SLEEP IN RATS RENDERED CHRONICALLY HYPERPROLACTINEMIC WITH ANTERIOR PITUITARY GRAFTS
F. Obál, Jr.1,2, B. Kacsóh3, S. Bredow2, N. Guha-Thakurta2, J.M. Krueger2
1
Dept. of Physiology, A. Szent-Györgyi Medical University, Szeged, HungaryKEY WORDS: sleep, REM sleep, prolactin, pituitary, brain temperature
ABSTRACT
A hyperprolactinemic rat model [rats bearing anterior pituitary grafts under the capsule of the kidney (AP-grafted rats)] was used to study sleep-wake activity and cortical brain temperature (Tcrt). Fisher 344 male rats (n = 24) were implanted with anterior pituitaries from rat pups; the control rats (n = 12) were sham-operated. Sleep-wake activity and Tcrt were recorded for two days between weeks 3 and 7 after surgery. The hyperprolactinemic state of the rats was confirmed by plasma prolactin (PRL) assays on week 7 and by determination of PRL mRNA levels in the anterior pituitary of the AP-grafted rats. Neither growth hormone plasma concentration nor pituitary mRNA levels were affected by the pituitary grafts. Duration of non-rapid eye movement sleep (NREMS) was slightly enhanced in the AP-grafted rats. A large increase in rapid eye movement sleep (REMS) during the 12-h light period was the major effect of the implantation of the extra pituitaries. Both the duration and the frequency of the REMS episodes increased and persisted for weeks 4 to 7 postimplantation. The nocturnal states of vigilance, Tcrt, and intensity of NREMS (EEG slow wave activity) were not altered. The results clearly indicate that the enhancements in REMS persist during hyperprolactinemia, and support the hypothesis that PRL possesses REMS-promoting activity.
INTRODUCTION
Prolactin (PRL) is one of the many hormones whose secretory pattern is associated in part with sleep [reviewed in 44]. Further, a selective rapid eye-movement sleep (REMS)-promoting activity is attributed to PRL; several findings support this notion. Jouvet et al [22] reported that systemic administration of PRL enhances REMS in pontine cats. The selective REMS promoting activity of exogenous systemic PRL also occurs in intact rabbits [32] and rats [37]. Stimulation of endogenous PRL secretion also enhances REMS [33]. Nevertheless, elimination of blood-borne PRL by antibodies results in only a slight suppression in REMS [31]. It has been proposed therefore, that intracerebral PRL might be more important for the regulation of REMS than systemic PRL circulating in normal concentrations [31, 43]. In the case of excess PRL secretions, however, PRL entering the brain via specific transport mechanisms [45] can contribute to stimulation of REMS. The possible importance of intracerebral PRL is indicated by the finding that intrahypothalamic injection of antibodies to PRL suppresses REMS [38]. The decreased REMS in hypoprolactinemic rats is also attributed to a deficiency in central PRL [43]. Finally, intracerebral injections of VIP in doses which enhance REMS increase levels of PRL mRNA in the hypothalamus [6].
With the exception of the alterations in sleep in hypoprolactinemic rats [43], all the other experimental findings summarized above were obtained by means of acute manipulations of systemic or intracerebral PRL. We report here that chronic hyperprolactinemia resulting from anterior pituitary grafts under the capsule of the kidney (AP-grafted rats) is associated with persistent enhancement of REMS.
METHODS
Animals. Inbred Fischer 344 rats were used. Freshly prepared anterior pituitaries one from either sex of 21-day old pups were implanted under the capsule of the left kidney of adult male rats. Thus each rat received 2 extra pituitaries. The rats were anesthetized with ketamine-xylazine (87 and 13 mg/kg, respectively), and the pituitaries were placed under the kidney capsule through an incision. Control rats were subjected to sham operation: the capsule of their kidney was incised. Twenty-four AP-grafted and 12 control rats were used. The rats were randomly selected for the surgeries, and this strategy resulted in a slight difference in the mean body weight of the 2 groups (AP-grafted rats: 266 ± 1.8 g; controls: 277 ± 2.8 g). Ten days later, the rats were implanted with stainless steel jewelry screws as electrodes for electroencephalograph (EEG) recording, and a thermistor for recording cortical brain temperature (Tcrt). The EEG electrodes were placed over the frontal and parietal cortices and over the cerebellum, whereas the thermistor was cemented over the parietal cortex.
Recording. The rats were housed in individual Plexiglas cages in the recording chambers. The ambient temperature was regulated at 26°C, and a 12:12-h light-dark cycle was maintained with light onset at 08:00 h. Food and water were continuously available. Before recording, the rats were connected to the recording tethers for 2-3 days for habituation. The tethers were attached to commutators. The movements of the rats were recorded by means of ultrasonic motion detectors. Cables from the commutators and motion detectors were connected to amplifiers in an adjacent room. The signals were digitized by an analog-to-digital converter (sampling rate 128 Hz) and stored on a computer. For evaluation of the states of vigilance, the EEG, motor activity, and Tcrt signals were displayed on the computer screen. The power density spectra were computed from the EEG by means of Fast Fourier Transformation for each 10-s epoch. The power density values were determined and displayed in 0.5-Hz bins between 0.5 and 20 Hz. The states of vigilance were scored visually in 10-s intervals (NREMS: high-amplitude EEG slow waves, lack of body movements, and declining Tcrt upon entry; REMS: highly regular theta activity in the EEG, general lack of body movements with occasional twitches, and rapid rise in Tcrt at onset; wakefulness: EEG amplitudes similar but less regular than in REMS, frequent movements, and a gradual increase in Tcrt after arousal). The duration of the states of vigilance was expressed as percentage of recording time for each hour and for the 12-h light and dark periods. Power density values between 0.5 and 4.5 Hz were integrated to characterize EEG slow wave activity (SWA), a measure of the intensity of NREMS. SWAs belonging to artifact-free uninterrupted 10-s epochs of NREMS were averaged, and mean SWA during NREMS was computed for each hour. The hourly SWA values obtained on the 2 consecutive recording days were averaged for each rat, thereby the number of missing values were greatly reduced. (Missing SWA values occurred when a rat did not sleep for 1 hour. If a rat failed to produce NREMS in a particular hour on both recording days then the mean of the preceeding and following hourly SWA was used to fill the missing value. This procedure, which was necessery because the absolute values of SWA are sensitive to interindividual differences, was used in 2 AP-grafted and 2 control rats to determine missing SWA values for 1 or 2 hours at night. Missing values never occurred during the light period). The 10-s Tcrt values were averaged for 1-h intervals.
Experimental protocol. Starting three weeks after pituitary implantation or sham operation, i.e. a minimum of two weeks after the implantation of the electrodes, the sleep-wake activity of 6 groups of rats (4 AP-grafted rats + 2 control rats in each group) were recorded on two consecutive days for 23 h (12 h in the light + 11 h in the dark) at 2 to 4-day intervals. Each group was recorded from only once, the last group was recorded on week 7 after pituitary implantation. The 2-day recording started at light onset at 08:00 h. In Fig. 3 results from each of the 2 days are presented separately.
During week 7 postimplantation, the rats were sacrificed by decapitation either in the morning 3 h after light onset (controls: n = 6, AP-grafted: n = 12) or in the afternoon 9 h after light onset (controls: n = 6, AP-grafted: n = 12). Each rat was housed in an individual environmental cage, and decapitation occurred within 20 sec after opening the door of the environmental cage housing a particular rat. Five rats were sacrificed at each time point on a day, and the procedure was repeated on the subsequent days until all rats were sacrificed. Trunk blood was collected for PRL and growth hormone (GH) assays. The pituitary was removed from the sella turcica and dissected removing the neurointermediate lobe and only the anterior pituitary was used to determine PRL, GH and b-actin mRNA levels in 8 AP-grafted and 8 control rats (4 AP-grafted and 4 control rats sacrificed in the morning, and another 4 from both groups sacrificed in the afternoon). Autopsy verified vascularized pituitary grafts under the kidney capsule in each experimental rat. The testis was removed and weighed to calculate testis/body weight ratios.
Hormone assay and mRNA determination. PRL and GH concentrations were measured by radioimmunoassay. The immunoreagents were a gift from Dr. A. F.Parlow and the National Hormone and Pituitary Program (Baltimore, MD). Plasma PRL and GH concentrations are reported in terms of reference preparations rPRL RP-3 and rGH RP-2, respectively. The hormone concentrations were measured in triplicates in one assay with the intra-assay coefficients of variations less than 5 %.
Transcript levels of PRL, GH and b-actin mRNAs (a housekeeping gene product which served as an internal standard) were analyzed by RT-PCR in the eutopic pituitaries as follows. Total RNA from anterior pituitary glands was prepared according to the method of Chomczynski and Sacchi [11] using 1 ml RNA STAT-60 (Tel-Test B, Inc., Friendswood, TX) as described previously [6]. RNA was precipitated by using 0.5 ml isopropanol/ml RNA STAT-60 and was collected by a 20 min centrifugation. The pellet was taken up in 20 ml sterile RNase-free water then reprecipitated in the presence of 0.2 M NaCl with two volumes of 100% ethanol. The final pellet was taken up in 20 ml of sterile RNase-free water. The amount of total RNA was determined by measuring the optical density at 260 nm. The integrity of the RNA was determined by running aliquots on denaturing, formaldehyde-containing agarose gels. First strand cDNA was synthesized using 1 mg of total RNA, 0.75 mg of oligo(dT)15 and 200 units of SuperScript II reverse transcriptase (Life Technologies, Gaithersburg, MD) in a final volume of 20 ml (90 min at 42°C). The reaction was terminated by heating the mixture to 95°C for 10 min. The cDNA was stored at -20°C until further use. Prior to PCR, the cDNA stock was diluted 3.5-fold. Two ml of the cDNA solution corresponding to 7 ng total RNA was used per amplification reaction in a final volume of 50 ml. The reaction mixture contained 1.5 mM MgCl2, 0.2 mM dNTPs, 0.4 mM of each primer and 2 units Taq DNA polymerase. The primers for PRL (corresponding to portions of exons 2 and 4) and b-actin have been previously described [6]. Primers for rat GH were identical with the ones described by Binder et al [5] (sense: 5'-CCAGTCTGTTTGCCAATGCTGTGCT-3', antisense: 5'-CGCAAAGCGG-CGACACTTCATGACC-3'). Reactions for PRL and b-actin were carried out at an annealing temperature of 60°C for 45 sec; annealing for GH was carried out at 66°C for 60 sec. The DNA was denatured for 45 sec at 94°C and the elongation was 2 min (or 7 min in case of the last cycle) at 72°C for all reactions. To remain in the linear range of signal amplification, the following cycle numbers were used: PRL: 20 cycles; GH: 15 cycles; and b-actin: 33 cycles. Ten ml of the PCR products were loaded onto 2% agarose gels, and separated by electrophoresis for 35 min at 160 V in 0.2xTAE buffer containing 0.2 mg/ml ethidium bromide. The gels were briefly washed and photographed using a UV transluminator.
Statistics. Corresponding hourly values of SWA, Tcrt, and the states of vigilance on the 2 recording days were averaged for each rat and used for comparisons between the control and the AP-grafted groups by means of two-way analysis of variance (ANOVA) for the 12-h light and dark periods. The group-effect (independent variables: AP-grafted vs. control rats) and the time-effect (repeated measures: variations in the consecutive hourly values during the light or dark periods) were the two factors of the ANOVA. One-way ANOVA for repeated measures was used to determine whether changes in sleep occurred among the 6 AP-grafted groups and 6 control groups recorded consecutively between week 3 and week 7 postimplantation. Differences between the plasma concentrations of PRL in the control and AP-grafted rats sacrificed in the morning and in the afternoon (4 groups) were evaluated by means of two-way ANOVA. The Student t-test was used to determine the differences between the control and the AP-grafted rats in the plasma concentrations of PRL and GH, in the mean duration of the REMS episodes, in the mean frequency of the REMS episodes, and in the time spent in REMS in the first and second 6-h portions of the light period. In all tests, an a-level of p < 0.05 was taken as an indication of statistical significance.
RESULTS
Indications of hyperprolactinemia. At the time of sacrifice, on week 7 postimplantation, plasma concentrations of PRL were significantly higher in the AP-grafted rats than in the controls [F(1,32) = 28.07, p < 0.05, ANOVA] (Fig. 1). Post hoc analysis by the Student-Newman-Keuls test indicated that PRL concentrations in the AP-grafted rats differed from those of the controls in both the morning and the afternoon. With the control and the AP-grafted rats pooled together, significant time of the day variations were obtained in PRL with higher PRL concentrations in the afternoon than in the morning [F(1,32) = 4.201, p > 0.05]. In fact, the mean plasma PRL concentration was more than 2-fold higher in the afternoon than in the morning in the control rats. Nevertheless, the post hoc comparison failed to detect significant differences in the plasma PRL concentrations between the morning and the afternoon when the control rats were analysed separately; this is attributed to the relatively small sample size (6 rats each). In the AP-grafted rats, the difference between the morning and afternoon concentrations of PRL was approximately 1 ng/ml, and was not statistically significant. The hyperprolactinemia was also verified in the Nb2 lymphoma cell proliferation assay which measures biologically active PRL (data not shown). Differences in plasma GH concentrations were not found between the AP-grafted and control rats (34.7 ± 7.3 ng/ml and 47.4 ± 16.5 ng/ml, respectively, pooled morning and afternoon samples for both groups).
The transcripts for PRL mRNA in the eutopic pituitary of the AP-rats were decreased compared to the control animals at both time points. The grafted pituitaries had no effect on the mRNA levels of GH in the anterior pituitary gland of the host. Similarly, the quantity of the transcripts of the housekeeping gene b-actin showed no difference between the control and the transplant-bearing rats (Fig. 2).
The AP-grafted rats tended to gain less weight than the controls during the 7 weeks after the surgery (46 ± 4 g vs. 58 ± 4 g) but this difference was not statistically significant. The testis weight/body weight ratio did not differ between the two groups of rats (AP-grafted rats: 0.0098 ± 0.00008; controls: 0.0099 ± 0.00002).
Alterations in sleep. Fig. 3 depicts the mean diurnal variations in sleep and Tcrt on two consecutive days recorded between week 3 and week 7 after the implantation of the pituitaries or sham operation. There were no variations in the daily pattern of sleep-wake activity during the 4-week recording period in the control rats. Duration of NREMS was high at the beginning of the light period and declined towards dark onset. Little time was spent in NREMS at night. As indicated by SWAs during NREMS, intensity of NREMS was maximum at the beginning of the light period, decreased during the day, and increased gradually from dark onset towards the end of the night. REMS peaked in the second portion of the light period and was low at night. Tcrt exhibited normal diurnal variations with low and high values during the light and dark period, respectively.
In general, the diurnal rhythms of sleep-wake activity and Tcrt were not influenced in the AP-grafted rats (Fig. 3). The major alteration observed in AP-grafted rats was an increase in REMS during the 12-h light period [AP-grafted vs. control rats: F(1,34) = 56.029, p < 0.05; time effect: F(11,374) = 7.467, p < 0.05; and group x time interaction: F(11,374) = 2.200, p < 0.05]. Although enhancements in the duration of REMS were significant in both the first and the second 6-h portions of the light period the increases in REMS were particularly marked in the morning hours. In contrast to the control rats where REMS peaked in the afternoon, in the the AP-grafted rats, the time spent in REMS was significantly higher in the morning (first 6 h of the recording) than in the afternoon (second 6 h of the light period). REMS was not altered at night. Comparisons among the 6 groups of rats recorded over the 4 week period failed to show significant differences: REMS was already enhanced 3 weeks after the implantation of the pituitaries, and the promotion of REMS persisted until week 7 when the last group was recorded from. The enhancements in REMS resulted from simultaneous increases in both the frequency and the duration of the REMS episodes (Table 1). Correlations were not found between plasma PRL concentrations measured in the morning or the afternoon and the duration of REMS (Pearson Product Moment Correlation).
Statistically significant, albeit very slight, increases in the duration of NREMS were found during the light period in the AP-grafted rats (Table 1) [group-effect: F(1,34) = 13.923, p < 0.05; time-effect: F(11,374) = 29.158, p < 0.05; and group x time interaction: F(11,374) = 0.895, not significant]. Although SWA during NREMS tended to be more intense in the AP-grafted rats than in the controls during the day (Fig. 3) the difference did not reach the level of statistical significance. Tcrt was not altered in the AP-grafted rats.
DISCUSSION
The major finding reported here is that hyperprolactinemic rats bearing pituitary grafts display significant increases in REMS. AP-grafting has been proposed as a reliable method for inducing a modest chronic hyperprolactinemia [3]. Plasma PRL is increased 1 week after the implantation of the pituitary grafts, and the high concentrations of PRL persist [10]. The rises in plasma PRL were confirmed in our experiments both in the morning when PRL secretion is normally low, and in the afternoon when a diurnal surge occurs in the male rats [12]. The suppressed PRL mRNA levels in the intrasellar pituitary in our studies is another indication for hyperprolactinemic state. Concentrations of PRL [2], and PRL mRNA levels [8] decrease in the eutopic pituitary as a result of negative feed-back regulation in the AP-grafted animals. Somatotropic functions are normal in the rats bearing extra pituitaries [1], and indeed, alterations were not found in plasma GH concentrations, GH mRNA levels in the eutopic pituitary, and in the body weight gain in our studies. The previously reported normal testicular weight of the AP-grafted rats is in agreement with the findings that testicular functions are not seriously affected in the hyperprolactinemic male rats [4]. The rise in plasma PRL is, however, not the sole endocrine alteration in the AP-grafted rats. The high PRL concentration induces suppression of gonadotropin secretions [4]. Bartke, et al [4] attribute the maintenance of testicular weight and plasma testosterone to a potentiation by PRL of the effects of LH on the testis. We are not aware of any findings which can link decreases in LH or FSH secretions to enhancements in REMS. Plasma corticosterone concentration increases after implantation of extra pituitaries [reviewed in 3]. Glucocorticoids, however, decrease REMS [17]. It is not clear how production of corticosterone is stimulated in the AP-grafted rats. It might result in part from an increased release of hypothalamic CRH [14]. The CRH-ACTH axis also fails to enhance REMS [34]. In conclusion, the increased PRL concentration is the only known feature of the AP-grafted rats which can explain the enhanced REMS.
Increases in REMS are observed after acute systemic administration of PRL in rabbits [32] and rats [37]. Pseudopregnant [47] and pregnant [25] rats, which are physiologically hyperprolactinemic, exhibit enhanced REMS though NREMS is also increased in these animals. Roky et al [37] found that injection of PRL into rats stimulated REMS only during the light period whereas REMS decreased in the dark period. Our rats slept very little at night and further suppressions were not observed. That the AP-grafted rats exhibited enhanced REMS only during the light period corroborates the report by Roky et al [37] and indicates that this effect of PRL persists during chronic hyperprolactinemia. It is not known why PRL stimulates REMS only during the light period. Roky et al [37] suggest that PRL acts on the circadian regulation of REMS. The observation that the peak of REMS is advanced to the morning hours in the AP-grafted rats may support the suggestion that PRL in fact modulates the rhythm of REMS.
The proposal that PRL influences the circadian regulation of REMS stems in part from the finding that the diurnal distribution of REMS is reversed in genetically hypoprolactinemic rats [43]. REMS is suppressed during the light period and is enhanced at night in these rats. PRL therefore might be involved in the maintenance of the normal diurnal rhythm of REMS. Interestingly however, a recent preliminary report [39] also describes decreased and increased REMS during the light and dark period, respectively, in hyperprolactinemic rats bearing PRL secreting tumors. Female rats were used for the implantation of the tumor and the difference in gender could contribute to the differences in REMS between the AP-grafted and the tumor bearing rats. It is perhaps more important that the plasma concentrations of PRL are several thousand-fold higher in the rats bearing PRL producing tumors than in the AP-grafted rats. Very high PRL concentrations may inhibit the formation of dimer receptor - hormone complexes which are essential for the stimulation of the intracellular machinery mediating PRL effects [18, 24]. As Roky [39] suggested, the changes in REMS in the tumor bearing rats may indicate a decreased rather than an increased stimulation of PRL receptors.
As for other behavioral effects of PRL [see 7, 15, 16 for reviews], the receptors mediating promotion of REMS by PRL are in the brain. Intracerebral administrations of PRL or antibodies to PRL enhances and suppresses REMS, respectively [38]. Blood-borne PRL is transported into the cerebrospinal fluid by a specific receptor-mediated carrier mechanism residing in the choroid plexus [45]. The activity of the transport is regulated by the concentrations of PRL in the blood; acute or chronic increases in PRL concentrations stimulate the cerebral PRL uptake by enhancing the expression of PRL receptors in the choroid plexus [19, 29]. The intracerebral mechanism, however, which is responsible for the mediation of the PRL-induced increases in REMS, is not known. Neurons containing PRL-like immunoreactivity [35, 41], and PRL mRNA [6, 40] are found in the hypothalamus. These neurons innervate practically the entire brain. PRL receptors are found in various cerebral structures [36]. It is supposed that the PRL transported from the blood into the brain act on the same receptors which also mediate the effects of the intracerebral PRL. PRL may modulate neuronal activity [9] and alters neurotransmission. The changes in dopaminergic transmission [20, 26] are the best documented central effects of PRL but PRL also alters VIPergic [30] transmission. These transmitters have been implicated in the regulation of REMS [21, 42] and therefore may be involved in the PRL-induced enhancement in REMS. PRL, however, is also a metabolic hormone. Jouvet [23] proposed that the stress-induced enhancement in REMS results from a stimulation of pyruvate dehydrogenase activity and consequent increases in acetylcholine production in those mesencephalic/pontine cholinergic neurons which have a decisive role in triggering REMS. PRL influences the activities of various neural and glial enzymes involved in carbohydrate metabolism [27]. Stimulation of pyruvate dehydrogenase by PRL, in fact, has been demonstrated in the prostate and the mammary gland [13, 46] but, PRL effects on this enzyme has not been studied in the brain.
In addition to REMS, slight increases in NREMS were also observed in the AP-grafted rats. This finding, if it has any biological significance, is different from the changes in sleep after acute PRL administration when NREMS is not altered [32, 37]. Chronic increases in the plasma concentrations of GH, a hormone structurally related to PRL, are associated with increased sleeping time, indicating enhanced duration of NREMS [28]. The enhancements in NREMS may therefore be attributed to a GH-like effect of the chronically increased PRL. Whatever is the explanation for the slight changes in NREMS, increases in REMS are clearly the dominant sleep alteration in the AP-grafted rats. These rats may provide an excellent model for determining the mechanism of PRL actions on sleep-wake activity.
ACKNOWLEDGMENTS
The authors thank Mr. Ying Wang for technical assistance and Ms. Maria Swayze for her secreterial assistance. This work was supported by the Hungarian Ministry of Welfare (ETT T-11559/93) to F.O., and by NIH NS27250 to J.K. We thank NIDDK (Bethesda, MD) through the NHPP (University of Maryland) for providing reagents used in the GH-RIA and the PRL-RIA.
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FIGURE LEGENDS
b-actin (bottom panel) in the anterior pituitary glands of individual control (C) and AP-grafted (AP-G) rats. The rats were sacrificed either at 11:00 h (A.M. group) or at 17:00 h (P.M. group). The transcripts were detected by reverse transcription polymerase chain reaction (PCR). The predicted sizes for the PCR products were 360, 533, and 764 bp, respectively. Compared to controls, PRL mRNA levels were selectively suppressed in AP-grafted rats both in the afternoon and in the morning groups. No consistent changes were observed either in GH or in b-actin transcripts.Fig. 1. Concentrations (mean ± SEM) of PRL in the plasma in control rats (Conts.) and in rats bearing anterior pituitary grafts (AP-Gr.). The rats were sacrificed either 3 h (morning, A.M.) or 9 h (afternoon, P.M.) after light onset. n = 6 for control and n = 12 for AP-grafted rats for both A.M. and P.M.
Fig. 2. Analysis of mRNA levels of prolactin (PRL, top panel), growth hormone (GH, middle panel) and
Fig. 3. Sleep (REM sleep: REMS; non-REM sleep: NREMS), EEG slow wave activity during NREMS (SWA), and cortical brain temperature (Tcrt) in AP-grafted rats (closed symbols, n = 24) and sham-operated controls (open symbols, n = 12). Six groups of rats (4 AP-grafted rats and 2 controls in each group) were successively recorded for two-23 hour periods between week 4 and week 7 after surgery. Data obtained on day 1 (circles) and day 2 (triangles) of the recordings were averaged separately across the 6 groups of AP-grafted and control rats and depicted as mean ± SEM for Tcrt, and durations of NREMS and REMS. For SWA, the corresponding hourly values on the 2 recording days were averaged for each rat, and these means were used to calculate the daily course of SWA (mean ± SEM) in the AP-grafted groups and the control rats. Hours 1-12: Light period; hours 13-24: dark period.
TABLE 1. Sleep parameters (mean ± SEM) in rats bearing anterior pituitary grafts (AP-grafted) and sham-operated controls during the 12-h light period.
Sham-Operated AP-Grafted
% recording time spent in NREMS 46.8 ± 0.9 50.1 ± 0.4*
% recording time spent in REMS 8.9 ± 0.4 13.1 ± 0.3*
frequency of REMS episodes 33.3 ± 1.1 41.3 ± 1.2#
duration of REMS episodes (min) 1.9 ± 0.06 2.3 ± 0.05#
*ANOVA, p < 0.05
#t-test, p < 0.05