Neuroanatomical Localization of Galanin in Zebrafish Telencephalon and Anticonvulsant Effect of Galanin Overexpression

Abstract

Galanin is a neuropeptide widely expressed in the nervous system, but it is also present in non-neuronal locations. In the brain, galanin may function as an inhibitory neurotransmitter. Several studies have shown that galanin is involved in seizure regulation and can modulate epileptic activity in the brain. The overall goal of the study was to establish zebrafish as a model to study the antiepileptic effect of galanin. The goal of this study was achieved by (1) determining neuroanatomical localization of galanin in zebrafish lateral pallium, which is considered to be the zebrafish homologue of the mammalian hippocampus, the brain region essential for initiation of seizures, and (2) testing the anticonvulsant effect of galanin overexpression. Whole mount immunofluorescence staining and pentylenotetrazole (PTZ)-seizure model in larval zebrafish using automated analysis of motor function and qPCR were used in the study. Immunohistochemical staining of zebrafish larvae revealed numerous galanin-IR fibers innervating the subpallium, but only scarce fibers reaching the dorsal parts of telencephalon, including lateral pallium. In three-month old zebrafish, galanin-IR innervation of the telencephalon was similar; however, many more galanin-IR fibers reached the dorsal telencephalon, but in the lateral pallium only scarce galanin-IR fibers were visible. qRT-PCR revealed, as expected, a strong increase in the expression of galanin in the Tg(hsp70l:galn) line after heat shock; however, also without heat shock, the galanin expression was several-fold higher than in the control animals. Galanin overexpression resulted in downregulation of c-fos after PTZ treatment. Behavioral analysis showed that galanin overexpression inhibited locomotor activity in PTZ-treated and control larvae. The obtained results show that galanin overexpression reduced the incidence of seizure-like behavior episodes and their intensity but had no significant effect on their duration. The findings indicate that in addition to antiepileptic action, galanin modulates arousal behavior and demonstrates a sedative effect. The current study showed that galanin overexpression correlated with a potent anticonvulsant effect in the zebrafish PTZ-seizure model.

Molecular organization of neuronal cell types and neuromodulatory systems in the zebrafish telencephalon

“…For example, the two galanin-expressing cell types in our dataset may potentially influence dozens of cell types throughout the telencephalon, consistent with the widespread distribution of galanin-immunoreactive fibers. 69 Generally, broadcasting networks are consistent with global functions of neuromodulation such as the control of brain states.…”

Guardian of Excitability: Multifaceted Role of Galanin in Whole Brain Excitability

“…To investigate if galanin by itself is able to reduce whole-brain activity, we employed a transgenic approach by using hsp70l:gal 10 expressing larvae. These transgenic fish express galanin under the control of the heatshock promoter hsp70l , enabling the induction of galanin expression by upregulating transcripts by over 300 fold 11 . Attempts to induce galanin overexpression through heat shock were discontinued due to a notable impact on the brain activity of wild type larvae compared to non-exposed wild type larvae (Suppl.…”

“…Figure 1). Yet, considering that hsp70l:gal larvae already display a basal elevation of galanin transcripts by approximately 8-fold 11 , comparable with the upregulation seen in eaat2a -/- mutants and PTZ rebound (Figure 1C and 1F), we chose to use larvae without inducing transcription via heat shock. We performed Ca 2+ imaging and found that indeed elevated expression of galanin in hsp70l:gal larvae leads to a decrease in whole-brain activity (Figure 2A) compared to wild type siblings.…”

“…Others found a decrease in locomotor activity upon galanin overexpression 10,11 . We similarly found that overexpression of galanin leads to a reduction in brain activity, while lack of galanin leads to neuronal hyperactivity.…”

Evaluation of the Antiseizure Activity of Endemic Plant Halfordia kendack Guillaumin and Its Main Constituent, Halfordin, on a Zebrafish Pentylenetetrazole (PTZ)-Induced Seizure Model

“…In our study, changes in galn expression after PTZ administration were not observed, which is consistent with previous reports. [49] Galanin is also expressed in many tissues outside the nervous system, so it might be concluded that changes in brain expression are masked by expression in other organs, as was postulated for c-fos. It should also be mentioned that it is not clear whether galanin expression is increased during the seizures, with some studies finding no changes in galanin levels in particular brain regions [50].…”