Enhancing medical student diversity through a premedical program: A Caribbean school case study.

Background: Physicians with backgrounds underrepresented in medicine (URiM) are more likely to practice in underserved communities. Recruitment into and assistance during medical education has the potential to increase the number of URiM physicians. This study analyzes URiM students' academic performance at a well-established Caribbean school with and without prior successful completion of the Medical Education Readiness Program (MERP). Methods: A retrospective analysis of premedical school requirements and achievements in medical school were performed for URiM students enrolled in Ross University School of Medicine between 2006 and 2012, through either MERP or direct admission. For MERP and non-MERP students, an independent sample two-tailed Student t-test was used to compare prerequisite Grade Point Average (p GPA), Medical College Admission Test (MCAT), and The United States Medical Licensing Examination (USMLE) Step 1 scores. Chi-square analysis was performed to compare the attrition rates for MERP and non-MERP URiM students in the first years of medical schools well as USMLE Step 1 pass rates. Results: A total of 1299 students entering medical school directly (n = 981) or through MERP (n = 318) were evaluated. The mean MCAT (19.6 for MERP vs. 21.6 for non-MERP, P < 0.001) and prerequisite GPA (2.8 for MERP vs. 3.1 for non-MERP, P < 0.001) were significantly lower for the MERP students. A similar percentage of MERP and non-MERP students reached the 2nd year (83.0% and 80.9% respectively, P = 0.407) and 3rd year (80.5% and 79.0% respectively, P = 0.565) of medical school. USMLE Step 1 pass rates for MERP (90.6%) and non-MERP (92.3%) as well as USMLE Step 1 mean scores (208.9 and 210.0 for MERP and non-MERP, respectively) were also comparable. Discussion: MERP-like programs can help URiM students with lower undergraduate scores succeed in medical school.

Melatonin signaling affects the timing in the daily rhythm of phagocytic activity by the retinal pigment epithelium.

Earlier studies in Xenopus have indicated a role for melatonin in the regulation of retinal disk shedding, but the role of melatonin in the regulation of daily rhythm in mammalian disk shedding and phagocytosis is still unclear. We recently produced a series of transgenic mice lacking melatonin receptor type 1 (MT1) or type 2 (MT2) in a melatonin-proficient background and have shown that removal of MT1 and MT2 receptors induces significant effects on daily and circadian regulation of the electroretinogram as well as on the viability of photoreceptor cells during aging. In this study we investigated the daily rhythm of phagocytic activity by the retinal pigment epithelium in MT1 and MT2 knock-out mice. Our data indicate that in MT1 and MT2 knock-out mice the peak of phagocytosis is advanced by 3 h with respect to wild-type mice and occurred in dark rather than after the onset of light, albeit the mean phagocytic activity over the 24-h period did not change among the three genotypes. Nevertheless, this small change in the profile of daily phagocytic rhythms may produce a significant effect on retinal health since MT1 and MT2 knock-out mice showed a significant increase in lipofuscin accumulation in the retinal pigment epithelium.

Localization of melatonin receptor 1 in mouse retina and its role in the circadian regulation of the electroretinogram and dopamine levels.

Melatonin modulates many important functions within the eye by interacting with a family of G-protein-coupled receptors that are negatively coupled with adenylate cyclase. In the mouse, Melatonin Receptors type 1 (MT(1)) mRNAs have been localized to photoreceptors, inner retinal neurons, and ganglion cells, thus suggesting that MT(1) receptors may play an important role in retinal physiology. Indeed, we have recently reported that absence of the MT(1) receptors has a dramatic effect on the regulation of the daily rhythm in visual processing, and on retinal cell viability during aging. We have also shown that removal of MT(1) receptors leads to a small (3-4 mmHg) increase in the level of the intraocular pressure during the night and to a significant loss (25-30%) in the number of cells within the retinal ganglion cell layer during aging. In the present study we investigated the cellular distribution in the C3H/f(+/+) mouse retina of MT(1) receptors using a newly developed MT(1) receptor antibody, and then we determined the role that MT(1) signaling plays in the circadian regulation of the mouse electroretinogram, and in the retinal dopaminergic system. Our data indicate that MT(1) receptor immunoreactivity is present in many retinal cell types, and in particular, on rod and cone photoreceptors and on intrinsically photosensitive ganglion cells (ipRGCs). MT(1) signaling is necessary for the circadian rhythm in the photopic ERG, but not for the circadian rhythm in the retinal dopaminergic system. Finally our data suggest that the circadian regulation of dopamine turnover does not drive the photopic ERG rhythm.

Circadian regulation of the PERIOD 2::LUCIFERASE bioluminescence rhythm in the mouse retinal pigment epithelium-choroid.

PURPOSE: The retinal pigment epithelium (RPE) plays an important role in the maintenance of the health and function of photoreceptors. Previous studies have shown that the RPE is also involved in the regulation of disc shedding, a process that is vital for photoreceptor health. This process has been shown to be under circadian control, although the mechanisms that control it are poorly understood. The aim of the present study was to investigate Period 2 (Per2) mRNA levels in the mouse RPE in vivo, and to determine whether the cultured RPE-choroid from PERIOD 2::LUCIFERASE (PER2::LUC) knockin mice expresses a circadian rhythm in bioluminescence. METHODS: Per2 mRNA levels were measured using real-time quantitative RT-PCR, and bioluminescence was measured in PER2::LUC knockin mice using a Lumicycle®. RESULTS: Per2 mRNA levels in the RPE-choroid show a clear circadian rhythm in vivo. A circadian rhythm in PER2::LUC bioluminescence was recorded from cultured RPE-choroid explants. Light exposure during the subjective night did not cause a circadian rhythm phase-shift of PER2::LUC bioluminescence. Finally, removal of the suprachiasmatic nuclei of the hypothalamus did not affect the bioluminescence circadian rhythm in the RPE-choroid. CONCLUSIONS: Our results demonstrate that the RPE-choroid contains a circadian clock, and the regulation of this circadian rhythm resides within the eye. These new data indicate that it may be useful to design studies with the aim of elucidating the molecular mechanisms responsible for the regulation of the rhythmic event in the RPE.

Melatonin: fifty years of scientific journey from the discovery in bovine pineal gland to delineation of functions in human.

Melatonin (N-acetyl-5-methoxytryptamine) was first purified and characterized from the bovine pineal gland extract by Aron Lerner and co-workers in 1958. Since then, a plethora of information has piled up on its biosynthesis, metabolism, time-bound periodicity, physiological and patho-physiological functions, as well as its interactions with other endocrine or neuro-endocrine organs and tissues in the body. Melatonin has wide range of applications in physiology and biomedical fields. In recent years, a significant progress has been made in the understanding mechanism of its actions at the cellular and molecular levels. Consistent efforts have uncovered the mystery of this indoleamine, and demonstrated its role in regulation of a large as well as diverse body functions in different groups of animals in general, and in humans in particular. Current review, in commemoration of 50 years of discovery of melatonin, while revisiting the established dogmas, summarizes current information on biosynthesis, secretion, metabolism and molecular mechanism of action of melatonin at cellular level and highlights the recent research on its role in human physiology and clinical biology.

Expression of mRNA and proteins for GnRH I and II and their receptors in primate corpus luteum during menstrual cycle.

The differential expression of mRNA and protein of GnRH I, II and their receptors (RI and RII) in the monkey corpus luteum (CL) were measured during different stages of the luteal phase of the menstrual cycle as an initial step towards considering the role and regulation of GnRH (I and II) system during luteinization and luteolysis in primates. RT-PCR confirmed the sequence identity of PCR products and real time PCR quantified specific mRNA expressions. Proteins were localized by immunohistochemistry (IHC). Changes in mRNA expression patterns of GnRH I and II (increased) and GnRH RII (decreased) were maximal at mid-late to late stages, that is, at CL regression, where as GnRH RI was low during the entire luteal phase. However, RT-PCR and IHC studies confirmed the presence of GnRH RI at both mRNA and protein levels, respectively. IHC results showed the presence of GnRH I, II and their receptors in steroidogenic cells (granulose-luteal cells and thecal-luteal cells) across the luteal phase. Hence, GnRH I and II systems may have a role on both luteinization (from early to mid stages of CL) and luteolysis (from mid-late to very-late stages of CL). These novel findings suggest that monkey luteal GnRH system may have a role in fertility regulation in paracrine and/or autocrine manner.

Presence of immunoreactive gonadotropin releasing hormone (GnRH) and its receptor (GnRHR) in rat ovary during pregnancy.

The present study aims at quantification of gonadotropin releasing hormone (GnRH) by radioimmunoassay, relative expression of its mRNA by real-time PCR accompanied by its cellular localization in the rat ovary by immunonohistochemistry (IHC) during different time points of pregnancy. To determine the involvement of endogenous ovarian GnRH in receptor mediated local autocrine/paracrine functions within the ovary, the cell specific localization of the classical receptor for GnRH (GnRHR) in the ovary by IHC and expression pattern of its mRNA were studied during pregnancy. Receptor expression during each time point within the ovary was reconfirmed by Western blot analysis accompanied by densitometric analysis of the signal intensity. Results reveal that the content of ovarian GnRH reaches its maximum on Day 20. The densitometric analysis of GnRHR receptor expression from Western blot study exhibits a decreasing trend by Day 20. Presence of GnRH and GnRHR mRNA in the ovary indicates the local synthesis of both ligand and receptor in the rat ovary. Differential expression of GnRH/GnRHR in the corpus luteum throughout pregnancy strengthens the hypothesis of the involvement of ovarian GnRH in local ovarian functions by receptor-mediated mechanisms. The expression of GnRH and GnRHR in the atretic antral follicles is indicative of the possible involvement of this decapeptide in processes like follicular atresia. The expression of GnRH/GnRHR in the nonatretic antral follicles and their oocytes requires further in-depth investigation. Collectively, this study for the first time reveals the presence of endogenous ovarian GnRH/GnRHR supporting their possible involvement in local autocrine/paracrine functions during pregnancy.

Expression and localization of gonadotropin-releasing hormone receptor in the rat oviduct during pregnancy.

A recent study from our laboratory has shown cellular and ultrastructural distribution of the gonadotropin-releasing hormone (GnRH) and the relative expression of its mRNA in the rat oviduct during the postimplantation period of pregnancy (days 7, 9, 16, and 20). To determine the possible autocrine/paracrine involvement of the oviductal GnRH during pregnancy in rats, the present investigation aims at the study of the relative expression of GnRH receptor (GnRHR) mRNA by real-time PCR followed by immunolocalization of the peptide in the oviduct during pregnancy. Semiquantitative analysis of the oviductal GnRHR expression by Western blot was done by densitometry of the signal intensity. Our results indicate the expression of GnRHR mRNA in the rat oviduct throughout the postimplantation period of pregnancy with no significant difference in expression between the selected time points. Immunoreactive GnRHR peptide was localized predominantly in the cytoplasm of the luminal epithelial cells, with less expression in the cytoplasm of the stromal cells and the smooth muscles throughout the oviduct. Signal intensity of GnRHR was significantly lower during day 16 when compared to days 7 and 20. These results, for the first time, support the transcription of GnRHR mRNA and its translation to protein in the rat oviduct throughout the postimplantation period of pregnancy. The lower protein content of GnRHR by day 16 may be indicative of ligand-induced downregulation of the receptor expression. The present investigation thus strengthens our previously postulated hypothesis regarding the receptor-mediated autocrine/paracrine role of oviductal GnRH during pregnancy in rats.

Localization of immunoreactive gonadotropin-releasing hormone and relative expression of its mRNA in the oviduct during pregnancy in rats.

This study was designed to determine the cellular and ultrastructural distribution of the gonadotropin-releasing hormone (GnRH) and the relative expression of its mRNA in the oviduct of rats during different time points (days 7, 9, 16, and 20) of pregnancy. Immunofluorescent localization and confocal microscopic techniques were used to determine the cellular distribution of GnRH in the oviduct. Immunogold electron microscopy indicated its localization at the ultrastructural level, and real-time PCR was used to study the expression pattern of GnRH mRNA in the oviduct during pregnancy. In general, GnRH was localized within the epithelial cells lining the oviductal lumen at each selected time point. A strong correlation between the fluorescence intensity of GnRH-immunoreactive cells and the relative expression of GnRH mRNA was noted on days 7 and 16, followed by a plateau by day 20. At the ultrastructural level, uniform labeling of colloidal gold particles was observed in secretory vesicles and lamella of the luminal epithelium as well as the lumen of the oviduct. Collectively, these results demonstrate for the first time that the oviductal epithelium synthesizes and secretes the decapeptide GnRH during pregnancy in rats, which may have a possible role in postimplantation embryonic development and the maintenance of pregnancy.

The pineal gland, but not melatonin, is associated with the termination of seasonal testicular activity in an annual reproductive cycle in roseringed parakeet Psittacula krameri.

The role of the pineal gland and its hormone melatonin in the regulation of annual testicular events was investigated for the first time in a psittacine bird, the roseringed parakeet (Psittacula krameri). Accordingly, the testicular responsiveness of the birds was evaluated following surgical pinealectomy with or without the exogenous administration of melatonin and the experimental manipulations of the endogenous levels of melatonin through exposing the birds to continuous illumination. An identical schedule was followed during the four reproductive phases, each characterizing a distinct testicular status in the annual cycle, namely, the phases of gametogenic quiescence (preparatory phase), seasonal recovery of gametogenesis (progressive phase), seasonal initiation of sperm formation (pre-breeding phase), and peak gametogenic activity (breeding phase). In each reproductive phase, the birds were subjected to various experimental conditions, and the effects were studied comparing the testicular conditions in the respective control birds. The study included germ cell profiles of the seminiferous tubules, the activities of steroidogenic enzymes 17beta-hydroxysteroid dehydrogenase (17beta-HSD), and Delta(5)3beta-hydroxysteroid dehydrogenase (Delta(5)3beta- HSD) in the testis, and the serum levels of testosterone and melatonin. An analysis of the data reveals that the pineal gland and its hormone melatonin may play an inhibitory role in the development of the testis until the attainment of the seasonal peak in the annual reproductive cycle. However, in all probability, the termination of the seasonal activity of the testis or the initiation of testicular regression in the annual reproductive cycle appears to be the function of the pineal gland, but not of melatonin.

Induction of blindness by formoguanamine hydrochloride in adult male roseringed parakeets (Psittacula krameri).

Formoguanamine (2,4-diamino-s-triazine) was known to be an effective chemical agent in inducing blindness in poultry chicks, but not in adult birds. The present study was undertaken to demonstrate the influences, if any, of this chemical on the visual performance and retinal histology in an adult sub-tropical wild bird the roseringed parakeet (Psittacula krameri). Formoguanamine (FG) hydrochloride was subcutaneously injected into adult parakeets at the dosage of 25 mg (dissolved in 0.75 ml physiological saline)/100 g body weight/day, for two consecutive days while the control birds were injected only with the placebo. The effects were studied after 10, 20, and 30 days of the last treatment of FG. Within 24 h of the treatment of FG, about 90% of the total birds exhibited lack of visual responses to any light stimulus and even absence of pupillary light reactions. The remaining birds became totally blind on the day following the last injection of FG and remained so till the end of investigation. At the microscopic level, conspicuous degenerative changes were noted in the outer pigmented epithelium and the photoreceptive layer of rods and cones in the retinas of FG treated birds. A significant reduction in the thickness of the outer nuclear layer was also found in the retinas of FG treated parakeets, compared to that in the control birds. However, the inner cell layers of the retina in the control and FG administered parakeets were almost identical. It deserves special mention that the effects of FG, noted after 30 days of last treatment, were not very different from those noted just after 10 days of treatment. Collectively, the results of the present investigation demonstrate that FG can be used as a potent pharmacological agent for inducing irreversible blindness through selective damage in retinal tissue even in the adult wild bird, thereby making FG treatment an alternative euthanasic device to a cumbersome, stressful, surgical method of enucleation of the ocular system for laboratory studies.