Neuropeptide Y Reduces Social Fear in Male Mice: Involvement of Y1 and Y2 Receptors in the Dorsolateral Septum and Central Amygdala

Neuropeptide Y (NPY) has anxiolytic-like effects and facilitates the extinction of cued and contextual fear in rodents. We previously showed that intracerebroventricular administration of NPY reduces the expression of social fear in a mouse model of social fear conditioning (SFC) and localized these effects to the dorsolateral septum (DLS) and central amygdala (CeA). In the present study, we aimed to identify the receptor subtypes that mediate these local effects of NPY. We show that NPY (0.1 nmol/0.2 µL/side) reduced the expression of SFC-induced social fear in a brain region- and receptor-specific manner in male mice. In the DLS, NPY reduced the expression of social fear by acting on Y2 receptors but not on Y1 receptors. As such, prior administration of the Y2 receptor antagonist BIIE0246 (0.2 nmol/0.2 μL/side) but not the Y1 receptor antagonist BIBO3304 trifluoroacetate (0.2 nmol/0.2 μL/side) blocked the effects of NPY in the DLS. In the CeA, however, BIBO3304 trifluoroacetate but not BIIE0246 blocked the effects of NPY, suggesting that NPY reduced the expression of social fear by acting on Y1 receptors but not Y2 receptors within the CeA. This study suggests that at least two distinct receptor subtypes are differentially recruited in the DLS and CeA to mediate the effects of NPY on the expression of social fear.

Differential NPY-Y1 Receptor Density in the Motor Cortex of ALS Patients and Familial Model of ALS

Destabilization of faciliatory and inhibitory circuits is an important feature of corticomotor pathology in amyotrophic lateral sclerosis (ALS). While GABAergic inputs to upper motor neurons are reduced in models of the disease, less understood is the involvement of peptidergic inputs to upper motor neurons in ALS. The neuropeptide Y (NPY) system has been shown to confer neuroprotection against numerous pathogenic mechanisms implicated in ALS. However, little is known about how the NPY system functions in the motor system. Herein, we investigate post-synaptic NPY signaling on upper motor neurons in the rodent and human motor cortex, and on cortical neuron populations in vitro. Using immunohistochemistry, we show the increased density of NPY-Y1 receptors on the soma of SMI32-positive upper motor neurons in post-mortem ALS cases and SOD1G93A excitatory cortical neurons in vitro. Analysis of receptor density on Thy1-YFP-H-positive upper motor neurons in wild-type and SOD1G93A mouse tissue revealed that the distribution of NPY-Y1 receptors was changed on the apical processes at early-symptomatic and late-symptomatic disease stages. Together, our data demonstrate the differential density of NPY-Y1 receptors on upper motor neurons in a familial model of ALS and in ALS cases, indicating a novel pathway that may be targeted to modulate upper motor neuron activity.

Peripheral-specific Y1 receptor antagonism increases thermogenesis and protects against diet-induced obesity

Obesity is caused by an imbalance between food intake and energy expenditure (EE). Here we identify a conserved pathway that links signalling through peripheral Y1 receptors (Y1R) to the control of EE. Selective antagonism of peripheral Y1R, via the non-brain penetrable antagonist BIBO3304, leads to a significant reduction in body weight gain due to enhanced EE thereby reducing fat mass. Specifically thermogenesis in brown adipose tissue (BAT) due to elevated UCP1 is enhanced accompanied by extensive browning of white adipose tissue both in mice and humans. Importantly, selective ablation of Y1R from adipocytes protects against diet-induced obesity. Furthermore, peripheral specific Y1R antagonism also improves glucose homeostasis mainly driven by dynamic changes in Akt activity in BAT. Together, these data suggest that selective peripheral only Y1R antagonism via BIBO3304, or a functional analogue, could be developed as a safer and more effective treatment option to mitigate diet-induced obesity.

The Effects of NPY1 Receptor Antagonism on Intervertebral Disc and Bone Changes in Ovariectomized Rats

Study Design: Basic science. Objective: To compare the effects of a neuropeptide Y1 receptor antagonist (NPY-1RA) to estrogen on maintaining vertebral bone microarchitecture and disc height in a rat model of menopause. Methods: This study was an institutional animal care approved randomized control study with 104 ovariectomized rats and 32 intact control animals. Comparison of disc height, trabecular bone, body weights, circulating levels of NPY and estrogen, and distribution of Y1 receptors in the intervertebral disc in an established rodent osteoporotic model were made at baseline and after 2, 4, and 8 weeks after receiving either an implant containing estrogen or an antagonist to the neuropeptide Y1 receptor. Data was compared statistically using One-way analysis of variance. Results: Circulating levels of estrogen increased and NPY decreased following estrogen replacement, with values comparable to ovary-intact animals. NPY-1RA-treated animals had low estrogen and high NPY circulating levels and were similar to ovariectomized control rats. Both NPY-1RA and estrogen administration were able reduce, menopause associated weight gain. NPY-1RA appeared to restore bone formation and maintain disc height, while estrogen replacement prevented further bone loss. Conclusion: NPY-1RA in osteoporotic rats activates osteoblast production of bone and decreased marrow and body fat more effectively than estrogen replacement when delivered in similar concentrations. Annulus cells had NPY receptors, which may play a role in disc nutrition, extracellular matrix production, and pain signaling cascades.

Sites and sources of sympathoexcitation in obese male rats: role of brain insulin

In males, obesity increases sympathetic nerve activity (SNA), but the mechanisms are unclear. Here, we investigate insulin, via an action in the arcuate nucleus (ArcN), and downstream neuropathways, including melanocortin receptor 3/4 (MC3/4R) in the hypothalamic paraventricular nucleus (PVN) and dorsal medial hypothalamus (DMH). We studied conscious and α-chloralose-anesthetized Sprague-Dawley rats fed a high-fat diet, which causes obesity prone (OP) rats to accrue excess fat and obesity-resistant (OR) rats to maintain fat content, similar to rats fed a standard control (CON) diet. Nonspecific blockade of the ArcN with muscimol and specific blockade of ArcN insulin receptors (InsR) decreased lumbar SNA (LSNA), heart rate (HR), and mean arterial pressure (MAP) in OP, but not OR or CON, rats, indicating that insulin supports LSNA in obese males. In conscious rats, intracerebroventricular infusion of insulin increased MAP only in OP rats and also improved HR baroreflex function from subnormal to supranormal. The brain sensitization to insulin may elucidate how insulin can drive central SNA pathways when transport of insulin across the blood-brain barrier may be impaired. Blockade of PVN, but not DMH, MC3/4R with SHU9119 decreased LSNA, HR, and, MAP in OP, but not OR or CON, rats. Interestingly, nanoinjection of the MC3/4R agonist melanotan II (MTII) into the PVN increased LSNA only in OP rats, similar to PVN MTII-induced increases in LSNA in CON rats after blockade of sympathoinhibitory neuropeptide Y Y1 receptors. ArcN InsR expression was not increased in OP rats. Collectively, these data indicate that obesity increases SNA, in part via increased InsR signaling and downstream PVN MC3/4R.