Noncycling Rats Research Articles

Virgin Coconut Oil Improved Discriminative Learning and Working Memory in Aging Cycling and Non-Cycling Female Sprague-Dawley Rats Supporting Its Beneficial Effect in Retarding Age-Related Cognitive Decline

Aim: Beneficial effects of virgin coconut oil (VCO) consumption to improve cognition in menopausal females remain inconclusive. This study examined the effect of VCO supplementation in aging cycling and non-cycling rodents to assess its impact on cognition. Methods: Sprague-Dawley rats (10 - 18 months) were randomly assigned to a supplemented VCO group (SVCO) that received oral doses of 1.42 mL/kg/day VCO (n = 10) and a non-supplemented (NVCO) group (n = 10). Their performance in a biased Y-maze discriminative learning paradigm was assessed over a 16-week period. Rats were initially allowed 3 minutes to explore the maze (habituated) and subsequently pre-trained in the non-preferred, white chamber to associate the presentation of a tone with a treat (reward). Training involved 4 daily trials initially for 3 weeks during which rats were rewarded if they entered the white arm within 15 sec after tone presentation. Time (days) to attain at least 75% correct responses (CR) determined acquisition latency (AL). Memory retention (MR1) of the learned task was assessed following a 1-week break from training and absence of supplementation (session T1). Following an additional 2-week break, supplementation of SVCO animals resumed and continued to week 16. In week 14, all animals received re-training for 1 week (session T2) followed by another 1-week break and subsequent assessment of memory (MR2). Vaginal smear cytology determinations were performed throughout the study to identify cycling and non-cycling rats. Student’s t-test and ANOVA with Brown-Forsythe and Tukey’s post-hoc tests were used to compare means. Results: C-SVCO rats attained lower AL, and higher CR and MR scores vs their NVCO counterparts (p Conclusion: VCO supplementation attenuated cognitive decline with a more positive impact on non-cycling rodents suggesting a beneficial effect on brain health in females in menopausal transition.

SUPPLEMENTATION WITH VIRGIN COCONUT OIL: CAN IT REALLY REDUCE COGNITIVE DECLINE?

The sudden decrease in bioavailable estrogen in menopause puts ageing females at increased risk of cognitive decline. Consumption of virgin coconut oil (VCO) which has been “classified as a highly nutritious functional food” has gained popularity recently due to claims of beneficial effects in people with cognitive impairment. This study was designed to compare the effect of VCO supplementation on learning and memory between mature, cycling and aged, non-cycling rats. Twelve 15-month old and twelve 22-month old female Sprague-Dawley rats completed the study. Vaginal smear cytology determined estrous cycle staging to identify cycling and non-cycling rats. A modified discriminative learning paradigm utilizing a Y-maze was adopted. Number of entries and time spent determined arm preference during a 3-minute maze exploration. Rats that exhibited preference (>75%) for the black arm of the maze were selected. Each age cohort was randomly assigned to either a VCO-treated or non-VCO (control) group (n=6). Treated rats were administered a daily oral dose of 1.42 ml/kg of cold pressed VCO. In pre-training, rats were confined to the non-preferred, white arm of the maze and learnt to associate the presentation of a tone with reward. Rats were then allowed 4 trials daily over 3 weeks and rewarded only if they entered the non-preferred arm within 15 seconds after presentation of a tone (i.e. correct response). Time to attain at least 75% correct responses (acquisition latency) was used to assess learning. Memory retention of the learnt task was assessed in all groups following a 2-week break. Data were analyzed using Students’ T-test and ANOVA. Cycling rats had lower acquisition latencies and significantly higher correct response rates than non-cycling rats (p=0.04). Cycling VCO-treated rats exhibited a significant enhancement of learning (p=0.04) compared with non-supplemented controls. VCO supplementation showed no improvement in memory retention across all groups, however VCO treated cycling rats had higher response rates than their non-cycling counterparts. VCO supplementation produced a small positive effect on cognition overall, but appears to be more effective when supplemented during the cycling period when estrogen levels are normal and provides better neuroprotection.

The feasibility of ultrasound biomicroscopy for non-invasive and sequential assessment of ovarian features in rodents

The current study assessed the usefulness of in vivo high frequency ultrasound imaging (ultrasound biomicroscopy, UBM) for dynamic study of the ovarian structures in laboratory rodents. UBM imaging was performed, by using a 40 MHz probe, in 12 C57BL/6J female mice and four Wistars female rats at breeding age and during different reproductive periods. UBM provided outstanding images of both follicles and corpora lutea in cycling and non-cycling rats and mice and was useful to evaluate the ovarian response after controlled ovarian stimulation in the mouse. Thus, UBM may be a very useful method for reproductive studies in rodents.

Estrogen treatment suppresses forebrain p75 neurotrophin receptor expression in aged, noncycling female rats.

There is increasing evidence that estrogen has beneficial effects on cognition, both in humans and in rodents, and may delay Alzheimer's disease onset in postmenopausal women. Several rodent studies have utilised the ovariectomy model to show estrogen regulation of the p75 neurotrophin receptor, TrkA, and markers of acetylcholine synthesis in the cholinergic basal forebrain. We studied estrogenic effects in aged (16-17-month-old), noncycling rats. Estrogen treatment for 10 days drastically reduced p75(NTR) immunoreactivity in the rostral parts of the basal forebrain. The number of p75(NTR)-immunoreactive neurons was decreased, and those neurons remaining positive for p75(NTR) showed reduced p75(NTR) staining intensity. In vehicle-treated rats, almost all choline acetyltransferase-immunoreactive neurons were p75(NTR) positive (and vice versa), but, in estrogen treated rats, large numbers of choline acetyltransferase-immunoreactive cells were negative for p75(NTR). Similar levels of p75(NTR) down-regulation in the rostral basal forebrain were found when estrogen treatment was extended to 6 weeks. There was no reduction in the number of p75(NTR)-immunoreactive neurons in the caudal basal forebrain after 10 days of treatment. After 6 weeks of treatment, however, there was evidence of p75(NTR) down-regulation in the caudal basal forebrain. There was no evidence of hypertrophy or atrophy of cholinergic neurons even after 6 weeks of estrogen treatment. Considering the evidence for the role of p75(NTR) in regulating survival, growth and nerve growth factor responsiveness of cholinergic basal forebrain neurons, the results indicate an important aspect of estrogen's effects on the nervous system.

Luteolytic effect of prolactin is dependent on the degree of differentiation of luteal cells in the rat.

We studied the morphological and quantitative changes in cyclic corpora lutea (CCL) and in CL of pregnancy (CLP) during structural luteolysis. Elimination of CCL takes several cycles, and cell death occurs as successive apoptotic bursts, from 2100 h in proestrus to 1300 h in estrus. Each apoptotic burst determined a 60% decrease in the CL volume and an 80% decrease in the number of steroidogenic cells (SC). All these changes were inhibited by blocking the preovulatory prolactin (PRL) surge with bromocryptine (CB154). Neither apoptotic cells nor changes in the number of SC were found in regressing CLP from Day 21 of pregnancy to Day 2 postpartum, although there was a 50% decrease in the CLP volume and a 30% decrease in the mean cross-sectional area of SC. Treatment with CB154 on the day of parturition did not modify these regressive changes. On Day 5 postpartum, the volume of the CLP and the number of SC were equivalent in lactating rats (showing high PRL concentrations induced by pup suckling) and nonlactating noncycling rats (in which cyclicity and, therefore PRL surges, were blocked by treatment with LHRH antagonist). However, on Day 10 postpartum, the CLP volume and the number of SC were significantly decreased in lactating rats, and apoptotic cells were frequent. In postpartum cycling rats, the CLP did not show apoptotic cells on the day of the second postpartum estrus (on Day 5 postpartum), whereas on the day of the third postpartum estrus (on Day 9 postpartum), apoptotic cells were abundant. These results indicate that PRL does not induce apoptosis in the CLP before Day 5 postpartum and strongly suggest that the proapoptotic effect of PRL is dependent on the degree of differentiation of luteal cells.

Luteinizing hormone response to N6, O2'-dibutyryl adenosine 3',5'-cyclic monophosphate in aged, young and androgenized rats: estradiol effect in vitro.

The studies in this report were designed to investigate whether the loss of pituitary luteinizing hormone (LH) responses to N6,O2'-dibutyryl adenosine 3',5'-cyclic monophosphate (DBcAMP) in aged noncycling rats was the result of age, endocrine status associated with diestrus, or noncyclic low estrogen status. Pituitary monolayer cultures were prepared from female Fischer 344 rats. Aged (18-month-old) persistent diestrous (PD) rats, young diestrous (D) rats, or noncycling neonatally androgenized-constant estrous (AN-CE) rats were used. Enzymatically dispersed cells were maintained in the same batch of medium supplemented with dextran-coated charcoal adsorbed serums. Total LH contents were 1.75 +/- 0.04, 1.15 +/- 0.03, and 1.71 +/- 0.02 micrograms LH/dish in Day 5 cultures prepared from aged PD, young D, and AN-CE rats, respectively. Incubations with 5 mM DBcAMP for 4 h significantly (P less than 0.05) stimulated LH release in cultures prepared from young D and AN-CE rats but inhibited LH release in cultures prepared from aged PD rats even though a 4-h incubation with 10 nM LH releasing hormone (LHRH) stimulated LH release similarly in cultures of all three types of cells. The loss of DBcAMP-induced LH release in cultures prepared from aged PD rats was reversed by 17 beta-estradiol (E2). This treatment also reduced the basal LH release and increased the cellular LH content. These results indicate that the loss of DBcAMP-induced LH response in the aged rat is not an irreversible aging phenomenon but appears to be associated with the chronically low E2 status of aged PD rats but not young cycling D or noncycling AN-CE rats.

Partial starvation, and “in vitro” contractions of rat uterine smooth muscle. Levels of glygogen and trigly-cerides

The effects of a restricted-diet (50% of the normal intake during 25 days) on the isometric developed tension (IDT) of uterine horns isolated from diestrous non-cycling rats, were explored. After 60 minutes following isolation and mounting the IDT of controls suspended in glucose containing solution was higher than in preparations from underfed animals but this was no the case in the absence of glucose. Glycogen levels of controls at 60 minutes were smaller in substrate-free than in the presence of glucose whereas no change was detected in horns from restricted-diet rats. Preparations from underfed animals had a significantly augmented basal concentration of triglycerides which diminished at 60 minutes following the removal of glucose from the suspending solution. This effect was abolished by the addition of 3-O-methyl glucose and by blockers of beta-adrenoreceptors such as propranolol or MJ-1999. A similar situation occurs when the animals were injected prior killing with 6-hydroxydopamine.

Dopaminergic neuronal function, anterior pituitary dopamine content, and serum concentrations of prolactin, luteinizing hormone and progesterone in the aged female rat

The serum concentrations of prolactin (PRL), progesterone and luteinizing hormone (LH), and the content and rate of synthesis of dopamine (DA) in selected brain regions were determined in young (3–6 months), intermediate (13–15 months) and aged (24–25 months) female Long-Evans rats. Young rats were examined on the days of diestrus 2 and estrus. Intermediate rats were divided into 2 groups, a group which was cycling regularly (examined on the day of estrus) and a group which exhibited constant estrus. Aged rats were divided into 3 groups one which cycled regularly (examined on day of estrus), one which exhibited constant estrus, and one which exhibited repetitive pseudopregnancies. Serum PRL was increased in all intermediate and aged rats when compared to values in young animals. Serum LH was increased and progesterone decreased in those intermediate and aged rats which exhibited constant estrous reproductive patterns. The DA content was generally decreased in the median eminence, posterior pituitary, striatum, nucleus accumbens and olfactory tubercle of all aged rats, while the rate of DA synthesis was decreased only in the median eminence of aged, non-cycling rats. This suggests that all DA neuronal systems except those in the tuberoinfundibular system are able to compensate for the age-related loss. Despite the apparent reduction of tuberinfundibular DA neuronal function the concentration of DA in the anterior pituitary, which is believed to represent amine released from the neurons, is dramatically increased in intermediate age rats in constant estrus, and in all groups of aged rats. The maintenance of high PRL secretion despite the elevated content of DA in the anterior pituitary suggests in age-related defect in the dynamics of DA in this gland; this defect may contribute to the loss of reproductive function in the aging rat.

Relaxin Immunoactivity Levels in Ovarian Extracts Obtained from Rats during Various Reproductive States and from Adult Cycling Pigs*

Relaxin immunoactivity levels were measured in the ovaries of rats during various reproductive states with a homologous rat relaxin RIA. Relaxin levels in the ovaries of immature noncycling rats were extremely low, approximately 2 pg/mg equivalent of fresh tissue (FT). Ovarian relaxin concentrations were low throughout the estrous cycle of adult rats but varied with the stage of the cycle. Maximal levels of approximately 20 pg/mgeq FT were obtained at estrus. Relaxin immunoactivity concentrations increased in the ovaries of both ordinary and deciduomata-bearing pseudopregnant rats. In both cases, relaxin levels increased from approximately 160 pg/mgeq FT on day 6 of pseudopregnancy (day 6) to levels ranging from 350–400 pg/mgeq FT on days 10 and 12. After day 12, however, the relaxin concentrations in the ovaries of the two groups of pseudopregnant rats differed. Relaxin levels in the ovaries of ordinary pseudopregnant rats declined by day 15, whereas relaxin levels in the deciduomata-bearing pseudopregna...

Temporal changes in serum progesterone in aging female rats.

The effect of age on serum progesterone was measured in female Long-Evans rats. Progesterone concentrations were measured in young (3 months old) and aged (12–24 months old) rats at proestrous, estrous, and diestrous stages of their ovarian cycles. In addition, progesterone was measured in aged noncycling rats with constant estrous, pseudopregnant, or constant diestrous vaginal cytological patterns. Serum progesterone was increased on the afternoon of proestrus in both young and aged rats. Both the magnitude of increase and the proportional increase over basal progesterone were greater in young than in aged animals. The increase in progesterone in young animals compared to aged groups was still present during estrus. Both young and aged groups had a diurnal surge in serum progesterone concentration on diestrous day 2. This increase in progesterone on diestrous day 2 was of greater mganitude and of longer duration in young compared to aged rats. Diurnal patterns of progesterone secretion were absent in age...