Disruption of iris adrenergic transmission as an index of poor endorphin modulation in headache
Fanciullacci, M.; Pietrini, U.; Boccuni, M.
Advances in Neurology 33: 365-374
1982
ISSN/ISBN: 0091-3952 PMID: 6119894 Document Number: 196706
Pupillometry was used to evaluate the effect of oral or topically applied adrenomimetic drugs and of local morphine on pupillary size in headache patients and controls. In headache sufferers, a disruption of adrenergic transmission is suggested since the iris adrenergic nerve terminal is apparently poor in NE; this neuron also exhibits a reduced capacity of neurotransmitter synthesis and an adrenoceptor hypersensitivity. The spontaneous reduction of pupillary size detected in headache sufferers also suggests a decreased sympathetic input. The miosis, registered after conjunctival instillation of morphine, demonstrates that iris is a possible example of an opioid-dependent adrenergic neuron in man. A poor modulation of the iris adrenergic transmission induces, in headache sufferers, a neuronal incontinence and therefore a chronic intrasynaptic leakage of NE, resulting in an exhausted empty neuron on the one hand and a compensatory hyperactivity of the effector muscular cell on the other. Since indirect evidence suggests a morphine modulation of the iris adrenergic neuron, a deficiency of endorphin modulation could be the mechanism of disruption of iris adrenergic transmission. Apart from the theoretical aspects, the exploration of iris neuroeffector junction represents a noninvasive an simple diagnostic tool in headache.