I am not ina field so question may be dumb. How do researchers control for possible non-neural factors and non-RNA factors? E.g. continuous light shocks increas

I am not ina field so question may be dumb. How do researchers control for possible non-neural factors and non-RNA factors? E.g. continuous light shocks increase the level of stress hormone responsible for slowing down muscle relaxation. This additional hormone is transferred, alongside RNA (how do you transfer only RNA?) and that increases response time in receiving slugs.