Football-related maxillofacial injuries

Maxillofacial injuries sustained playing sports are becoming increasingly common, and in the UK where football is the most popular team sport, associated maxillofacial injuries are a regular occurrence. This study retrospectively examined data on patients who were referred with facial injuries sustained playing football between 2007 and 2019 (n = 265). Demographics, mechanism of injury, diagnosis, and treatment received were analysed. The mean (SD) age was 25 (11.0) years (range 3-85) and there was a strong male predominance (n = 256, 97% male). Facial fractures were diagnosed in 143 (54%) patients. The most common injury was a midface fracture and the most common mechanism of injury was a clash of heads. Patients with a facial fracture were significantly more likely to have sustained a concurrent head injury (p = 0.006). Those who were elbowed or punched were significantly more likely to have a facial fracture than a soft tissue or dentoalveolar injury (p ≤ 0.05). Players who clashed heads were significantly more likely to have a midface fracture (p ≤ 0.001). In conclusion, football-related maxillofacial injuries predominantly affect young adult males following a clash of heads. An elbow or punch to the face carries a significant risk of facial fracture and concurrent head injury. Therefore, to reduce the percentage of maxillofacial injuries seen in this sport, observed intentional contact between players, using an elbow or fist to the face in particular, must continue to carry the highest sanction.

Merkel cell carcinoma of the head and neck in the south-east of England

Merkel cell carcinoma (MCC) is a rare and highly aggressive neuroendocrine malignancy of the skin. Its incidence is increasing with half of cases involving the head and neck. To the best of our knowledge, few large studies have been published in the UK, and to date this is the largest reported series of head and neck MCC. We retrospectively reviewed the outcomes of patients with MCC in three hospitals in the south-east of England over a 12-year period (2008-2019). Diagnosis was based on histological data following biopsy. Overall survival and disease-specific survival were calculated using Kaplan-Meier and log-rank tests. Fifty-eight patients met the inclusion criteria (24 stage I, 22 stage II, 9 stage III, and 3 unclassified). Median disease-free survival was 36 months (95% CI 0 to 77.2) and median overall survival 50 months (95% CI 29.9 to 70). Overall five-year survival was 34.4% (95% CI 17% to 52%) with two-year survival at 62% (95% CI 48% to 76%). Five-year disease-free survival was 26.7% (95% CI 17 to 52%) with two-year disease-free survival at 54% (95% CI 40% to 68%). To date, this is the largest UK based study reporting overall and disease-free survival associated with MCC of the head and neck. Half the patients presented late, and surgery was the mainstay of treatment, augmented by adjuvant radiotherapy. There is a need to better stratify patients at risk of developing metastatic disease, with the use of sentinel lymph node biopsy and positron-emission tomography-computed tomography (PET-CT), as immunotherapy and targeted agents are now available to treat advanced disease.

Operative time, length of stay and reoperation rates for orthognathic surgery

Orthognathic surgery improves quality of life in terms of oral function and facial aesthetics. Our aim was to establish and compare operative time and length of inpatient stay for orthognathic procedures, and to assess the reoperation rate. Departmental electronic data base was used to identify all patients undergoing orthognathic surgery in a single unit between the 01/01/2016 and the 01/08/2018. 251 patients were identified who underwent 409 orthognathic surgery procedures. The mean operating time for a bimaxillary osteotomy (n=107) was 139.3 min. For single jaw procedures, the mean operating time for a Le Fort I osteotomy (n= 42) was 82.2 min and for a bilateral sagittal split osteotomy (BSSO) (n= 102) was 80.3min. Bimaxillary osteotomy combined with genioplasty (n=17) this increased the operating time on average by 31 min. and of a BSSO combined with a genioplasty (n=14) by 27 mins. The mean postoperative hospital stay was 1.2 ± 0.2 days. 96.4% patients spent only one postoperative night in hospital. 6/251 (2.4%) patients required re-operation. In regression analysis, age was the only significant factor in increasing length of stay (p<0.008), 95% CI 0.03-0.2). Our review shows short operating times and postoperative inpatient stays in a large cohort of patients undergoing orthognathic surgery. This is combined with a low reoperation rate. This may point to a patient benefit from high volume orthognathic centres.

Process mapping and Lean principles applied to orthognathic surgery

Process mapping in industry is a well-established tool to improve efficiency. It is defined as a quality improvement technique that breaks down a process, or task, into its individual components, or steps, then analyses it. Lean principles are used to reduce waste and produce consistently good outcomes. Improving the operative efficiency of orthognathic surgery has many benefits. There is increasing demand for this complex surgery, and patients have appropriately high expectations with relation to their outcome. There are also increasing pressures for hospitals to reduce costs. In a recent paper by our group (Bowe et al, in press), we have published operating times for orthognathic procedures that are significantly shorter than in previously available series, with an average time for a bimaxillary osteotomy of 2 hours and 19 mins. Through observation of the senior authors' uniform technique, refined from experience of over 2,000 cases, a bimaxillary osteotomy was broken down into individual steps, all arranged in a process-mapped template with which to increase efficiency and results. We show here the multiple small operative efficiencies we have developed, and the Lean surgical principles which we use. This has enabled us to reduce the operative time of these common procedures, without compromising outcomes. This study presents an approach to process map bimaxillary orthognathic operations and shows how the application of Lean principles improves operative efficiency, and produces consistent results.

Pleomorphic dermal sarcoma: a clinical and histological review of 49 cases

Pleomorphic dermal sarcoma (PDS) is a rare mesenchymal neoplasm that shares histopathological features with atypical fibroxanthoma (AFX), but has additional features of deep invasion of the superficial subcutis, tumour necrosis, and vascular and perineural invasion, which confers a risk of local recurrence and metastases. To study the clinical and pathological spectrum more comprehensively, we retrieved 49 cases of pleomorphic dermal sarcoma from our departmental files. There was a strong male predominance (n=45). The mean (range) age at presentation was 80 (47-97) years. The tumours had a median (range) maximum dimension of 23.5 (5-75) mm. There was a strong predilection for the head and face (n=47), with the scalp (n=32) being the most common site. Ulceration was observed in 21 patients, tumour necrosis in seven, perineural infiltration in six, and lymphovascular invasion in two. CD10 was expressed in all cases. Smooth muscle actin was expressed in 15 and CD68 in 14. Follow up was available in 41 cases (mean (range) 22.4 (2-90) months). Six patients had local recurrences, despite all having originally undergone primary surgical resections and having reports of clear margins. Progressive metastatic disease was observed in one patient who died from their disease. Based on the Kaplan Meier method, median overall survival was 70.8 (8.4-133.1) months. Although AFX and PDS may be part of a spectrum, distinction is important to emphasise the potential for malignant behaviour in PDS.

Challenges and outcomes in establishing a sentinel lymph node biopsy service for oral squamous cell carcinoma in a regional district specialist hospital

UK national guidelines in 2016 recommended that sentinel lymph node biopsy (SLNB) should be offered to patients with early oral squamous cell carcinoma (OSCC). We review the establishment of an OSCC SLNB service with specific consideration to resources, service implications and patient outcomes. A review of processes was performed to identify key stages in establishing the service, and subsequently a retrospective cohort study consisting of 46 consecutive patients with T1/T2 N0 OSCC was undertaken. The key stages identified were: coordinating a nuclear medicine pathway and reliable cost-appropriate pathology service, constructing a Trust business case, and gaining approval of a new interventional service policy. A median (range) of 3.3 (1-8) sentinel nodes (SLN) were removed, with 17 patients having a positive SLN. The negative predictive value of SLNB was 100%, with 12 having a SLN outside the field if elective neck dissection (END) was planned. There was a significantly increased risk of a positive SLN with increasing depth of invasion (DOI) (p=0.007) and increased diameter (p=0.036). We also identified a longer-than-ideal time to completion neck dissection and inadequate ultrasound follow up of negative SLNB patients. Establishment of a service requires careful planning. Our results were in keeping with those reported in the literature, and showed that SLNB for OSCC has a high negative predictive value and can identify at-risk SLN outside the traditional END levels, even in well-lateralised tumours. Our findings show that DOI and size of SLN were significantly associated with a positive SLN, and also identified areas requiring improvement.

Comparison of the eighth edition of the TNM and Brigham Women's Hospital staging systems for cutaneous squamous cell carcinoma of the head and neck: a six-year review

This study was undertaken with the aim to compare the T stages in a series of cutaneous squamous cell carcinoma (cSCC) patients using both the eighth edition of the Union for International Cancer Control (UICC) TNM Classification of Malignant Tumours (TNM8) and Brigham and Women's Hospital (BWH) staging systems. This would allow comparison of the two to determine suitability with regards to T stage and the effect on local recurrence and nodal disease. This was a six-year retrospective cohort study of patients with primary invasive cSCC of the head and neck who were diagnosed and treated at Western Sussex Hospitals Trust in the United Kingdom between 2007 and 2012. The TNM8 and BWH staging systems were applied to these primary cSCCs. A total of 695 invasive cSCCs treated in 604 patients over six years were identified. Most patients were male (76%), with a mean (range) age of 81 (50-103) years. The most common location for local recurrence was the scalp (n=26, 58%). Regional metastasis occurred most commonly in the parotid gland (n=20, 63%). All tumours were classified using both staging systems. Specifically, 432 tumours remained in the same T stage (61%), and 192 were downstaged (27%) and 71 upstaged using the BWH (10%). The median (SD) follow-up time was 23 (28) months (range 1-123). The BWH alternative staging system overlapped with the TNM8 in high-stage and low-stage tumour assignment. The highest percentage of local recurrence and regional metastasis occurred in T2b tumours.

Management of regional metastatic disease in cutaneous malignancy of the head and neck. 3. Merkel cell carcinoma

This is the third of three articles that give an overview of the current evidence for management of the neck and parotid in patients with cutaneous cancers of the head and neck. In this paper we discuss Merkel cell carcinoma (MCC) and review the latest evidence for management of the regional nodes.

Presynaptic congenital myasthenic syndrome due to quantal release deficiency

OBJECTIVE

To provide clinical, electrophysiologic, and ultrastructural findings in three patients with a presynaptic congenital myasthenic syndrome (CMS).

BACKGROUND

Familial infantile myasthenia and paucity of synaptic vesicles are the only two fully characterized CMS. We are describing here three patients with another form of presynaptic CMS characterized by deficiency of the action potential-dependent release without reduction of the spontaneous release of neurotransmitter from the nerve terminal.

METHODS

The authors performed electromyography and anconeus muscle biopsies that included intracellular recordings and electron microscopy of the neuromuscular junction in three patients with presynaptic CMS. They also sequenced part of the P/Q-calcium alpha(1)-subunit gene (CACNA1A) and the acetylcholine receptor subunit (AChR) genes in these patients.

RESULTS

In these patients there were additional neurologic findings including nystagmus and ataxia. In all three patients the end-plate potential quantal content (m) was markedly reduced but neither the amplitudes nor the frequencies of miniature end-plate potentials were diminished. Ultrastructurally, postsynaptic end-plate folds, nerve terminal size, and synaptic vesicle number were normal but double-membrane-bound sacs containing synaptic vesicles were present in the nerve terminal of all three patients. The screening of reported pathogenic mutations in the CACNA1A and a mutational analysis of AChR subunit genes were negative.

CONCLUSION

This form of CMS appears to result only from a deficiency of the quantal release of neurotransmitter that may be due to an abnormal calcium mechanism or impaired endocytosis and recycling of synaptic vesicles.

D-2-Hydroxyglutaric aciduria: biochemical marker or clinical disease entity?

D-2-Hydroxyglutaric aciduria has been observed in patients with extremely variable clinical symptoms, creating doubt about the existence of a disease entity related to the biochemical finding. An international survey of patients with D-2-hydroxyglutaric aciduria was initiated to solve this issue. The clinical history, neuroimaging, and biochemical findings of 17 patients were studied. Ten of the patients had a severe early-infantile-onset encephalopathy characterized by epilepsy, hypotonia, cerebral visual failure, and little development. Five of these patients had a cardiomyopathy. In neuroimaging, all patients had a mild ventriculomegaly, often enlarged frontal subarachnoid spaces and subdural effusions, and always signs of delayed cerebral maturation. In all patients who underwent neuroimaging before 6 months, subependymal cysts over the head or corpus of the caudate nucleus were noted. Seven patients had a much milder and variable clinical picture, most often characterized by mental retardation, hypotonia, and macrocephaly, but sometimes no related clinical problems. Neuroimaging findings in 3 patients variably showed delayed cerebral maturation, ventriculomegaly, or subependymal cysts. Biochemical findings included elevations of D-2-hydroxyglutaric acid in urine, plasma, and cerebrospinal fluid in both groups. Cerebrospinal fluid gamma-aminobutyric acid was elevated in almost all patients investigated. Urinary citric acid cycle intermediates were variably elevated. The conclusion of the study is that D-2-hydroxyglutaric aciduria is a distinct neurometabolic disorder with at least two phenotypes.

Functional properties and nodal spacing of myelinated fibers in developing rat mental and sural nerves

While the postnatal length growth of the largest internodes in the rat sural nerve (SN) is proportional to nerve elongation, in the developing inferior alveolar nerve (IAN), early postnatal myelin sheath remodelling allows internodal lengthening to exceed the growth rate of the whole nerve. To assess the functional consequences of ongoing myelin sheath remodelling in a developing nerve, we examined the physiological properties of the mental nerve (MN), a cutaneous IAN branch and the SN during maturation. In addition, the nodal spacing and the microscopic anatomy of the nodes in the two nerves were studied. The youngest MNs and SNs (2 weeks) exhibited comparable sensitivities to K(+)-channel blockade with 4-aminopyridine (4-AP), although myelin sheath remodelling was more frequent in the MNs. Subsequently, myelin sheath remodelling ceased in both nerves but the MNs exhibited a greater sensitivity to 4-AP. Large fibers in adult MNs and SNs had a similar nodal anatomy but the former had shorter internodes. Thus, myelin sheath remodeling, per se, does not appear to be a determinant of 4-AP sensitivity in mammalian myelinated fibers. Rather, sensitivity to potassium channel blockade is more likely mediated at the internodal or molecular level.

Delayed depolarization and slow sodium currents in cutaneous afferents

1. Intraaxonal recordings were obtained in vitro from the sural nerve (SN), the muscle branch of the anterior tibial nerve (ATN), or the deafferented ATN (dATN) in 5- to 7-wk-old rats. Whole-nerve sucrose gap recordings were obtained from the SN and the ATN. This allowed study of cutaneous (SN), mixed motor and muscle afferent (ATN), and isolated muscle afferent (dATN) axons. 2. Application of the potassium channel blocking agent 4-aminopyridine (4-AP) to ATN or dATN resulted in a slight prolongation of the action potential. In contrast, a distinct delayed depolarization followed the axonal action potential in cutaneous afferents (SN) exposed to 4-AP. The delayed depolarization could be induced by a single whole-nerve stimulus or by injection of constant-current depolarizing pulses into individual axons. The delayed depolarization often gave rise to bursts of action potentials and was followed by a prominent afterhyperpolarization (AHP). 3. In paired-pulse experiments on single SN axons, the recovery time (half-amplitude of the action potential) was 3.06 +/- 1.82 (SE) ms (n = 12). After exposure to 4-AP the recovery time of the delayed depolarization was considerably longer (half-recovery time: 99.0 +/- 28.3 ms; n = 15) than that of the action potential (18.8 +/- 9.1 ms; n = 16). 4. Application of tetraethylammonium (TEA) to cutaneous or muscle afferents alone had little effect on single action potential waveform. However, TEA reduced the amplitude of the AHP elicited by a single stimulus in cutaneous afferent axons after exposure to 4-AP and resulted in repetitive spike discharge. 5. The delayed depolarization and spike burst activity induced by 4-AP in SN was present in Ca(2+)-free solutions containing 1 mM ethylene glycol-bis (beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid and was not blocked by Cd2+ (1.0 mM). 6. We obtained whole-cell patch-clamp recordings to study Na+ currents from either randomly selected dorsal root ganglion neurons or cutaneous afferent neurons identified by retrograde labeling with Fluoro-Gold. The majority of the randomly selected neurons had a singular kinetically fast Na+ current. In contrast, no identified cutaneous afferent neurons had a singular fast Na+ current. Rather, they had a combination of kinetically separable fast and slow currents or a singular relatively slow Na+ current.(ABSTRACT TRUNCATED AT 400 WORDS)

Different effects of 4-aminopyridine on regenerated cutaneous and muscular rat sciatic nerve branches

Developing and regenerated myelinated rat dorsal and ventral root fibers respond differently to the fast potassium channel blocking agent 4-aminopyridine (4-AP). To pursue this issue further, we made unilateral sciatic nerve crushes in adult rats. Sural (SN) and lateral gastrocnemius (LGN) nerve branches were collected 4-6 months later, for physiological and morphological examination. Regenerated and control nerves in Ringers solution showed generally similar compound action potential (CAP) waveforms, but CAPs of regenerated SNs and LGNs in 4-AP were markedly different. While regenerated SNs showed a prominent late CAP negativity with a "rippled" appearance and markedly compromised recovery properties, the CAP and recovery properties of regenerated LGNs were minimally changed. Light and electron microscopic examination of SN and LGN fibers failed to reveal any features obviously related to the observed physiological differences. We conclude, that the effect of 4-AP on regenerated cutaneous afferents differs from its action on regenerated muscular afferents and efferents. This physiological diversity lacks obvious structural correlates.

Gastrointestinal hemorrhage associated with gastric polyps in Menkes disease

We describe two infants with Menkes disease who had serious gastrointestinal bleeding from solitary gastric polyps. Hemorrhage in one patient was acute and proved fatal. Histopathologic examinations showed submucosal vascular ectasia with mucosal hyperplasia, edema, and ulceration. Gastric polyps may represent an underappreciated clinical abnormality in Menkes disease.

Progressive morphological abnormalities observed in rat spinal motor neurons at extended intervals after axonal regeneration

It is generally accepted that mammalian spinal motor neurons return to normal after axotomy if their regenerated axons successfully reinnervate appropriate peripheral targets. However, morphological abnormalities, recently observed in spinal motor neurons examined 1 year after nerve crush injury, raise the possibility that delayed perikaryal changes occur after regeneration is complete. In order to distinguish between chronic and progressive alterations in neurons with long-term regenerated axons, rat spinal motor neurons and dorsal root ganglion cells were examined at 5 and 10 months following unilateral sciatic nerve crush. Neurons with regenerated axons were identified by retrograde labelling with horseradish peroxidase. The structural properties of neurons ipsilateral to nerve injury were compared to those of neurons from the spinal cord and dorsal root ganglia on the contralateral side and from age-matched control rats. At 5 months postcrush, the morphology of motor and sensory neurons ipsilateral to injury was comparable to that of control cells. However, several features of the motor neurons with regenerated axons distinguished them from control motor neurons at 10 months postcrush. Mean perikaryal area of ipsilateral spinal motor neurons was larger than the means for control motor neurons (p less than .001). Ipsilateral spinal motor neurons also appeared clustered within the spinal cord and had thicker dendrites. Dorsal root ganglion cells with regenerated axons were slightly larger than control cells at 10 months postcrush but they exhibited no other morphological changes. The present findings indicate that spinal motor neurons are progressively altered after their regenerated axons have reestablished functional synapses with their peripheral targets.

Morphological and physiological properties of neurons after long-term axonal regeneration: observations on chronic and delayed sequelae of peripheral nerve injury

Axonal regeneration has been the focus of extensive investigation of mechanisms which mediate structural and functional recovery after injury to mammalian peripheral nerves and has proven to be a valuable model for development and plasticity in the nervous system. Although details of the acute morphological and physiological responses to nerve injury are well-described, less information is available to nerve injury are well-described, less information is available about long-term alterations which persist or develop after regenerated axons have established connections with their targets. The present paper briefly discusses the mammalian neuron's initial response to peripheral nerve injury and subsequent events which occur during regeneration. Morphological and physiological alterations observed in neurons after long-term axonal regeneration are described and are considered in the context of their potential implications for clinical recovery after nerve injury, as well as their potential contribution to the appearance of delayed neurological dysfunction. Selective responses to neuronal injury during development and in different fiber populations are discussed.

Morphological changes in spinal motor neurons giving rise to long-term regenerated sciatic nerve axons

Morphological properties of rat spinal motor neurons were examined 14-16 months following unilateral sciatic nerve crush and compared to the properties observed in neurons contralateral to injury and in cord segments from age-matched control rats. Regenerated and control motor neurons were identified by retrograde labelling with HRP applied to sciatic nerves distal to the site of crush or at a comparable location in control nerves. Many of the experimental motor neurons were enlarged and had thickened dendritic processess compared to the finer dendrites seen in control cells. Mean cell area ipsilateral to the crush lesions was larger than mean control cell area (P-value less than 0.001) despite representation of all control cell areas in the regenerated population. These data suggest that persistent or continued morphological abnormalities occur in mammalian motor neurons following simple sciatic crush injury when examined at extended times beyond the period of axonal regeneration and clinical recovery.

Sensitivity to 4-aminopyridine observed in mammalian sciatic nerves during acute pyridoxine-induced sensory neuropathy and recovery

In vitro physiologic properties of rat sciatic nerve were examined during pyridoxine-induced sensory neuropathy and following recovery. Compound action potential waveform characteristics, recovery cycle properties during paired stimulation, and ability to follow stimuli presented at high frequencies were examined. All parameters were assessed before and after potassium channel blockade with 4-aminopyridine in nerves from acutely toxic, recovered, and age-matched control rats. Compound action potential waveforms recorded from acutely toxic nerves were less affected by application of 4-aminopyridine than were those recorded from control nerves. Recovery cycles were less prolonged and frequency-following abilities less compromised a 3-month recovery period, experimental nerves demonstrated a more pronounced sensitivity to 4-aminopyridine than did age-matched control nerves. It is proposed that these differences in the physiological effects of 4-aminopyridine reflect the selective loss of large-caliber sensory fibers during the acute toxic phase and the increased sensitivity to the drug of regenerated sensory fibers following recovery.

Physiological effects of 4-aminopyridine on demyelinated mammalian motor and sensory fibers

The selective response of demyelinated sensory fibers to 4-aminopyridine (4-AP) has been proposed as a mechanism underlying the reported paresthesias that complicate the use of this potassium-channel blocking agent in clinical trials for the treatment of multiple sclerosis and neuromuscular disorders. To identify differences in the electrophysiological response of specific fiber types to the application of 4-AP, rat ventral and dorsal spinal roots, demyelinated by intrathecal injections of lysophosphatidylcholine, were examined in vitro before and during potassium-channel blockade. The compound action potentials of demyelinated ventral roots showed a prominent postspike negativity associated with a broadening of single action potentials following application of 4-AP. Under similar conditions, whole root responses of demyelinated dorsal root axons also developed a late negativity, but individual fibers were observed to fire repetitively in response to a single stimulus. The data support the hypothesis that the prominent sensory dysfunctions reported in clinical trials of 4-AP are due to the selective response characteristics of sensory fibers.

Physiological properties of regenerated rat sciatic nerve following lesions at different postnatal ages

Electrophysiological properties of regenerated sciatic nerves were examined in vitro following sciatic crush lesions performed on rats at 1 week to 4 months of age. Pharmacological blockade of potassium channels with 4-aminopyridine (4-AP) in control nerves resulted in only minimal changes in the waveform of whole nerve responses, but was associated with slight prolongation of relative refractory periods and compromised frequency-following abilities at all ages examined. A more marked sensitivity to application of 4-AP was observed in all regenerated nerves compared to control nerves. This sensitivity was characterized by the development of a prominent delayed negativity of the compound action potential. Specific features of the waveform alterations differed for nerves crushed before age 3 weeks compared to those injured at the older postnatal ages. Alteration of refractory properties and frequency-following abilities of regenerated nerves following 4-AP were also more pronounced than in control nerves with the most marked disruption being observed in nerves from animals lesioned at the older ages. These data suggest that the process of regeneration is modified by ongoing maturation at the time of crush.

The association of the supernormal period and the depolarizing afterpotential in myelinated frog and rat sciatic nerve

Excitability properties of isolated frog and rat sciatic nerve fibers were examined using intra-axonal and sucrose-gap recording techniques. Paired stimulation experiments on rat myelinated fibers indicate that a small proportion (11%; n = 84) of these axons demonstrate decreased threshold indicative of a supernormal period. In contrast, 81% (n = 23) of frog axons displayed a supernormal period. A depolarizing afterpotential was observed in most of the rat and frog fibers having a supernormal period and the depolarizing afterpotential increased in magnitude and duration during hyperpolarization. In addition to whole nerve stimulation, a supernormal period could be induced by stimulation of a single axon via current passage through the recording microelectrode. Brief (2-5 ms) subthreshold depolarizing pulses were followed by a slowly decaying depolarization and a period of increased excitability that mimicked the supernormal period. A supernormal period was also observed in the whole nerve preparation using a sucrose-gap technique. The magnitude and duration of the supernormal period, as measured in the sucrose-gap, were greater for frog nerve than for rat nerve. Additionally, a larger postspike negativity, the extracellular equivalent of the intra-axonally observed depolarizing afterpotential, was present in sucrose-gap recordings for frog nerve than for rat nerve. The results indicate that the depolarizing afterpotential is an important determinant of the supernormal period, and that both the depolarizing afterpotential and supernormal period are more prominent in frog than in rat sciatic nerve.

Differences in intramembranous particle distribution in the paranodal axolemma are not associated with functional differences of dorsal and ventral roots

Freeze-fracture methods were used to study intramembranous particles, which are believed to represent ectopic sodium channels in the paranodal axolemma, and their possible association with differences in action potential electrogenesis of maturing rat dorsal and ventral root fibers. Our results indicate that there is no significant association between paranodal axon membrane structure and the functional difference of dorsal and ventral root axons.

Different effects of 4-aminopyridine on sensory and motor fibers: pathogenesis of paresthesias

Mammalian motor and sensory fibers respond differently to the potassium channel-blocking agent, 4-aminopyridine (4-AP). The action potentials of the motor fibers increase in duration after 4-AP, while the sensory fibers respond with bursts of action potentials after a single stimulus. These differences may account for the paresthesias reported by patients with multiple sclerosis following treatment with 4-AP.

Differences between mammalian ventral and dorsal spinal roots in response to blockade of potassium channels during maturation

Differences in potassium channel organization between motor and sensory fibres have been described in amphibians but have not previously been examined in mammals. In the present investigation, we studied whole nerve and single axon responses following pharmacological blockade of potassium conductance in rat ventral and dorsal spinal roots during maturation. Our results indicate a differential sensitivity in maturing mammalian motor and sensory fibres which is most apparent in younger roots. Specifically, application of 4-aminopyridine (4-AP) results in a broadening of the compound action potential in ventral roots which is associated with a delayed repolarization of the individual action potential of single fibres. In contrast, blockade of potassium channels in young dorsal roots results in a late negativity in the compound response which is correlated with multispike bursting activity recorded from single sensory fibres. The effects of 4-AP on ventral root fibres diminish earlier in the course of maturation than do the effects of 4-AP in dorsal root fibres. These results demonstrate developmental differences in the functional organization of potassium channels in mammalian motor and sensory axons which may have implications for differences in coding properties between these two classes of axons.