Combined effects of the contraceptive hormones, ethinyl estradiol and levonorgestrel, on the use of place and response memory in gonadally-intact female rats

Hormonal contraceptives during adolescence impact the female brain and behavior in a rat model

Millions of people take hormonal contraceptives (HCs), often starting during adolescence when ovarian hormones influence brain and behavioral maturation. However, there is a fundamental lack of information about the neurobehavioral consequences of hormonal alterations via adolescent HC use. To begin addressing this gap, we validated a rodent model of adolescent HC administration and characterized its impact on endocrine, transcriptional, and behavioral endpoints. Cohorts of intact post-pubertal female Sprague-Dawley rats received daily subcutaneous injections of either vehicle or HC [10 μg ethinyl estradiol (EE) + 20 μg levonorgestrel (LNG)] for the duration of adolescence from postnatal day (PND) 35 to PND56. Blood and brain tissue was collected at PND57. Other cohorts received daily injections of vehicle or HC from PND35 until behavioral assays were completed on PND57-64. HC treatment was effective, as vaginal lavage indicated disrupted estrous cycling and ELISA indicated suppressed serum luteinizing hormone in HC-treated rats. Liquid chromatography-mass spectrometry analysis showed EE and LNG in serum and brain as well as diminished serum and brain levels of allopregnanolone and testosterone in HC-treated rats. NanoString nCounter analysis indicated that adolescent HC administration impacted expression of genes related to synapses, white matter, neuroimmune, monoamine, and hormone signaling in the hypothalamus and medial prefrontal cortex. While no effects of HCs were seen on sociability in the social preference test or stress coping behavior in the forced swim test, adolescent HC administration diminished risk-assessment behaviors in the novelty-induced hypophagia paradigm and altered anxiety-like behavior in the open field test and elevated plus maze. Overall, these data suggest that exposure to contraceptive hormones during the critical developmental period of adolescence may shape the brain and behavior.

Beyond Birth Control: The Neuroscience of Hormonal Contraceptives

Hormonal contraceptives (HCs) are one of the most highly prescribed classes of drugs in the world used for both contraceptive and noncontraceptive purposes. Despite their prevalent use, the impact of HCs on the brain remains inadequately explored. This review synthesizes recent findings on the neuroscience of HCs, with a focus on human structural neuroimaging as well as translational, nonhuman animal studies investigating the cellular, molecular, and behavioral effects of HCs. Additionally, we consider data linking HCs to mood disorders and dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis and stress response as a potential mediator. The review also addresses the unique sensitivity of the adolescent brain to HCs, noting significant changes in brain structure and function when HCs are used during this developmental period. Finally, we discuss potential effects of HCs in combination with smoking-derived nicotine on outcomes of ischemic brain damage. Methodological challenges, such as the variability in HC formulations and user-specific factors, are acknowledged, emphasizing the need for precise and individualized research approaches. Overall, this review underscores the necessity for continued interdisciplinary research to elucidate the neurobiological mechanisms of HCs, aiming to optimize their use and improve women's health.

Levonorgestrel maintains goal-directed behavior in habit-trained intact female rats

Hormonal contraceptives are utilized by millions of women worldwide. However, it remains unclear if these powerful endocrine modulators may alter cognitive function. Habit formation involves the progression of instrumental learning as it goes from being a conscious goal-directed process to a cue-driven automatic habitual motor response. Dysregulated goal and/or habit is implicated in numerous psychopathologies, underscoring the relevance of examining the effect of hormonal contraceptives on goal-directed and habitual behavior. This study examined the effect of levonorgestrel (LNG), a widely used progestin-type contraceptive, on the development of habit in intact female rats. Rats were implanted with subcutaneous capsules that slowly released LNG over the course of the experiment or cholesterol-filled capsules. All female rats underwent operant training followed by reward devaluation to test for habit. One group of females was trained at a level that is sub-threshold to habit, while another group of females was trained to a level well over the habit threshold observed in intact females. The results reveal that all sub-threshold trained rats remained goal-directed irrespective of LGN treatment, suggesting LNG is not advancing habit formation in female rats at this level of reinforcement. However, in rats that were overtrained well above the threshold, cholesterol females showed habitual behavior, thus replicating a portion of our original studies. In contrast, LNG-treated habit-trained rats remained goal-directed, indicating that LNG impedes the development and/or expression of habit following this level of supra-threshold to habit training. Thus, LNG may offset habit formation by sustaining attentional or motivational processes during learning in intact female rats. These results may be clinically relevant to women using this type of hormonal contraceptive as well as in other progestin-based hormone therapies.

Nicotinic acetylcholine receptors and learning and memory deficits in Neuroinflammatory diseases

Animal survival depends on cognitive abilities such as learning and memory to adapt to environmental changes. Memory functions require an enhanced activity and connectivity of a particular arrangement of engram neurons, supported by the concerted action of neurons, glia, and vascular cells. The deterioration of the cholinergic system is a common occurrence in neurological conditions exacerbated by aging such as traumatic brain injury (TBI), posttraumatic stress disorder (PTSD), Alzheimer's disease (AD), and Parkinson's disease (PD). Cotinine is a cholinergic modulator with neuroprotective, antidepressant, anti-inflammatory, antioxidant, and memory-enhancing effects. Current evidence suggests Cotinine's beneficial effects on cognition results from the positive modulation of the α7-nicotinic acetylcholine receptors (nAChRs) and the inhibition of the toll-like receptors (TLRs). The α7nAChR affects brain functions by modulating the function of neurons, glia, endothelial, immune, and dendritic cells and regulates inhibitory and excitatory neurotransmission throughout the GABA interneurons. In addition, Cotinine acting on the α7 nAChRs and TLR reduces neuroinflammation by inhibiting the release of pro-inflammatory cytokines by the immune cells. Also, α7nAChRs stimulate signaling pathways supporting structural, biochemical, electrochemical, and cellular changes in the Central nervous system during the cognitive processes, including Neurogenesis. Here, the mechanisms of memory formation as well as potential mechanisms of action of Cotinine on memory preservation in aging and neurological diseases are discussed.