Acute effects of taVNS in ZDF rats.

<p>Comparison between naïve ZDF rats (left column, n = 5) and pinealectomized ZDF rats (two weeks after pinealectomy operation) (right column, n = 5), as well as among day 1, 3, and 5 of the consecutive once-daily-30min-taVNS treatment (shadow area), changes in plasma concentration of melatonin (a, b), glucagon (c, d), and insulin (e, f), and blood glucose levels (g, h). 0.0–3.0, elapsed time in hour beginning from the start of the taVNS treatment. *, **, *** P<0.05, 0.01, 0.001 vs. baseline (0.0) of the same day; #, ### P<0.05, 0.001 vs. day 1 at the same abscissa point, respectively. Sample size estimated based on power level of 0.8.</p

The electroacupuncture procedure.

<p>Showing the auricular stimulation posture (a) and location (b) of the procedure. AMEA: stimulation applied at auricular margin; taVNS: stimulation applied at auricular concha.</p

Plasma 5-HT concentration (ng/L) in rats at last time point.

<p>Each value represents mean ± SD (n = 6).</p><p>*, P<0.05, versus N-ZL;</p><p>#, P<0.05 versus N-ZDF.</p><p>Plasma 5-HT concentration (ng/L) in rats at last time point.</p

Plasma melatonin concentration (ng/L) in rats at last time point.

<p>Each value represents mean ± SD (n = 6).</p><p>*, P<0.05, versus N-ZL;</p><p>#, P<0.05 versus N-ZDF.</p><p>Plasma melatonin concentration (ng/L) in rats at last time point.</p

Average daily food intake (grams) of rats during the experiment.

<p>Each value represents mean ± SD (n = 6).</p><p>*P<0.05 as compared with naïve ZDF rats.</p><p>Average daily food intake (grams) of rats during the experiment.</p

Chronic effects of taVNS in rats.

<p>Comparing blood glucose concentrations in naïve and taVNS treated ZDF rats (a, n = 6 each), in pinealectomized ZDF rats (immediately after pinealectomy operation) with or without taVNS treatment (b, n = 5 each), and in naïve, taVNS, and AMEA treated ZL rats (c, n = 4 each). ZL, ZDF, naïve ZL or ZDF rats; taVNS, taVNS treated rats; AMEA, auricular margin electroacupuncture treated rats; Px, pinealectomized rats; Px/VS, taVNS treated pinealectomized rats; Mel, daily melatonin injected rats. Bas, baseline (before taVNS); W1–W5, 1–5 weeks after consecutive taVNS treatment. *, **, *** P<0.05, 0.01, 0.001 <i>vs</i>. Bas of the same group; #,##,### P<0.05, 0.01, 0.001 <i>vs</i>. naïve at the same time point, respectively. Concentrations of plasma HbA_1c (d, e) and insulin (f, g) upon sampling were compared in naïve ZDF and ZL rats (d, f) and in ZDF rats subjected to different treatments (e, g). *, *** P<0.05, 0.001 <i>vs</i>. ZDF, respectively; ### P<0.001 <i>vs</i>. remaining groups. Sample size estimated based on power level of 0.8.</p

Correlations between plasma melatonin concentration and immobility time in FST.

<p>Correlations between plasma melatonin concentration and immobility time in FST.</p

Acute plasma melatonin concentration change upon taVNS.

<p>Showing that each taVNS administration (shielded area) would trigger acute and tidal melatonin secretion in pineal intact (A) and pinealectomized ZDF rats (B). Note that the melatonin secretion tides existing both during and after tsVNS session and that the after-taVNS tides tended to be higher (A and B) or more frequent (B) with the increase of treatment days.</p

Correlation of melatonin concentration and immobility time in FST on day 35.

<p>Linear regression analysis found a strong negative correlation between the plasma melatonin concentration and the immobility time in forced swimming test in ZDF (R = −0.544) but not ZL rats (R = 0.254, also see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0111100#pone-0111100-t003" target="_blank">Table 3</a>).</p

Immobility time in FST on day 35.

<p>Immobility time in FST on day 35.</p