Search results for "STRAINS"
showing 10 items of 589 documents
The effects of short pulses of light at night on numbers of pineal "synaptic" ribbons and serotonin N-acetyltransferase activity in male Sprague-Dawl…
1986
To characterize further the functionally enigmatic "synaptic" ribbons (SR) of the mammalian pineal gland and to study possible relationships to melatonin synthesis, in the present investigation rats were exposed to short pulses of light at night when both SR numbers and serotonin N-acetyltransferase (NAT) activity are high in comparison to day-time values. Male Sprague-Dawley rats were killed at 13:00 and 01:00 h, respectively, and at 01:10 and 02:00 h after exposure to light for 10 and 60 min, respectively. The pineals were rapidly taken out and cut sagittally in half. One half was processed for electron-microscopic quantitation of SR numbers and the other half for NAT determinations. It w…
24-hour-variation of pineal gland volume, pinealocyte nuclear volume and mitotic activity in male Sprague-Dawley rats
1983
In two experiments carried out on two alternate days, the 24-h-rhythmicity of pineal gland volume, pinealocyte nuclear size in cortex and medulla and mitotic activity were studied in male Sprague-Dawley rats, to assess to what extent morphological parameters reflect the pronounced day/night differences in pineal melatonin formation. Pineal volume exhibited statistically significant changes in the second experiment only, with a distinct trough at 6 p.m. Karyometry revealed highly variable patterns. In the first experiment, pinealocyte nuclear changes lacked parallelism in cortex and medulla. The cortex exhibited a bimodal curve with peaks at noon of the first day and at 6 a.m. of the second …
Circadian and photoperiodic correlation between the number of pineal gland synaptic ribbons and serum melatonin levels in the rat.
1987
A study is made of the number of pineal gland synaptic ribbons in 35 maleWistar rats over a 24-hour period during the months of September and February, in correlation to the serum melatonin levels during the same periods and photophases.The results of the study confirm those reported by others authors and suggest that the synaptic ribbons may be the stimuli-transmitting organs facilitating pineal secretory function.
Atypical 24-hour rhythms of serotonin N-acetyltransferase activity in the rat pineal gland.
1988
Previous long-term studies have shown that in the pineal gland of rats melatonin synthesis is subject to infradian rhythms with periods between 4 and 7 days. Since in these studies melatonin-related parameters were measured at one timepoint of a 24-hr cycle only, the aim of the present investigation was to extend these experiments by more frequent sampling, to characterize the infradian rhythmicity in more detail. Male Sprague-Dawley rats kept under a light schedule of LD 12:12 (lights on at 0700) were killed at 6-hr intervals on 8 consecutive days. After decapitation the pineal gland was rapidly dissected out, followed by measurements of one of the melatonin-forming enzymes, serotonin N-ac…
Synaptic ribbons of the rat pineal gland: responses to in-vivo and in-vitro treatment with inhibitors of protein synthesis.
1990
To elucidate the role of protein synthesis in the nocturnal increase of synaptic ribbons in the rat pineal gland, actinomycin-D, which inhibits transcription, and cycloheximide, an inhibitor of translation, were used. To assure that the drugs were effective and to relate morphological changes to pineal biosynthetic phenomena, the activity of N-acetyltransferase and levels of pineal indoleamine were measured. Results of in-vivo, short-term and long-term treatment with either drug suggest that transcription of proteins related to synaptic ribbon formation occurs during the first half of the light phase, whereas translation takes place during the first few hours of the dark phase. In contrast,…
Effects of chemical and surgical ganglionectomy on electrical activity of the pineal gland of male rats.
1986
In order to elucidate further the role of sympathetic innervation for pineal function, the influence of sympathectomy on the spontaneous electrical activity of single cells in the pineal gland of adult male rats was investigated. Extracellular single-unit recordings were made during nighttime in the pineal gland of urethane-anesthetized, blinded adult male rats that had been treated neonatally with 6-hydroxydopamine, or that were ganglionectomized either during, or 12-16 h or 36-40 h, prior to the recording experiment. These experiments revealed that the excitatory influence of the sympathetic system on pineal nocturnal electrical activity can be abolished by either chemical sympathectomy o…
The role of the hypothalamic paraventricular nuclei for the regulation of pineal melatonin synthesis: New aspects derived from the vasopressin-defici…
1990
Abstract There is evidence for an involvement of the hypothalamic paraventricular nuclei (PVN) in the regulation of pineal melatonin synthesis in rats. Since electrical stimulation of the PVN or the systemic administration of arginine-vasopressin (AVP) result in a depression of the nocturnal melatonin surge, this neuropeptide appears to be pivotal for the transduction of PVN-efferent, pinealopetal signals. We therefore used an AVP-deficient animal model, the Brattleboro rat, to further investigate the mechanisms responsible for pineal regulation. Anesthetized adult male animals received 2 min of bilateral electrical stimulation of the PVN either during the day or at night. Thirty min later,…
The role of arginine-vasopressin for pineal melatonin synthesis in the rat: involvement of vasopressinergic receptors.
1991
Abstract The endogenously synthesized nonapeptide arginine vasopressin (AVP) is thought to be involved in transduction of photic information to the pineal gland. The enhancement of circulating AVP leads to a suppression of the nocturnal melatonin surge the mechanisms of which are unknown so far. We therefore studied the effect of dDAVP, an AVP analog with antidiuretic but without vasopressor activity, on pineal melatonin synthesis in Sprague-Dawley and AVP-deficient Brattleboro rats. The nocturnal intra-arterial application of dDAVP mimicked the inhibitory effect of AVP on the activity of the rate-limiting enzyme for pineal melatonin synthesis, N-acetyltransferase (NAT), in both rat strains…
Sex differences in GABAA receptor binding in rat brain measured by an improved in vitro binding assay.
1990
The distribution of GABAA receptor sites was studied in female and male rat brain by an improved in vitro binding assay using 3H-muscimol and carefully washed membrane fractions. The binding studies revealed a single class of binding sites exhibiting the properties of GABAA receptors. The specific binding of 3H-muscimol was measured in four brain areas: the preoptic brain area, mediobasal hypothalamus, corticomedial amygdala and cerebral cortex. The equilibrium dissociation constants (KD) ranged from 11.2 to 23.3 nM in diestrous females and from 13.1 to 50.4 nM in males, the maximal number of binding sites (Bmax) from 3290 to 10240 fmol/mg protein in females and from 5495 to 17449 fmol/mg p…
Dependence of hepatic gluconeogenesis on PO2: inhibitory effects of halothane
1987
The dependence of gluconeogenesis and O2 uptake on PO2 in isolated rat hepatocytes is presented. Maintenance of steady-state PO2 was achieved with an oxystat system (Biochem. J. 236: 765–769, 1986). O2 uptake showed a half-maximal (K0.5) value of 0.5 Torr PO2, whereas the glucose synthesis rate was half-maximal at 1.2 Torr PO2. Halothane at concentrations greater than 1 mM exerted a parallel inhibition of O2 uptake and glucose synthesis at all PO2 levels studied. In contrast, at halothane concentrations less than 1 mM, inhibition of glucose synthesis occurred only at less than 20 Torr PO2. At these low concentrations, halothane was without significant effects on cellular O2 uptake. In isol…