Diet induced obesity alters the excitability of liver-related PVN neurons

Abstract

Stimulation of hepatic sympathetic nerves increases glucose production and glycogenolysis. Activity of pre-sympathetic neurons in the paraventricular nucleus (PVN) of the hypothalamus and in the ventrolateral and ventromedial medulla (VLM/VMM) largely influence the sympathetic output. Despite the importance of these central circuits, the cellular properties of pre-sympathetic liver-related neurons remain to be determined. Here, we tested the hypotheses that the activity of pre-sympathetic liver-related neurons in the PVN and VLM/VMM is altered in diet induced obese (DIO) mice, as well as their sensitivity to insulin. Whole-cell patch-clamp recordings were conducted from liver-related neurons in male DIO (15–19-week-old) and control mice. During a step protocol, current steps (0-30pA, duration 1s) were applied to reveal the firing activity of neurons. Our data showed increased excitability of liver-related PVN neurons in DIO mice (n=9) compared to Control mice (n=10) (simple linear regression, different elevation, p=0.04). Moreover, in DIO mice, insulin decreased the frequency of action potentials (basal: 0.83±0.28 Hz vs insulin: 0.47±0.22 Hz, n=10; Wilcoxon test, p=0.01), while it had no effect on the firing in control mice (basal: 0.79±0.37 Hz vs insulin: 0.51±0.26 Hz, n=8, Wilcoxon test, p=0.11). Similarly, in DIO mice, insulin decreased the firing of liver-related PVN neurons after current injection (simple linear regression, different elevation, p=0.01, n=9). Next, liver-related PVN neurons were identified based on their projection to the VLM/VMM, and we found that the excitability of pre-sympathetic liver-related PVN neurons (n=7) was increased compared to liver-related PVN neurons (n=10) (simple linear regression, different elevation, p=0.00). Intriguingly, insulin did not alter the excitability of pre-sympathetic liver-related PVN neurons neither in control (n=8) or DIO mice (n=7) (simple linear regression, different elevation (Control: p=0.27; DIO: p=0.21). Since insulin sensitivities of liver-related PVN and pre-sympathetic liver-related PVN neurons were different, recordings were conducted from liver-related neurons in the VLM/VMM, which is well-known for its control over the sympathetic tone. In control mice, during the step protocol insulin had no effect on the excitability (simple linear regression, different elevation, p=0.37 n=7) whereas it decreased the firing rate of liver-related VLM/VMM neurons in DIO mice (nonlinear fit, different curve, p=0.03, n=4). Additionally, insulin receptor expression was confirmed by single cell digital droplet PCR in a subset of liver-related neurons by collecting mRNA from the cytoplasm of the recorded neurons. In summary, these results demonstrate that the firing activity of liver-related neurons are altered in DIO mice as well as their sensitivity to insulin. These data provide further evidence for cellular changes involving neurons regulating the sympathetic output to the liver. This work was supported by the NIH (DK-122842 to AZs and AVD), and Marko Spark Innovation Research Fund to AZs and AVD. We also thank the Tulane Brain Institute Cell and Tissue Imaging Core and the NIH Center for Neuroanatomy and Neurotropic viruses for the PRVs (P40 OD010996). This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.