Sensory nerve somatosensory evoked potentials (SEP) in the evaluation of patients with sciatica: false P1 latency prolongation may be due to admixture of dermatomal SEP.

Patient-reported stimulus-related radiating sensory symptoms within the territory of the stimulated nerve have been used to verify stimulation in sensory nerve scalp recorded somatosensory evoked potentials (SEP). The main aim of the present study of false positive P1 latency prolongation in lumbosacral sensory nerve SEP was to investigate whether elicitation of such symptoms secures adequate sensory nerve stimulation. Nerve roots were studied on the asymptomatic side in 64 patients with unilateral sciatica. Saphenous (L4), superficial peroneal (L5), and sural (S1) nerve SEP were registered in all patients. Pretibial dermatomal SEP were registered in ten of them. Stimulation was equidistant from the registration electrode in all SEP registrations. The false positive rate was lower in saphenous nerve SEP with than without verified supramaximal stimulation (1/30 vs. 6/22, P = 0.03) in spite of radiating stimulus-related sensory symptoms in both groups. This difference was not caused by subclinical myelographic nerve root compression or general peripheral nerve dysfunction. The P1 latency was longer in the pretibial dermatomal SEP than in the saphenous and superficial peroneal nerve SEP with the same conduction distance (mean difference 4.7 (95% CI = 3.8 to 5.6) and 4.4 ms (95% CI = 3.4 to 5.4), respectively). It is concluded that dermatomal SEP have longer P1 latency than sensory nerve SEP. Verified supramaximal nerve simulation is recommended to avoid false results due to admixture of dermatomal to sensory nerve SEP.     

合并移行椎腰椎间盘突出症患者腰骶神经根支配区的变化

背景:腰骶移行椎是一种常见的先天脊柱畸形,国内外学者均有报道移行椎患者的腰骶神经根支配I区可能会发生改变,但并未系统阐述其支配区的变化以及该种改变对腰椎间盘突出症患者手术的指导意义。目的:探讨当存在腰骶移行椎时,腰骶神经根的运动和感觉支配区发生改变的可能性。方法:研究方案的实施符合滨州医学院附属医院对研究的相关伦理要求,参与试验的患病个体及其家属对试验过程完全知情同意。回顾分析321例单一节段腰椎间盘突出症行手术治疗患者的病历资料。其中38例(11.8%)存在腰骶移行椎,包括骶椎腰化26例、腰椎骶化12例。26例骶椎腰化患者中,23例为L5/S1(L6)椎间盘突出,压迫S1(L6)神经根。12例腰椎骶化患者中,8例为L3/4椎间盘突出,压迫L4神经根。在283例正常结构的患者中,138例患者L5/S1椎间盘突出压迫S1神经根,95例患者L4/L5椎间盘突出压迫L5神经根,47例患者L3/L4椎间盘突出压迫L4神经根。比较术前骶椎腰化患者S1神经根受压的症状、腰椎骶化患者L4神经根受压的症状与正常腰骶椎患者L4、L5或S1神经根受压的症状。结果与结论:(1)S1神经根受压所致运动功能减退的分布在骶椎腰化患者组和正常组之间差异有显著性意义(P<0.05);(2)L4神经根受压所致运动功能减退的分布在腰椎骶化患者组和正常组之间差异有显著性意义(P<0.05);(3)骶椎腰化患者S1神经根受压所致的运动功能减退与正常状态下L5神经根受压所致的运动功能减退相似;而腰椎骶化患者L4神经根受压所致的运动功能减退与正常状态下L5神经根受压所致的运动功能减退相似;皮肤感觉异常的分析也显示了相似的结果;(4)结果说明,腰骶神经根的功能在移行椎患者中发生改变,使得骶椎腰化患者的S1神经根起到L5神经根的通常功能(神经根功能上移),腰椎骶化患者的L4神经根起到L5神经根的通常功能(神经根功能下移)。     

Excitation and inhibition of motoneurones in the tortoise

1. Intracellularly recorded responses of lumbosacral motoneurones in the tortoise are described. The preparation was decerebrate and unanaesthetized. Cells were tested by stimulation of the main branches of the ipsilateral sciatic nerve.2. The distribution of cells according to resting membrane potential is given; highest recorded values were around 70 mV.3. The action potential has a step on the rising phase and has a total duration in the region of 4 msec.4. The motoneurone input resistance, measured by the spike height method, was 5-8 MOmega.5. Orthodromic excitation of motoneurones occurred after a central latency of 2 msec.6. Inhibition, and inhibitory (hyperpolarizing) potentials were demonstrated. Peak amplitude of maximum response was frequently greater than 10 mV. The potentials were influenced by injected currents in a manner resembling IPSPs in mammalian motoneurones. Minimum central latency for inhibitory potentials was about 3 msec.7. Membrane potentials and dimensions of action potentials for motoneurones in the cat are given for purposes of comparison with the tortoise.     

Influence of amygdala stimulation on the activity of identified tuberoinfundibular neurones in the rat hypothalamus.

1. Extracellular action potentials were recorded from 1246 neurones in the mediobasal hypothalamus of pentobarbitone or urethane anaesthetized male rats. Antidromic invasion from the surface of the median eminence identified 165 cells, located in the arcuate and ventromedial nuclei and the periventricular area, as tuberoinfundibular neurones. The majority (65%) of these cells displayed no spontaneous activity. 2. Latencies for antidromic invasion from median eminence ranged from 0-5 to 14-0 msec (mean 4-3 +/- 2-9 msec, S.D.). Conduction velocities for axons of tuberoinfundibular neurones were under 1-0 m/sec, and were slowest (under 0-2 m/sec) for those tuberoinfundibular neurones located in the arcuate nucleus. 3. Single 1 HZ stimulation of amygdala evoked short latency (mean 18-8 +/- 7-0 msec; n = 30) excitation of tuberoinfundibular neurones in the ventromedial nucleus. Stria terminalis stimulation evoked similar responses at a shorter latency (mean 10-2 +/- 3-5 msec; n = 12) from other ventromedial tuberoinfundibular neurones. Three of these neurones were also excited by amygdala stimulation at comparably longer latencies. In spontaneously active tuberoinfundibular cells, the initial excitation was followed by a decrease in excitability lasting 70-150 msec. Tuberoinfundibular neurones soldom followed orthodromic activation at frequencies beyond 30 HZ. 4. An initial decrease in activity at latencies of 18-40 msec (mean 29-2 +/- 10-2 msec) characterized the amygdala evoked responses from nine tuberoinfundibular neurones. A similar response from one other tuberoinfundibular neurone followed stria terminalis stimulation at a latency of 11 msec. Most of these tuberoinfundibular neurones were located in the dorsal part of the ventromedial nucleus. 5. Two ventromedial tuberoinfundibular neurones also displayed antidromic invasion from the amygdala; interaction studies suggested an axon collateral pathway that originated close to the origin of the axon. 6. Tuberoinfundibular neurones unresponsive to amygdala stimulation were usually located in the arcuate nucleus or periventricular area. 7. These results provide electrophysiological evidence for a direct influence of the amygdala on the activity of tuberoinfundibular neurones in the ventromedial hypothalamic nucleus. There are also data to indicate that some ventromedial tuberoinfundibular neurones have axon collaterals that return to the amygdala. These reciprocal connexions between the amygdala and ventromedial tuberoinfundibular neurones may indicate neural circuits important for extrahypothalamic modulation of adenohypophyseal secretion.     

Quantitative studies of intracellular postsynaptic potentials in the lateral geniculate nucleus of the cat with respect to optic tract stimulus response latencies

Summary LGN cells were intracellularly recorded with glass micropipettes. Electrical stimuli of different amplitude and frequency were applied to the optic tract close to the optic chiasm. The cells were classified according to stimulus response latencies of action potentials as belonging to class I (1.0–1.6 msec) or class II (1.7–3.0 msec).Class I EPSPs had shorter latencies (1.0–1.5 msec), durations (4–12 msec), rise times to peak (0.5–1.4 msec), and decay times (3.0–8.5 msec); the synaptic transmission time was on the average 0.41 msec. Class II EPSPs (1.6–2.6 msec latency) had longer durations (10–30 msec), rise times (1.6–3.7 msec), and decay times (9.0–25 msec); the synaptic transmission time was on the average 0.67 msec.With repetitive stimulation the EPSPs of latency class I revealed almost no stimulus frequency dependence between 1 and 120 Hz, while class II EPSPs decreased in amplitude between 30 and 70% with increasing frequency. Comparable temporal summation of excitation occurred in cells of both latency classes. Negative serial correlation coefficients of first order were found for consecutive EPSP amplitudes of all cells recorded for sufficient periods of time.The IPSPs were subdivided into two groups according to their optic tract response latency. Group 1 IPSPs had shorter latencies (2.0–2.6 msec), durations (15–50 msec), and times from the onset to maximal hyperpolarization (2.4–4.2 msec) than group 2 IPSPs (3.0–4.8 msec latency, 40–100 msec duration, 2.7–7.5 msec time from onset to extremum).The group 2 IPSPs decreased in amplitude by about 90% when the stimulus frequency was increased from 1 to 50 Hz, while the group 1 IPSPs displayed a comparable decrease in the frequency range between 50 and 120 Hz. Effective temporal summation was found in group 2 IPSPs in the frequency range below 70 Hz, and in group 1 IPSPs at stimulus frequencies between 70 and 120 Hz.The EPSP peak latencies and the latencies to the minimum of IPSPs proved to be invariant with respect to PSP amplitude and stimulus frequency in individual cells. The latencies to the extrema of EPSPs and IPSPs as well as the amplitude values were symmetrically distributed.     

腰椎术中高频电刀对皮节体感诱发电位的影响

目的：通过观察腰椎术中L5神经根减压后高频电刀使用后不同时间短潜伏期皮节体感诱发电位（DSEP）P40波潜伏期和波幅的变化,探讨高频电刀对皮节体感诱发电位（DSEP）的影响。方法：对36例单侧L5神经根压迫接受开窗手术患者,在术中进行受累神经根DSEP监测,观察并记录减压后使用高频电刀不同时间节点（使用前,电刀停止即刻、停止后5min及10min）的P40波潜伏期、波幅的数据,通过对照评价术中高频电刀对DSEP监测的影响。结果：与减压后（使用电刀前）相比,电刀停止后即时P40波潜伏期明显延长、波幅明显下降（P＜0．05）;停止后5min时P40波潜伏期、波幅无明显恢复（P＜0．05）;10min时,潜伏期和波幅变化无显著差异（P＞0．05）。结论：在术中高频电刀的使用将影响DSEP的监测结果,应在电刀停止10min后记录波形才准确。     

Influence of medial preoptic-anterior hypothalamic area stimulation of the excitability of mediobasal hypothalamic neurones in the rat.

1. Extracellular action potentials recorded from 798 neurones in the mediobasal hypothalamus (MBH) of pentobarbitone anaesthetized male rats were analysed for a change in excitability following stimulation in the medial preoptic and anterior hypothalamic areas. 2. An increase in excitability characteristic of orthodromic excitation was observed from 11-5% (n=92) of MBH neurones. Latencies for excitation were shorter for cells tested with anterior hypothalamic area stimulation (n=42; mean 5-4 +/- 2-6 msec S.D.) than for cells tested with medial preoptic stimulation (n=50; mean 15-2 +/- 7-2 msec S.D.). With spontaneously active neurones, excitation was followed by a decrease in excitability lasting 150-250 msec. An initial decrease in excitability, suggestive of post-synaptic inhibition, over a wide latency range (4-30 msec) and with duration of 100-400 msec was observed from 3-6% of MBH neurones. 3. Features of antidromic invasion were observed from 149 MBH neurones. From the medial preoptic area, the latency range was 0-5-38 msec (mean 7-8 +/- 5-5); from the anterior hypothalamic area the latency range was 0-4-9-5 msec (mean 3-1 +/- 2-3). Occasionally an abrupt decrease in latency followed an increase in stimulus intensity. Most cells followed paired stimuli at frequencies up to 500 Hz. Axon conduction velocities were estimated to be under 2-0 m/sec. Antidromic invasion was usually followed by a decrease in excitability lasting approximately 100-150 msec. 4. Twenty MBH neurons displayed antidromic invasion from both the medial preoptic or anterio hypothalamic areas and one other stimulation site: the median eminence (five cells); the amygdala (six cells); the region of thalamic nucleus medialis dorsalis (three cells) and the midbrain periaqueductal gray (six cells). Interaction studies indicated that the axons of these cells branched close to the origin of the axon itself. 5. Antidromic invasion from the surface of the median eminence identified thirty-nine tuberoinfundibular neurones. Stimulation in the medial preoptic and anterior hypothalamic area produced orthodromic excitatory (n = 5) and inhibitory (n = 4) actions on HVM neurones, but was without an action on most other neurones (n = 30). Tuberoinfundibular neurones in the ventromedial nucleus also responded to stimulation in the amygdala, but usually at latencies greater than that for medial preoptic area evoked responses. 6. These observations indicate a close relationship between MBH neurones and cells located in both the amygdala and the medial preoptic-anterior hypothalamic area. The data for tuberoinfundibular neurones indicates that several extrahypothalamic areas may send fibres to these cells. These pathways may be important for the adaptive neuroendocrine responses reported in the literature.     

Dural ectasia in children with Marfan syndrome: a prospective, multicenter, patient-control study

The clinical diagnosis of Marfan syndrome in childhood is difficult, because symptoms may not have developed to their full expression until adulthood. The Ghent nosology for the diagnosis of Marfan syndrome classifies dural ectasia as a major diagnostic criterion. More than two thirds of adult patients with Marfan syndrome show dural ectasia, while the frequency in childhood is unknown. This prospective multicenter observational patient-control study was performed to identify pathologic changes of the lumbosacral spine in young patients with Marfan syndrome. Design: Prospective clinical trial, multicentric, cross-sectional. Setting: MRI of the lumbosacral spine. Patients: Twenty patients with proven Marfan syndrome, 20 patients suspicious for Marfan syndrome and 38 healthy controls. Outcome measures: Vertebral body diameter (VBD) from L1 to S1, dural sac diameter (DSD) from L1 to S1, dural sac ratio (DSR), qualitative assessment of the lumbosacral spine. Results: DSD and VBD in different age groups were higher in patients with proven or suspected Marfan syndrome than in healthy controls (DSD: L1, 6-8 years, P < 0.05). VBD related to body height showed a similar growth related increase in patients with proven or suspected Marfan syndrome and controls. DSD related to body height was elevated in patients with proven or suspected Marfan syndrome at different levels of the lumbar spine. DSD at levels L1, L5, and S1, and DSR at levels L5 and S1 of patients with proven Marfan syndrome were significantly higher (P < 0.05) than in controls. Conclusion: Even during childhood pathologic changes inside the lumbosacral spine of patients with Marfan syndrome can be observed. Dural ectasia, which occurs at different levels of the lumbar spine, can be detected at levels L5 and S1 in up to 40% of patients with Marfan syndrome.     

Synaptic linkage in the vestibulo-ocular and cerebello-vestibular pathways to the VIth nucleus in the rabbit

Summary Intra- and extra-cellular responses were recorded with glass microelectrodes from motoneurons in the VIth cranial nuclei of anesthesized rabbits. VIth nucleus motoneurons were identified by their antidromic activation from the VIth nerve. In these motoneurons stimulation of the ipsilateral VIIIth nerve produced IPSPs with disynaptic latencies (mean and S.D., 1.08 ± 0.1 msec) while stimulation of the contralateral VIIIth nerve produced EPSPs with disynaptic latencies (mean and S.D., 1.20 ± 0.18 msec). Correspondingly, direct stimulation of the ipsilateral medial vestibular nucleus (MV), produced IPSPs with monosynaptic latencies (mean and S.D., 0.61±0.15 msec) while direct stimulation of the contralateral MV produced EPSPs with monosynaptic latencies (mean and S.D., 0.61±0.09 msec). Further, with the recording electrode placed within the VIth nucleus to observe the extracellular potentials corresponding to the intracellularly recorded IPSPs and EPSPs, the medulla was systematically tracked with a monopolar stimulating electrode. It was demonstrated that the inhibitory relay cells could be effectively stimulated in the rostral half of the ipsilateral MV and the excitatory relay cells in the rostral half of the contralateral MV.Pharmacological investigation suggested that the inhibitory transmitter involved in the vestibular inhibition is gamma amino-butyric acid or a related substance.Electric stimulation of the flocculus produced a prominant depression in the inhibitory vestibulo-ocular reflex pathway to the VIth nucleus, while the excitatory pathway was free of any similar flocculus inhibition.     

F-wave latencies of the deep peroneal nerve in diabetic polyneuropathy

The F-wave latency of the deep peroneal nerve in function of leg length was determined in 66 normal persons and 25 diabetic patients with known polyneuropathy. The latencies were measured by stimulating the nerve at the ankle and recording the F-wave at the musculus extensor digitorum brevis using a needle electrode. The leg length was represented by the distance between the spina iliaca anterior superior and the lateral malleolus. The F-wave latencies obtained in diabetic patients were significantly higher than in controls (p less than 0.01). The method is suitable to detect polyneuropathy, especially in early cases where the conventional techniques (determination of the motor and/or sensory latencies and/or conduction velocities at the lower limbs) may still yield normal or borderline values. The upper limits of the normal values of the F-wave latencies in function of leg length is given by a non-linear curve, which can be represented by the equation: F-wave latency (msec) = 14.7 + 47.5 x (leg length in m)2. For practical purposes, the upper limit of the normal value for a given leg length can be readily determined from a latency-length curve.     

Changes in latency and duration of neural responding following developmental auditory deprivation

Summary The initial latency of spikes evoked by click stimulation and the duration over which spiking occurred were observed in the inferior colliculi of rats. One ear of these animals had been deprived of early auditory stimulation by ligation of the external meatus. Clicks presented to the normally experienced ears evoked spikes in the opposite colliculus with latencies that depended on the characteristic frequency of the unit. Low-frequency (< 5 kHz) units had latencies from 6–10 msec. Latencies declined to 3–4 msec for high frequency (> 20 kHz) units. After an ear had been deprived of sound from 10 days after birth, response latencies of units in the opposite colliculus with characteristic frequencies below about 10 kHz were comparable to controls, but most units above 10 kHz had latencies 2–3 times control latencies. Spike activity evoked in these units did not continue as long as that for most comparable control units. Ears sound deprived for an equal period from 60 days after birth also had changes in latencies and response durations, but these were much less than in the developmentally deprived. Latencies of gross potentials at the auditory nerve were not affected by early deprivation, indicating a central origin for the latency changes.This work was supported by NIH Grant NS-13052     

A comparison of the responses of frog skin receptors to mechanical and electrical stimulation

1. The latencies of spike responses evoked alternatively by brief mechanical (M) and electrical (E) pulses applied to single mechanoreceptive terminals in frog skin were compared on the same receptor.2. Latency was found to be a maximum at threshold and to decrease with increased stimulus strength for both modes of excitation, but at all strengths M latency exceeded E latency. Mean maximum and minimum values for M latency were 4.8 and 2.85 msec; for E latency the maximum was 2.8 and minimum 2.3 msec.3. At high frequency and strength of E stimulation there was an abrupt and marked shortening of latency to a fixed minimum value which ranged from 0.5 to 1.2 msec (mean 0.8). This was taken to be the response of the parent myelinated axon excited directly. The gap (1.5 msec) between the minimum value for the receptor response (2.3 msec) and the axonal response (0.8 msec) was taken to represent conduction time in the terminal branches of the sensory axon.4. The response latency for excitation of the sensory terminal was also dependent on the duration of the stimulus pulse, but whereas the latency range for the M stimulus could be greatly extended that for the E stimulus was only slightly affected by increase in pulse duration.5. The responses evoked by direct currents were complex, and consisted of an early brief discharge at the start of a cathodal current followed after a delay of 5-30 sec by a prolonged multi-fibre discharge which out-lasted the stimulus. It is proposed that the sensory terminal is rapidly accommodating to current flow and that the delayed discharge is due to release of chemical material.6. It is suggested that delay in mechanical excitation may be due to non-rigid coupling of the receptor terminal to the skin tissues.     

The anatomical relationship of the iliocava junction to the lumbosacral spine and the aortic bifurcation

This study dissected 42 cadavers to investigate the level of the iliocava junction and the relationship with the lumbosacral spine and the aortic bifurcation. The iliocava junction was between L4 and S1, most often at the level of L5 (64%) and on the median third of the spine (55%). The average height of the iliocava junction was 15.5 mm. The mean interiliac angle was 69°. It was not related to the width of the iliocava junction. The iliocava junction covered the whole of the L5-S1 disc in 12% of cases. The iliocava junction was located above the aortic bifurcation only in 1 case. The mean distance between iliocava junction and aortic bifurcation was 19 mm. The variability of the iliocava confluence is high and complicates the anterior approach to the lumbosacral spine.     

A study of binocular convergence in cat visual cortex neurons

Summary The average latency of cortical neuronal responses to electrical optic nerve (ON) stimulation was 3.0±0.7 s.d. msec. No significant difference between latencies to ipsi- and contralateral ON stimulation was found. Binocularly excitable cells showed almost equal response latencies to stimulation of both nerves. The average latency of subcortically recorded geniculo-cortical fibers was 0.3 msec less, but showed the same variance as that of cortical cells, suggesting that in all cases direct monosynaptic excitation of cortical cells by fibers of either ocularity is possible. Classes of ocular dominance based on electrical stimulation were positively, but not 100% correlated with classes of ocular dominance to visual stimulation. An anatomical study revealed that in cat terminals of geniculo-cortical projection are segregated to a lesser degree into ocularity stripes than in monkey. Direct monosynaptic excitation of cells by fibers of either ocularity which was found physiologically would also on these grounds appear possible for all cells.A preliminary report has been presented at the 46th German Physiological Society Meeting in Spring 1976, Pflügers Archiv, Vol. 362, Abstract No. 155, 1976     

Trunk-ocular reflex in the rabbit

The trunk-ocular reflex of the rabbit was investigated by recording EMGs of right lateral rectus and splenius muscles. The skull and the chest of the rabbit were restrained and the lower part of the trunk was flexed laterally around the axis at the TH10--11 intervertebral joint. Two kinds of eye movements, small with short latencies and large with longer latencies, were induced counter to the direction of the lateral flexion. The latency of the former was 158 msec (range: 64--200 msec) and that of the latter was 255 msec (range: 180--380 msec).     

Auditory event-related potentials (ERPs) in healthy subjects and patients with dementia

To study the effects of aging and gender differences of ERP components, auditory ERPs were recorded in 106 healthy subjects. Forty-three patients with dementia of the Alzheimer type and 24 patients with vascular dementia were also studied. In healthy subjects, there was a significant positive linear correlation between P300 latency and age, with P300 latency increasing at the rate of 1.5 msec/year. Neither N100 nor P200 component was correlated with age. The amplitudes of N100, P200 and P300 components in females were slightly larger than those in males, but the differences were not significant. Not only P300 latencies but also P200 latencies were significantly different in healthy subjects, patients with dementia of the Alzheimer type and those with vascular dementia. In 74.4% of patients with dementia of the Alzheimer type and 62.5% of those with vascular dementia, the P300 latency was over 2 SE above the age-estimated regression line. The difference of the P300 latency prolongation may have resulted from the severity of dementia but not from the etiology of dementia.     

222例腰骶移行椎影像学形态特点及其临床意义

目的：探讨腰骶移行椎的影像学形态特点,为腰椎间盘突出症、腰椎滑脱症的诊治提供参考。方法：对临床及影像资料完整的腰骶移行椎222例,根据横突形态特点,按Castellvi法进行分类,并对病变节段进行分析。结果：Ⅰ型79例,占35．6％,其中L4～5突出8例,L5～S1突出15例,L4峡部裂、滑脱3例;Ⅱ型51例,占23％,其中L4～5,突出20例,L3～4突出4例,L4峡部裂、滑脱12例;Ⅲ型80例,占36％,其中L4～5,突出38例,L4峡部裂12例,L3～4突出3例;Ⅳ型9例,占4．1％,其中L4～5突出4例;特殊类型3例,占1．3％,均为L4～5突出。结论：Ⅰ型移行椎L4-5,L5～S1均可能发生腰椎间盘突出症,与正常腰椎无明显区别,Ⅱ、Ⅲ、Ⅳ型只发生L4～5和L3～4节段腰椎间盘突出,而不发生L5～S1椎间盘突出,即移行椎以上的节段可发生病变。本组中没有L5部裂及滑脱病例,均为L4峡部裂和L4～5以上节段滑脱,据此提出了腰骶移行椎的特殊类型,即单纯椎间融合型。     

The anatomical relationship of the aortic bifurcation to the lumbar vertebrae: a MRI study

The objective of this study was to determine the level of the aortic bifurcation in relation to the lumbar spine by MRI and the effect of lumbosacral anomalies on the aortic bifurcation. A prospective study of 441 patients was performed. Sagittal MR images of the entire spine were obtained along with the standard protocol for imaging of the lumbar spine. The vertebrae were counted caudally from C2 instead of cranially from the presumed L5 vertebra. The aortic bifurcation in relation to the lumbar vertebrae was determined. The aorta bifurcated at the L4 vertebral body in 67% of cases. In patients with sacralization of L5 the aortic bifurcation was at the L3 vertebral body in 59%. In those patients with lumbarization of S1 the aorta bifurcated at the level of the L4 vertebral body in 40% and at the L4/5 disc space in 33%. There was no demographic variation of the aortic bifurcation in relation to age or sex. The aorta bifurcated at L4 in two-thirds of cases and was variably located in the remaining third. The stability of this as a landmark is disturbed by the significant high incidence of lumbosacral transitional segments.     

Synaptic actions on mitral and tufted cells elicited by olfactory nerve volleys in the rabbit.

1. A unitary study has been carried out of mitral and tufted cell responses to olfactory nerve volleys in the olfactory bulb of rabbits lightly anaesthetized with urethane-chloralose. 2. With volleys of different strengths, some mitral cells responded with a spike whose latency decreased considerably as the strength increased (elastic response); other cells responded at an invariant latency (inelastic response). The former may reflect diffuse olfactory nerve inputs to the dendritic tufts in the olfactory glomeruli, while tha latter may reflect input from discrete bundles of fibres. 3. The shortest spike latencies are consistent with monosynaptic excitation by the olfactory nerves; longer latencies may be due to longer pathways through the nerves, or polysynaptic pathways within the glomerular layer. 4. Facilitation, in terms of lower threshold and shorter spike latency, was found when testing with paired volleys of weak intensity at relatively short intervals (less than 40 msec). Suppression, in terms of raised threshold, longer latency and briefer repetitive discharges, was found at intervals up to several hundred msec. The facilitation and suppression are consistent with the hypothesis of synaptic excitation and inhibition, respectively, mediated through interneurones in the olfactory bulb. 5. Presumed tufted cells were similar in response properties to identified mitral cells. 6. Intracellular recordings revealed long-lasting hyperpolarization and in some cases, an initial depolarization leading to spike initiation, in response to an olfactory nerve volley.     

Comparative threshold studies of the acoustic pinna, jaw and startle reflex in the rat

Electromyograms of M. Levator auris and M. Temporalis and movement produced by whole body startle were recorded simultaneously in awake, freely moving rats. Thresholds were 78 db SPL for the L. auris, 80 dB SPL for the ballistic and 81 dB SPL for the Temporalis. The rank ordering of the three thresholds was extremely strict, 188 suprathreshold M. L. auris responses could be observed without M. Temporalis responses, but only once was a M. Temporalis response observed without a M. L. auris response. Thresholds as well as amplitudes and latencies measured by the different methods show correlated fluctuations. While the rise in amplitude which accompanies increasing stimulus intensity is similar in the three measures, the latency decrease is not. The latency difference between M. Temporalis EMG and M. L. auris EMG is intensity dependent, increasing from 0 msec at 78 dB SPL to 1.1 msec at 115 dB SPL, with a faster response for the M. L. auris.