Vol.:(0123456789) 1 3 Brain Structure and Function https://doi.org/10.1007/s00429-020-02057-y ORIGINAL ARTICLE Sources and lesion‑induced changes of VEGF expression in brainstem motoneurons Silvia Silva‑Hucha 1  · Génova Carrero‑Rojas 1  · María Estrella Fernández de Sevilla 1  · Beatriz Benítez‑Temiño 1  · María América Davis‑López de Carrizosa 1  · Angel M. Pastor 1  · Sara Morcuende 1 Received: 30 July 2019 / Accepted: 6 March 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020 Abstract Motoneurons of the oculomotor system show lesser vulnerability to neurodegeneration compared to other cranial motoneu- rons, as seen in amyotrophic lateral sclerosis (ALS). The overexpression of vascular endothelial growth factor (VEGF) is involved in motoneuronal protection. As previously shown, motoneurons innervating extraocular muscles present a higher amount of VEGF and its receptor Flk-1 compared to facial or hypoglossal motoneurons. Therefore, we aimed to study the possible sources of VEGF to brainstem motoneurons, such as glial cells and target muscles. We also studied the regulation of VEGF in response to axotomy in ocular, facial, and hypoglossal motor nuclei. Basal VEGF expression in astrocytes and microglial cells of the cranial motor nuclei was low. Although the presence of VEGF in the diferent target muscles for brainstem motoneurons was similar, the presynaptic element of the ocular neuromuscular junction showed higher amounts of Flk-1, which could result in greater efciency in the capture of the factor by oculomotor neurons. Seven days after axotomy, a clear glial reaction was observed in all the brainstem nuclei, but the levels of the neurotrophic factor remained low in glial cells. Only the injured motoneurons of the oculomotor system showed an increase in VEGF and Flk-1, but such an increase was not detected in axotomized facial or hypoglossal motoneurons. Taken together, our fndings suggest that the ocular moto- neurons themselves upregulate VEGF expression in response to lesion. In conclusion, the low VEGF expression observed in glial cells suggests that these cells are not the main source of VEGF for brainstem motoneurons. Therefore, the higher VEGF expression observed in motoneurons innervating extraocular muscles is likely due either to the fact that this factor is more avidly taken up from the target muscles, in basal conditions, or is produced by these motoneurons themselves, and acts in an autocrine manner after axotomy. Keywords Oculomotor system · VEGF · Flk-1 · Brainstem motoneurons · Axotomy · Amyotrophic lateral sclerosis Introduction Brainstem motoneurons are diferentially afected by degen- eration, induced either by nerve insults or by neurodegenera- tive diseases, such as amyotrophic lateral sclerosis (ALS) (Reiner et al. 1995; Nimchinsky et al. 2000; Haenggeli and Kato 2002). Specifcally, motoneurons of the oculomotor system, located in the oculomotor (III; OCM), trochlear (IV; TRO), and abducens (VI; ABD) nuclei, have less vul- nerability to neurodegeneration compared to other cranial motoneurons, as seen in ALS. Commonly, facial (VII) and hypoglossal (XII; HYPO) motor nuclei are more afected in this disease. Trophic factors are known to play a principal role in neu- ronal survival in adult motoneurons, including motoneurons of the oculomotor system (for review see Benítez-Temiño et al. 2016). In recent years, vascular endothelial growth fac- tor (VEGF) has been included in the group of trophic factors acting on motoneurons (Storkebaum et al. 2004; Bogaert et al. 2006; Lange et al. 2016; Calvo et al. 2018b). VEGF was initially discovered as a vascular permeability factor (Senger et al. 1983) and considered an endothelial specifc growth factor. However, VEGF’s role in neuroprotection became evident when mice with reduced level of VEGF (VEGF δ/δ ) developed adult-onset progressive motoneuronal degeneration, resembling ALS (Oosthuyse et al. 2001). Recent discoveries prove that VEGF has direct efects on * Sara Morcuende smorcuende@us.es 1 Departamento de Fisiología, Facultad de Biología, Universidad de Sevilla, Seville, Spain