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The circadian rhythm of oxytocin in primate cerebrospinal fluid: effects of destruction of the suprachiasmatic nuclei

The effects of lesions of the suprachiasmatic nuclei (SCN) on the circadian rhythm of oxytocin concentrations in cerebrospinal fluid (CSF) were examined in the rhesus monkey. In the two sham-operated animals, the rhythm was normally entrained to the daily lightdark cycle and persisted in constant lighting conditions at both 4 and 8 months after surgery. Similarly, the oxytocin rhythm was clearly manifested in the two animals with complete SCN ablation 4 months after surgery. At 8 months after surgery, however, the daily CSF rhythm was disrupted in one of the lesioned animals, while it persisted in the other animal. The data show that the SCN are not required for the expression of the daily rhythm of CSF oxytocin, suggesting that a circadian system outside the SCN normally generates the oxytocin rhythm.

Role of the suprachiasmatic nuclei in the circadian timing system of the squirrel monkey. II. Light-dark cycle entrainment

The role of the suprachiasmatic nuclei (SCN) in light-dark (LD) cycle entrainment in the squirrel monkey (itSaimiri sciureus) was evaluated by continuously monitoring core body temperature and drinking behavior in both intact and SCN-lesioned animals exposed to different LD conditions. In a 24-h LD cycle with 12 h of light per day (LD 12:12), both intact and SCN-lesioned monkeys had a prominent rhythm in body temperature with an acrophase 6.51 ± 0.36h (SCN-lesioned) after light onset. In a 23-h LD cycle composed of 1 hr of light and 22 h of dark (LD 1:22), the temperature rhythm in both intact and SCN-lesioned monkeys became synchronized with the 23-h period of the LD cycle. Studies examining the effects of LD cycle exposure on the temporal pattern of drinking behavior indicated that both intact and SCN-lesioned monkeys confined their drinking to the daily period of light. Each monkey was subsequently exposed to an LD cycle with 6 h of bright light and 18 h of darkness or dim background illumination (i.e. 60:0, 66:6 and 76:16 lux cycles). In intact monkeys systematic increases in the average intensity of the daily LD cycle produced corresponding delays in the phase of the daily offset of drinking behavior but did not alter the basic 24-h rhythmicity in the behavior. In contrast, increasing the intensity of the 24-h LD cycle in SCN-lesioned monkeys produced no delay in the daily termination of drinking, but instead produced a disintegration in the 24-h rhythm of drinking behavior. These data indicate that 24-h drinking rhythms in SCN-lesioned monkeys housed under LD cycles are not generated by the circadian system but are the result of a ‘masking’ effect of the LD cycle on drinking behavior. These studies demonstrate that the SCN play a fundamental role in LD cycle entrainment of circadian drinking behavior but are not required for LD cycle entrainment of the circadian rhythm of core body temperature, or the mediation of the masking effects of LD cycles on drinking behavior.

Antidipsogenic action of naloxone under different water deprivation conditions

1. 1. Naloxone (1mg/kg s.c.), in the light phase of the daily light-dark cycles during the 30 and 60 min of the test, shows an antidipsogenic effect of the same intensity in chronically water-deprived rats which drink more (+ 176% and + 162%) than the acutely water-deprived animals. 2. 2. In chronically water-deprived rats, the time interval from the drug introduction (5,30,60 and 90 min) is not critical for the intensity of the antidipsogenic action of naloxone. 3. 3. When water intake is controlled by a 20% variable ratio schedule that does not allow the animals to satisfy, during the session, more than 50% of their thirst, the time interval from the introduction of naloxone is critical. 4. 4. When the rats can drink freely for 30 min in their home-cage after they satisfied their thirst partially by means of bar-pressing, naloxone, paradoxically shows a weaker and not significant antidipsogenic action. 5. 5. The results and the usefulness of the behavioural test are briefly discussed .

Effects of Pinealectomy and Pineal Incubation Medium and Sonicates on Insulin Release by Isolated Pancreatic Islets In Vitro

The present studies were designed to investigate the mechanism of previously-reported nocturnal hyperinsulinemia in the pinealectomized rat. Isolated islets were obtained from anesthetized control, sham-pinealectomized and pinealectomized rats, with 5 rats per surgical groups, during the early dark phase of the daily lightdark cycle. Batches of 3 islets each were incubated in various combinations of 2, 10 or 30 mM glucose with control buffer, medium in which cerebral cortex or pineal glands had previously been incubated for 2 hours, or sonicates of these same tissues. Insulin released into the culture medium was measured by radioimmunoassay. A significant hypersecretion of insulin was demonstrable in the islets from the pinealectomized animals. A stimulatory effect of both pineal medium and sonicates upon insulin release was similarly observed. Neither of these effects displayed an interaction with the concentration of glucose in the islet incubation medium and they, therefore, appear to be mediated by a mechanism which operates independently of stimulation by glucose. These results indicate that the rat pineal gland can exert direct effects upon insulin release from the islets, possibly through a humoral route. Further studies are in progress to characterize the nature and mode of action of the insulinotropic agent present in and released from the pineal gland.

Effects of pinealectomy and of sham-pinealectomy on blood glucose levels in the alloxan-diabetic rat.

Alloxan-diabetic male rats were used to test effects of pinealectomy (PX) and of sham-pinealectomy (SPX) on blood glucose levels at mid-dark in the daily light-dark (LD 12:12) cycle. Animals received a diabetogenic dose of alloxan 10 days postoperatively. Blood glucose was measured on days -1,1,2,3,4,5,7,10 and 15 after 8-hour fasts. Pinealectomized (PX) and non-operated (C) animals were equivalent in their hyperglycemia following alloxan. SPX animals contrastingly showed significantly less response to alloxan than did animals of the other two groups. This difference of the SPX animals was in terms of lower hyperglycemia, better maintenance of body weight and of survival. It is concluded that intracranial surgery alone (SPX) and without visible brain damage can affect mechanisms of glucose homeostasis, and that at least in some circumstances such a surgical effect is not only different from effects of surgical pinealectomy (PX), but is also probably not pineal-dependent.

Light cycle controlled weight changes in pigeons

Abstract The effect of continuous illumination and a daily light dark cycle on the free feeding weights of pigeons was determined. Small unsystematic fluctuations occurred within each day during continuous illumination while substantial gains occurred immediately before the dark cycle. The daily accentuation in weight gain did not occur when a daily period without food was substituted for the period of darkness.

Hour-glass behavior of the circadian clock controlling eclosion of the silkmoth Antheraea pernyi.

The emergence of the Pernyi silkmoth from the pupal exuviae is dictated by a brain-centered, photosensitive clock. In continuous darkness the clock displays a persistent free-running rhythm. In photoperiod regimens the interaction of the clock with the daily lightdark cycle produces a characteristic time of eclosion. But, in the majority of regimens (from 23L:1D to 4L:20D), the eclosion clock undergoes a discontinuous "hourglass" behavior. Thus, during each daily cycle, the onset of darkness initiates a free-running cycle of the clock. The next "lights-on" interrupts this cycle and the clock comes to a stop late in the photophase. The moment when the Pernyi clock stops signals the release of an eclosion-stimulating hormone and is demonstrated to be a function of the time when the free-running cycle is interrupted by lights-on. Moreover, the width (duration) of the eclosion peak in a photoperiod is shown to be dependent upon the length of the dark phase, and, consequently, upon the amount of the free-running cycle that is completed. This relationship demonstrates that the free-running cycle may be divided into two parts. The attainment of maximal accuracy (and thus the narrowest eclosion peak) is dependent upon the completion of only the first 2 hr of the free-running cycle. The completion of succeeding portions of the cycle, while having an effect upon the time of eclosion, no longer affects the accuracy of the clock. A mechanistic model of the eclosion clock is presented.