Days Of Cold Research Articles

Encapsulation, Germination, and Conversion of Somatic Embryos in Sugarbeet

Sugarbeet (Beta vulgaris L.) somatic embryos of biotech clone REL-2, obtained from callus grown with absci­ sic acid, were encapsulated with 2 % alginate and sub­ sequently germinated and converted into plantlets, in initial efforts necessary for eventual routine produc­ tion of artificial seeds. Factors examined were embryo size, alginate companion solution, cold storage dura­ tion, and germination substrate. Unencapsulated so­ matic embryo length category (0.5-1.9,2.0-2.9, or 3.0­ 3.9 mm) did not affect germination (98,99, 100%) or conversion (87, 89, 87%, respectively) rates into com­ plete plantlets on hormone-free Murashige-Skoog (MS) medium. Alginate companion solutions (either hor­ mone-free MS medium or H 20) had no differential ef­ fect on germination rate (100%) but did differ in con­ verting embryos to plantlets (81 vs. 64%, respectively). Subsequent experiments examining duration of cold storage of encapsulated embryos at 4°C found no lower rate of conversion at 25°C after 21 days of cold com­ pared with unstored embryos, but after 64 days of cold, the germination and conversion rates (70 and 45 %, respectively) at 25°C of embryos encapsulated with alginate in MS medium were lower compared with unstored embryos. With alginate in H20, germination after 64 days of storage at 4°C was 60%, and conver­

Sinusitis in the common cold

Background: Acute community-acquired sinusitis is considered a bacterial complication of the common cold. Radiologic abnormalities in sinuses occur, however, in most patients with upper respiratory virus infections. Objective: Assessment of the occurrence, clinical profile, laboratory findings, and outcome of radiologically confirmed sinusitis was carried out as part of a common cold study in young adults. Methods: Clinical examinations and radiography of the paranasal sinuses were carried out on days 1, 7, and 21 in 197 patients with the common cold. The symptoms were recorded on diary cards on days 1 to 20. Ten viruses and 5 bacteria were studied as etiologic agents of common cold as reported earlier. Serum C reactive protein concentrations, erythrocyte sedimentation rates, and total white blood cell counts with differentials were determined in 40 randomized subjects on day 7. The effect of 6 days of intranasal fluticasone propionate treatment of the common cold in the prevention of sinusitis was analyzed. Results: On day 7, 39% of patients with the common cold in the placebo group ( n = 98) had sinusitis, which we would prefer to call viral sinusitis. The symptoms of patients with sinusitis and those without it were not clinically distinguishable. Viral infection was detected in 81.6% of patients with sinusitis. No significantly increased levels of antibodies to bacteria were detected. Serum C reactive protein concentrations, erythrocyte sedimentation rates, and white blood cell counts were low in patients with sinusitis. All patients made a clinical recovery within 21 days without antibiotic treatment. Fluticasone propionate treatment tended to prevent paranasal sinusitis, especially in rhinovirus-positive subjects. Conclusion: Viral sinusitis frequently occurs in the early days of the common cold, but it is a self-limited illness. The sinuses should not be imaged in patients with the common cold if the signs and symptoms of illness gradually become less severe and no specific signs suggestive of bacterial sinusitis occur. (J Allergy Clin Immunol 1998;102:403-8.)

The effects of prior chronic stress on cardiovascular responses to acute restraint and formalin injection

Exposure to acute stressors activates both the hypothalamic-pituitary–adrenal (HPA) and cardiovascular systems. Prior chronic stress enhances HPA responses to novel, acute stressors, but whether it alters cardiovascular responsivity to novel, acute stress is unknown. In the present study, we examined mean arterial blood pressure (MAP) and heart rate (HR) to two distinct stimuli, restraint and formalin, following prior exposure to 7 days of intermittent cold. In two sets of control and chronically stressed animals, we measured MAP and HR for 60 min following onset of 30 min restraint and MAP, HR and behavioral responses to intraplantar injection of formalin. Chronic stress raised MAP and HR under resting conditions and elevated HR during, but not following termination of, restraint. These increases in HR during restraint were due to the differences in resting levels of HR, since both control and chronically stressed animals exhibited similar increases from resting levels in HR during restraint. Conversely, chronically stressed animals exhibited lower changes in MAP and HR from resting levels following termination of restraint. Formalin produced the characteristic biphasic pattern of cardiovascular and behavioral responses. Prior chronic stress did not alter behavior, but increased MAP and HR in Interphase and only MAP in Phase 2. The increases in MAP during Interphase and Phase 2 were a result of the elevations in resting levels of MAP, but even when differences in resting levels were taken into account, HR remained elevated in the Interphase in chronically stressed animals. Together, these data demonstrate that prior chronic intermittent cold stress modifies cardiovascular function both under resting conditions and, in very specific ways, under stimulated conditions produced by restraint and formalin. We propose that these modifications are produced by brain regions that are known to regulate cardiovascular function and which are activated by chronic stress.

Arbuscular-mycorrhizal colonization dynamics of cotton ( Gossypium hirsutum L.) growing under several production systems on the Southern High Plains, Texas

The arbuscular-mycorrhizal (AM) colonization patterns of cotton ( Gossypium hirsutum L.) growing under the range of management conditions that are employed for the production of this important crop on the Southern High Plains of Texas was examined in 1991 and 1992. Specifically, the mycorrhizal development of cotton grown under continuous center-pivot irrigation, noncontinuous linear-drive irrigation, continuous center-pivot irrigated cotton planted into terminated winter wheat, supplemental dryland, strict dryland, and supplemental dryland cotton planted into terminated winter wheat was evaluated. During 1991, colonization levels were highest for cotton planted into terminated winter wheat. Furthermore, cotton planted into terminated winter wheat developed more arbuscules and had higher levels of mycorrhizae earlier than any of the other production systems examined. During 1992, at 3 weeks after planting, 5 days of cold, wet weather resulted in almost 100% mortality of cotton not previously planted into terminated winter wheat. Mycorrhizal colonization levels were greater for cotton associated with winter wheat than for cotton grown under conventional practices. The higher colonization levels associated with young cotton plants that were grown with winter wheat as compared with cotton under conventional tillage practices suggests that AM-inoculum levels may have been greater before planting in the cotton+wheat management system for both the 1991 and 1992 studies. Maintenance of a hyphal network for developing cotton seedlings may be crucial for cotton to become colonized rapidly during the seedling stage. Seedling establishment on the Southern High Plains is a critical time for cotton because of abiotic stress from high or low temperatures or inadequate moisture. As a result, any benefit from the symbiosis at this time should have a positive effect on survival and subsequent yields.

Effect of IAA content modulators on peroxidase activity and on endogenous IAA during cold pretreatment of maize anthers prior to androgenesis

A cold pretreatment is usually applied to induce maize androgenesis. Peroxidase activity, including indole-3-acetic acid (IAA) oxidase activity, and endogenous IAA concentrations were followed during a cold pretreatment (14 days, 7°C) in anthers of two maize genotypes, Seneca 60 and DH5×DH7, respectively with a low or high androgenetic response. The most prominent result was the absence of a detectable IAA oxidase activity in DH5×DH7. Adding effectors of IAA-oxidase activity or IAA transport did not affect significantly the crude peroxidase activity of DH5×DH7 anthers while inducing a clear inhibition of androgenesis at higher concentrations. No strict correlation was found between IAA level and physiological response, the low responding variety having as much IAA as DH5×DH7. However, for DH5×DH7, every treatment that lowered the IAA level after 14 days of cold resulted in a decrease in androgenetic response.

The Effect of Cold Stress on Lymphocyte Proliferation in Fetal Ethanol‐Exposed Rats

Prenatal ethanol exposure and stress have each been shown to have significant effects on the immune system. This study examined the possible interactive effects of prenatal ethanol exposure and exposure to stress later in life on the immune system. Differential vulnerability to these challenges in female and male offspring was assessed. At 5 to 6 months of age, female and male offspring from prenatal ethanol-exposed (E), pair-red (PF), and ad libitum-fed control (C) conditions were exposed to 0, 1 or 3 days of cold (4 degrees C). At the end of the cold period, the proliferative response of splenic lymphocytes to the mitogens concanavalin A (Con A) and pokeweed mitogen (PWM) was assessed. The data demonstrate a significant interactive effect between prenatal ethanol exposure and cold stress in female offspring. After 1 day of cold stress, E females had significantly increased PWM-induced lymphocyte proliferation compared with PF and C females, and significantly increased Con A-induced lymphocyte proliferation compared with PF females. There were no differences in PWM or Con A-induced lymphocyte proliferation among E, PF, and C females after 0 or 3 days of cold stress, nor among E, PF, and C males on any test day. Regardless of prenatal treatment, females exposed to 1 or 3 days of cold had significantly greater basal plasma corticosterone levels than females not exposed to cold. In contrast, only E males exposed to 1 or 3 days of cold had significantly increased basal plasma corticosterone levels, compared with E males not exposed to cold; PF and C males showed no significant change in basal corticosterone after cold stress. These data demonstrate that, in response to the challenge of cold stress, changes in lymphocyte proliferation to PWM and Con A may occur selectively in E females. Moreover, the interactive effects of prenatal ethanol and cold stress may result in enhanced rather than suppressed immune responsiveness.

Effects of Storage on Serum Ionized Calcium and pH From Horses With Normal and Abnormal Ionized Calcium Concentrations

It has been previously shown that Ca(I) concentration is stable in serum collected from healthy horses for 10 days if stored at 40 degrees C. This may not be true for horses with abnormal Ca(I) concentrations. Thus the stability of ionized calcium (Ca(I)) concentration and pH measurement in serum from horses with both normal and abnormal Ca(I) concentrations stored for various times at 40 degrees C and -10 degrees C was evaluated. Our results indicated that serum Ca(I) concentration was stable throughout 7 days of cold or frozen storage, after being received by the Clinical Chemistry Laboratory. Serum Ca(I) concentration showed a significant decrease by 14 days of frozen storage (-10 degrees C). Serum pH showed a statistically significant increase by 7 days of cold storage, and within 3 days of frozen storage. If equine serum is collected, handled and stored anaerobically, and kept cold or frozen, Ca(I) concentration can be accurately measured for approximately 7 days after collection, regardless of the health status of the animal. An accurate measurement of pH may be made within 3 days of cold or 1 day of frozen storage.

Changes in cell cycle status and expression of p34cdc2 kinase during potato tuber meristem dormancy

Potato (Solanum tuberosum L. cv. Russet Burbank) tubers undergo a period of endodormancy that is characterized by cell division arrest. At the time of harvest, the tubers used in this study were completely endodormant (i.e. 0% sprouting). After 120 days of storage at 3°C, tubers transferred to 20°C had begun to exit endodormancy and exhibited ca 50% sprouting. After 223 days of 3°C storage, tubers transferred to 20°C were completely nondormant and exhibited 100% sprouting. Based on flow cytometry, about 70% of nuclei isolated from endodormant meristems are arrested in the G1/G0 phase of the cell cycle. Storage of tubers at 3°C did not alter the cell cycle position nor did transfer of tubers from 3 to 20°C for 7 days prior to analysis unless tubers had been stored for at least 223 days. After 223 days of cold (3°C) storage, tubers transferred to 20°C for 7 days showed sprout growth in excess of 5 mm and an increase in the percentage of nuclei in the G2 phase of the cell cycle. Uptake and incorporation of 3H‐thymidine into DNA was low in all tubers up until 120 days postharvest. After that time, only tubers incubated at 20°C for 7 days prior to analysis exhibited an increase in 3H‐thymidine incorporation. This increase coincided with visible sprout growth, demonstrating that cell cycle shifts in tuber meristems relate directly to sprout growth and not the breakage of the endodormancy per se. Using degenerate primers, a portion of a p34cdc2 homolog was amplified from RNA isolated from logphase potato suspension culture cells by polymerase chain reaction. Northern analysis with this probe demonstrated that mRNA levels for two p34cdc2 homologs were present throughout the endodormant period. Immunoblot analysis demonstrated that levels of at least four proteins containing a PSTAIRE epitope (i.e. cdc2‐like) were present at reduced levels in endodormant meristems and increased in reactivated tuber meristems that showed a shift in cell cycle kinetics based on flow cytometry and increased 3H‐thymidine incorporation. These results indicate that the temporal shift in competence for cell division in potato meristems induced by dormancy is not accompanied by alterations in the level of mRNA for p34cdc2 homologues but is correlated with a change in the level of PSTAIRE‐containing proteins. This suggests that during endodormancy cell division in potato tuber meristems is regulated indirectly by posttranscriptional regulation of genes controlling the cell cycle.

Antihistamines and the common cold. A review and critique of the literature.

To determine if antihistamines provided clinically significant relief from the symptoms of the common cold. Structured literature review following standardized guidelines of primary studies published after 1975. Improvements in symptom scores for total symptoms and nasal symptoms over the first three days of a common cold. Three of five studies reporting on sneezing found a statistically significant improvement in the antihistamine group; similarly, three of seven studies reporting on nasal discharge found a statistically significant improvement with therapy. No study reported improvement in total symptom score at the level of p < .05. The validity of these findings was weakened by several flaws in the literature such as inattention to clinical significance and functional impact, inappropriate use of statistical tests, and poorly described methodology. The clinical significance of these improvements was not demonstrated. The primary literature offers little support for the use of antihistamines in the common cold.

Changes in the activity of the adrenal cortex in fasted echidnas ( Tachyglossus aculeatus) exposed to low ambient temperatures

1. 1. The adrenal cortex is necessary for survival of echidnas at low ambient temperatures. In this study, adrenal gland activity was investigated in echidnas exposed to 2 days of cold (14°C) and fasting, alternating with 2 days at room temperature and feeding ad lib. 2. 2. In the cold. 2.75 ± 0.29% (SD) of the initial body weight was lost daily. Plasma amino acid concentration did not change while glucose concentration decreased from 2.6 ± 0.3 to 1.5 ± 0.3 mmol/l with consecutive sessions of cold. 3. Plasma concentrations of corticosterone (7.2 ± 1.4 nmol/l) and cortisol (4.4 ± 1.9 nmol/l) were unchanged by repeated cold exposure. However, the adrenal response to ACTH stimulation decreased and the clearance of corticosteroids increased after cold exposure. 4. It was concluded that exposure to cold increases the utilization of glucocorticoids and decreases the capacity for their biosynthesis.

Effects of Cold-Treatment on Protein Synthesis and mRNA Levels in Rice Leaves

The effects of cold on protein and RNA metabolism in leaves of rice (Oryza sativa L.) seedlings were investigated. Treatment with a diurnal cycle of 15/10 degrees C or 11/6 degrees C for up to 1 week resulted in progressive changes in the protein synthesis pattern after in vivo labeling of intact rice leaves with [(35)S]methionine. These changes were reversed when the seedlings were returned to normal growth temperatures. While de novo accumulation of several abundant proteins was suppressed, some polypeptides were consistently found to be cold-induced. Synthesis of ribulose 1,5-bisphosphate carboxylase (Rubisco) was drastically reduced after 7 days of cold. Using immunoprecipitation of Rubisco, evidence was obtained that the suppression was greater for the small subunit (over 90%) than for the large subunit (80%), indicating a partial loss of coordination in their synthesis. Preformed Rubisco as well as other cold-suppressed proteins were stable for up to 7 days at 11/6 degrees C. Cold-sensitive rice cultivars responded with similar but more drastic changes in the protein synthesis pattern when compared to cold-tolerant varieties. The suppression of Rubisco synthesis by cold was shown to result from reduced levels of the mRNAs encoding both subunits; their decrease paralleled the lower protein synthesis of each. The levels of other chloroplast-encoded mRNAs, especially psaB, and of the nuclear encoded chlorophyll a/b binding protein, also strongly decreased in the cold, whereas the transcripts of the mitochondrial genes apt9, coxIII, and most nuclear genes analyzed were unaffected or only slightly reduced. These data indicate that some chloroplast functions are disturbed during cold stress. One nuclear gene known to be induced by water stress and ABA (Rab21) was also found to be induced by cold treatment.

Levels of ethylene, ACC, MACC, ABA and proline as indicators of cold hardening and frost resistance in winter wheat

Changes in ethylene production and in the contents of 1‐aminocydopropane‐1‐carboxylic acid (ACC), 1‐(malonylamin6)‐cyclopropane‐1‐carboxylic acid (MACC), abscisic acid (ABA) and L‐proline were determined after 40 days of cold hardening at 4°C in three wheat cultivars differing in frost resistance. Proline and especially ABA accumulated with hardening in all varieties in parallel with the degree of frost resistance, e.g. proline and ABA increases in the non‐resistant cv. Slávia were 2x and 5x, whilst in the resistant cv. Mironovská 808 increases were 4X and 20X. Ethylene production and MACC level showed no significant changes with hardening in any of the cultivars after 40 d, but ACC levels did increase with hardening. The production of ethylene, ACC and MACC was studied during hardening. Ethylene production decreased sharply at low temperature and rose rapidly (within 1 day) on return to normal temperature, while ACC production reacted in the opposite direction. MACC levels rose rapidly during the first 4 days of cold, then more slowly for about 2 weeks, thereafter decreasing again steadily. The only varietal differences occurring at maximum levels were correlated with the degree of frost resistance.

Cough and the Common Cold

To determine whether the cough of the common cold arises from upper respiratory stimuli and whether antihistamine-decongestant therapy is an effective treatment for this cough, we prospectively evaluated volunteers with uncomplicated common colds in a randomized, double-blind, placebo-controlled study. After completing a standardized questionnaire and undergoing a physical examination, throat-culturing, and pulmonary function testing, subjects took the active drug or identical-appearing placebo for 7 days while they kept a diary in which they ranked the severity of 17 symptoms for 14 days. Pulmonary function testing was repeated, on average, on Days 4, 8, and 14. Forty-six percent of the variation in cough severity could be explained by throat-clearing and 47% of the variation in throat-clearing severity by postnasal drip. FIF50%, the only physiologic parameter that significantly correlated with cough, rose as cough severity fell. Antihistamine-decongestant therapy reduced postnasal drip and significantly decreased the severity of cough, nasal obstruction, nasal discharge, and throat-clearing during the first few days of the common cold. In addition, cough was 20 to 30% less prevalent in the active drug group within 3 days of starting therapy. We conclude that the cough of the common cold arose from upper respiratory tract stimuli and that cough and other cardinal symptoms of the common cold were reduced with antihistamine-decongestant therapy when these symptoms were at their worst.

Enhanced hepatic insulin sensitivity and peripheral glucose uptake in cold acclimating rats.

Cold-exposed rats exhibit hypermetabolism, hyperphagia, and increased glucose oxidation. Their counterregulatory hormone secretion is markedly elevated, while insulin levels fall acutely, gradually returning to basal during acclimation. We assessed both hepatic and peripheral sensitivity to insulin in rats in the basal state and after 5 days of cold (5 C) exposure. The contribution of gluconeogenesis to total glucose turnover was measured and compared to daily urinary corticosterone excretion. Hepatic glucose production was equally suppressed by the infusion of insulin at 1.2 mU/kg X min in both control and cold-acclimated rats, but enhanced hepatic sensitivity to low dose (0.6 mU/kg X min) insulin infusion was only observed after cold exposure. The metabolic clearance of glucose was elevated with cold stress and was insensitive to the infusion of insulin at either level. Insulin resistance was not observed. Urinary excretion of corticosterone and urea nitrogen were markedly increased, but creatinine excretion was unchanged, suggesting that the concurrent increase in gluconeogenesis resulted from increased protein intake rather than increased catabolism of muscle protein.

Germination Ecophysiology of Hydrophyllum appendiculatum, a Mesic Forest Biennial

In north central Kentucky, seeds of the mesic forest biennial Hydrophyllum appendiculatum Michx., are innately dormant at maturity in June. Under natural and simulated seasonal temperature changes, dormancy break occurred in two stages. Root dormancy was broken by high summer temperatures, and shoot dormancy was broken by low winter temperatures. Consequently, roots emerged from seeds during autumn, and cotyledons emerged the following spring. A 90-day warm (30/15 C) stratification treatment broke root dormancy, but the roots emerged only after transfer to lower temperatures. After the warm stratification treatment, roots emerged from 93, 73, 6 and 9% of the seeds incubated at 5, 15/6, 20/10 and 30/15 C (12/12 hr), respectively. Zero, 28, 56 and 84 days of cold (5 C) stratification of seeds with emerged roots resulted in 9, 21, 49 and 82% cotyledon emergence, respectively, at 20/10 C. Thus, H. appendiculatum exhibits a type of morpho-physiological dormancy known as epicotyl dormancy. Although many seeds germinate the first year, others remain dormant and germinate in successive years until the fourth season after ripening.

GERMINATION ECOPHYSIOLOGY OF HYDROPHYLLUM APPENDICULATUM, A MESIC FOREST BIENNIAL

In north central Kentucky, seeds of the mesic forest biennial Hydrophyllum appendiculatum Michx., are innately dormant at maturity in June. Under natural and simulated seasonal temperature changes, dormancy break occurred in two stages. Root dormancy was broken by high summer temperatures, and shoot dormancy was broken by low winter temperatures. Consequently, roots emerged from seeds during autumn, and cotyledons emerged the following spring. A 90‐day warm (30/15 C) stratification treatment broke root dormancy, but the roots emerged only after transfer to lower temperatures. After the warm stratification treatment, roots emerged from 93, 73, 6 and 9% of the seeds incubated at 5, 15/6, 20/10 and 30/15 C (12/12 hr), respectively. Zero, 28, 56 and 84 days of cold (5 C) stratification of seeds with emerged roots resulted in 9, 21, 49 and 82% cotyledon emergence, respectively, at 20/10 C. Thus, H. appendiculatum exhibits a type of morpho‐physiological dormancy known as epicotyl dormancy. Although many seeds germinate the first year, others remain dormant and germinate in successive years until the fourth season after ripening.

Effect of cold exposure on liver and muscle cAMP content and cAMP phosphodiesterase activity.

Adenosine 3',5'-cyclic monophosphate (cAMP) concentration and 3',5'-cyclic-nucleotide phosphodiesterase (PDE) activity were measured in skeletal muscle, heart, and liver of rats exposed to 1, 3, 5, and 7 days of cold. Cyclic nucleotide concentration increased in fast-twitch red muscle at the same time that PDE activity was decreasing. Nucleotide concentration and enzyme activity of slow-twitch red muscle were not altered by the cold exposure. The PDE activity of fast-twitch white muscle was elevated approximately 50% above control after 1 and 3 days of cold exposure. By the 5th day in the cold, white muscle PDE activity had returned to control levels and remained there through the 7th day of experimentation. cAMP concentration in hearts of cold-exposed rats was significantly (P less than 0.01) elevated above control at all time points measured. Myocardial PDE activity was elevated above control (P less than 0.05) at 1 and 3 days of cold exposure but returned to control levels by the 5th day in the cold. Hepatic cAMP and PDE activity were elevated above control at all time points analyzed. These data suggest that changes in cyclic nucleotide metabolism play a role in attaining homeostasis during acute cold exposure.

The effects of cold-stress. Hibernation, and prolonged inactivity on bone dynamics in the golden hamster, Mesocricetus auratus.

The effects of cold-stress and hibernation on bone dynamics in the femurs of hamsters were investigated using histometric analyses. Control animals were maintained at 27 degrees C for 90 days; experimental animals were kept at 5 degrees C and hibernated for 7, 15, 21, 50, or 90 days. Histometric analyses of cross sections indicated that bone diameter and cortical thickness at the femoral midshaft increased after 83 days of extreme cold and 7 days of hibernation but decreased significantly after 69 days of cold stress and 21 days of hibernation. Osteoporosis was evident although the number of osteons per unit area of bone increased during hibernation. An initial decrease in the number of non-Haversian longitudinal vessels per unit area of bone was seen in experimental animals which was apparently related to a corresponding reduction in cortical thickness. Lacunar area increased in these animals, suggesting that osteocytic osteolysis may be a significant mechanism for calcium regulation during hibernation.

The cold requirement of tulip cultivars

Results of 8 years of trials have been used to assess the cold requirements of 116 tulip cultivars, expressed as the number of days of cold (9°C) required to produce flowers in 21 days at 18°C. The data are compared with commercial recommendations for the dates of transferring tulips to the glasshouse for forcing.

Free-feeding patterns of rats in response to changes in environmental temperature

Four adult Sprague-Dawley rats (430-450 g), maintained on a 12:12 h dark/light cycle and 15% casein diet, were exposed to cold (5 degrees C) for 77 days and then transferred back to 24 degrees C. Throughout thisperiod, the feeding patterns of the rats were measured with recording balances. Cold exposure caused an immediate reduction in nocturnal meal frequency that remained low during the cold exposure. In contrast, diurnal meal frequency was unaltered. Average nocturnal meal size, which did not significantly increase before 8 days of cold, reached a plateau in 2 wk, whereas the average diurnal meal size did not significantly change until late in the exposure period. "Warm" (24 degrees C) reentry elicited an abrupt increase in nocturnal meal frequency and a reduction in average nocturnal as well as diurnal meal size. It thus appears that even in the face of a sudden increase in energy expenditure resulting from cold exposure, adult rats do not immediately adjust their daily food intake. On the other hand, the adaptive hyperphagic response occurring after cold acclimation is abolished when the energy demand is eliminated, i.e., when the animals are removed from the cold.