Hormonal contraceptives alter amphetamine place preference and responsivity in the intact female rat.

Hormonal contraceptives (HCs) containing synthetic ovarian hormones are commonly used among reproductive aged women; HCs alter the physiological state of the user by interfering with endogenous hormone concentrations and their actions on the reproductive tract. As ovarian hormones modulate the incidence of substance abuse disorders in women, this experiment explores how modulating female rat ovarian hormonal states with an HC containing the synthetic progestin levonorgestrel influences measures of drug preference and responsivity. First, rats underwent food-light Pavlovian conditioning to measure conditioned orienting, a known predictor of amphetamine (AMP) place preference. Then, rats were conditioned and tested for AMP place preference with either an HC implant or during estrous cycle stages associated with opposing ovarian hormone levels, that is, proestrus (P) or metestrus/diestrus (M/D), while recording ultrasonic vocalizations (USVs) as an index of he donic drug responsivity. Because of dopamine's (DA's) role in reward learning and memory, DA cell number and activity were examined using tyrosine hydroxylase and FOS immunohistochemistry after a final AMP challenge. Conditioned orienting did not differ between cycling and HC-implanted rats. HC rats emitted fewer USVs in response to AMP, showed marginally less AMP place preference, and had lower DA cell activity in the substantia nigra after AMP compared to P rats. M/D rats showed a similar behavioral profile and neural response as HC rats. This experiment suggests ovarian hormones affect drug preference and responsivity, while providing novel insight into how hormone-altering contraceptives may reduce these measures. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Low temperature and high field regimes of connected kagome artificial spin ice: the role of domain wall topology.

Artificial spin ices are frustrated magnetic nanostructures where single domain nanobars act as macrosized spins. In connected kagome artificial spin ice arrays, reversal occurs along one-dimensional chains by propagation of ferromagnetic domain walls through Y-shaped vertices. Both the vertices and the walls are complex chiral objects with well-defined topological edge-charges. At room temperature, it is established that the topological edge-charges determine the exact switching reversal path taken. However, magnetic reversal at low temperatures has received much less attention and how these chiral objects interact at reduced temperature is unknown. In this study we use magnetic force microscopy to image the magnetic reversal process at low temperatures revealing the formation of quite remarkable high energy remanence states and a change in the dynamics of the reversal process. The implication is the breakdown of the artificial spin ice regime in these connected structures at low temperatures.