Amyloid-Beta Modulates Low-Threshold Activated Voltage-Gated L-Type Calcium Channels of Arcuate Neuropeptide Y Neurons Leading to Calcium Dysregulation and Hypothalamic Dysfunction.

Weight loss is an early manifestation of Alzheimer's disease that can precede the cognitive decline, raising the possibility that amyloid-ß (Aß) disrupts hypothalamic neurons critical for the regulation of body weight. We previously reported that, in young transgenic mice overexpressing mutated amyloid precursor protein (Tg2576), Aß causes dysfunction in neuropeptide Y (NPY)-expressing hypothalamic arcuate neurons before plaque formation. In this study, we examined whether Aß causes arcuate NPY neuronal dysfunction by disrupting intracellular Ca2+ homeostasis. Here, we found that the L-type Ca2+ channel blocker nimodipine could hyperpolarize the membrane potential, decrease the spontaneous activity, and reduce the intracellular Ca2+ levels in arcuate NPY neurons from Tg2576 brain slices. In these neurons, there was a shift from high to low voltage-threshold activated L-type Ca2+ currents, resulting in increased Ca2+ influx closer to the resting membrane potential, an effect recapitulated by Aß1-42 and reversed by nimodipine. These low voltage-threshold activated L-type Ca2+ currents were dependent in part on calcium/calmodulin-dependent protein kinase II and IP3 pathways. Furthermore, the effects on intracellular Ca2+ signaling by both a positive (ghrelin) and negative (leptin) modulator were blunted in these neurons. Nimodipine pretreatment restored the response to ghrelin-mediated feeding in young (3-5 months), but not older (10 months), female Tg2576 mice, suggesting that intracellular Ca2+ dysregulation is only reversible early in Aß pathology. Collectively, these findings provide evidence for a key role for low-threshold activated voltage gated L-type Ca2+ channels in Aß-mediated neuronal dysfunction and in the regulation of body weight.SIGNIFICANCE STATEMENT Weight loss is one of the earliest manifestations of Alzheimer's disease (AD), but the underlying cellular mechanisms remain unknown. Disruption of intracellular Ca2+ homeostasis by amyloid-ß is hypothesized to be critical for the early neuronal dysfunction driving AD pathogenesis. Here, we demonstrate that amyloid-ß causes a shift from high to low voltage-threshold activated L-type Ca2+ currents in arcuate neuropeptide Y neurons. This leads to increased Ca2+ influx closer to the resting membrane potential, resulting in intracellular Ca2+ dyshomeostasis and neuronal dysfunction, an effect reversible by the L-type Ca2+ channel blocker nimodipine early in amyloid-ß pathology. These findings highlight a novel mechanism of amyloid-ß-mediated neuronal dysfunction through L-type Ca2+ channels and the importance of these channels in the regulation of body weight.

Adolescent changes in hindbrain noradrenergic A2 neurons in male rats.

During adolescence, the increased susceptibility to stress-related dysfunctions (e.g., anxiety, drug use, obesity) may be influenced by changes in the hormonal stress response mediated by the hypothalamic-pituitary-adrenal (HPA) axis. We have previously reported that restraint stress leads to significantly prolonged HPA responses in pre-adolescent compared to adult rats. Further, pre-adolescent animals exposed to restraint show greater levels of neural activation than adults in the paraventricular nucleus of the hypothalamus (PVN), a key nucleus integrating information from brain regions that coordinate HPA responses. Here, we examined the potential contribution of the noradrenergic A2 region of the nucleus of the solitary tract (NST) as a contributor to these age-dependent shifts in HPA reactivity. Specifically, we used double-labeled immunohistochemistry for FOS and dopamine-ß-hydroxylase (DßH) to measure cellular activation and noradrenergic cells, respectively, before or after restraint stress in pre-adolescent (30days old) and adult (70days old) male rats. We also measured the density of DßH-immunoreactive fibers in the PVN as an index of noradrenergic inputs to this area. We found that pre-adolescent animals have a greater number of DßH-positive cells in the A2 region compared to adults, yet the number and percentage of double-labeled DßH/FOS cells were similar between these two ages. We found no differences between the ages in the staining intensity of DßH-immunoreactive fibers in the PVN. These data indicate there are adolescent-related changes in the number of noradrenergic cells in the A2 region, but no clear association between the increased stress reactivity prior to pubertal maturation and activation of A2 noradrenergic afferents to the PVN.

Adolescence and the ontogeny of the hormonal stress response in male and female rats and mice.

Adolescent development is marked by many changes in neuroendocrine function, resulting in both immediate and long-term influences on an individual's physiology and behavior. Stress-induced hormonal responses are one such change, with adolescent animals often showing different patterns of hormonal reactivity following a stressor compared with adults. This review will describe the unique ways in which adolescent animals respond to a variety of stressors and how these adolescent-related changes in hormonal responsiveness can be further modified by the sex and previous experience of the individual. Potential central and peripheral mechanisms that contribute to these developmental shifts in stress reactivity are also discussed. Finally, the short- and long-term programming effects of chronic stress exposure during adolescence on later adult hormonal responsiveness are also examined. Though far from a clear understanding of the neurobehavioral consequences of these adolescent-related shifts in stress reactivity, continued study of developmental changes in stress-induced hormonal responses may shed light on the increased vulnerability to physical and psychological dysfunctions that often accompany a stressful adolescence.