Experimental models for the study of chronoimmunomodulation (rhythms of the springtail Folsomia candida, Collembola: Isotomidae).

A third-generation cephalosporine, cefodizime, was tested in two experiments on the springtail, Folsomia candida, used as a model of infradian rhythmicity. Any effect on ecdysis (molt), oviposition and oviproduction was sought for 6, 20 or 60 ng of cefodizime administered with brewer's yeast every other day, as compared to controls given only the yeast. Results indicate that a 20-ng dose of cefodizime on alternate days may shorten an infradian period (of molt) in the springtail.

Unexpected responses of the hypothalamic gonadotropin-releasing hormone "pulse generator" to physiological estradiol inputs in the absence of the ovary.

In the rhesus monkey (Macaca mulatta), the frequency of pulsatile gonadotropic hormone release is relatively constant in the face of widely varying levels of estradiol (E2) in the peripheral circulation--e.g., in the course of the follicular phase of the menstrual cycle and after ovariectomy. This suggests that modulation of the hypothalamic gonadotropin-releasing hormone (GnRH) "pulse generator" by this steroid is not of major physiological importance. Herein is described the unexpected inhibition or total blockade of the electrical activity of this pulse generator in ovariectomized monkeys by physiological levels of exogenous E2. This inhibition began 2-4.5 hr after the initiation of E2 infusion and was noted 1 to 3 weeks after subcutaneous implantation of E2-containing capsules. Pulse generator activity was also arrested during the initiation and subsequent development of estrogen-induced surges of luteinizing hormone. We propose that this inhibition of hypothalamic GnRH pulse generator activity by E2 in ovariectomized monkeys reflects the absence of an ovarian factor that normally protects this neuronal system from the inhibitory action of estrogen during the menstrual cycle.

Cyclic variation in fetal heart rate and sympathetic activity.

The effects of alpha- and beta-adrenergic blockade on electrocortical activity-related cyclic variability in fetal heart rate and mean arterial pressure were investigated in eight fetal lambs between 119 and 138 days of gestation. In the absence of adrenergic blockade, fetal heart rate during high-voltage slow activity was significantly higher than that during low-voltage fast activity. Propranolol (2.0 mg/hr) produced a decrease in fetal heart rate, but the decrease was only statistically significant during high-voltage slow activity. Phentolamine (5.0 mg/hr) induced a significant increase in fetal heart rate with a small but statistically significant decrease in mean arterial pressure. The cyclic variability in fetal heart rate between low-voltage fast activity and high-voltage slow activity was abolished by propranolol and enhanced by phentolamine. These results indicate that the cyclic variability in the fetal heart rate associated with electrocortical activity can be accounted for by cyclic fluctuation in sympathetic activity.

Apparent role of melatonin and prolactin in initiating winter fur growth in mink.

A study was conducted to determine the effects of exogenous melatonin and bromocriptine (CB-154), an inhibitor of prolactin synthesis and secretion, on the induction of winter fur growth in mink. Melatonin (10 and 120 mg) was administered to mink (N = 5/group) via silastic implants inserted sc over the scapular area during the last week of June 1985. Treatment of mink (N = 5) with CB-154 alone or in combination with 10 mg melatonin (N = 5) consisted of daily sc injections of 2 mg of the drug in sterile saline from June 25 through July 30. Control animals (N = 5) did not receive injections of vehicle or sham implants. Administration of CB-154 alone or in combination with 10 mg melatonin, as well as 120 mg melatonin alone, initiated growth of the winter fur significantly earlier than that of controls or mink treated with 10 mg melatonin (P less than 0.05). These data suggest that inhibition of prolactin secretion by melatonin is requisite for induction of molt of summer fur and growth of winter fur of mink.

Neonatal monosodium glutamate dosing alters the sleep-wake cycle of the mature rat.

Alterations of the sleep-wake cycle have been studied in male adult rats after neonatal administration of monosodium glutamate (MSG; 4 X 4 mg/g body wt.). Results indicated that MSG treatment caused: an almost complete disappearance of ACTH and alpha-MSH immunoreactive (IR) perikarya in the rostral part of the arcuate nucleus; an increase in total sleep duration with a more pronounced effect on paradoxical sleep. Regarding circadian rhythmicity there was a trend to a decomposition of the 24 h period into ultradian components (12 h, 8 h, 6 h harmonics). The participation of pro-opiomelanocortin peptides in sleep regulation is discussed.

The effects of 4-aminopyridine on the spinal cord: rhythmic discharges recorded from the peripheral nerves.

The effects of an intravenous injection (20 mg/kg) of 4-aminopyridine (4-AP) were initially investigated in acute low spinal cats (Th 13), in which L-DOPA had induced fictive locomotion after paralysis. 4-AP first accelerated the locomotor rhythm and could also change markedly the pattern of activation of some muscle nerves. Shortly after, the locomotor activity was replaced by synchronous rhythmic discharges (2.5-8.5 Hz) in flexor and extensor muscle nerves of the same limb girdle. Similar rhythmic activity was recorded after 4-AP alone (5-20 mg/kg) in the acute decerebrate spinal cat. Whilst the mean rate of the rhythmic activity could differ in the two limb girdles, discharges generated in one girdle appeared to be strongly influenced by those generated in the other. After a complete section of the spinal cord (Th13), the activity persisted in both the rostral and caudal segments although the interactions between the two disappeared. The persistence of the rhythmic activity caudal to the section underscores its spinal origin. In the chronic spinal rat, such rhythmic activity could still be induced in the lumbo-sacral cord despite degeneration of descending pathways. It appears that large doses of 4-AP exert potent effects on the spinal cord which can override other patterns of activity and synchronize the electrical activity of many neuronal elements.

The effect of nifedipine and verapamil on KC1-induced rhythmic contractions of guinea pig ureter in vitro.

Addition of KC1 (40 mM) produced rhythmic contractions of guinea-pig ureters in vitro which were unaffected by phentolamine, atropine or tetrodotoxin. KC1 failed to elicit rhythmic contractions of ureters incubated in a Krebs solution with no added Ca++; in these conditions the addition of CaC12 in concentrations of 1.5 mM, or higher, produced rhythmic contractions whose frequency, but not amplitude, was proportional to CaC12 concentration in the bathing medium. EDTA reduced the frequency of KC1-induced rhythmic contractions without affecting their amplitude. Nifedipine and verapamil reduced both the frequency and the amplitude of KC1-induced rhythmic contraction; verapamil was more effective than nifedipine in reducing their amplitude. Urethane reduced the amplitude without significantly affecting the frequency of KC1-induced rhythmic contractions. An increase in the extracellular Ca++ concentration reverted the suppressive effect of all drugs under study. These results suggest that an influx of Ca++ from the extracellular space is responsible for the initiation of KC1-induced rhythmic contractions and is involved in the mechanism(s) which regulates their frequency, but that a separate mechanism regulates their amplitude.

Studies on the mode of action of octopamine, 5-hydroxytryptamine and proctolin on a myogenic rhythm in the locust.

The modes of action of the modulatory compounds octopamine, 5-hydroxytryptamine (5-HT) and proctolin on the frequency of the myogenic rhythm of the extensor-tibiae muscle of the hindleg of the locust, Schistocerca americana gregaria, have been investigated. 5-HT and proctolin increase the frequency of the myogenic rhythm and the results of the present study suggest that they may mediate their effects by increasing the levels of cyclic AMP in the pacemaker of the myogenic bundle. In contrast, octopamine reduces the frequency of the myogenic rhythm and appears to mediate its effects by a mechanism that does not involve an elevation of cyclic AMP. A number of other possible mechanisms for the action of octopamine are discussed.

[Effect of ethanol on the electrical activity of rat hippocampal neurons in tissue culture]. / Vliianie étanola n élektricheskuiu aktivnost' neironov gippokampa krys v kul'ture tkani.

Unit activity of hippocampal neurones of rat tissue culture was studied before and after local application of ethanol or its adding to the nutrient medium. By means of autocorrelational analysis it was shown that activity of 52% of neurones was of a periodic character. Ethanol in a concentration of 100 mmol depressed the activity of most of sensitive neurones independently of the mode of its administration. However there were twice as many activating effects at local application of ethanol as at its adding to the medium. Changes of firing pattern under the influence of ethanol were accompanied by a complete disturbance of the initial rhythmic activity of some neurones and by an appearance of such kind of activity within the frequency range of 0,2-0,6 Hz in other nerve cells. On the ground of analysis of autocorrelograms the axcitatory processes in nerve cells are supposed to be more sensitive to ethanol than the inhibitory ones.

Rhythmic circumnutation movement of the shoots in Phaseolus vulgaris L.

The apex of growing stems in twining plants describes a rhythmic movement in space called circumnutation. By the method of orthogonal projections, the position in space of the apex can be determined constantly. The mathematical analysis of data allowed us to determine that for Phaseolus vulgaris L. (cv. Mangetout Blanc de Juillet) grown under constant illumination and temperature (25 degrees C) the period is about 100 min. This movement has been related to rhythmic changes in the osmotic potential of the cells located in the bending zone of the stem for a constant period. These variations are longitudinally and laterally coordinated. Treatment with a solution of LiCl at 7 X 10(-3) M supplied to the root system induces a lengthening of the period. The effect of the treatment is reversed by K+ ions. From these results we deduce that rhythmic changes of the membranes are implicated in the circumnutation movements of twining plants.

Octopamine alters rhythmic activity in the isolated cardiac ganglion of the crab, Portunus sanguinolentus.

When applied to the isolated cardiac ganglion of Portunus, octopamine decreases the ganglionic burst frequency and increases the burst duration in a dose-dependent manner over the concentration range 10(-8) M to 10(-6) M. These effects are accompanied by a hyperpolarization (maximum 5 mV) of the cardiac ganglion motor neurones and a decrease in the magnitude of the interburst pacemaker potential in these neurones. The evidence that octopamine plays a cardiomodulatory role in vivo is discussed.

Circannual body weight rhythms of ground squirrels: role of gonadal hormones.

The influence of ovarian and testicular hormones on circannual body weight cycles was assessed in golden-mantled ground squirrels (Spermophilus lateralis), maintained in a LD 14:10 photoperiod at 23 degrees C. Animals were gonadectomized or sham operated at 47 days of age and implanted with empty capsules or capsules filled with estradiol benzoate (EB) or testosterone propionate (TP). Body weight, food intake, and reproductive condition were recorded at weekly intervals. Gonadectomized and intact squirrels of both sexes manifested robust circannual rhythms of body weight; cyclic secretion of gonadal hormones was not necessary for the expression of this circannual cycle. Intact and gonadectomized males weighed substantially more than their female counterparts but only during part of the annual cycle. This sex difference waxed and waned on a circannual basis in the absence of concurrent gonadal hormone secretions. EB phase-delayed attainment of peak body weights in ovariectomized squirrels but did not affect timing of trough body weights. EB increased the amount of food consumed by ovariectomized squirrels particularly during the weight gain phase. TP accelerated attainment of trough body weights in orchidectomized animals. Gonadal hormones modify the magnitude and timing of body weight peaks and troughs but are not necessary for the generation or expression of the circannual body weight cycle or for the sex difference in this cycle.

Seasonal and individual effects on ovarian and endocrine responses of mares to a synchronization treatment with progestagen-impregnated vaginal sponges.

The 8 saddle-type mares were treated with progestagen-impregnated vaginal sponges for 8 days and prostaglandin on the day of sponge removal. The treatment was given at random days of the cycle in April, May, July and September. Sponge insertion induced a sharp decrease in LH levels; at sponge removal, there was an immediate increase in LH and a large FSH rebound. Ovulation was synchronized 11 +/- 2 . 8 days (s.d.) after the end of treatment. In April the interval from sponge removal to ovulation was longer (14 days compared with 10 . 1, 10 . 7 and 10 . 2 days), the basal and peak LH levels lower, and follicular growth more delayed than in the 3 other months. In July, there was a prolonged oestrogen preovulatory rise and reduced FSH levels. Numerous individual differences were shown, but none was significantly linked to the interval from sponge removal to ovulation. Within the 3 months when response was unaffected by season, the interval from end of treatment to ovulation was correlated with progesterone (r = 0 . 45 and r = 0 . 50) and FSH (r = -0 . 48 and r = -0 . 49) levels at Days 5 . 6 and 7 . 8 after sponge insertion. This means that in treated mares that have an active corpus luteum at the end of treatment there will be low FSH levels at this time and ovulation will be late. A good prediction of the ovulation time after such a synchronization treatment must therefore take into account season, animal and time of treatment in the oestrous cycle.

Effect of adenosine 3',5'-monophosphate on neuronal pacemaker activity: a voltage clamp analysis.

Bursting pacemaker activity in nerve cells can be modified for long periods by synaptic input of short duration. There is evidence that cyclic nucleotides may play a role in these modifications. The predominant effect of elevated levels of adenosine 3',5'-monophosphate in Aplysia neurons was an increased slope conductance to hyperpolarizing pulses, evident in voltage clamp records. A similar increase in slope conductance was seen as one component of maximum strength synaptic stimulation, which is consistent with the idea that cyclic nucleotides are important in the expression of synaptic alteration of bursting pacemaker activity.

Burst reset and frequency control of the neuronal oscillators in the cardiac ganglion of the crab, Portunus sanguinolentus.

1. The five large and four small neurones in the cardiac ganglion of the crab, Portunus, are electrotonically coupled and behave as a single relaxation oscillator, exhibiting periodic bursting activity in vitro. Recorded from the large neurone somata, this activity consists of 200-400 ms slow depolarizations called 'driver potentials' (Tazaki & Cooke, 1979a), accompanied by attenuated action potentials and EPSP's from small neurone input. 2. There is a strong positive correlation between the duration of the driver potential and the duration of the following interburst interval in the spontaneously active ganglion. This correlation is preserved during prolonged depolarization and hyperpolarization. 3. When a driver potential is prematurely terminated by an injected current pulse, the following interburst interval is shortened in direct proportion to the decrease in driver potential duration. 4. When a driver potential or a burst of high-frequency action potential activity is evoked by a depolarizing current pulse, the cardiac oscillator resets to the point of maximum hyperpolarization of the burst cycle, and the following interburst interval is of normal duration. Resetting following an evoked driver potential is complete. Partial resetting occurs only after short, evoked action potential bursts in the absence of a driver potential. 5. Reset of the oscillator causes phase shifts in the subsequent cycles of activity, which vary with the phase of application and duration of the injected current pulse. Response curves have been constructed for a comprehensive range of durations and intensities of hyperpolarizing and depolarizing current pulses applied at all phases of the oscillator cycle. 6. The phase shifts are composed of contributions from the duration of the current pulse, from the premature initiation of the slow depolarizing pacemaker potential due to early termination of the burst, and from the change in interburst interval correlated with truncation of the driver potential. 7. Considering the cardiac ganglion as a relaxation oscillator, frequencey control by entrainment to periodically applied current pulses was quantitatively predicted from the phase-response curves and experimentally confirmed. 8. A high concentration (10(-5) M) of octopamine can inhibit driver potential activity in the large neurones. This was used to examine possible frequency modulating effects of electrotonic feedback from the large neurone driver potentials onto the small neurone pacemaker activity. 9. The observations are discussed in relation to the ionic model for driver potentials and slow pacemaker potential activity in the cardiac ganglion, as proposed by Tazaki & Cooke (1979a, b).

Carbon dioxide balance in rat stomach and peripheral tissue: effects of histamine.

Total carbon dioxide content of arterial, gastric venous, and peripheral venous blood of the rat has been measured by a gas extraction-gas solid chromatographic technique. In control animals total contents were 24 to 29 mmol/l and the venous/arterial ratio 1.148 +/- 0.020 (xav +/- SEM). Net change of carbon dioxide content (delta CO2) was 1.17 +/- 0.56 and 1.11 +/- 0.45 mmol/l in gastric and peripheral circulations and these were not significantly different from each other or zero. Infusion of histamine at 10 mg/kg/h led to oscillations in delta CO2 with peaks as high as 4.7 mmol/l and a period of 20 min. Similar oscillations occurred in the venous/arterial ratio with values up to 1.35. The results confirm previous reports of oscillations of carbon dioxide venous/arterial ratios induced by histamine as revealed by pulse radiolabeling experiments. The positive, if oscillatory, carbon dioxide balance in the presence of histamine supports the concept of sequestration of carbon dioxide in tissue with subsequent release on histamine stimulation.