Which of the following might be considered examples of trophic interactions between cells and/or tissues? (Select all that apply)

1 Reduced frequency of neuronal action potentials results in reduction of muscle mass.
2 Consumption of high carbohydrate meal results in increased secretion of insulin.
3 Contractile force of muscle increases bone density in the areas of tendon attachments of muscle.
4 High intensity exercise results in increased heart rate.
5 Exposure to novel environments or mental stimulation leads to more dense receptive areas in the active neurons