Apelin-13 regulates electrical activity in the globus pallidus and induces postural changes in rats

Abstract

The globus pallidus is the relay nucleus of the basal ganglia, and changes in its electrical activity can cause motor impairment. Apelin-13 is widely distributed in the central and peripheral nervous systems. It has been demonstrated that apelin-13 plays important roles in the regulation of blood pressure and other non-motor functions. However, its role in motor function has rarely been reported. In the present study, apelin-13 (10 μM/100 μM) was injected into the globus pallidus of rats. The results showed that apelin-13 increased the spontaneous discharges in the majority of pallidal neurons. However, an apelin-13-induced inhibitory effect on the firing rate was also observed in a few pallidal neurons. In postural tests, after the systemic administration of haloperidol, unilateral pallidal injection of apelin-13 caused a contralateral deflection. Together, these findings suggest that apelin-13 regulates the electrical activity of pallidal neurons and thus participates in central motor control in rats. The study was approved by the Animal Ethics Committee of Qingdao University (approval No. 20200615Wistar0451003020) on June 15, 2020.

Keywords: apelin-13; basal ganglion; electrophysiology; firing rate; globus pallidus; microinjection; motor behavior; movement disorder.

Figure 1

Different firing patterns of pallidal neurons in rats. (A–C) Regular (A), irregular (B), and bursting (C) firings were obtained from pallidal neurons. Upper left: ISI histogram; upper right: autocorrelogram; lower: basal firing. ISI: Interspike intervals.

Figure 2

Effects of 10 μM apelin-13 on the discharge rate of pallidal neurons in rats. (A) Frequency histograms displaying an increased firing rate in a neuron after 10 μM apelin-13 administration. (B) Typical frequency histograms showing inhibition of the discharge frequency of a neuron after 10 μM apelin-13 administration. The lower segments (a, b, and c) are from three different time phases of the experiment. a: Stable firing before drug application; b: the maximal change following drug application; c: stable firing after recovery from the drug application. (C) Pooled data demonstrating the effects of normal saline and apelin-13 on the discharge frequency of pallidal neurons. The numbers of recorded pallidal neurons in the saline group, apelin-13-induced excitatory neurons, and apelin-13-induced inhibitory neurons were 11, 24, and 7, respectively. Data are expressed as the mean ± SEM. *P < 0.05, ***P < 0.001 (paired t-test). ns: Not significant.

Figure 3

Effects of apelin-13 injection in the GP on postural behavior in rats. (A) Postural data demonstrating that unilateral intrapallidal injection of 10 μM apelin-13 induced contralateral dystonic posture in rats receiving haloperidol. Data are represented as median values, and were analyzed using the Mann–Whitney U test. (B) Verification of the correct position of microinjection in the GP. GP: globus pallidus.