Intrafascicular recordings of afferent multi-unit activity from the human supraorbital nerve

Denervation injury of scalp hair due to trigeminal ganglion ischemia: the first experimental study

Aim: Scalp hairs are mainly innervated by sensitive fibers of trigeminal nerves. Ischemic neurodegeneration of trigeminal ganglion can cause denervation injury of scalp hairs. We investigated if there is a relationship between the degenerated neuron densities of trigeminal ganglion neuron densities and the numbers of degenerated hair follicles numbers following subarachnoid hemorrhage (SAH). Material and Method: Five normal (n=5), five SHAM (n=5), and ten (n=10) male rabbits were chosen from formerly experimental SAH created by cisternal homologous blood injection (0.75cc) group, which followed for three weeks. Degenerated neuron numbers of trigeminal ganglion and atrophic hair follicles numbers in the frontal areas of the scalp were examined by stereological methods. Degenerated neuron densities of trigeminal ganglions and atrophic hair follicles numbers were analyzed by the Mann-Whitney U test. Results: The mean degenerated neuron densities trigeminal ganglions (n/mm3) and atrophic hair follicles (n/mm2) were determined as 5±2/m3 and12±4/mm2 in control; 12±3/m3 and 41±8/mm2 in Sham and, 168±23/m3 and 79±14/mm2 in the study group (p>0.001). In the post-hoc analysis, all groups differed significantly from each other. A linear association was observed between the degenerated neuron densities of trigeminal ganglions and atrophic hair follicles (r: 0.343, p: 0.007). Conclusion: Trigeminal ganglion neurodegeneration may be an essential factor in hair follicles atrophy after SAH, which has not been mentioned in the literature so far.

Predictive role of trigeminal ganglion ischemia on scalp survival affected by temporal artery diameters: The first experimental study

Scalp arteries are mainly innervated by trigeminal, facial, and vagal nerves. The ischemic neurodegeneration of the trigeminal ganglion can impede scalp circulation via vasospasm-creating effects. This study was designed to investigate whether there is any link between the vasospasm index of deep temporal arteries and ischemic neuron densities of the trigeminal ganglion after subarachnoid hemorrhage. The study subjects included five normal control rabbits, six sham rabbits, and nine rabbits chosen from a formerly established experimental subarachnoid hemorrhage group created by cisternal homologous blood injection (0.75 mL). These rabbits, all male, were followed up for 3 weeks. The trigeminal ganglion and deep temporal artery vasospasm indexes were examined by stereological methods. Ischemic neuron densities of the trigeminal ganglion and vasospasm index values of deep temporal arteries were compared statistically. Postmortem examinations showed important vasospasms of deep temporal arteries, foramen magnum herniations, and neurodegeneration of the trigeminal ganglion. The mean vasospasm index values and degenerated neuron densities of the trigeminal ganglion were determined as 1.03 ± 0.13 and 10 ± 3/mm³ (p > 0.5) in the control group, 1.21 ± 0.18 and 35 ± 9/mm³ in the sham group (p < 0.005 for sham vs. control), and 2.54 ± 0.84 and 698 ± 134/mm³ in the experimental group (p < 0.0005 for sham vs. control and p < 0.00001 for study vs. control). There was an inverse relationship between the vasospasm index values and the degenerated neuronal density of the trigeminal ganglion. The high degenerated neuron density in the trigeminal ganglion had a facilitative effect on temporal artery vasospasm. Trigeminal ganglion neurodegeneration may promote temporal artery vasospasms after subarachnoid hemorrhage, which has not been previously mentioned in the literature.

Augmented supraorbital skin sympathetic nerve activity responses to symptom trigger events in rosacea patients

Facial flushing in rosacea is often induced by trigger events. However, trigger causation mechanisms are currently unclear. This study tested the central hypothesis that rosacea causes sympathetic and axon reflex-mediated alterations resulting in trigger-induced symptomatology. Twenty rosacea patients and age/sex-matched controls participated in one or a combination of symptom triggering stressors. In protocol 1, forehead skin sympathetic nerve activity (SSNA; supraorbital microneurography) was measured during sympathoexcitatory mental (2-min serial subtraction of novel numbers) and physical (2-min isometric handgrip) stress. In protocol 2, forehead skin blood flow (laser-Doppler flowmetry) and transepithelial water loss/sweat rate (capacitance hygrometry) were measured during sympathoexcitatory heat stress (whole body heating by perfusing 50°C water through a tube-lined suit). In protocol 3, cheek, forehead, forearm, and palm skin blood flow were measured during nonpainful local heating to induce axon reflex vasodilation. Heart rate (HR) and mean arterial pressure (MAP) were recorded via finger photoplethysmography to calculate cutaneous vascular conductance (CVC; flux·100/MAP). Higher patient transepithelial water loss was observed (rosacea 0.20 ± 0.02 vs. control 0.10 ± 0.01 mg·cm(-2)·min(-1), P < 0.05). HR and MAP changes were not different between groups during sympathoexcitatory stressors or local heating. SSNA during early mental (32 ± 9 and 9 ± 4% increase) and physical (25 ± 4 and 5 ± 1% increase, rosacea and controls, respectively) stress was augmented in rosacea (both P < 0.05). Heat stress induced more rapid sweating and cutaneous vasodilation onset in rosacea compared with controls. No axon reflex vasodilation differences were observed between groups. These data indicate that rosacea affects SSNA and that hyperresponsiveness to trigger events appears to have a sympathetic component.

A method for intraoperative microneurographic recording of unitary activity in the trigeminal ganglion of patients with trigeminal neuralgia

The etiology of trigeminal neuralgia appears to be vascular compression of the nerve at the root entry zone. However, the physiologic mechanism of trigeminal neuralgia remains uncertain. To gain insight into the pathophysiology of the disorder, we developed a method for intraoperative microneurographic recordings from the trigeminal ganglion of patients with trigeminal neuralgia. The recordings are performed immediately prior to standard percutaneous trigeminal gangliolysis for pain relief. Spontaneous or evoked single- and multi-unit action potential activity can be recorded and the location of receptive fields determined. The method should facilitate the testing of hypotheses concerning the origin of this unique pain disorder.

The effect of trigeminal nociceptive stimulation on blink reflexes and pain evoked by stimulation of the supraorbital nerve

The aim of this study was to investigate the effect of painful conditioning stimuli on pain and blink reflexes to supraorbital nerve stimulation. Electromyograph activity was recorded bilaterally from the orbicularis oculi muscles in 13 normal participants in response to low (2.3 mA) and high-intensity (18.6 mA) electrical stimulation of the left supraorbital nerve before, during and after the application of ice to the left or right temple or immersion of the left hand in ice-water for 60 s. The pain evoked by the high-intensity electrical stimulus was greater during painful conditioning stimulation of the ipsilateral temple than during the recovery period afterwards, and was greater than during painful conditioning stimulation of the contralateral temple. These findings imply that spatial summation of nociceptive signals across different divisions of the trigeminal nerve can heighten pain. However, painful conditioning stimulation, particularly to the right temple, strongly suppressed the R2 component of the blink reflex to the low-intensity stimulus, and also suppressed R2 to the high-intensity stimulus. Thus, an inhibitory influence (e.g. diffuse noxious inhibitory controls) appeared to mask ipsilateral segmental facilitation of R2 during ice-induced headache. This finding contrasts with recent electrophysiological evidence of trigeminal sensitization in migraine.

Stretch sensitivity of cutaneous RA mechanoreceptors in rat hairy skin

Twenty-five rapidly adapting mechanoreceptor afferents were recorded in an in vitro preparation of rat skin and nerve. Single units were recorded while the skin was subjected to dynamic uniaxial stretch using a pseudo-Gaussian noise (PGN) input waveform. Force was the controlled variable in stretch stimuli. Measured loads and displacements were used to calculate tensile stresses, strains, and their rates of change. Associations between spike responses and individual stimulus components such as tensile stress or strain were determined in a reverse correlation design using multiple logistic regression. Spikes were strongly associated with stress, at memory times from 0 to 14 ms, and with the rate of change of stress, at a memory times between 6 and 18 ms. There was a strong interaction between stress and its rate of change, with a maximum value at a memory time of 10 ms. We found no relationship between spike responses and strain.

Stretch sensitivity of cutaneous afferent neurons

Experiments were done to characterize responses to stretch and to determine what stretch-related mechanical variables are most closely associated with stretch. Cutaneous afferent neurons were recorded using an in vitro preparation of rat hairy skin. SA2 afferents and mechanically sensitive C afferents were studied using static stretch stimuli in which the skin was stretched along different directions. RA afferents were studied using uniaxial, dynamic stimuli. Both applied loads and skin deformations were recorded; they were used to calculate tensile stresses and strains, respectively. SA2 afferents were highly directionally sensitive and had low thresholds for activation. Their responses to static stimuli were closely related to tissue stress and poorly related to strain. C mechanoreceptors lacked directional selectivity, and had thresholds for activation that were similar to SA2s. Their responses to static stretch were more strongly related to stress than to strain variables. The main focus of this chapter is RA afferents. It was possible to apply powerful methods for determining the relationship between RA responses and cutaneous stresses and strains. RA responses were strongly driven by rate of change of stress, with a very small contribution from the static component of stress. There were strong memory effects. The strongest influence on RA afferents was by the rate of change of stress approximately 30 msec prior to the occurrence of a spike.

Responses of rapidly adapting afferent neurons to dynamic stretch of rat hairy skin

Twenty-four rapidly adapting (RA) cutaneous afferents were recorded from a preparation of isolated, innervated hairy skin from the rat hindlimb for the purpose of identifying the mechanical variables associated with the initiation of afferent discharge. Neurons were studied while the skin was stretched dynamically along a single direction with the use of a linear actuator and a feedback controller. Input signals were load- or displacement-controlled stretches that followed either periodic or pseudorandom Gaussian noise control signals. When the tissue was actuated, loads and displacements were measured along the direction of stretch and neuronal responses were recorded. All RA afferents were activated by dynamic stretching. None had a sustained response to static stretch. Cross-correlation products, calculated between neuronal responses and either stress- or strain-related variables observed at the time of the spike, revealed a strong relationship between neuronal responses and tensile stress. Neuronal responses were observed at rates of change of stress between +1,000 and -800 kPa/s. Neuronal responses were poorly related to skin strain. Two loading conditions were used along the direction transverse to the stretch. In one condition the sides were unconstrained, so that on axial loading there was zero stress and negative strain along the transverse axis. In the other condition the sides were constrained so that when the tissue was loaded axially there was zero strain and positive stress along the transverse axis. In these two conditions the same level of axial stress was associated with two levels of axial strain. The neuronal responses were determined by the stress and not the strain. Neuronal responses were observed at stresses >5 kPa. It appears that RA afferents make little contribution to signaling limb movements or position in rat hindlimb on the basis of the behavior of rat hindlimb skin, as observed when the limb is rotated.

Trigemino-cervical reflexes in normal subjects

Trigemino-cervical reflexes, recorded from the semispinalis capitis muscle (SCM) in the posterior neck, were studied in 35 healthy volunteers, in response to electrical stimulation of the supraorbital trigeminal nerve and glabellar tapping. Simultaneous responses evoked from the ipsilateral orbicularis oculi muscle (OOM) were also recorded i.e. blink reflexes. Electrical stimulation of the supraorbital nerve elicited a reflex response with a latency of about 50 ms from the ipsilateral SCM which was called C3. An early reflex response, which sometimes had two components with latencies of 18 ms and 35 ms, was elicited with glabellar taps. They were called C1 and C2 respectively. When C1 and C2 were elicited with usual glabellar taps, C3 was suppressed. With electrical stimulation, suppression of C1 and C2 was noted, though C3 could easily be obtained. Electrophysiological characteristics of C1 (and C2) were compatible with an oligosynaptic, innocuous reflex, whereas C3 seemed to be multisynaptic and nociceptive in nature. A negative interaction between these two reflexes was observed.