Scalp,basal epidural and intravascular far-field recordings after median nerve stimulation: evidence for a separate N18a potential

Far-field somatosensory evoked potentials (SSEPs) after median nerve stimulation were recorded from scalp- (Fz), epidural(ED) and intravascular electrodes (basilar artery [Bas]) to study the nature of the controversial N18a component of the widespread N18 potential. In healthy volunteers frequently an N18a potential was recorded at Fz. Simultaneous Fz and ED recordings at the pontomesencephalic junction as well as Bas-recordings at the caudal basilar artery showed N18a components identical in latency and shape. With intravascular recordings the shapes differed between the top of the basilar artery and the caudal artery recordings. These findings support the existence of a separate N18a potential. The generator of the N18a is likely to be localized within the upper brainstem.     

Widespread N18 in median nerve SEP is preserved in a pontine lesion

Widespread N18 potential to median nerve stimulation was preserved in a patient who had profound unilateral disturbance of deep sensation and a lesion of the pontine medial lemniscus confirmed by MRI. It was concluded from this result that at least a significant part of the N18 potential was generated caudal to the pontine level or at higher levels via extralemniscal pathways. Careful review of studies in man with intraoperative recordings seemed to support that the N18 potential already exists at the medullary level. We suggested that the potential generated at the cuneate nucleus which was described in cats may correspond to part of the N18 potential.     

Origin of frontal N15 component of somatosensory evoked potential in man

Origin of the frontal somatosensory evoked potential (SEP) by median nerve stimulation was investigated in normal volunteers and in patients with localized cerebrovascular diseases, and the following results were obtained.

• 1.(1) In normal subjects, SEPs recorded at F3 (or F4) contralateral to the stimulating median nerve were composed of P12, N15, P18.5 and N26. Similar components were recognized in SEP recorded at Fz.
• 2.(2) In patients in whom putaminal or thalamic hemorrhages had destroyed the posterior limbs of the internal capsules, frontal N15 and parietal N18 (N20) disappeared. These components were also absent in patients with cortical (parietal) infarctions. Among these patients, the thalamus was not affected in cases with putaminal hemorrhages and cortical infarctions.

These facts indicate that the generator of the frontal N15 does not exist in the thalamus but that it originates from the neural structure central to the internal capsule, which suggests a similarity to the generator of the parietal N18.Because N15 was recorded in the midline of the frontal region with shorter latency than parietal N18, the frontal N15 might represent a response to the sensory input of the frontal lobe via the non-specific sensory system.     

Long-range afferents in the rat spinal cord. 1. Numbers, distances and conduction velocities.

The caudal extent of the penetration of primary afferent axons from the T12 and L1 dorsal roots and sural nerve has been investigated in adult decerebrate spinal rats. Microelectrode stimulation at the root entry zone (REZ) and at further caudal points in the spinal cord was used to generate antidromic action potentials in single fibres recorded in dorsal roots or peripheral nerves. A total of 209 units were recorded in T12 and L1 dorsal roots and 27% of these could be antidromically activated 10 mm caudal to the REZ. Fifteen percent of the units could be stimulated at the L4-5 border, 15 mm caudal to the T12 segment whereas 4.5% of the axons could be stimulated 25 mm caudally in the S4 segment, 11 segments caudal to the entry segment. Similar recordings made from units in the sural nerve showed that of all the sural axons that penetrated to the L6 segment 50%, 18% and 2% of these reached the S1, S2 and S4 segments respectively. The conduction velocities of these units were clearly in the A-beta range when recorded in the nerve but decreased on entering the spinal cord and were reduced by 83% at their caudal end point. The results show that substantial numbers of primary afferents have long-ranging caudal branches in areas beyond the regions of known postsynaptic effects. The functions of these caudal projections are unclear but they may represent a potential substrate for the development of functional connections under conditions of disease or denervation.     

Nasopharyngeal recordings of somatosensory evoked potentials document the medullary origin of the N18 far-field

Because the nasopharyngeal electrode provides non-invasive access to the ventral brain-stem at the medullo-pontine level we used it for recording somatosensory evoked potentials (SEPs) to median nerve stimulation (non-cephalic reference). After the P9 and P11 far-fields, the nasopharyngeal SEPs disclosed a negative-going component which was interpreted as the near-field equivalent of the P14 scalp far-field generated in the caudal part of the medial lemniscus. Nasopharyngeal SEPs also revealed a large N18 with voltage and features strikingly similar to those of the scalp-recorded N18 far-field. These results suggest that N18 is generated in the medulla and not more rostrally in the brain-stem. The use of a nasopharyngeal electrode as reference for topographic brain mapping is discussed. The paper documents the feasibility and relevance of nasopharyngeal recordings for non-invasive analysis of short-latency SEPs.     

Negative correlation of P50 peak latencies and reaction times in a simple reaction task

We investigated the influence of stimulus characteristics and tasks (count and simple reaction tasks) on auditory P50. Ten normal volunteers served as subjects. EEGs and auditory evoked potentials were obtained from Fz, Cz, Pz, C3, C4, T3 and T4 referred to linked earlobes (LE) and balanced non-cephalic (BN) electrodes. In the recordings using a BN reference there were significant negative correlations between the reaction times and P50 peak latencies at Fz, Cz, Pz, C3 and C4. In the LE reference recordings there were negative correlations but these did not reach statistical significance. The results are discussed with reference to the activation of the LE reference and the neural sources of P50. The findings suggest the possibility that reaction times are determined at the very early stage of auditory information processing.     

Arachidonate dilates basilar artery by lipoxygenase-dependent mechanism and activation of K(+) channels

Dilatation of cerebral arterioles in response to arachidonic acid is dependent on activity of cyclooxygenase. In this study, we examined mechanisms that mediate dilatation of the basilar artery in response to arachidonate. Diameter of the basilar artery (baseline diameter = 216 +/- 7 micrometer) (means +/- SE) was measured using a cranial window in anesthetized rats. Arachidonic acid (10 and 100 microM) produced concentration-dependent vasodilatation that was not inhibited by indomethacin (10 mg/kg iv) or N(G)-nitro-L-arginine (100 microM) but was inhibited markedly by baicalein (10 micrometerM) or nordihydroguaiaretic acid (NDGA; 10 microM), inhibitors of the lipoxygenase pathway. Dilatation of the basilar artery was also inhibited markedly by tetraethylammonium ion (TEA; 1 mM) or iberiotoxin (50 nM), inhibitors of calcium-dependent potassium channels. For example, 10 microM arachidonate dilated the basilar artery by 19 +/- 7 and 1 +/- 1% in the absence and presence of iberiotoxin, respectively. Measurements of membrane potential indicated that arachidonate produced hyperpolarization of the basilar artery that was blocked completely by TEA. Incubation with [(3)H]arachidonic acid followed by reverse-phase and chiral HPLC indicated that the basilar artery produces relatively small quantities of prostanoids but large quantities of 12(S)-hydroxyeicosatetraenoic acid (12-S-HETE), a lipoxygenase product. Moreover, the production of 12-HETE was inhibited by baicalein or NDGA. These findings suggest that dilatation of the basilar artery in response to arachidonate is mediated by a product(s) of the lipoxygenase pathway, with activation of calcium-dependent potassium channels and hyperpolarization of vascular muscle.     

Neural organization of the ventilatory activity in the frog,Rana catesbeiana. II

The paralyzed, decerebrate frog, Rana catesbeiana, displays “fictive” oropharyngeal and pulmonary ventilations. In order to evaluate the neuronal correlates of these two centrally programmed ventilatory bursting patterns, we have performed intra-and extracellular recordings of bulbar respiratory neurons in this fictively breathing preparation. A total of 123 respiratory neurons were recorded from the caudal medulla. Of 51 antidromically activated neurons, 20 were vagal motoneurons and 31 were hypoglossal motoneurons. Respiratory neurons that depolarized during the lung (L) or non-lung (N) ventilatory phases were classified as L or N neurons, respectively. Phase spanning neurons (S) were active during both L and N phases. Some neurons showed oscillations of membrane potential synchronous with oropharyngeal ventilation. Those active during the buccal elevation phase were exclusively L neurons whereas those having buccal depressor activity were exclusively N neurons. Synaptic drive potentials were observed in all neurons recorded intracellularly. In some neurons, hyperpolarization was caused by inhibitory postsynaptic potentials, as demonstrated by reversal of membrane potential trajectory after intracellular chloride iontophoresis. Some individual motoneurons and interneurons exhibited both pulmonary and buccal ventilatory activity, indicating that both pattern generators project to a common motor control system. 1994 John Wiley & Sons, Inc.     

An immunohistochemical study on the innervation of SP-IR nerves in the cerebral arteries of the bent-winged bat

Summary The overall distribution of substance P (SP) immunoreactive (IR) nerves surrounding the cerebral arteries of the bent-winged bat were investigated immunohistochemically. In this microchiropteran species, the walls from the vertebral artery to the caudal part of the basilar artery have considerably well-developed plexuses of SP-IR nerves, whereas no demonstrable SP-IR fibers were found in the crostral part of the basilar artery, and in more rostrally located arteries the nerve supply was very sparse or occasionally lacking. This innervation pattern has not yet been established for the cerebral arterial systems of other mammals that have been studied under normal conditions, but it is very similar to the pattern of SP-IR innervation observed in the guinea pig and cat of which the trigeminal ganglia have been destroyed. From the combination of this and other immunohistochemical findings, it is suggested that SP-IR nerves innervating the vertebral and basilar arteries of the bent-winged bat originate from the upper cervical dorsal root ganglia (DRG) and enter the cranial cavity along the vertebral artery and through the meninges.Abbreviations BA basilar artery - CSN cervical spinal nerves - ICS internal carotid system - SCG superior cervical ganglion - SNB sympathetic nerve bundle - VA vertebral artery - VBS vertebro-basilar system     

Detailed analysis of the latencies of median nerve somatosensory evoked potential components, 1: selection of the best standard parameters and the establishment of normal values

In order to objectively select the standard parameters best suited for the evaluation of somatosensory conduction in median nerve somatosensory evoked potentials (SEP), we performed a detailed statistical analysis of intersubject variability for the latencies of SEP components based on the recordings of 62 normal subjects. Multiple regression analyses for height, age, (age - 20)² and sex were performed for the latencies of 13 components and 78 intercomponent intervals, and the residual variance was used as an indicator of the stability of each parameter. As a result, N9 onset in EPi-NC lead, N11′ onset in C6S-Fz lead, P13/14 onset in scalp-NC leads, for which N13′ onset recorded in C6S-Fz lead may substitute, and N20 onset in CPc-Fz lead were the most stable time-points selected as standards. N11 onset in C6S-NC, which other authors have recommended as the standard point representing spinal entry, was not recorded consistently, and P11 onset in scalp-NC leads was also unstable. N20 and peak and N13′-N20 interval (equivalent to conventional central conduction time) were extremely unstable. We presented the nomograms to find normal limits of the standard parameters corresponding to the given values of the predictor variables (height, age or sex). As the standard recording montage in routine clinical examinations, we recommended a simple method using Fz reference, for example (1) EPi-Fz, (2) C6S-Fz, (3) CPc-Fz, because this montage is sufficient to measure the stable standard parameters.     

An immunohistochemical study on the innervation of SP-IR nerves in the cerebral arteries of the bent-winged bat

The overall distribution of substance P (SP) immunoreactive (IR) nerves surrounding the cerebral arteries of the bent-winged bat were investigated immunohistochemically. In this microchiropteran species, the walls from the vertebral artery to the caudal part of the basilar artery have considerably well-developed plexuses of SP-IR nerves, whereas no demonstrable SP-IR fibers were found in the rostral part of the basilar artery, and in more rostrally located arteries the nerve supply was very sparse or occasionally lacking. This innervation pattern has not yet been established for the cerebral arterial systems of other mammals that have been studied under normal conditions, but it is very similar to the pattern of SP-IR innervation observed in the guinea pig and cat of which the trigeminal ganglia have been destroyed. From the combination of this and other immunohistochemical findings, it is suggested that SP-IR nerves innervating the vertebral and basilar arteries of the bent-winged bat originate from the upper cervical dorsal root ganglia (DRG) and enter the cranial cavity along the vertebral artery and through the meninges.     

Establishment and characterization of a mouse embryonic heart slice preparation.

BACKGROUND: In contrast to isolated cells, the anatomic and functional integrity of tissue slices remains preserved. Aim of the study was to establish the slice technique in embryonic mouse hearts in order to perform physiological and pharmacological investigations of wild-type mice and genetically engineered mouse models of heart disease. METHODS: Ventricular slices (thickness: 300 mum) were cut from agar-embedded embryonic mouse hearts (ED 16.5-18.5) with a vibratome. Histology, immunostaining with markers for apoptosis induction, intracellular recordings with sharp electrodes and field potential recordings using microelectrode arrays were performed to assess viability. RESULTS: Slices exhibited normal histology without prominent signs of apoptosis for at least 24 hours. Intracellular recordings revealed the typical electrophysiological fingerprint of ventricular cardiomyocytes. Field potential recordings proved that adrenergic and muscarinic signaling was preserved. CONCLUSION: Functionally intact heart slices can be generated from murine embryos.     

Activation of Rho-associated kinase during augmented contraction of the basilar artery to serotonin after subarachnoid hemorrhage

Delayed cerebral vasospasm after subarachnoid hemorrhage (SAH) may be due, in part, to altered regulation of arterial smooth muscle contraction. Contraction of cerebral arteries to serotonin is augmented after experimental SAH. We hypothesized that activation of Rho-associated kinase (Rho kinase) contributes to augmented contraction of cerebral arteries to serotonin after SAH. Autologous arterial blood (SAH) or artificial cerebrospinal fluid (control) was injected into the cisterna magna of anesthetized rabbits. At 2 days after injection, the basilar artery was excised and isometric contraction of arterial rings was recorded. Maximum contraction of the basilar artery to serotonin was augmented about fourfold in SAH compared with control rabbits (P < 0.01). Contraction to histamine was similar in the two groups. Fasudil hydrochloride (3 mumol/l), an inhibitor of Rho kinase, markedly attenuated serotonin-induced contraction. Fasudil had little effect on contractions induced by histamine or phorbol 12,13-dibutyrate. In addition, phosphorylation of myosin phosphatase, a major target of Rho kinase in regulation of smooth muscle contraction, in the basilar artery was examined by Western blotting. In basilar arteries of SAH, but not control, rabbits, serotonin increased phosphorylation of myosin phosphatase about twofold at Thr(853) of the myosin-targeting subunit. These results suggest that enhanced activation of Rho kinase contributes to augmented contraction of the basilar artery to serotonin after SAH.     

Influence of exercise on dilatation of the basilar artery during diabetes mellitus.

Our goal was to examine whether exercise training alleviates impaired nitric oxide synthase (NOS)-dependent dilatation of the basilar artery in Type 1 diabetic rats. To test this hypothesis, we measured in vivo diameter of the basilar artery in sedentary and exercised nondiabetic and diabetic rats in response to NOS-dependent (acetylcholine) and -independent (nitroglycerin) agonists. To determine the potential role for nitric oxide in vasodilatation in sedentary and exercised nondiabetic and diabetic rats, we examined responses after NG-monomethyl-l-arginine (l-NMMA). We found that acetylcholine produced dilatation of the basilar artery that was similar in sedentary and exercised nondiabetic rats. Acetylcholine produced only minimal vasodilatation in sedentary diabetic rats. However, exercise alleviated impaired acetylcholine-induced vasodilatation in diabetic rats. Nitroglycerin produced dilatation of the basilar artery that was similar in sedentary and exercised nondiabetic and diabetic rats. l-NMMA produced similar inhibition of acetylcholine-induced dilatation of the basilar artery in sedentary and exercised nondiabetic and diabetic rats. Finally, we found that endothelial NOS (eNOS) protein in the basilar artery was higher in diabetic compared with nondiabetic rats and that exercise increased eNOS protein in the basilar artery of nondiabetic and diabetic rats. We conclude that 1) exercise can alleviate impaired NOS-dependent dilatation of the basilar artery during diabetes mellitus, 2) the synthesis and release of nitric oxide accounts for dilatation of the basilar artery to acetylcholine in sedentary and exercised nondiabetic and diabetic rats, and 3) exercise may exert its affect on cerebrovascular reactivity during diabetes by altering levels of eNOS protein in the basilar artery.     

Estrogen and progesterone withdrawal increases cerebral vasoreactivity to serotonin in rabbit basilar artery.

An in vitro animal model which examines the effects of sex hormone variations during the menstrual cycle on basilar artery reactivity is presented. Three groups of rabbits were utilized: a chronically depleted control group which received no further hormonal treatment after bilateral surgical oophorectomy (O), simulating menopause, and two groups of intact females, one of which was treated to mimic the estrogen and progesterone surge during the luteal phase (H) and the third group which was acutely estrogen and progesterone depleted after the luteal surges to simulate the immediate premenstrual state (W). We show that both acute and chronic estrogen and progesterone withdrawal significantly increase serotonin sensitivity (ED50) in basilar artery rings. There was no difference between groups for maximum contraction (Tmax) to serotonin, nor optimal resting tension. Furthermore, there was no difference in vasoreactivity and contractility to norepinephrine between groups. In order to distinguish between the effects of chronic and acute treatment we examined acute estrogen and progesterone superfusion in basilar artery rings from intact non-treated female rabbits. Acute superfusion of pre-contracted and non-pre-contracted artery segments resulted in significant dilatation only when supraphysiologic concentrations of estrogen and progesterone were used. We conclude that both acute and chronic female sex hormone withdrawal selectively increases cerebral vasoreactivity to serotonin.     

Event-related potential measures of attention in moderately depressed subjects

Prior research has inferred attentional changes related to depression from evidence concerning other cognitive processes. The present experiment investigated attentional changes related to depression in a more direct manner. Subjects were 32 young adults attending college. Depression was measured by self-report measures. In an auditory selective attention task similar to that of Hansen and Hillyard (1980), auditory event-related potentials(ERPs) were recorded from central (Cz) and frontal (Fz) scalp locations. Evidence for selective attention was manifest as the difference wave (Nd), which showed larger mean and peak amplitudes for the less difficult of two attention conditions. Nd was also shown to have an earlier peak latency at the Cz scalp location. However, there was no significant difference between the Depressed and Control groups as measured by the Nd wave. Significant differences were found between groups for the amplitude of the N1 peak of the ERP at the Fz scalp location. This suggests that the Depressed group differed in arousal level or sensory sensitivity from the Control group.     

Alterations of Voltage-Dependent Calcium Channel Currents in Basilar Artery Smooth Muscle Cells at Early Stage of Subarachnoid Hemorrhage in a Rabbit Model

Objective

To investigate the changes in the currents of voltage-dependent calcium channels (VDCCs) in smooth muscle cells of basilar artery in a rabbit model of subarachnoid hemorrhage (SAH).

Methods

New Zealand white rabbits were randomly divided into five groups: sham (C), normal (N), 24 hours (S1), 48 hours (S2) and 72 hours (S3) after SAH. Non-heparinized autologous arterial blood (1ml/kg) was injected into the cisterna magna to create SAH after intravenous anesthesia, and 1 ml/kg of saline was injected into cisterna magna in the sham group. Rabbits in group N received no injections. Basilar artery in S1, S2, S3 group were isolated at 24, 48, 72 hours after SAH. Basilar artery in group C was isolated at 72 hours after physiological saline injection. Basilar artery smooth muscle cells were isolated for all groups. Whole-cell patch-clamp technique was utilized to record cell membrane capacitance and VDCCs currents. The VDCCs antagonist nifedipine was added to the bath solution to block the Ca⁺⁺ channels currents.

Results

There were no significant differences in the number of cells isolated, the cell size and membrane capacitance among all the five groups. VDCC currents in the S1–S3 groups had higher amplitudes than those in control and sham groups. The significant change of current amplitude was observed at 72 hours after SAH, which was higher than those of 24 and 48 hours. The VDCCs were shown to expression in human artery smooth muscle cells.

Conclusions

The changes of activation characteristics and voltage-current relationship at 72 hours after SAH might be an important event which leads to a series of molecular events in the microenvironment of the basilar artery smooth muscle cells. This may be the key time point for potential therapeutic intervention against subarachnoid hemorrhage.     

Influence of restricted knee motion during the flat first serve in tennis

The aim of this study was to examine the influence of restricted knee motion during the serve in tennis players of different performance levels. Thirty subjects distributed in 3 groups (beginner, B; intermediate, I; elite, E) performed 15 flat first serves with normal (normal serve, S(N)) and restricted (restricted serve, S(R)) knee motion. In S(R), the legs were kept outstretched by splints with a knee joint angle fixed at 10 degrees (0 degrees fully extended) to prevent any knee flexion/ extension. Vertical maximum ground reaction forces (Fz(max)), ball impact location (L(impact)), and ball speed (S(ball)) were measured with force platform, video analysis, and radar, respectively. Fz(max), L(impact,) and S(ball) were higher (p < 0.001) in S(N) than in S(R). S(ball) was significantly (p < 0.001) dependent on performance level, with higher values recorded in E than in B or I. From S(R) to S(N), increase in L(impact) was greater (p < 0.01) in E than in other groups and increases in Fz(max) and S(ball) were correlated (r = 0.69, p < 0.01) in E only. Knee motion is a significant contributor to serving effectiveness whatever the performance level. Skilled players perform faster serves than their less skilled counterparts, and this is partly related to a more forceful lower limb drive.     

Olfactory event-related potentials: older males demonstrate the greatest deficits

Olfactory event-related potentials (OERPs) were recorded monopolarly at the Fz, Cz, and Pz electrode sites in 16 young adults (8M/8F) and 16 older adults (8M/8F) with inter-stimulus intervals (ISI) of 45, 60 and 90 s using amyl acetate as the odorant stimulus. N1, P2, and N2 peak amplitudes and latencies were measured. Young participants demonstrated significantly shorter peak latencies than older participants. Older males demonstrated significantly smaller peak amplitudes than the other participant groups. Peak amplitudes also increased with longer ISIs for older males. The OERP is compared to traditional olfactory psychophysical testing.     

Origin of scalp far-field N18 of SSEPs in response to median nerve stimulation

To identify the origin of scalp-recorded far-field negativity of short-latency somatosensory evoked potentials to median nerve stimulation (designated N18), direct records were made from the thalamus and ventricular system during 4 stereotaxic and 3 posterior fossa operations.In the thalamus a negative potential with almost the same latency as the scalp N18 was restricted to the Vim nucleus, but there was a large positive potential in the VC nucleus and medial lemniscus. Vim negativity increased in amplitude when high frequency stimulation was given to the median nerve, indicative of a facilitation effect. In contrast, the amplitude of scalp N18 decreased at high frequency stimulus.Direct recordings made through the medulla oblongata to the mid-brain showed a negative potential with gradually increasing latency. Above the upper pons, there was stationary negativity with no latency shift. The similarity between this negative potential and N18 is shown by their having the same latency and same response to the amplitude reduction and latency prolongation produced by high frequency stimulus.Our data suggest that scalp N18 comes from brain-stem activity between the upper pons and the mid-brain rather than from the thalamus.