Prenatal protein malnourished rats show changes in sleep/wake behavior as adults

Prenatal protein malnutrition significantly elevates brain levels of serotonin in rats, and these levels remain elevated throughout their lives. This biogenic amine is involved in the regulation of many physiological functions, including the normal sleep/wake cycle. The present study examined the effects of prenatal protein malnutrition on the sleep/wake cycle of freely moving adult rats. Six prenatally protein malnourished (6% casein) and 10 well-nourished (25% casein) male rats (90-120-day-old) were chronically implanted with a standard set of electrodes (to record cortical electroencephalogram, neck muscle electromyogram, electrooculogram, and hippocampal theta wave) to objectively measure states of sleep and wakefulness. Six-hour polygraphic recordings were made between 10.00 and 16.00 h; a time when the rats normally sleep. Prenatally malnourished rats spent 20% more time in slow wave sleep (SWS) compared to the well-nourished rats. The total percentage of time spent in rapid eye movement (REM) sleep was 61% less in prenatally malnourished rats compared to well-nourished control rats. These findings demonstrate the adverse consequences of prenatal protein malnutrition on the quality and quantity of adult sleep in rats. These sleep changes are potentially detrimental to normal social behavior and cognitive functions. Prenatally malnourished rats are an excellent animal model to study the role of endogenous serotonin in the regulation of the normal sleep/wake cycle.     

The effects of leptin on REM sleep and slow wave deltain rats are reversed by food deprivation

Leptin (ob protein) is an adipose tissue derived circulating hormone that acts at specific receptors in the hypothalamus to reduce food intake. The protein is also critically involved in energy balance and metabolic status. Here the effect of leptin on sleep architecture in rats was evaluated because food consumption and metabolic status are known to influence sleep. Sprague-Dawley rats were chronically implanted with electrodes for EEG and EMG recording and diurnal sleep parameters were quantified over 9-h periods following leptin administration. Murine recombinant leptin (rMuLep) was administered systemically to rats that either had undergone 18 h of prior food deprivation or had received food ad libitum. In the normally fed rats, leptin significantly decreased the duration of rapid eye movement sleep (REMS) by about 30% and increased the duration of slow wave sleep (SWS) by about 13%, the latter effect reflecting enhanced power in the delta frequency band. These results are consistent with studies that have linked changes in metabolic rate with effects on sleep. Leptin administration has previously been shown to alter neuroendocrine parameters that could have mediated these changes in sleep architecture. Unexpectedly, prior food deprivation negated the effect of leptin on both REMS and SWS, a result that emphasizes the significance of the apparent coupling between sleep parameters and energy status.     

Fever alters characteristics of sleep in rats

This study examined the effects of a fungal infection on body temperature (Tb) and sleep states. Tb and sleep were recorded in male rats for 24 hr after a saline injection and 48 hr after a subcutaneous injection of live brewer's yeast, at ambient temperatures (Ta's) of 20 degrees and 30 degrees C. Peak fevers of 1.6-3.1 degrees C occurred within 6-10 hr at both Ta's. The rats remained febrile for the next 12-24 hr. For the first 24 hr postyeast, amounts of SWS increased by 19 +/- 3% at 20 degrees C and 12 +/- 2% at 30 degrees C. Specifically, SWS was significantly increased from hr 5-8 (lights-on) and 13-24 (lights-off) at 20 degrees, and from hr 5-8 and 17-24 at 30 degrees C. Ta did not affect the changes in Tb or the changes in SWS after either saline or yeast. Duration of REMS varied with Ta after saline. After yeast, REMS increased by 21 +/- 12% at 20 degrees and decreased by 28 +/- 6% at 30 degrees C, with the net result that REMS at the two Ta's was equal during the fever. Furthermore, while the rats were febrile the normal diurnal variation in REMS was eliminated. Sleep and Tb returned to control values during the second fever day. These results suggest that an activated immune system both increases SWS and overrides the diurnal and thermoregulatory modulations of REMS.     

Long-term effect of cued fear conditioning on REM sleep microarchitecture in rats

STUDY OBJECTIVES: To study long-term effects of conditioned fear on REM sleep (REMS) parameters in albino rats. DESIGN: We have investigated disturbances in sleep architecture, including muscle twitch density as REMS phasic activity, and freezing behavior in wakefulness, upon reexposure to a conditioned stimulus (CS) on Day 1 and Day 14 postconditioning. SUBJECTS: Male Sprague-Dawley rats prepared for polysomnographic recordings. INTERVENTIONS: After baseline sleep recording, the animals in the experimental group received five pairings of a 5-sec tone, co-terminating with a 1-sec, 1 mAfootshock. The control rats received similar numbers of tones and shocks, but explicitly unpaired. On postconditioning days, after reexposure to tones alone, sleep and freezing behavior were recorded. MEASUREMENTS AND RESULTS: Conditioned fear significantly altered REMS microarchitecture (characterized as sequential-REMS [seq-REMS: < or =3 min episode separation] and single-REMS [sin-REMS: >3 min episode separation]) on Day 14. The total amount and number of seq-REMS episodes decreased, while the total amount and number of sin-REMS episodes increased. Further, the CS induced significant increases in freezing and REMS myoclonic twitch density in the experimental group. Reexposure to the CS produced no alterations in controls. CONCLUSIONS: The results suggest that conditioned fear causes REMS alterations, including difficulty in initiating a REMS episode as indicated by the diminution in the number of seq-REMS episodes. Another finding, the increase in phasic activity, agrees with the inference from clinical investigations that retrieval of fearful memories can be associated with the long-term REMS disturbances characteristic of posttraumatic stress disorder.     

Differential effect of sleep-wake states on lingual and dorsal neck muscle activity in rats

Postural tone is reduced during slow-wave sleep (SWS) and absent during rapid eye movement sleep (REMS). In obstructive sleep apnea subjects, upper airway dilating muscles, including those of the tongue, show a similar pattern; this contributes to sleep-related airway obstructions. However, in healthy subjects, state-dependent changes in the activity of pharyngeal muscles are variable. In seven chronically instrumented Sprague-Dawley rats, an animal model used to study sleep and sleep-disordered breathing, we quantified lingual and postural muscle activity across the sleep-wake states by measuring the root mean square levels of the electromyograms (EMG) in successive 10s intervals collected during 2h of recording at a constant circadian time (1-3p.m.). The nuchal EMG was low and steady during SWS and further reduced with occasional twitches during REMS. In contrast, the mean lingual EMG during SWS was only 5.9+/-1.6% (S.E.) of its mean in wakefulness, and during REMS, it increased to 46+/-15% (S.E.) (p<0.03) due to the appearance of phasic bursts, the intensity of which progressively increased. The lingual and nuchal activities also had different time courses during state transitions. In obstructive sleep apnea subjects, the sleep-wake changes in the activity of pharyngeal muscles may become similar to those in postural muscles as a result of pharyngeal tone adaptations to the disorder.     

Electromyographic activity at the base and tip of the tongue across sleep–wake states in rats

Obstructive sleep apnea (OSA) patients have elevated tonic and phasic inspiratory activity in the genioglossus and other upper airway muscles during wakefulness; this protects their upper airway from collapse. In this group, sleep-related decrements of upper airway motor tone result in sleep-related upper airway obstructions. We previously reported that in the rat, a species widely used to study the neural mechanisms of both sleep and breathing, lingual electromyographic activity (EMG) is minimal or absent during slow-wave sleep (SWS) and then gradually increases after the onset of rapid eye movement sleep (REMS) due to the appearance of large phasic bursts. Here, we investigated whether sleep–wake patterns and respiratory modulation of lingual EMG depend on the site of EMG recording within the tongue. In nine chronically instrumented rats, we recorded from 17 sites within the tongue and from the diaphragm across sleep–wake states. We quantified lingual EMG in successive 10 s intervals of continuous 2 h recordings (1–3 p.m.). We found that sleep–wake patterns of lingual EMG did not differ between the base and tip of the tongue, and that respiratory modulation was extremely rare regardless of the recording site. We also determined that the often rhythmic lingual bursts during REMS do not occur with respiratory rhythmicity. This pattern differs from that in OSA subjects who, unlike rats, have collapsible upper airway, exhibit prominent respiratory modulation of upper airway motor tone during quiet wakefulness, retain considerable tonic and inspiratory phasic activity during SWS, and show nadirs of activity during REMS.     

Effects of methoxamine and alpha-adrenoceptor antagonists, prazosin and yohimbine, on the sleep-wake cycle of the rat

A study was carried out on the effects of methoxamine, prazosin, and yohimbine on the sleep-wake cycle in rats prepared for chronic sleep recordings. Methoxamine (4-8 mg/kg), an alpha 1-adrenoceptor agonist, induced a dose-related increase in wakefulness (W) and a decrease in slow-wave sleep (SWS) and REM sleep (REMS). Prazosin (0.125-1 mg/kg), which selectively blocks alpha 1-adrenoceptors, modified only slightly the amount of time spent in W and SWS, and consistently decreased REMS values. Prazosin (0.5 mg/kg) reversed the effects of methoxamine, decreasing W and increasing sleep. Yohimbine (3 mg/kg), which blocks alpha 2-adrenoceptors, augmented W and diminished sleep. Methoxamine (4 mg/kg) in animals pretreated with yohimbine (3 mg/kg) induced a further decrease of SWS and REMS and an increase of W. Thus, pharmacological activation of alpha 1- or blocking of alpha 2-adrenoceptors appears to decrease sleep and increase W. Further, blocking of alpha 1-adrenoceptors decreases REMS. Rapid eye movement sleep depression by the alpha 1-agonist or the alpha 1-antagonist is tentatively ascribed to a critical change in noradrenergic transmission in the brain.     

REM sleep control during aging in SAM mice: a role for inducible nitric oxide synthase

Evidence that nitric oxide (NO) is involved in the regulation of rapid-eye-movement sleep (REMS) is supported by recent studies. During aging, NO generation encounters marked changes mainly related to the activation of the inducible NO-synthase (iNOS). To investigate links existing between iNOS and REMS impairments related to aging, we examine the age-related variations occurring in: mRNA and activity of iNOS in brainstem and frontal cortex; sleep parameters under baseline and after treatment by a selective iNOS inhibitor (AMT) in Senescence Accelerated Mice (SAM). SAMR1 (control) mice are a model of aging while SAMP8 are adequate to study neurodegenerative processes. RT-PCR analysis does not reveal significant variation in iNOS mRNA expression in both strains. However, significant age-related increases in iNOS activity occur in SAMR1 but such variation is not observed in SAMP8. In baseline conditions, aging induces a slight increase in slow-wave sleep (SWS) amounts in both groups and deteriorates greatly REMS architecture in SAMP8 compared to SAMR1. AMT reduces REMS amounts for 4–6 h after treatment in a dose and age-dependent manner in SAMR1. Almost no changes occur in SAMP8. Data reported suggest that NO derived from iNOS contributes to trigger and maintain REMS during aging.     

Sleep architecture and regulation of male dusky antechinus,an Australian marsupial

Study ObjectivesIn this study, we (1) describe sleep behavior and architecture, and (2) explore how sleep is regulated in dusky antechinus (Antechinus swainsonii), a small insectivorous marsupial. Our aim is to provide the first investigation into sleep homeostasis in a marsupial.MethodsWild-caught male dusky antechinus (n = 4) were individually housed in large indoor cages under a natural photoperiod of 10.5 h light/13.5 h dark. Continuous recordings of EEG, EMG, and tri-axial accelerometry were performed under baseline conditions and following 4-h of extended wakefulness.ResultsAntechinus engage in SWS and REM sleep. Some aspects of these states are mammal-like, including a high amount (23%) of REM sleep, but other features are reminiscent of birds, notably, hundreds of short sleep episodes (SWS mean: 34 s; REM sleep: 10 s). Antechinus are cathemeral and sleep equally during the night and day. Immediately after the sleep deprivation ended, the animals engaged in more SWS, longer SWS episodes, and greater SWS SWA. The animals did not recover lost REM sleep.ConclusionsSleep architecture in dusky antechinus was broadly similar to that observed in eutherian and marsupial mammals, but with interesting peculiarities. We also provided the first evidence of SWS homeostasis in a marsupial mammal.     

Sleep continuity and the REM-nonREM cycle in the rat under baseline conditions and after sleep deprivation

Wakefulness, nonrapid eye movement sleep (nonREMS) and REMS of rats were scored in 4-s epochs during the first 8 h of the 12-h light period of a baseline (BL) day and during recovery (REC) from 24-h sleep deprivation (SD). Vigilance state continuity was investigated by analyzing the distribution of state episodes. After SD, state continuity was enhanced. The reduced occurrence of short wake episodes resulted in a consolidation of sleep states. The distribution of the REM-nonREM cycle length showed a mode at 10-13 min for both BL and REC. The variability of the cycle length was reduced after SD. The mean cycle length was markedly influenced by the criteria of minimum REMS episode duration and maximal allowed REMS episode interruption.     

Effects of physostigmine infusion on healthy volunteers deprived of rapid eye movement sleep

Rapid eye movement sleep (REMS) deprivation is believed to alter the sensitivity of various neurotransmitter systems. In the present article, we studied 20 healthy volunteers divided into three groups. Group A attended the sleep laboratory for three nights: acclimatization, a baseline night, and one night of physostigmine infusion. Group B attended for eight nights; acclimatization, baseline, four nights of REMS deprivation, and two recovery nights. With the exception of the first recovery night, when group C volunteers were administered physostigmine, group C's schedule was identical to group B's. The infusions received by group A and C were composed of 1.0 mg of physostigmine, dissolved in 100 ml of saline solution. These were administered 5 min after sleep onset and thereafter every hour, except when the subjects were either awake or in REMS. All of the subjects receiving the cholinomimetic infusion were given a peripheral anticholinergic. Group A experienced a great number of awakenings with a decrease in REMS percentage. Group B recovery occurred over two nights, with an increase in the average length of REMS. Group C exhibited maximum REMS rebound on the first recovery night with an increased number of REMS episodes, as well as significant reductions in the first REMS latency. Our findings suggest that physostigmine alters REMS rebound following REMS deprivation.     

Dorsal subcoeruleus nucleus (SubCD) involvement in context-associated fear memory consolidation

The neurobiological mechanisms of emotional memory processing can be investigated using classical fear conditioning as a model system, and evidence from multiple lines of research suggests that sleep influences consolidation of emotional memory. In rodents, some of this evidence comes from a common finding that sleep deprivation from 0 to 6 h after fear conditioning training impairs processing of conditioned fear memory. Here, we show that during a 6-h session of sleep–wake (S–W) recording, immediately after a session of context-associated fear conditioning training, rats spent more time in wakefulness (W) and less time in slow-wave sleep (SWS) and rapid eye movement (REM) sleep. This context-associated fear conditioning training-induced reduction in SWS lasts for 2 h, and the REM sleep reduction lasts throughout the entire 6-h post-training S–W recording period. Interestingly, these reductions in SWS and REM sleep during this 6-h period did not impair memory consolidation for context-associated fear conditioning. The results of this study show, for the first time, that lesions within the dorsal part of the subcoeruleus nucleus (SubCD), which were unintentionally caused by the implantation of bipolar recording electrodes, impair consolidation of context-associated fear conditioning memory. Together, the results of these experiments suggest that emotional memory processing associated with fear conditioning can be completed successfully within less than a normal amount of sleep, but it requires a structurally and functionally intact SubCD, an area in the brain stem where phasic pontine wave (P-wave) generating cells are located.     

Estradiol and Progesterone Modulate Spontaneous Sleep Patterns and Recovery from Sleep Deprivation in Ovariectomized Rats

Study Objectives:

Women undergo hormonal changes both naturally during their lives and as a result of sex hormone treatments. The objective of this study was to gain more knowledge about how these hormones affect sleep and responses to sleep loss.

Design:

Rats were ovariectomized and implanted subcutaneously with Silastic capsules containing oil vehicle, 17β-estradiol and/or progesterone. After 2 weeks, sleep/wake states were recorded during a 24-h baseline period, 6 h of total sleep deprivation induced by gentle handling during the light phase, and an 18-h recovery period.

Measurements and Results:

At baseline and particularly in the dark phase, ovariectomized rats treated with estradiol or estradiol plus progesterone spent more time awake at the expense of non-rapid eye movement sleep (NREMS) and/or REMS, whereas those given progesterone alone spent less time in REMS than ovariectomized rats receiving no hormones. Following sleep deprivation, all rats showed rebound increases in NREMS and REMS, but the relative increase in REMS was larger in females receiving hormones, especially high estradiol. In contrast, the normal increase in NREMS EEG delta power (an index of NREMS intensity) during recovery was attenuated by all hormone treatments.

Conclusions:

Estradiol promotes arousal in the active phase in sleep-satiated rats, but after sleep loss, both estradiol and progesterone selectively facilitate REMS rebound while reducing NREMS intensity. These results indicate that effects of ovarian hormones on recovery sleep differ from those on spontaneous sleep. The hormonal modulation of recovery sleep architecture may affect recovery of sleep related functions after sleep loss.

Citation:

Deurveilher S; Rusak B; Semba K. Estradiol and progesterone modulate spontaneous sleep patterns and recovery from sleep deprivation in ovariectomized rats. SLEEP 2009;32(7):865-877.     

Renal function in juvenile rats subjected to prenatal malnutrition and chronic salt overload

Dietary sodium may contribute to hypertension and to cardiovascular and renal disease if a primary deficiency of the kidney to excrete sodium exists. In order to investigate whether chronic 1% NaCl in the drinking water changes blood pressure and renal haemodynamics in juvenile Wistar rats subjected to prenatal malnutrition, an evaluation of plasma volume, oxidative stress in the kidney, proteinuria and renal haemodynamics was carried out. Malnutrition was induced by a multideficient diet. Mean arterial pressure, renal blood flow and glomerular filtration rate (GFR) were measured using a blood pressure transducer, a flow probe and inulin clearance, respectively. Plasma volume and oxidative stress were measured by means of the Evans Blue method and by monitoring thiobarbituric acid reactive substances (TBARS) in the kidneys, respectively. Urinary protein was measured by precipitation with 3% sulphosalicylic acid. It was observed that prenatally malnourished rats presented higher values of plasma volume (26%, P < 0.05), kidney TBARS (43%, P < 0.01) and blood pressure (10%, P < 0.01) when compared with the control group. However, they showed no change in renal haemodynamics or proteinuria. Neither prenatally malnourished nor control rats treated with sodium overload presented plasma volume or blood pressure values different from their respective control groups, but both groups presented elevated proteinuria (P < 0.01). The prenatally malnourished group treated with sodium overload presented higher values of kidney TBARS, GFR and filtration fraction (58, 87 and 72% higher, respectively, P < 0.01) than its respective control group. In summary, sodium overload did not exacerbate the hypertension in juvenile prenatally malnourished rats, but induced renal haemodynamic adjustments compatible with the development of renal disease.     

Nerve growth factor enhances sleep in rabbits.

Nerve growth factor (NGF) elicits rapid-eye-movement sleep (REMS) in cats. Removal of NGF receptor-positive cholinergic basal forebrain neurons inhibits REMS in rats. The aim of the present study was to determine the effects of NGF on sleep and brain temperature (Tbr) in rabbits. Male rabbits were implanted with electroencephalograph (EEG) electrodes, a brain thermistor and an intraventricular (i.c.v.) guide cannula. Rabbits received human beta-NGF i.c.v. (0.01, 0.1, 1.0 or 10 microg] and on a separate day, 25 microl pyrogen-free saline i.c.v. as control. EEG and Tbr were recorded for 23 h after injections. The highest two doses of NGF increased both non-REMS and REMS across the 23-h recording period. REMS was enhanced dose-dependently. Tbr was not affected by any dose of NGF. These results suggest that NGF is involved in both REMS and non-REMS regulation.     

Significance of slow wave sleep: considerations from a clinical viewpoint

Previous experimental observations, almost exclusively carried out with young healthy subjects, have been interpreted as showing a particular restorative role for human slow wave sleep (SWS). This article considers whether findings from polygraphic sleep studies in patients and elderly subjects lead to similar inferences about the meaning or "function" of SWS. The question was approached in three different ways: (a) by presenting results from a long-term study in elderly subjects whose SWS data were correlated with baseline medical and psychometric findings and with 5-year follow-up results; (b) by correlating nonmanipulated wake-time during days with parameters of SWS on subsequent nights in a group of 30 demented inpatients undergoing 72-h continuous sleep-wake recording; (c) by reviewing and comparing published polygraphic sleep studies for a number of psychiatric conditions. None of these three approaches provided unequivocal evidence for a clinically significant role for SWS. Reasons for the different outcome of SWS studies in young experimental subjects and clinical populations are discussed.     

Sleep and temperature regulation during restraint stress in rats is affected by prior maternal separation.

During restraint stress, 30-day-old rats uniformly show an abrupt and persistent decrease in activity with a corresponding increase in quiet wakefulness. However, the effect of restraint on sleep and body temperature depends on whether maternal separation had previously occurred at the customary age (day 22) or 7 days earleir (day 15). If maternal separation took place on day 22, subsequent restraint on day 30 has no effect on the amount of time spend in sleep or on body temperature, relative to a comparison sgroup of unrestrained rats. But if maternal separation took place on day 15, restraint on day 30 elicits a marked initial increase in sleep and a later decrease in sleep and body temperature. The results are consistent with the interpretation that premature maternal separation retards the normal maturation of these behavioral and thermoregulatory responses to restraint stress.     

Sleep architecture as correlate and predictor of symptoms and impairment in inter‐episode bipolar disorder: taking on the challenge of medication effects

This study was designed to clarify the association between inter‐episode bipolar disorder (BD) and sleep architecture. Participants completed a baseline symptom and sleep assessment and, 3 months later, an assessment of symptoms and impairment. The effects of psychiatric medications on sleep architecture were also considered. Participants included 22 adults with BD I or II (inter‐episode) and 22 non‐psychiatric controls. The sleep assessment was conducted at the Sleep and Psychological Disorders Laboratory at the University of California, Berkeley. Follow‐up assessments 3 months later were conducted over the phone. Results indicate that, at the sleep assessment, BD participants exhibited greater rapid eye movement sleep (REM) density than control participants with no other group differences in sleep architecture. Sleep architecture was not correlated with concurrent mood symptoms in either group. In the BD group, duration of the first REM period and slow‐wave sleep (SWS) amount were positively correlated with manic symptoms and impairment at 3 months, while REM density was positively correlated with depressive symptoms and impairment at 3 months. The amount of Stage 2 sleep was negatively correlated with manic symptoms and impairment at 3 months. In contrast, for the control group, REM density was negatively correlated with impairment at 3 months. SWS and Stage 2 sleep were not correlated with symptoms or impairment. Study findings suggest that inter‐episode REM sleep, SWS and Stage 2 sleep are correlated with future manic and depressive symptoms and impairment in BD. This is consistent with the proposition that sleep architecture may be a mechanism of illness maintenance in BD.     

Cold exposure and sleep in the rat: REM sleep homeostasis and body size

STUDY OBJECTIVES: Exposure to low ambient temperature (Ta) depresses REM sleep (REMS) occurrence. In this study, both short and long-term homeostatic aspects of REMS regulation were analyzed during cold exposure and during subsequent recovery at Ta 24 degrees C. DESIGN: EEG activity, hypothalamic temperature, and motor activity were studied during a 24-h exposure to Tas ranging from 10 degrees C to -10 degrees C and for 4 days during recovery. SETTING: Laboratory of Physiological Regulation during the Wake-Sleep Cycle, Department of Human and General Physiology, Alma Mater Studiorum-University of Bologna. SUBJECTS: 24 male albino rats. INTERVENTIONS: Animals were implanted with electrodes for EEG recording and a thermistor to measure hypothalamic temperature. MEASUREMENTS AND RESULTS: REMS occurrence decreased proportionally with cold exposure, but a fast compensatory REMS rebound occurred during the first day of recovery when the previous loss went beyond a "fast rebound" threshold corresponding to 22% of the daily REMS need. A slow REMS rebound apparently allowed the animals to fully restore the previous REMS loss during the following 3 days of recovery. CONCLUSION: Comparing the present data on rats with data from earlier studies on cats and humans, it appears that small mammals have less tolerance for REMS loss than large ones. In small mammals, this low tolerance may be responsible on a short-term basis for the shorter wake-sleep cycle, and on long-term basis, for the higher percentage of REMS that is quickly recovered following REMS deprivation.     

Fetal protein malnutrition impairs acquisition of a DRL task in adult rats

Developing rats were either malnourished or adequately nourished during the prenatal period by feeding their dams diets of 6% (low) or 25% (adequate) casein content 5 weeks prior to mating and throughout pregnancy. All pups received adequate nutrition from the day of birth onwards. Beginning at 160 days of age male rats were tested in a DRL-18 sec operant task. It was found that prenatal malnutrition impaired performance during acquisition, though asymptomatic levels were not significantly different. Subsequent limited hold DRL-18 sec schedules in which late as well as early responses went unrewarded indicated that the timing ability of the prenatally malnourished rats was excellent and similar to that of the controls. These late effects of fetal protein malnutrition are discussed in terms of the difficulty in adapting to the change from CRF to DRL-18 sec (possibilities include a reduced ability to develop a timing strategy or increased sensitivity to the change in reinforcement contingencies), while retaining the ability to time responses accurately once the task was acquired.