Search results for "rhythm"
showing 10 items of 822 documents
Day/night serotonin levels in the pineal gland of male BALB/c mice with melatonin deficiency
1988
Abstract. Studies from another laboratory have shown that several strains of laboratory mice have a genetic defect for melatonin synthesis. In non-deficient species, melatonin synthesis undergoes a typical, β-adrenergically regulated day/night rhythm with low melatonin levels during daytime and high levels at night, the precursor serotonin showing an inverse behaviour. This study examines whether a day/night rhythm of pineal serotonin levels exists in melatonin-deficient male BALB/c mice. Mice kept under a lighting schedule of 12 h light (lights on at 07.00 h) and 12 h dark were killed at 13.00 and 01.00 h, respectively. Serotonin amounted to 12-15 ng/pineal and did not show regular day/nig…
The pineal complex in Roman high avoidance and Roman low avoidance rats.
1990
Previous studies have shown that the pineal gland of Roman high avoidance (RHA/Verh) rats is larger than that of Roman low avoidance rats (RLA/Verh). In the present study measurement of enzyme activities (serotonin-N-acetyl-transferase, hydroxyindole-O-methyltransferase) revealed that pineals of RHA/Verh rats are twice as active in melatonin production than pineals of RLA/Verh rats. Indoleamine content was also higher in RHA/Verh rats, whereas noradrenaline content was the same in both lines. When values were expressed per mg protein, these differences disappeared except for N-acetyl-serotonin and noradrenaline which were higher or lower in RHA/Verh rats, respectively. Both lines had higher…
Melatonin formation in different parts of the guinea-pig pineal complex as assessed over 24 hours.
1985
There is morphological evidence that the pineal gland is not a uniformly built organ but rather a complex. In the guinea-pig the gland is 6--7 mm in length and dumbbell-shaped, the proximal part coming into intimate contact with central commissural fibres. The aim of the present 24-hour study was to examine in male guinea-pigs whether the proximal, intermediate and distal areas of the gland are involved in melatonin formation and to compare their rhythmicities. Levels of melatonin in serum and the whole pineal gland as assessed by RIA show day/night ratios of 1 : 1.25 and 1 : 3.3, respectively. Serotonin N-acetyltransferase activity was found to exhibit ratios of 1 : 1.75 (Experiment I) and…
Response of pineal serotonin N-acetyltransferase activity in male guinea pigs exposed to light pulses at night.
1988
Serotonin N-acetyltransferase (NAT), which is crucial for the formation of melatonin, undergoes a typical day/night rhythm in the pineal gland with low levels during daytime and high levels at night. Short pulses of light given at night have been shown to rapidly depress NAT activity in some species, but not in others, the reasons for this difference being unclear. As diurnality and nocturnality of the experimental animals may play a role and since diurnally active animals have been little investigated in this respect, in the present study the diurnally active guinea pig was investigated. Male guinea pigs kept under a lighting regimen of LD 12:12 (lights off at 1700 hrs) were killed between…
Control of irregular cardiac rhythm
2018
International audience; The aim of this work is to investigate the chaos control of the one di- mensional map which modelizes the duration of the current cardiac action potential (APD) as a function of the previous one. Using OGY control method, we obtain very satisfactory numerical results to stabilize the irregular heart rhythm into the normal rhythm.
Rhythmic variations in reaction times and evoked potentials
1995
The present work aimed to assess the existence of a regular ultradian cyclicity underlying the variations in amplitude of the N1-P2 component of acoustic EP during a relatively long recording session and investigate its relationship with behavioral measure as RT to the same stimulus. 128 tones were presented to each subject; 128 RTs and the associated EPs to target stimuli were recorded. N1-P2 amplitude has been measured at a single trial level through Woody adaptive filter modified by Wastell. Results showed that there are ultradian rhythmic variations of N1-P2 and RT, with a periodicity from about 5 to 40 min and these variations have similar patterns in the two measures in most of the su…
Red cell sorbitol concentration in relation to short- and medium-term variation of plasma glucose.
1989
To evaluate the time course of changes in red cell sorbitol (RCS) concentration in relation to variations of plasma glucose levels, RCS was determined in 7 normal subjects during i.v. glucose infusion (IVGTT); in 6 hyperglycemic insulin-dependent diabetic subjects while glycemia was normalized with Biostator GC 115 and in 4 diabetic patients in previously poor metabolic control, in whom normal glycemia was obtained in 8–10 days by intensive insulin therapy. During IVGTT, plasma glucose levels increased with significant differences from baseline at 5, 10, 16, 25, 60, 100 and 160 min and returned to basal levels after 3h; RCS concentration showed small and insignificant increases. During i.v.…
Ultradian rhythms in avoidance behavior of DBA mice
1994
This study investigates ultradian rhythm in avoidance behavior of mice, which may constitute a basic rest activity cycle (BRAC). Reaction times (RTs) of an avoidance response to a visual warning stimulus that preceded an electric shock were measured by the use of a computer-controlled shuttle box. The male naive DBA mice were brought to a criterion of 98% correct responses in numerous training sessions. For each subject, all the temporal sequences of the RTs in the trials following achievement of the criterion were examined with discrete Fourier transform. Periodograms were obtained from three sessions for each of the two animals in the first experiment and from 15 subjects in the second ex…
Is the nonREM–REM sleep cycle reset by forced awakenings from REM sleep?
2002
In selective REM sleep deprivation (SRSD), the occurrence of stage REM is repeatedly interrupted by short awakenings. Typically, the interventions aggregate in clusters resembling the REM episodes in undisturbed sleep. This salient phenomenon can easily be explained if the nonREM–REM sleep process is continued during the periods of forced wakefulness. However, earlier studies have alternatively suggested that awakenings from sleep might rather discontinue and reset the ultradian process. Theoretically, the two explanations predict a different distribution of REM episode duration. We evaluated 117 SRSD treatment nights recorded from 14 depressive inpatients receiving low dosages of Trimipram…