Older horses have higher ACTH concentrations in several fall and winter months and higher insulin concentrations in September than do younger horses. Seasonally specific reference ranges are required for α-MSH and insulin concentrations, with significantly higher concentrations detected in the fall. Practitioners should be advised to submit samples only to local laboratories that can provide such reference ranges for their local geographic region.
Background: Results of diagnostic tests for equine pituitary pars intermedia dysfunction (PPID), including endogenous ACTH concentration and the overnight dexamethasone suppression test (DST), are affected by season. New and potentially more sensitive diagnostic tests for equine PPID, such as thyrotropin-releasing hormone (TRH)-stimulated ACTH response, have been developed, but have had limited evaluation of seasonality.Objective: Our purpose was to evaluate seasonal changes in plasma ACTH and alpha-melanocyte-stimulating hormone (a-MSH) responses to TRH administration.Animals: Nine, healthy, aged horses with normal DST results. Methods: Synthetic TRH (1 mg) was administered IV. Plasma ACTH and a-MSH concentrations were measured at 0,5, 10,15,20, 25,30, 45, 60, and 180 minutes. Testing was performed in February, July, August, September, October, and November. Mean TRH-stimulated ACTH and a-MSH concentrations were compared across months and time by repeated measures analysis of variance. Significance was set at the P o .05 level.Results: Concentrations of ACTH and a-MSH significantly increased after TRH administration. Endogenous and TRHstimulated ACTH and a-MSH concentrations were significantly different across months with higher concentrations in the summer and fall compared with February.Conclusions and Clinical Importance: Plasma ACTH and a-MSH responses to TRH administration experience seasonal variation, with TRH-stimulated ACTH and a-MSH concentrations increasing from summer through fall. These results support previous evidence of a seasonal influence on the equine pituitary-adrenal axis. More research is warranted with a larger number of horses to determine if seasonal reference ranges for TRH stimulation testing need to be defined.
Autism spectrum disorder (ASD) is a perplexing and pervasive developmental disorder characterized by social difficulties, communicative deficits, and repetitive behavior. The increased rate of ASD diagnosis has raised questions concerning the genetic and environmental factors contributing to the development of this disorder; meanwhile, the cause of ASD remains unknown. This study surveyed mothers of ASD and non-ASD children to determine possible effects of labor and delivery (L&D) drugs on the development of ASD. The survey was administered to mothers; however, the results were analyzed by child, as the study focused on the development of autism. Furthermore, an independent ASD dataset from the Southwest Autism Research and Resource Center was analyzed and compared. Indeed, L&D drugs are associated with ASD (p = .039). Moreover, the Southwest Autism Research and Resource Center dataset shows that the labor induction drug, Pitocin, is significantly associated with ASD (p = .004). We also observed a synergistic effect between administrations of L&D drugs and experiencing a birth complication, in which both obstetrics factors occurring together increased the likelihood of the fetus developing ASD later in life (p = .0003). The present study shows the possible effects of L&D drugs, such as Pitocin labor-inducing and analgesic drugs, on children and ASD.
We present a nonstandard discretization method related to the methods of Mickens and Elaydi and Sacker for converting single species population models from continuous time to discrete time. The method falls in the category of the so‐called nonstandard discretization schemes, that is more advantageous than the classical discretization methods (such as adaptive step‐size) since it allows large step sizes. For instance, a large step size could better represent a generation time or a time interval between empirical measurements. Examples of single‐species models with and without negative density dependence, with an Allee effect, and with an alternative positive stable equilibrium (predator pit) are studied. Comparative analyses of bifurcations of ordinary differential equations and difference equations show how the new discretization proposed here preserves the dynamical properties of the continuous‐time models. Recommendations for Resource Managers The discretization method we propose preserves the original dynamic properties of the continuous model, in the sense of equilibria, their stability, and bifurcation characteristics. Unlike the traditional numerical methods that are widely used in ecology, the dynamical consistency of our method does not depend on the size of the step size used. The discretization method we propose produces solution trajectories in a remarkable agreement with those of the corresponding continuous models irrespective of the size of the time interval used. Results presented here will be important to future ecological studies that seek to evaluate the pervasiveness and strength of negative density dependence as well as Allee effects, along with the prospects of alternative stable states, in natural populations.
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