The trigemino-pupillary reflex: a model of sensory-vegetative integration

[Irreversible loss of brain function-Part 1: pitfalls in clinical diagnosis]

A significant change in the fourth update of the German guidelines on determining brain death is that it includes an explicit profile of requirements on physicians involved in ILBF diagnosis. These requisite qualification criteria have also been formulated due to the fact that, in many hospitals, ILBF diagnosis is only rarely carried out and, as a result, uncertainty frequently arises. Typical difficulties emerge at all stages of ILBF diagnosis, and numerous relevant pitfalls arise that need to be taken into consideration and which might also be relevant in the selection of the method(s) to detect irreversibility. The approaches presented here are suited to achieving a valid result in the evaluation of equivocal ILBF.

A dual physiological character for sexual function: the role of serotonergic receptors

Anatomically, sexual reflexes are mixed (somatic-autonomic) circuits, represented by emission (sympathetic centre and somatic afferents), expulsion (parasympathetic centre and somatic efferents) and erection (parasympathetic centre and somatic afferents). Physiologically, ejaculation has a dual autonomic mediation, consisting of two distinct and opposite autonomic centres (emission and expulsion), both with a positive contribution to the respective function. Experimentally, serotonin (5HT) has two distinct, opposite and positive effects on sexual function, with 5HT-(1A) agonists decreasing intravaginal ejaculatory latency and erection, and 5HT-(2C) agonists increasing both erection and ejaculatory latency. In this review I assume that 5HT modulates sexual reflexes, establishing a functional connection between the involved somatic and autonomic structures. The 5HT-(1A) receptors are assumed to make the connection between somatic pathways and sympathetic centres while the 5HT-(2C) receptors could establish the connection between somatic pathways and parasympathetic centres. Further studies will develop the cerebral sexual duality, explaining the implication of psychological factors in sexual function and the role of sexuality in psychosocial behaviour.

[What is needed to develop a headache? Anatomical and pathophysiological implications]

The shared anatomical and physiological substrate for headache syndromes is the neural innervation of the cranial circulation. Evidence suggests, that the observed dilatation of vessels in trigeminal pain is not inherent to a specific headache syndrome but rather a feature of the physiology of the trigeminal neural innervation of the cranial circulation. Moreover, the impact of vascular changes for the generation of headaches remains elusive. The trigeminal nerve innervates blood vessels within ipsilateral meninges. Upon activation neuropeptides such as CGRP are released. Blockade of both the trigeminal nerve system and neuropeptides are crucial targets for headache alleviating drugs. While these mechanisms are well known the events within and outside the CNS which initiate headaches are poorly understood. This article will review the anatomy and physiology of the trigeminovascular system which demand renewed consideration of the neural influences in many primary headaches.

Visual system dysfunction in migraine: a review of clinical and psychophysical findings

This paper reviews both clinical and experimental literature relating to visual dysfunction in migraine, starting with the eye and progressing via the retina and visual pathways to the visual cortex. Migraine is associated with (i) a pupillary sympathetic hypofunction, and (ii) a cortical hypersensitivity to visual stimuli (perhaps only in migraine with aura), the pathogenesis of which remains to be determined. Various hypotheses are discussed, and it is proposed that the methods of visual psychophysics may represent a useful approach in the future study of cortical hyperexcitability in migraine. Paradoxically, little research has been directed towards understanding (i) the photophobia of migraine attacks, and (ii) how migraine may be triggered by visual stimuli. Research aimed at elucidating the mechanisms of these phenomena may enhance understanding of the pathogenesis of migraine.

Pupillary and cardiovascular responses to the cold-pressor test

Little is known about the structures and mechanisms involved in the autonomic response to sensory and nociceptive stimulation. In this study, we recorded simultaneously pupil diameter, blood pressure, heart rate and pain levels during a cold-pressor test in 10 healthy subjects. The aim was to evaluate the different components of the Autonomic Nervous System involved in the response to a thermal-painful stimulus. A biphasic pupillary response was observed: an initial, short-lasting mydriasis, followed by a miotic phase, this latter characterized by rhythmic fluctuations of pupil diameter. The blood pressure response was monophasic with a moderate increase observed from the second minute of the test. Pain intensities remained stable on medium-high levels throughout the test. The topical application of thymoxamine and homatropine clarified some aspects of the pupillary response. The systemic administration of naloxone suggested a role of opiates in the modulation of pupillary and cardiovascular response to the cold-pressor test.

The trigemino-pupillary response in cluster headache

Central impairment of the integrative neural systems controlling vegetative function and pain perception has been demonstrated in cluster headache (CH). Recently, we described the human pupillary response (trigeminal reflex) to quantified (painless and painful) corneal stimulation with a combined neurophysiological and pharmacological technique. In this study, the trigeminal reflex was evaluated in 26 subjects with episodic cluster headache. During the active phase of the disease, on the side of the pain we observed reduced mydriasis to electrical stimuli with an intensity equal to the corneal reflex threshold, and on both sides to stimuli with intensity that equalled the pain threshold. No difference was found when amplitude of the miotic phase was compared in the different groups. These suggest disordered pupillary activation in response to pain, probably sympathetic in origin, which is bilateral, detectable also during the remission phase and which cannot be explained simply by the antidromic release of pain-related peptides.