Modification of the beta- and alpha2-adrenergic sensitivity of rat submandibular glands by environmental stimuli and stress

In man, the rate of resting salivary secretion can be influenced by environmental stimuli related to light dark cycles or by noxious stimuli (stressors) of psychological origin. The sympathetic branch of the autonomic nervous system and the adrenal medulla play an important part in homeostatic responses. Previous observations have shown that chronic exposure of rats to constant light promotes degranulation of parotid acini and desensitization of submandibular beta-adrenergic receptors. Now the submandibular secretory response elicited by beta- and alpha2-adrenergic agonists was studied in rats chronically exposed to environmental conditions that modified the activities of sympathetic efferents to the pineal, salivary and adrenal glands. Adult male rats were exposed to constant light (LL) or constant darkness (DD) for 20 days, or to stress (2 h daily immobilization) for 14 days. Control animals were kept under the usual lighting conditions and without immobilization. Dose response curves to isoproterenol (i.v), before and after administration (i.v.) of a dose (20 microg/kg) of clonidine were obtained. Beta-adrenergic desensitization was observed in all the experimental groups, while alpha2-adrenergic desensitization was only observed in the stress and LL groups. The results suggest that circulating catecholamines could mediate light and stress effects on submandibular beta-adrenergic secretory responses. Extrasynaptic alpha2-adrenoceptors might modulate the submandibular secretory response when predictable environmental stimuli (daily light phase) or unpredictable stressors raise the concentrations of circulating catecholamines.     

The butyrylcholinesterase gene is neither independently nor synergistically associated with late-onset AD in clinic- and community-based populations

Pituitary adenylate cyclase-activating polypeptide (PACAP) was recently demonstrated to stimulate melatonin synthesis in the rat pineal gland. Circadian rhythms of melatonin concentration are well known. However, it has not been clarified whether PACAP contents in the pineal gland show circadian rhythm. In this study, we measured PACAP contents in the rat pineal gland throughout the day under 12:12 h light-dark cycle or constant dark conditions. A significant fluctuation was observed in the PACAP content under light-dark conditions but not under constant darkness. On the other hand, the pituitary gland showed no significant variation throughout the day under either conditions. These observations suggest that PACAP may participate in the modulation of melatonin synthesis depending on light conditions in the pineal gland.     

Effects of near-ultraviolet light on the nocturnal serotonin N-acetyltransferase activity of rat pineal gland

Effects of near-ultraviolet (UV-A; 325-390 nm, peak at 365 nm) light on the activity of the pineal serotonin N-acetyltransferase (NAT; a penultimate and key regulatory enzyme in melatonin biosynthesis) were examined in rats. Acute exposure of dark-adapted animals to UV-A radiation produced a marked suppression of NAT activity of the pineal gland, the effect being dependent on exposure time. The decrease in the night-time NAT activity evoked by a 1-min pulse of UV-A light (as well as by a 15-s pulse of broad-band visible light) gradually deepened during the first 40 min of treatment of animals with constant darkness, then the enzyme activity began to rise reaching control values by 3 h. Treatment of rats with a protein synthesis inhibitor, cycloheximide, attenuated this night-driven reactivation of the pineal NAT activity. The presented results provide evidence that UV-A light is a powerful signal capable of controlling melatonin biosynthesis in rat pineal gland.     

Processing of pain- and body-related verbal material in chronic pain patients: central and peripheral correlates

Earlier experimental results show the role of altered pineal function in the development of the constant estrous-anovulatory (CEA) state induced by neonatal androgen sterilization (NA) or in the spontaneously developed anovulatory syndrome in the aging rat (AG-CEA state). Since norepinephrinergic (NE) innervation of pineal gland represents the main stimulus for melatonin secretion in mammals, in the present experimental series, the reactivity of pineal tissue to NE was investigated in in vitro perifusion system in rats suffering from NA-CEA or AG-CEA state, using the model of pineal body deprived from neural inputs. The data indicate that the 'melatonin deficiency' observed in the 2 types of anovulatory syndrome (NA-CEA and AG-CEA states) is due to disturbance of norepinephrinergic innervation of the pineal gland rather than to deficient secretory capacity of pineal tissue.     

Inconsistent suppression of nocturnal pineal melatonin synthesis and serum melatonin levels in rats exposed to pulsed DC magnetic fields

The purpose of these experiments was to determine whether the exposure of rats at night to pulsed DC magnetic fields (MF) would influence the nocturnal production and secretion of melatonin, as indicated by pineal N-acetyltransferase (NAT) activity (the rate limiting enzyme in melatonin production) and pineal and serum melatonin levels. By using a computer-driven exposure system, 15 experiments were conducted. MF exposure onset was always during the night, with the duration of exposure varying from 15 to 120 min. A variety of field strengths, ranging from 50 to 500 microT (0.5 to 5.0 G) were used with the bulk of the studies being conducted using a 100 microT (1.0 G) field. During the interval of DC MF exposure, the field was turned on and off at 1-s intervals with a rise/fall time constant of 5 ms. Because the studies were performed during the night, all procedures were carried out under weak red light (intensity of <5 microW/cm2). At the conclusion of each study, a blood sample and the pineal gland were collected for analysis of serum melatonin titers and pineal NAT and melatonin levels. The outcome of individual studies varied. Of the 23 cases in which pineal NAT activity, pineal melatonin, and serum melatonin levels were measured, the following results were obtained; in 5 cases (21.7%) pineal NAT activity was depressed, in 2 cases (8.7%) studies pineal melatonin levels were lowered, and in 10 cases (43.5%) serum melatonin concentrations were reduced. Never was there a measured rise in any of the end points that were considered in this study. The magnitudes of the reductions were not correlated with field strength (i.e., no dose-response relationships were apparent), and likewise the reductions could not be correlated with the season of the year (experiments conducted at 12-month intervals under identical exposure conditions yielded different results). Duration of exposure also seemed not to be a factor in the degree of melatonin suppression. The inconsistency of the results does not permit the conclusion that pineal melatonin production or release are routinely influenced by pulsed DC MF exposure. In the current series of studies, a suppression of serum melatonin sometimes occurred in the absence of any apparent change in the synthesis of this indoleamine within the pineal gland (no alteration in either pineal NAT activity or pineal melatonin levels). Because melatonin is a direct free radical scavenger, the drop in serum melatonin could theoretically be explained by an increased uptake of melatonin by tissues that were experiencing augmented levels of free radicals as a consequence of MF exposure. This hypothetical possibly requires additional experimental documentation.     

The effect of cervical sympathectomy on the pituitary and pineal endocrine system

It was reported previously that continuous exposure to light in male rats increased serum luteinizing hormone (LH) and bilateral cervical sympathectomy inhibited such a change. In the present report, to examine the effect of cervical sympathectomy on the pineal endocrine function, 30 male rats were assigned to five groups. The control (C) group and the light (L) group underwent sham sympathectomy as well as sham pinealectomy. The sympathectomy (S) group underwent sympathectomy and sham pinealectomy. The pinealectomy (P) group and pinealectomy-melatonine (PM) group underwent sympathectomy and pinealectomy. The C group was kept under a normal circadian rhythm for 10 days, and the other groups were kept under continuous exposure to light for the same period. The PM group received subcutaneously 10 mg.kg-1 of melatonine every day. Serum LH levels were measured 10 days following these experiments. With regard to serum LH levels, the differences among C group, L group, and S group were similar to those previously reported. It was higher in P group (2.53 +/- 0.40 ng.ml-1) than in S group (1.58 +/- 0.61 ng.ml-1), and lower in PM group (2.08 +/- 0.31 ng.ml-1) than in P group. In conclusion, it is suggested that the endocrine activity of melatonine from the pineal gland plays an important role in the appearance of the effect of cervical sympathectomy.     

Effects of constant light exposure and blindness on the oxidative metabolism of selected brain areas in male rats

Male rats were housed in continuous illumination or blinded when 21 day-old and killed 69 days later. The continuous illumination exposure increased the weights of testes and sex accessory organs and reduced the pineal gland weight. Blindness decreased weights of testes, sex accessory organs and anterior pituitary. The oxygen consumption rate of the hypothalamus was higher in the blinded animals than in the controls and lower in the continuously illuminated rats. No one of such groups showed significant changes in the oxygen consumption by either the amygdala or the hippocampus.     

Tripartite hemolysin BL from Bacillus cereus. Hemolytic analysis of component interactions and a model for its characteristic paradoxical zone phenomenon

This study describes the use of the microdialysis technique to elucidate specific properties of the circadian pacemaking system in the hypothalamus, by measurement of melatonin production in the pineal gland. Melatonin has appeared to be a reliable marker of the pacemaker activity, which is influenced by the light/dark cycle. A phase shift in the light/dark cycle was applied to perturb the rhythm generating system. An 8-h phase advance resulted in the disappearance of melatonin production over two days, with basal levels comparable to normal daytime levels. In the subsequent return of rhythmic melatonin production, new clock characteristics could be revealed, due to the high time-resolution measurements of microdialysis. While half of the animals still did not show any rhythmicity, the other half of the animals regained rhythmicity with entrained onset of melatonin production, while the offset was variable and not stably entrained to lights on. Ten days after the shift, the system had completely recovered and all animals regained normal rhythmicity, in phase with the new light/dark cycle. The results are interpreted in terms of the two-oscillator model, with one oscillator reacting with a phase advance and the other with a phase delay to adapt to the phase shift.     

The development of the serum corticosterone rhythm in rats

The purpose of this study was to determine whether the sequence of changes that occur in the adrenal rhythm in maturing female rats (development of a peak, shift in acrophase and amplitude) requires experience with a photoperiodic stimulus or a change in ovarian status. The emergence of the serum corticosterone (CS) rhythm occured more quickly in adult rats placed in a 14 h light, 10 h dark (14:10) cycle at 50 days of age after rearing in constant light (LL) than in weanling rats placed in 14:10. Ovariectomy at weaning age did not alter the pattern of CS development in 14:10 although the amplitude of the peak was reduced even in 25-day-old rats. Adult rats reared in 14:10 held a population rhythm of CS longer after they were placed in LL than did weanling rats placed in LL. This difference was not dependent upon the presence of the ovaries since acutely and chronically ovariectomized (OVX) adult rats responded in a similar manner to adult controls. It can be concluded that the adrenal rhythm emerges as a function of age rather than as a result of a change in ovarian status. The capacity to synchronize serum CS to light-dark cycles develops in the absence of photoperiodic cues.     

The melatonin antagonist luzindole protects retinal photoreceptors from light damage in the rat

PURPOSE: Systemic administration of melatonin can increase retinal light damage in the rat. The role of retinal melatonin receptors in modulating light-damage susceptibility was investigated by intravitreally injecting the melatonin receptor antagonist luzindole into rats. METHODS: Nine Sprague-Dawley albino rats 8 to 9 weeks of age were kept in 50 lux cyclic light for at least 7 days before receiving an intravitreal injection of 1 microl 1 mM luzindole in one eye and 1 microl vehicle in the other eye. The injection was given just before the beginning of the normal 12-hour dark phase. At the end of this dark period, animals were exposed to constant light of 2500 lux for 48 hours. Animals were returned to dim cyclic light for 7 days, and dark-adapted electroretinograms (ERGs) were then recorded from the two eyes simultaneously. The eyes were processed for retinal morphology. Photoreceptor nuclei were counted in the outer nuclear layer (ONL), and the thickness of the ONL and that of the rod outer-segment plus inner-segment layer were measured at several points along sections through the vertical meridian. Two age-matched control rats were maintained in dim cyclic light but received no injections. RESULTS: Luzindole-treated eyes had ERG b-wave thresholds of 2.7 +/- 0.5 (mean +/- SEM) log candela (cd)/m2 lower than the fellow eyes injected with vehicle (P < 0.001), and the maximum b-wave amplitude was 1.0 +/- 0.2 log microV greater in luzindole-treated eyes (P < 0.001). Thresholds of the scotopic threshold response were 0.5 +/- 0.1 log cd/m2 lower than those in vehicle-injected eyes (P < 0.05). Luzindole-treated eyes on average had twice as many photoreceptor cells remaining (P < 0.005). In some areas, several rows of photoreceptor nuclei and outer segments remained in the luzindole-treated eye, whereas the fellow control eye showed cells only occasionally and no outer segments. CONCLUSIONS: Eyes pretreated with the melatonin receptor competitive antagonist luzindole before the dark phase preceding constant light exposure were substantially protected from light damage to the retinal photoreceptors. These results implicate the intraocular melatonin-dopamine system in the regulation of light-damage susceptibility.     

Influence of colony lighting conditions on home-cage spontaneous aggression

In a series of experiments the effects of colony lighting conditions on home-cage aggression were examined, and the relation among measures of home-cage aggressive behavior and shock-induced aggression were determined. In each experiment rats were maintained under either a light/dark (LD) cycle or a continous light (LL) schedule. Experiments 1A and 1B indicated that for cages of LD rats the highest rates of home-cage aggression occurred during the dark segment of the light cycle whereas the lowest rates of aggression characterized the light segment. In contrast, the rate of home-cage aggression was low and constant across time periods for cages of LL rats. Reflecting these differences between lighting conditions, regression analyses in Experiment 1B identified a periodic trend following the fundamental sine curve in the home-cage aggression data from cages of LD rats but not in the data from cages of LL rats. In Experiment 2 the relation between individual differences in home-cage aggression and shock-induced aggression and shock-induced aggression was found to be time dependent for pairs of LD rats. Correlations based on scores of home-cage aggression and shock-induced aggression obtained during the dark segment were positive and statistically significant. Correlations of these two aggressive behaviors based on scores obtained during the light segment were not statistically significant. For pairs of LL rats, no time-dependent pattern in the relation of home-cage aggression to shock-induced aggression was observed.     

Structural plasticity of optic synapses in the rat suprachiasmatic nucleus: adaptation to long-term influence of light and darkness

Synapses of optic afferents (optic synapses) in the suprachiasmatic nucleus of hooded rats were morphometrically evaluated after exposing the animals to 12 h, 14 days, 2 months, and 8 months of constant light (light rats) and darkness (dark rats). Compared with dark rats, optic synapses from light rats have larger boutons with larger mitochondria, more clear vesicles, fewer dense-core vesicles and front-line vesicles, smaller presynaptic dense projections, a smaller amount of postsynaptic density material, a smaller relative number of Gray-type I (asymmetric) junctions, a greater relative number of Gray-type II (symmetric) junctions, as well as more and larger mitochondria in the postsynaptic dendrites. Junctions of optic synapses are mostly straight, but the small number of positively curved contacts are more flattened in light rats than in dark rats. An age-related increase in the size of presynaptic dense projections was also observed. There are no changes in the sizes of clear and dense-core vesicles, in the size of synaptic junctions and their numerical density in area, and in the unspecific contact area between pre- and postsynaptic elements. The changes in optic boutons are characteristic for activated and relatively disused synapses with a slow, tonic firing rate. It appears that (1) the amount of postsynaptic density material is proportional to the strength of Gray-type I synapses, and that (2) some excitatory optic synapses become inhibitory after long-term activity, whereas some inhibitory synapses turn into excitatory contacts after long-term disuse.     

Differential effects of nerve impulses on adrenergic storage vesicles in rat heart

The effects of increasing and decreasing activity in sympathetic neurons on light (D420 = 1.05) and heavy (D420 = 1.15) populations of adrenergic vesicles have been determined. Norepinephrine (NE) was used as a marker for the soluble contents of the vesicles, and dopamine beta-hydroxylase was used as a marker for the vesicle membranes. Cold exposure was used to increase activity in the sympathetic nervous system. A 40% decrease in the NE content of the rat heart with no change in the activity of dopamine beta-hydroxylase was observed after 70 minutes at 5 degrees C. The fall in NE content was completely blocked by pretreating the animals with chlorisondamine. Separation of light and heavy populations of vesicles was achieved with linear sucrose density gradients. Cold stress of 70 minutes duration led to a marked decrease in the NE content of the light vesicles. Blocking adrenergic nerve impulses with chlorisondamine resulted in an increase in total NE in the heart but had no effect on dopamine beta-hydroxylase activity. The initial effect of chlorisondamine was to increase the NE content of the light vesicles. The administration of alpha-methyl-p-tyrosine for 6 hours caused an approximately equal loss of NE from both vesicle populations. The decrease in total heart NE was about 25% and could be prevented by pretreating the animals with chlorisondamine. These results suggest that the light vesicle fraction is involved in the rapid or short-term responses to changes in nerve impulse frequency. Changes in the NE content of the heavy vesicles in rat heart were seen only after longer times, suggesting that these particles may function only as auxiliary storage sites for the neurotransmitter.     

Treatment of systemic hypertension in cats with amlodipine besylate

Electrolytic lesions aimed at the suprachiasmatic nuclei (SCN) were made in male Long-Evans rats. Body temperature (Tb), activity, and drinking were monitored continuously in a 12-h light:12-h dark (12:12 LD) cycle at an ambient temperature of 23 degrees C. Large SCN lesions eliminated activity and drinking rhythms and abolished or reduced the circadian rhythm of Tb. The Tb responses of the rats were measured in L after exposure to cold and injection of lipopolysaccharide (LPS), a fever-producing drug, and in both L and D during a 30-min exposure to a novel cage. Rats with SCN lesions (SCNX) maintained their Tb as well as did controls during 2-h exposure to 2 degrees C. They also showed the expected increases in Tb in response to novelty and LPS. Nevertheless, there were differences between SCNX rats and other rats. When measured 9 h after LPS injection, SCNX rats had lower Tb in D than did sham-lesioned or intact rats or rats with lesions that missed the SCN. This is not surprising; the Tb of SCNX rats does not go as high as that of intact rats in D. However, it was surprising that at night SCNX rats increased their Tb in response to novelty (lights on in the test situation), whereas normal rats did not. For some reason, light inhibits the Tb rise to novelty in normal rats but does not do so in rats with SCN lesions.     

Interactions of the light-dark cycle, adrenal glands and time of steroid administration in determining the temporal sequence of LH and prolactin release in female rats

The purpose of this study was to determine the effects of the light-dark cycle, adrenal glands and steroid treatment schedule on LH and prolactin release in rats. Rats maintained in either a 14 h light: 10 h dark schedule (LD) or constant illumination (LL) were ovariectomized (Ovx) or ovariectomized and adrenalectomized (Ovx-Adx). Three weeks later at 1000 h, animals received a SC injection of estradiol benzoate (EB 10 mug/100 g BW) or oil. Three days after EB administration, rats were given a 2 mg injection of progesterone (P) or oil at either 0200, 0500, or 0900 h, and were sequentially bled at four-hour intervals until 1700 h. P administered at all three times increased the amplitude of the plasma LH surge and advanced it, though by no more than 4 hours, in LD. In LL, P was more effective in advancing the time of LH release, although peak plasma LH levels were considerably less than those observed in LD. Adrenalectomy increased the sensitivity of Ovx rats to the effects of EB and P on LH release. P administration at either 0200, 0500 or 0900 h advanced prolactin release in EB-primed Ovx and Ovx-Adx in LL and LD, but only in LL did P increase the amplitude of the plasma prolactin surge. The lighting conditions did not alter the effectiveness of P in advancing prolactin release. Our study demonstrates that the light-dark cycle and adrenal steroids interact to synchronize the timing of LH release in rats, but the regulatory mechanism controlling prolactin release is less strictly cued to these environmental factors.     

Identification of A and B forms of monoamine oxidase in the iris-ciliary body, superior cervical ganglion, and pineal gland of albino rabbits

The properties of monoamine oxidase activity in homogenates of the iris-ciliary body, superior cervical ganglion, and pineal gland of albino rabbits have been studied. Inhibition curves using specific inhibitors support the concept of A and B enzyme forms, with the following ratios of A/B activity: iris-ciliary body, 40/60; superior cervical ganglion, 90/10; pineal gland, 13/87. Experiments on enzymes from animals with superior cervical ganglionectomy indicate that both A and B forms in the iris-ciliary body have a predominantly extraneuronal location. No significant differences in activity were observed between iris-ciliary body preparations from normal and denervated animals with substrates specific for A or B forms, or with substrates deaminated by both A and B forms. With tryptamine as substrate the iris enzyme can be inhibited by a variety of common monoamine oxidase inhibitors. Topical application of the inhibitor pargyline lowers intraocular pressure in the normal rabbit eye but not in the sympathetically denervated eye. This observation and in vitro data suggest that the mechanism of action of pargyline is through the adrenergic system and not dependent upon intrinsic activity.     

Isolation and characterization of an alpha 1,2-mannosidase cDNA from the lepidopteran insect cell line Sf9

Norepinephrine (NE) (2.5 micrograms/kg/min) was administered to 5-week-old male Sprague Dawley rats by subcutaneous osmotic mini pumps for 14 days to generate an in vivo cardiac hypertrophy model and the responses with respect to aging examined. In the model, ventricles were significantly hypertrophied without myocardial necrosis and without significant increases in heart rate or blood pressure; the beta adrenergic system was down-regulated. In 37-week-old rats receiving 1.0 microgram/kg/min NE, there was a tendency towards heart failure, and myocardial necrosis and interstitial fibrosis were revealed by histological examinations. The density of beta adrenergic receptors and adenylyl cyclase activity was lower in the older rats. The excess stimulation of adrenergic receptors caused severe cardiac injury in old rats regardless of down regulation of beta adrenergic receptors.     

Endothelial nitric oxide synthase in hypoxic newborn porcine pulmonary vessels

AIMS: To determine if the failure of neonatal pulmonary arteries to dilate is due to a lack of nitric oxide synthase (NOS). METHODS: A monoclonal antibody to endothelial NOS was used to demonstrate the distribution and density of NOS in the developing porcine lung after a period in hypobaric hypoxia. Newborn piglets were made hypertensive by exposure to hypobaric hypoxia (50.8 kPa) from < 5 minutes of age to 2.5 days of age, 3-6 days of age or 14-17 days of age. A semiquantitative scoring system was used to assess the distribution of endothelial NOS by light microscopy. RESULTS: NOS was present in the arteries in all hypoxic animals. However, hypoxia from birth caused a reduction in NOS compared with those lungs normal at birth and those normal at 3 days. Hypoxia from 3-6 days led to a high density of NOS compared with normal lungs at 6 days. Hypoxia from 14-17 days had little effect on the amount of NOS. On recovery in room air after exposure to hypoxia from birth there was a transient increase in endothelial NOS after three days of recovery, mirroring that seen at three days in normal animals. CONCLUSIONS: Suppression of NOS production in the first few days of life may contribute to pulmonary hypertension in neonates.