David I. Whitmoyer

Changes in sleep-wakefulness in female rats during circadian and estrous cycles.

Abstract Continuous EEG records from chronically implanted cerebral electrodes have been made of sleep-wakefulness in 5 female rats throughout their 4-day or 5-day estrous cycles, under controlled lighting conditions with 14 h light and 10 h darkness per day. Percentages of alertness, slow wave sleep (SS) and paradoxical sleep (PS) in each 10-min period were punched on IBM cards and introduced to a computer system capable of plotting these percentages daily in each rat and averaging across animals for each time period on corresponding days of the estrous cycle. The results reveal rapid shifts from relative alertness to sleep after the lights come on in the morning. Highest levels of alertness generally occur during the early evening and PS during the afternoon, including the afternoon of proestrus. The day of vaginal cornification (‘estrus’) shows a high percentage of PS — after a night characterized by alertness and virtual absence of PS,i.e., the night of behavioral estrus and ovulation. The female rat, like the male, sleeps on the average about two-thirds of the daylight hours and only one-third of the dark period. Hormonal changes during the day of proestrus appear to increase alertness that night, compensated by an increase in sleep, especially PS, the following day.

Effects of progesterone and sensory stimulation on EEG and neuronal activity in the rat

Abstract The effects of intravenous injections of progesterone and the application of various sensory stimuli on neuronal activity in the hypothalamus, cortex, and thalamus were investigated in urethane-anesthetized rats. Multiple facets of neural activity were registered by simultaneously recording cortical EEG, single-unit firing and integrated multiple-unit activity in these brain regions. Changes in adjacent single- and multiunit activity recorded from the cerebral cortex and thalamus were closely correlated with alterations in cortical EEG, while hypothalamic activity was relatively independent of the cortical EEG. Intravenous progesterone quickly induced a sleeplike EEG which lasted between 20 and 60 min, and single- and multiunit activity changed to the patterns characteristic of sleep. During this period arousal responses to all types of sensory stimuli were partially or completely blocked. Progesterone in this preparation is thus considered to exert differential effects on neurons through a nonspecific depression of arousal. Since the activity of individual neurons is bound more or less closely to the arousal level, neurons are differentially affected by the general depression induced by progesterone.

Circadian sleep-wakefulness patterns in rats after ovariectomy and treatment with estrogen

Abstract Electroencephalographic records were obtained from unanesthetized freely moving rats with electrodes permanently implanted in the olfactory bulb, hippocampus, and frontal cortex while the animals were housed in large glass cylinders within a sound-, temperature-, and light-controlled chamber. The EEG records were converted to percentages of alertness, slow-wave sleep, and paradoxical sleep for each 10-min. interval around the clock and analyzed by computer. After ovariectomy, the records showed greater amounts of slow-wave sleep per day largely because of major increases in nighttime slow-wave sleep levels. Furthermore, the circadian pattern of paradoxical sleep was altered by ovariectomy: the daily (24-hour) amounts of paradoxical sleep remained constant but the night-time hours contained more and the daylight hours concomitantly less, almost obscuring the circadian rhythm. Estrogen injections restored the circadian pattern by sharply reducing the amount of paradoxical sleep at night, resulting in significant diminution in total paradoxical sleep per 24 hours.

Differential effects of central adrenoceptor agonists on luteinizing hormone release.

This study examined the alterations in episodic luteinizing hormone (LH) release in response to third ventricle infusions of various alpha- and beta-adrenoceptor agonists in ovariectomized (OVX) rats as well as the effects of steroid priming with 50 micrograms estradiol benzoate (EB) and 25 mg progesterone (P) on the LH responses to these agonists. Unanesthetized rats with indwelling atrial cannulae were bled at 10-min intervals for 0.5-1.5 h prior to infusion and up to 1.5 h following infusion of equimolar amounts (0.06 or 0.3 mumol in 2 microliters saline adjusted to pH 5.5 and infused slowly over a 2-min period) of norepinephrine (NE), phenylephrine (Phen, alpha 1-agonist), isoproterenol (Iso, beta-agonist) or clonidine (Clon, alpha 2-agonist). In unprimed OVX rats, 0.06 mumol NE induced a significant lengthening (by approximately 121%) of the episodic interval between the peak LH levels and caused a decrease in mean blood LH levels of approximately 24%, which began almost immediately and lasted for approximately 1 h after infusion. When administered in the same manner and dosage, both alpha- and beta-adrenergic agonists were similarly effective in suppressing pulsatile LH release in OVX unprimed rats, with the following rank order being apparent: Clon greater than NE congruent to Phen greater than Iso. However, in OVX-EBP-primed rats, while 0.06 mumol NE significantly stimulated LH release, none of the other adrenoceptor agonists administered at this dosage was effective in altering the low nonpulsatile levels of blood LH characteristic of the steroid-primed animal. Nevertheless, at a concentration 5 times higher (0.3 mumol) Clon and Phen did induce LH surges while Iso, even at this higher dose, was not stimulatory to LH release. These results suggest that the inhibitory action of NE on LH secretion in OVX rats may be exerted via activation of both alpha- and beta-adrenoceptors, whereas primarily alpha-adrenoceptors are responsible for mediating the NE-induced stimulation of LH release in OVX steroid-primed animals.

Temperature changes in the rabbit brain during paradoxical sleep

Abstract To clarify functional and metabolic conditions in the brain during paradoxical sleep as compared with slow wave sleep and alertness, simultaneous recordings were made of brain temperature, cortical and subcortical EEG, and DC potential shifts, together with the local temperatures of such organs as the liver and uterus, and the skin of the neck. Blood flow in the ipsilateral common carotid artery was also measured in five rabbits. The following results were obtained: 1. 1. During paradoxical sleep the temperature of the brain rose very markedly (0.1–0.4°C). The temperature of the cortex was lower than that of the brain-stem but the two regions showed parallel shifts. 2. 2. The elevation of brain temperature associated with an arousal reaction without vigorous body movements was usually considerably less than the elevation during sustained paradoxical sleep. 3. 3. During the slow wave sleep stage the temperature of the brain usually dropped but before the arousal reaction appeared, a gradual temperature elevation was often observed. In some cases the temperature rose slightly even during the slow wave stage of sleep. 4. 4. During paradoxical sleep the temperatures of the neck skin, uterus and liver failed to show elevations parallel with that of the brain temperature. 5. 5. Measurements of blood flow in the common carotid artery revealed that, although there were some phasic increases, no definite increase in average level of blood flow occurred during paradoxical sleep over that of the preceding stage of slow wave sleep. There was no evidence that the elevation in brain temperature during paradoxical sleep was due to warming by increased flow of arterial blood of a higher temperature than that of the brain and it was concluded that the cause of elevation in brain temperature was increased metabolic activity in the forebrain.

Effects of acth, dexamethasone and asphyxia on electrical activity of the rat hypothalamus

Summary A study has been made of the effects of ACTH and dexamethasone on multiple unit activity in the diencephalon of the intact and the adrenalectomized rat under light urethane anesthesia. In the intact rat exogenous ACTH caused short-latency effects, principally excitatory in nature, and secondary long-latency inhibitory effects. The latter were duplicated in the adrenalectomized rat by treatment with dexamethasone suggesting that they were responses to released adrenal corticoids in the intact subjects. The short-latency effects of ACTH, especially the excitatory influences on the arcuate nucleus, were also observed in adrenalectomized rats, and they were considered internal ‘short-loop’ feedback influences. Their latency, location and excitatory nature suggest that they may represent positive feedback effects acting prior to the more widely recognized inhibitory or negative feedback actions. The subcortical multi-unit recording sites were quite sensitive to asphyxia, and irreversible inhibitory changes were observed which necessitate the monitoring of EEG, EKG and respiration in experiments of this type.

Effects of hormones on the electrical activity of the brain in the rat and rabbit

Abstract A study has been made of the effects of various hormones on the electrical activity (EEG and background activity) of the brain in the rat and rabbit. In the rat under weak urethane or ether anesthesia the intravenous injection of vasopressin, epinephrine or progesterone induced EEG synchronization and a concomitant decrease in diencephalic background activity. These electrical changes were invariably associated with a rise in blood pressure and were probably the result of activation of baroceptors. In rabbits under urethane, injections of these hormones also elevated the blood pressure but in this species the rise was associated with EEG activation and an increase in background activity. These effects were apparently due to direct excitation of the reticular activating system by the sudden rise in blood pressure.

Prolactin responsive neurons in the rabbit hypothalamus

Abstract The effects of intravenous injections of Prolactin on the firing rates of individual hypothalamic neurons have been studied in 45 units in 11 unanesthetized rabbits. The rabbits were chronically implanted with cortical silver ball electrodes, a silastic intravenous cannula and a stainless steel adaptor to hold a positionable microelectrode guide tube through which the electrode could be advanced into the hypothalamus by a remote hydraulic drive. Appropriate connections to the implanted facilities could be made at a plastic platform fixed rigidly to the skull. Out of 40 neurons tested with Prolactin, 11 increased and 14 decreased their rate of firing; the remaining 15 showed no change of activity. The findings suggest a short-loop feedback action of Prolactin on the brain but do not localize the pathways employed.

Effect of thyrotropin-releasing hormone, luteinizing hormone-releasing hormone, and somatostatin on neuronal activity of brain stem reticular formation and hippocampus in the female rat

Abstract Changes in the multiunit activity of the brain stem reticular formation and dorsal hippocampus were studied in environmentally habituated, freely moving, regularly cyclic female rats with chronically implanted “macro” and “semimicro” depth electrodes. Cortical electroencephalograms and multiunit activity were recorded continuously. An inverse relationship was observed between the brain stem reticular formation and the dorsal hippocampus multiunit activity. The multiunit activity in the brain stem reticular formation was variably high during attentive behavior, stable and low under slow-wave sleep, and reached very high values in paradoxical sleep (REM). Conversely, the dorsal hippocampus multiunit activity was high during slow-wave sleep and variably low during attentive behavior or REM sleep. Samples of raw multiunit activity were tape-recorded during slow-wave sleep for analysis of interspike intervals of amplitude-discriminated cell discharges prior to and after hormonal treatments. The analysis revealed that intraperitoneal injection of either thyrotropin-releasing hormone ( 3 μ g 100 g body weight) or luteinizing hormone-releasing hormone (500 ng/rat) resulted in a rapid decrease in interspike intervals of amplitude-discriminated spikes in the brain stem reticular formation and a concomitant increase in intervals between hippocampal cell discharges. Somatostatin ( 3 μ g 100 g body weight), on the other hand, resulted in a general depression of firing rates of neurons in both the brain stem reticular formation and the dorsal hippocampus. In the administered doses, none of the hormones interfered with the regular vaginal cycle of the rats.

Differential Gonadotropin Secretion: Blockade of Periovulatory LH but Not FSH Secretion by a Potent LHRH Antagonist

The dependence of periovulatory gonadotropin secretion on LHRH was assessed with the use of a potent LHRH antagonist [ ALHRH ; (Nac-L- Ala1 ,p-Cl-D-Phe2,D-Trp3,6)LHRH]. Blood samples were collected hourly from 14.00 h proestrus (P) through 09.00 h estrus (E) from intact cycling female rats. ALHRH was administered at 09.00 or 13.00 h P before the proestrous increases in gonadotropins had commenced or at 23.00 h P after the LH and primary FSH surges had occurred but preceding the secondary FSH surge. Antagonist given at 09.00 or 13.00 h P completely blocked the LH release with levels remaining undetectable in most animals (less than 30 ng/ml) throughout the sampling period. However, administration of antagonist at these times failed to block completely the primary FSH surge although peak values were reduced when compared with controls, which displayed normal gonadotropin surges. In addition, ALHRH administered at 23.00 h failed to alter the magnitude or other characteristics of the secondary FSH surge when compared with controls. The present study demonstrates that the estrous surge of FSH in the rat is independent of acute hypothalamic release of LHRH. Furthermore, although the proestrous release of FSH is to a large extent LHRH dependent, our data suggest that some other mechanism may also contribute to this primary FSH surge.