuli, under situations where light/dark differences were minimized. It was found that MFC rats were slowed in leaving an open field to enter a small box. In the open field, MFC subjects showed signs of enhanced reactivity, but only when the field was novel and the subjects unhandled. When allowed to choose between four alleys containing varying stimuli, brain-damaged rats avoided novel objects and complex stimuli, but spent more time than controls in contact with other rats in the apparatus. In a test of food neophobia, MFC subjects were not neophobic in a familiar test environment, but did avoid the experimenter more than controls. Finally, duration of barbiturate anesthesia was shortened by MFC lesions, but only under conditions of high novelty. It is concluded that MFC lesions produce a timidity which is not restricted to photophobia.

Circadian variations in radioligand binding to muscarine receptors in rat brain dependent upon endogenous agonist occupation

Although total levels of muscarine receptors in the rat forebrain and brainstem are constant at different times of day, there are large circadian changes in the numbers and carbachol-affinities of unoccupied receptors, which appear to reflect varying levels of endogenous acetylcholine-receptor complexes and the activity of cholinergic synapses.

Factors influencing lung histamine content

Histamine is an important amine within the lung. The purpose of the present study was to evaluate in rats the factors that affect the measurement of lung histamine concentration. We found that the lung content was not clearly altered by pentobarbital anesthesia or by freezing of the lung. Heparin administration and inhalational ether anesthesia appeared to result in elevated lung histamine contents by an unknown mechanism. Pulmonary edema rapidly lowered the histamine content. The histamine content is better related to DNA content than to the amount of protein in the lung.

Changes in body temperature after administration of antipyretics, LSD, delta 9-THC, CNS depressants and stimulants, hormones, inorganic ions, gases, 2,4-DNP and miscellaneous agents

This survey concludes a series of complications of data from the literature, primarily published since 1965, on thermoregulatory effects of antipyretics in afebrile as well as in febrile subjects, LSD and other hallucinogens, cannabinoids, general CNS depressants, CNS stimulants including xanthines, hormones, inorganic ions, gases and fumes, 2,4-dinitrophenol and miscellaneous agents including capsaicin, cardiac glycosides, chemotherapeutic agents, cinchona alkaloids, cyclic nucleotides, cycloheximide, 2-deoxy-D-glucose, dimethylsulfoxide, insecticides, local anesthetics, poly I:poly C, spermidine and spermine, sugars, toxins and transport inhibitors. The information listed includes the species used, route of administration and dose of drug, the environmental temperature at which the experiments were performed, the number of tests, the direction and magnitude of body temperature change and remarks on the presence of special conditions such as age or lesions, or on the influence of other drugs, such as antagonists, on the response to the primary agents.

Circadian variation of diazepam acute toxicity in mice

The LD50 of i.p. injected diazepam was determined every 4 h over a 24-h period in albino mice adapted to a 12-h dark/12-h light programmed illumination cycle. Results show that diazepam is more toxic during the light phase of the cycle than during the dark phase and demonstrate circadian variation in the toxicity of the compound in mice.

Chronopharmacological studies of neuroleptics

Studies were carried out to clarify the mechanism of appearance and the laws controlling the appearance of such phenomena as circadian fluctuation in the effects of neuroleptics. A detailed review was initially made of previous studies on drugs closely related to neuroleptics; then data obtained by the authors was analyzed. Significant circadian fluctuation was found in the effect of chlorpromazine, haloperidol, and tetrabenazine, varying with the time of administration, with the kind of drug, and even with the dose of the same drug. There was also circadian fluctuation in lethality rate, which was seen to be a phenomenon controlled by a law different from that controlling circadian fluctuation in the effect of a drug. Circadian fluctuation in the effect of a drug was regulated externally by clock time, setting the light-dark rhythm of the raising environment. Different times of administration of a drug did not affect chronological changes in the blood level or intracerebral concentration of a drug after administration. From these results, it was assumed that this phenomenon might be induced by the circadian rhythm of drug sensitivity of a brain where the drug acts.

Twenty-four hour toxicity rhythms of sedative-hypnotic drugs in mice

Twenty-four hour LD50 values of secobarbital, pentobarbital, phenobarbital, in male Swiss-Webster mice weighing approximately 30 g each. The animals were adapted for three weeks in an environmental room equipped with an automatically-timed photoperiod lasting from 0800 to 2000 h daily. Each mouse was injected intraperitoneally at 6 h time intervals with either phenobarbital or chloral hydrate for toxicity analysis. Secobarbital, pentobarbital and hexobarbital were injected at 3 h time intervals. Peak toxicity was reached at D-0600 with all drugs screened except chloral hydrate which was 180 degrees out of phase. The drugs were least toxic at 1200 h with the exception of chloral hydrate which was least toxic at D-0600 h. These results suggest circadian periodicity in the toxicity of sedative hypnotics. Factors that could be responsible for these variations are discussed.

Brain histamine: plasma corticosterone spontaneous locomotor activity and temperature

Hypothalamic histamine exhibited circadian fluctuations in male Sprague-Dawley rats; low values were found during the dark period when spontaneous locomotor activity (S.L.A.) and temperature were elevated. A relatively high hypothalamic histamine level was observed during the early period of the light cycle and was associated with decreased S.L.A. and temperature. Histamine concentration was high when corticosterone levels were low at the end of the dark cycle and during the morning hours (4 a.m.-1 p.m.); but histamine levels were relatively constant while corticosterone concentration dropped during afternoon and early night hours (4 p.m.-10 p.m.). Furthermore, the lowest hypothalamic histamine level (at 1 a.m.) was associated with the average plasma corticosterone value, thus no consistent relationship between histamine and corticosterone levels could be observed. Circadian fluctuations in brain histamine may support its role in brain function.

Environmentally induced differences in susceptibility of rats to CNS stimulants and CNS depressants: evidence against a unitary explanation

It has been suggested that socially isolated rats are more aroused then rats raised in social groups. This hypothesis was tested by examining amphetamine-induced activity and stereotypy in social and isolated rats of both sexes in both the active and inactive phases of their diurnal activity cycle. In socially raised rats it was possible to produce behavioural profiles similar to those of isolated rats by increasing the arousal level of the social rat. However, the complex interaction of housing conditions, diurnal variation and gender with drug dose suggests that one intervening variable such as arousal is too simplistic an explanation. In subsequent experiments, stereotypy was enhanced by a familiar environment, and there was a clear dissociation between the effects of CNS stimulants and CNS depressants. The increased susceptibility of isolates to CNS stimulants depends on social isolation for a short period before 45 days of age; the decreased susceptibility of isolates to CNS depressants may be produced by isolation at any age. We conclude that there is no evidence that isolated rats are hyperaroused.

Chronopharmacological study of neuroleptics. II. Circadian susceptibility rhythm to chlorpromazine

In order to study differences in the effect of the neuroleptics due to time of administration, rats were administered chlorpromazine (CPZ) in a variety of combinations of dose and time and the sedation period was measured. There was daily fluctuation in the sedative effect and the pattern of fluctuation differed according to dosage. A similar study under the condition of reversed light and dark gave a reversed curve of the daily fluctuation, showing that the rhythm of light and dark controls the fluctuation externally. In an attempt to elucidate the mechanism of these phenomena, CPZ was administered at two different times, between which there was a significant difference in the sedation period, and time-course changes in plasma and brain concentration of the drug and its metabolites were measured. No difference was found. These results are interpreted as indicating that the phenomena could arise at the level of amine-receptor activity in the brain. In addidtion, daily fluctuation due to time of administration was noted in lethality.

Circadian oscillations of nucleic acid and protein content in functionally different neuron-neuroglia units of rat central nervous system

Scanning integrating visible cytospectrophotometry of gallocyanin-, amido black-, fast green- or ammoniacal silver-stained sections of various areas of the central nervous system of adult rats sacrificed at 4 h intervals has demonstrated the presence of circadian changes in RNA, total protein and total histone content as well as in arginine-rich to lysine-rich histone ratio in the neurons and in their perineuronal satellite neuroglia. The peak of the content per cell of the macromolecular components studied was in some cases elevated above their lowest level up to 1.7-fold. The zenith in the content of neuronal RNA coincided as a rule with the nadir in the content of glial RNA whereas no such opposition was observed with respect to the protein or histone content as well as to the arginine- to lysine-rich ratio in the neurons and in their glial satellite cells. The data obtained have confirmed earlier observations that under changed conditions of neuron functioning, the changes in the nervous system metabolism occur which are localized not only in the neurons but also in the neuroglia, the metabolic response in the glial cells being characterized, depending on peculiarities of the particular neuron activity, both by similarity and by some differences as compared with the neuronal metabolic response. A synchronizing effect of environmental and/or internal factors on the macromolecular metabolism within various cell populations of the central nervous system is discussed.

Effect of isolation on barbiturate anaesthesia in the rat

The duration of barbiturate-induced sleeping in rats was found to be reduced by isolation housing. It was also lower in males than females, and lower in the dark phase of the diurnal cycle. These variables were shown to be additive in their effects. Sex differences in barbiturate action were found to be reduced by gonadectomy in males; and the effects of isolation were found to depend upon housing conditions at the time of testing rather than upon early rearing environment. The implication for theories of arousal is discussed.

The effects of pentobarbitone and pethidine on foetal breathing movements in sheep

1 Small doses of pentobarbitone (4 mg/kg i.v.) administered to sheep in the last third of pregancy had little overt effect on the mothers. In the foetus they caused arrest of breathing movements, an alteration in the character of the electrocorticogram and cardiovascular changes which varied with gestational age. 2 In contrast, relatively large doses of pethidine (100-200 mg) admininstered to the mother had no consistent effect on normal foetal breathing movements, though they abolished the foetal response to hypercapnia. 3 The results are discussed in relation to feotal sleep state.

Effects of thyrotropin-releasing hormone on prolactin, growth hormone and corticosterone secretions in adult male rats treated with pentobarbital or morphine

Thyrotropin-releasing hormone (TRH) injected either IP (10 mg/kg) or intraventricularly (10 mug/rat) antagonized the pentobarbital-induced secretion of prolactin (PRL). This effect was not blocked by propranolol. In thyroidectomized animals the effect was not apparent; tri-iodothyronine (T3) injection was however ineffective. The injections of luteinizing hormone-releasing hormone (LH-RH) and of melanocyte stimulating hormone release-inhibiting factor (MIF) were also ineffective. Of six TRH analogues, only those containing histidine antagonized pentobarbital-induced PRL release, but none modified plasma levels of growth hormone (GH) or corticosterone (B). Brain levels of serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) were not modified by TRH. Morphine-induced secretion of PRL and GH was also significantly antagonized by TRH. Since pentobarbital and morphine-induced hormonal changes are probably exerted through a central nervous system depressant action, these data indicate that TRH can influence brain activity through an extrapituitary mechanism.

Gamma-butyrolactone sleep: A 24-hour rhythm paralleling normal sleep in the rat and CNS amine changes

The duration of sleep induced by a fixed dose of gamma-butyrolactone (GBL) (350 mg/kg, IP) FOllows the normal circadian sleep pattern of rats. GBL sleep duration is maximal at 1800 hr and minimal at 0600 hr. CNS amine changes are not extensive, but when normal sleep is anticipated, GBL treatment increases dopamine and serotonin levels and decreases norepinephrine levels.

In vivo rates of tyrosine and tryptophan hydroxylation in regions of rat brain at four times during the light-dark cycle

The in vivo rates of tyrosine and tryptophan hydroxylation were studied in three regions of young adult rat brains at 4 times the light-dard cycle. The procedure utilized was to analyze the accumulation of Dopa and 5-HTP after injection of a centrally effective L-amino acid decarboxylase inhibitor, NSD 1015. Monoamine levels were also determined in all control animals and some treated animals. The reate of tyrosine dydrosylation in the telencephalon was significantly higher 7 hrs after dard onset than at the other three times tested. Smaller variations in tyrosine and tryptophan hydroxylation rates as a function of time of day were also observed. 5-HT levels were significantly higher during the light phase than the dark in the telencephalon with the same trend occurring in the diencephalon and brainstem. NA was stable in the telencephalon but reached lower levels in the light and higher levels in the dark in the other two regions. In the telencephalon DA reached high levels early in the light and in the dark phases, showing a biphasic variation. Of particular interest was the apparent lack of carrelation between cyclic changes in the monoamine levels and the changes in hydroxylation rates. Rates of hydroxylation can be considered indicative of rates of monoamine synthesis. This observation is discussed in relation to feedback and other mechanisms regulating synthesis and release of monoamines.