Abstract
Primary sensory nerves do not only transfer messages to the central nervous system but also transmit messages to the periphery. The peripheral response is one of defense, including neurogenic inflammation such as miosis and a breakdown of the blood aqueous barrier in the eye or vasodilatation and plasma extravasation in the skin. Recent pharmacological, biochemical and immunohistochemical studies have revealed that tachykinins are the most likely transmitters at peripheral as well as central endings of primary sensory nerves. Furthermore, studies with trigeminal nerve-innervated and isolated rabbit iris sphincter muscle have clearly shown that the peripheral neurotransmission is affected by many neuromodulators and irritants. It is not unlikely that the neurotransmission mechanisms at peripheral endings are analogous to those at central endings in the primary sensory nerves.
