Neuroendocrine signaling modulates specific neural networks relevant to migraine

Abstract

Migraine is a disabling brain disorder involving abnormal trigeminovascular activation and sensitization. Fasting or skipping meals is considered a migraine trigger and altered fasting glucose and insulin levels have been observed in migraineurs. Therefore peptides involved in appetite and glucose regulation including insulin, glucagon and leptin could potentially influence migraine neurobiology. We aimed to determine the effect of insulin (10U·kg^-1), glucagon (100μg·200μl^-1) and leptin (0.3, 1 and 3mg·kg^-1) signaling on trigeminovascular nociceptive processing at the level of the trigeminocervical-complex and hypothalamus. Male rats were anesthetized and prepared for craniovascular stimulation. In vivo electrophysiology was used to determine changes in trigeminocervical neuronal responses to dural electrical stimulation, and phosphorylated extracellular signal-regulated kinases 1 and 2 (pERK1/2) immunohistochemistry to determine trigeminocervical and hypothalamic neural activity; both in response to intravenous administration of insulin, glucagon, leptin or vehicle control in combination with blood glucose analysis. Blood glucose levels were significantly decreased by insulin (p<0.001) and leptin (p<0.01) whereas glucagon had the opposite effect (p<0.001). Dural-evoked neuronal firing in the trigeminocervical-complex was significantly inhibited by insulin (p<0.001), glucagon (p<0.05) and leptin (p<0.01). Trigeminocervical-complex pERK1/2 cell expression was significantly decreased by insulin and leptin (both p<0.001), and increased by glucagon (p<0.001), when compared to vehicle control. However, only leptin affected pERK1/2 expression in the hypothalamus, significantly decreasing pERK1/2 immunoreactive cell expression in the arcuate nucleus (p<0.05). These findings demonstrate that insulin, glucagon and leptin can alter the transmission of trigeminal nociceptive inputs. A potential neurobiological link between migraine and impaired metabolic homeostasis may occur through disturbed glucose regulation and a transient hypothalamic dysfunction.

Keywords: Appetite; Glucose; Headache; Migraine; Trigeminovascular activation; pERK1/2.

Fig. 1

Schematic representation of neuroendocrine signaling in healthy individuals during two different feeding conditions (fasting and immediate post-feeding). Leptin is released from adipose tissue and insulin and glucagon are release by the pancreas into the blood circulation. These peptides are able to cross the blood brain barrier (BBB) and act in the hypothalamus to regulate appetite and blood glucose levels. There is a potential hypothalamic output (dashed arrow) towards the trigeminocervical complex (TCC) and these peptides may additionally act directly at the TCC, modulating nociceptive trigeminovascular activation. PVN: hypothalamic paraventricular nucleus; ARC: hypothalamic arcuate nucleus; DMN: hypothalamic dorsomedial nucleus; CNS: Central nervous system.

Fig. 2

Overview of the experimental setup and neuronal characteristics. A) Experimental setup with dural electrical stimulation and recording of neurons in the TCC. MMA: middle meningeal artery; TCC: trigeminocervical complex; C1: spinal cord cervical 1; TNC: trigeminal nucleus caudalis. B) An original tracing from a typical unit (second-order neurons) responding to electrical stimulation of the dura mater adjacent to the MMA (latencies in the Aδ-fiber range). Black arrow represents stimulus artefact. C) The location of recording sites in the TCC from which recordings of nociceptive neurons, receiving convergent input from the dura mater and facial receptive field, were made. The locations were reconstructed from lesions (•) and are located in laminae II–V, predominantly in lamina V. D) A histological example for the lesion mark (brown lesion as indicated by the arrow) of the recording site in the TCC (lamina V), marked by electrothermolytic lesion (4–6 μA for 60 s). The section was counterstained with thionin.

Fig. 3

Effects of insulin and glucagon on blood glucose levels and on dural-evoked neuronal firing in the trigeminocervical complex (TCC). A) Time course changes in blood glucose levels before surgery, before administration of drugs and following intravenous administration of insulin (10 U·kg^− 1) and glucagon (100 μg·200 μl^− 1) throughout the 60 min post-injection. Insulin (10 U·kg^− 1) significantly decreased blood glucose levels to a maximum of 1.9 mmol/L. Glucagon (100 μg·200 μl^− 1) significantly increased blood glucose levels to a maximum of 10.4 mmol/L at 30 min and returned to pre-injection levels at 60 min. Vehicle control had no effect on responses and blood glucose levels were kept in the physiological range of 5.4–5.5 mmol/L. B) Time course changes in the average response of dural-evoked Aδ-fiber trigeminal neuronal firing in response to insulin (10 U·kg^− 1) and glucagon (100 μg·200 μl^− 1), which significantly decreased neuronal responses across the 60 min study. Vehicle control had no effect on responses. *p < 0.05; **p < 0.01; ^#p < 0.001.

Fig. 4

Effects of leptin on blood glucose levels and on dural-evoked neuronal firing in the trigeminocervical complex (TCC). A) Time course changes in blood glucose levels before surgery, before administration of drugs and following intravenous administration of leptin (1 mg·kg^− 1) throughout the 60 min post-injection. Leptin (1 mg·kg^− 1) significantly decreased blood glucose levels to a maximum of 4.7 mmol/L, respectively. Vehicle control had no effect on responses and blood glucose levels were kept in the physiological range of 5.4–5.5 mmol/L. B) Bar graph of the maximum effect of leptin (0.3, 1 and 3 mg·kg^− 1) at the ‘45 min time point’ of the change from baseline of dural-evoked Aδ-fiber activity in the TCC. Leptin (1 mg·kg^− 1) significantly inhibited dural-evoked Aδ-fiber activity in the TCC, demonstrating an optimal dose effect for leptin. Vehicle control had no effect on responses. *p < 0.05; **p < 0.01; ^#p < 0.001.

Fig. 5

Effect of intravenous administration of insulin, glucagon and leptin on pERK1/2 cell expression within the trigeminocervical complex (TCC). A) Box plots summarising pERK1/2 expression in the TCC, consisting of the trigeminal nucleus caudalis (TNC) and C1 and C2 dorsal horn laminae I–V. Insulin (10 U·kg^− 1) and leptin (1 mg·kg^− 1) significantly decreased pERK1/2 labelling within the TCC, as oppose to glucagon (100 μg·200 μl^− 1), which significantly increased pERK1/2 expression, when compared to control sham group, 60 min post-injection. B) Photomicrographs showing the localization of pERK1/2 staining in the TCC. C) Photomicrograph showing pERK1/2 stained neurons in the TCC of an animal administered with glucagon (100 μg·200 μl^− 1). Arrows indicate cell bodies. *p < 0.05; **p < 0.01; ^#p < 0.001.

Fig. 6

Effect of intravenous administration of insulin, glucagon and leptin on pERK1/2 cell expression within the hypothalamic arcuate nucleus (ARC) and paraventricular nucleus (PVN) A) Leptin (1 mg·kg^− 1) significantly reduced pERK1/2 cell expression within the ARC, while insulin (10 U·kg^− 1) and glucagon (100 μg·200 μl^− 1) did not significantly affect pERK1/2 expression, when compared to control sham group, 60 min post-injection. B) Photomicrographs showing the localization of pERK1/2 staining in the hypothalamic ARC. Dotted line shows the ARC nucleus; 3V: third ventricle. C) Photomicrograph showing the localization of pERK1/2 staining in the hypothalamic ARC of an animal administered with glucagon (100 μg·200 μl^− 1). Arrows indicate cell bodies; 3V: third ventricle. D) Photomicrographs displaying the localization of pERK1/2 staining in the PVN showing no significant difference between groups. *p < 0.05; **p < 0.01; ^#p < 0.001.