The circadian rhythm of brain acetylcholine levels and motor activity in the rat

Sentra PM (a Medical Food) and Trazodone in the Management of Sleep Disorders

Sleep disorders are a common and poorly treated disease state. This double blind, four arm placebo-controlled, randomized trial compared (1) low dose trazodone, (2) Sentra PM, a neurotransmitter based medical food, (3) the joint administration of trazodone and the medical food Sentra PM and (4) placebo. There were 111 subjects studied in 12 independent sites. Subjects underwent baseline screening, informed consent and an initial sleep questionnaire. After 14 days subjects underwent a second evaluation by questionnaire. At baseline and Day 14 the subjects underwent 24 hour ECG recordings that were analyzed in the frequency domain of heart rate variability. The specific high frequency parasympathetic autonomic nervous system activity was analyzed. The primary endpoints were sleep latency and parasympathetic autonomic nervous system improvement in sleeping hours. The results showed improvement in sleep latency for the Sentra PM and combination of Sentra PM and trazodone (−41 and −56 minutes P < 0.001). There was an improvement in quality of sleep for the amino acid formulation Sentra PM and the combination (3.86 and 6.48 Likert units on a 10 point scale P < 0.001). There was an activation of circadian activity percent at night in the medical food and combination groups while there was no change in parasympathetic activity in either the placebo or trazodone group. These data indicate that Sentra PM can improve the quality of sleep, the response to trazodone as a sleep medication and parasympathetic autonomic nervous system activity.

Diurnal variation in thermoregulatory response to chlorpyrifos and carbaryl in the rat

Time of day of exposure is rarely considered in the study of insecticide toxicology. It would be expected that the circadian temperature rhythm (CTR) as well as the circadian rhythms of other physiological processes would affect the efficacy of anticholinesterase (antiChE) insecticides. The ability of antiChE insecticides to alter core temperature (T(c)) could be affected by time of exposure in relation to the CTR. To this end, we assessed time of exposure on the efficacy of the antiChE insecticides chlorpyrifos (CHP) and carbaryl (CAR) to alter T(c) in the rat. T(c) and motor activity (MA) were monitored by radiotelemetry. Rats were dosed orally with 0, 30, and 50 mg/kg CHP or 0, 25 and 75 mg/kg CAR at 09:00 and 15:00 h. Both insecticides caused an acute decrease followed by a delayed increase in T(c) by 24-48 h post-exposure. The temperature index (TI) (area under curve of DeltaT(c) with time) was significantly greater when CHP was given at 15:00 h as compared with 09:00 h. The maximum decrease in T(c) was similar for morning and afternoon CHP. The TI following CAR was similar for morning and afternoon exposure. CHP suppressed the 24 h MA equally when given in the morning and afternoon. CAR was more effective in reducing MA when given in the morning as compared with the afternoon. The T(c) increase measured 24 h after dosing was greater when CHP was given in the morning. Overall, time of day affected the thermoregulatory toxicity of CHP but not CAR. Another experiment showed that the hypothermic efficacy of oxotremorine, a muscarinic agonist, was greater when injected at 09:00 h as compared with 15:00 h. Hence, cholinergic stimulation is probably not the only mechanism to explain the effects of the chronotoxicogical effects of some antiChE insecticides.

Daily changes in the release of acetylcholine from rat primary somatosensory cortex

Using microdialysis, acetylcholine (ACh) release was measured in the somatosensory cortex of 14 rats over a 24-h period. The release of ACh was 0.195 pmol/min during the day and 0.344 pmol/min at night. The length of exposed dialysis membrane within the cortex was an important source of variability in the absolute amounts of ACh collected. Even after rejecting some cases where the membrane contacted only the superficial cortical layers, this factor accounted for 25% of the variation of absolute amounts collected in different animals. After correcting for the length of exposed membrane, the release of ACh was shown to increase 52% at night during the time when the animals were awake, feeding and grooming. Variability in the measures of ACh release obtained during periods of activity was greater than its variability during periods of inactivity. These data were interpreted in the context of several hypothesized roles for ACh in sensory cortex.

Acetylcholine release in the rat hippocampus as measured by the microdialysis method correlates with motor activity and exhibits a diurnal variation

Extracellular levels of acetylcholine were measured by the microdialysis method coupled to high performance liquid chromatography in the dorsal hippocampus of freely moving rats over a period of 24 h to examine whether the acetylcholine release in the hippocampus exhibited a diurnal variation. Spontaneous motor activity was simultaneously measured with an automatic animal activity monitor. The amount of acetylcholine collected per 20-min sample varied markedly, in a range from about 5 to 90 pmol. There appeared to be variations in the amount with a 2-4 h periodicity as well as an apparent diurnal periodicity. In all five rats studied, the overall mean value for the dark cycle (11.1-34.5, average 20.9 pmol/20 min) was significantly greater than that for the light cycle (5.1-21.3, average 12.3 pmol/20 min), showing a 70% average increase. Cross-correlation analysis performed between the amount of acetylcholine and the motor activity count for the animal during the sampling revealed a significant positive correlation coefficient in four rats studied. The present study demonstrates for the first time that the acetylcholine release shows a diurnal variation.

Scanning-integrating cytophotometric analyses of brain neuronal RNA and acetylcholinesterase in acute soman toxicated rats

Cytophotometric analyses of RNA and acetylcholinesterase responses of caudate and cerebrocortical neurons of soman toxicated rats were conducted to characterize impairments in regulatory aspects of neuronal metabolism occurring in the acute phase of cholinesterase impairment. There was a severe and dose-dependent suppression (20-60%) in neuronal acetylcholinesterase activity in both a.m. and p.m.-treated rats; no diurnal differences were apparent in control acetylcholinesterase levels or neuronal acetylcholinesterase responsiveness to soman toxication. RNA levels, however, were markedly higher in p.m. than in a.m. saline-treated controls. Soman depressed caudate neuron RNA contents in the afternoon, but not in the morning. Cerebrocortical neuron RNA levels were suppressed in both a.m. and p.m.-toxicated rats, although this RNA depletion was more severe in the afternoon. These results indicate that soman can elicit marked alterations in neuronal transcriptional-translational capabilities and that there are diurnal variations in cellular metabolic responsiveness to soman toxication. Although functional relationships between soman-induced cholinesterase inhibition and RNA depletion remain to be elucidated, depressed RNA metabolism appears to be a maladaptive response preventing rapid regeneration of cholinesterase following poisoning.

Diurnal fluctuation in striatal choline acetyltransferase activity and strain difference in brain protein content of the rat

Choline acetyltransferase (CAT) activity was measured in two brain regions of rat at different times of the day. A diurnal fluctuation of the CAT activity was found in the striatum with a high activity during the light period and a low activity during the dark period. In the hippocampus + cortex the CAT activity remained constant. A marked difference in the brain protein content was found between two strains of Sprague-Dawley rats. This finding emphasizes the importance of expressing enzyme activity both per g tissue and g protein especially when comparing data between different research groups.

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.

Relation of rat brain acetylcholine levels to duration of self-stimulation and escape behavior

Total brain acetylcholine (ACh) was assayed in groups of animals after various periods of operant responding maintained by electrical stimulation of the lateral posterior hypothalamus or of escape behavior induced by electrical stimulation of the midbrain tegmentum. Different groups of trained rats were placed in identical Skinner boxes for periods of 1 to 24 hr. The following groups were studied: controls, self-stimulators receiving electrical stimulation, escapers from brain stimulation or peripherally applied aversive stimulation, self-stimulators not receiving electrical stimulation prior to decapitation, tubocurarine-paralyzed respired rats with electrodes in the posterior-lateral hypothalamus not receiving stimulation, and a group of tubocurarine-paralyzed, respired rats receiving electrical stimulation automatically. It was found that brain stimulation decreased total brain ACh, regardless of whether the stimulation was positive, as during self-stimulation behavior, or negative, as during escape behavior. Animals that receivied positive stimulation while being paralyzed showed similar decreases in total brain ACh, but the change in ACh was smaller. No changes occurred in animals that were paralyzed that recieved no electrical stimulation. It is concluded that brain usage produced by electrical stimulation of discrete functional pathways causes a reduction of total ACh, but this is unrelated to the specific motivational properties of the electrical stimuli.