Topical prostaglandins are known to stimulate _____________ which results in long eyelashes as a potential side effect.

Topical prostaglandins, particularly prostaglandin analogs like bimatoprost, have been shown to stimulate the growth of eyelashes as a notable side effect. This growth is largely attributed to the action of prostaglandin F2α, which interacts with specific receptors in the hair follicles to enhance the anagen (growth) phase of the hair cycle.

The question asks about what is stimulated, and prostaglandin F2α specifically plays a crucial role in this mechanism. Thus, the correct answer highlights the physiological process by which these agents influence eyelash growth. Phospholipase C is involved in various signaling pathways but does not directly relate to eyelash growth caused by prostaglandin stimulation. Cyclooxygenase is an enzyme implicated in the synthesis of prostaglandins, while glutamate is a neurotransmitter that does not have a direct connection to eyelash growth in this context.

Overall, the stimulation of prostaglandin F2α is the primary reason behind the increased length and fullness of eyelashes observed with the use of certain topical prostaglandins.