DOI: 10.1002/lio2.70621 ISSN: 2378-8038

Local Administration of Insulin‐Like Growth Factor 1 Attenuates Neuronal Loss and Muscle Atrophy in a Guinea Pig Model of Severe Facial Paralysis

Takemichi Tanaka, Hiroyuki Yamada, Ryota Takagi, Shinji Iwata, Takuya Kimura, Tomonori Joko, Hiroyuki Wakisaka, Naohito Hato
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ABSTRACT

Objective

To investigate the effects of locally administered insulin‐like growth factor‐1 (IGF‐1) on facial motor neurons, nerve fibers, and muscles in a severe facial paralysis model.

Methods

Severe unilateral facial paralysis was induced in guinea pigs ( Cavia porcellus ) by 5‐s cryospray injury to the facial nerve canal with the bony wall intact. Animals were assigned to an IGF‐1 or control group, and gelatin hydrogel impregnated with IGF‐1 or distilled water, respectively, was applied directly to the cryoinjury site. Facial movement was evaluated weekly for 10 weeks. Electroneurography (ENoG) was performed at 1 week. Histological analyses of the orbicularis oculi muscle and facial motor neurons were conducted at 4 and 10 weeks, and nerve fibers were qualitatively assessed by scanning electron microscopy.

Results

All animals showed complete facial paralysis at 1 week, with recovery beginning at 3 and 4 weeks. At 10 weeks, facial movement scores were higher in the IGF‐1 group than controls (5.6 ± 0.8 vs. 4.1 ± 0.7, p  < 0.05). ENoG values were 0% at 1 week. The affected‐side low Feret's diameter fiber ratio was lower in the IGF‐1 group at 10 weeks, indicating reduced muscle atrophy. Facial neuron mortality rates were lower in the IGF‐1 group at both time points and increased over time only in the control group. Nerve fibers appeared more organized in the IGF‐1 group.

Conclusion

Local administration of IGF‐1 suppressed neuronal loss, improved nerve fiber organization, and reduced muscle atrophy, suggesting beneficial effects on neural–muscular recovery in severe facial paralysis.

Level of Evidence

NA.

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