The nerves in frog skin

In the epidermis of frog skin, most nerves are situated at the top of the basal layer. More superficial nerve fibres are usually adjacent to flask cells; it is concluded that this is not a functional association, but a consequence of the pattern of moulting. There are nerve fibres in the walls of the granular glands; mucous glands appear to have no intrinsic innervation although nerves pass within a short distance of their walls. The smooth muscle bundles of the dermis are innervated, and have a physical attachment to the overlying epidermis.     

Effects of potassium,sodium, and azide on the ionic movements that accompany activity in frog nerves

Stimulation of intact or desheathed frog sciatic nerves produced an increase in the sodium content and a decrease in the potassium content of this tissue. In desheathed preparations the magnitudes of the changes in ionic contents decreased as the concentration of the potassium in the bathing solution was increased, while changing the external sodium concentration produced small effects on the ionic shifts. During tetanization, the rate of decline of the compound action potential also decreased as the external potassium concentration increased. Eliminating the activity respiration with 0.2 mM azide did not greatly modify the changes in sodium and potassium distribution that accompanied activity in either intact or desheathed nerves.     

Effects of azide and choretone on the sodium and potassium contents and the respiration of frog sciatic nerves

Azide (0.2 to 5.0 mM) and chloretone (2.0 to 15.0 mM) reversibly inhibited 20 to 90 per cent of the resting respiration of frog sciatic nerves, and caused a loss of potassium and a gain of sodium in this tissue. The changes in ionic contents that developed after 5 or 10 hours were roughly correlated with the degree of respiratory depression, but the time courses of these changes were different with the two reagents. In azide these changes appeared to begin immediately, while in chloretone, at concentrations between 3.0 and 5.0 mM, the ionic shifts developed after a delay of several hours. Fifteen millimolar chloretone produced immediate changes in ionic contents several times greater than those produced by anoxia. The changes in ionic distribution produced in 5 hours by anoxia, 5.0 mM azide, or 5.0 mM chloretone were at least partially reversible; those produced by 15.0 mM chloretone were irreversible. With the exception of 15.0 mM chloretone the ionic shifts produced by these reagents may be due primarily to the depression of the respiration, although there are indications that azide acts, in addition, by another pathway. Concentrations of azide or chloretone that depressed the resting rate of oxygen consumption more than 50 per cent produced a slow conduction block, while 15.0 mM chloretone blocked conduction within 15 minutes.     

The polyphosphoinositides and other lipids of peripheral nerves

1. A detailed lipid analysis of the peripheral nerves of the crab (claw, leg), lobster (claw, leg), cow (splenic), hen, rabbit, sheep and monkey (sciatic) is presented. 2. The so-called ;myelinic lipids', cholesterol, sphingomyelin, ethanolamine plasmalogen and phosphatidylserine, occurred in the highest proportion in the lipids of vertebrate myelinated nerves, whereas the percentage of lecithin was greatest in the lipids of non-myelinated nerve fibres of both vertebrates and invertebrates. 3. Triphosphoinositide was found in all nerves examined and its concentration in the extracted lipids supports the concept that it is predominantly localized in the myelin sheath. 4. In crustacean nerve 12-14% of the phospholipids was in the form of alkyl ether phospholipids, which in the lobster were approximately half choline-containing and half ethanolamine-containing.     

The dorsomedial nuclear group of cranial nerves in the frog.

The dorsomedial motor nuclei were demonstrated by the cobalt-labeling technique applied to the so-called somatic motor cranial nerves. The motoneurons constituting these nuclei are oval-shaped and smaller than the motoneurons in the ventrolateral motor nuclei. They give rise to ventral and dorsal dendrite groups which have extensive arborization areas. A dorsolateral cell group in the rostral three quarters of the oculomotorius nucleus innervates ipsilateral eye muscles (m.obl.inf., m.rect.inf., m.rect.med.) and a ventromedial cell group innervates the contralateral m. rectus superior. Ipsilateral axons originate from ventral dendrites, contralateral axons emerge from the medial aspect of cell bodies, or from dorsal dendrites, and form a "knee" as they turn around the nucleus on their way to join the ipsilateral axons. A few labeled small cells found dorsal and lateral to the main nucleus in the central gray matter are regarded as representing the nucleus of Edinger-Westphal. The trochlearis nucleus is continuous with the ventromedial cell group of the oculomotorius nucleus. The axons originate in dorsal dendrites, run dorsally along the border of the gray matter and pierce the velum medullare on the contralateral side. A compact dendritic bundle of oculomotorius neurons traverse the nucleus, and side branches appear to be in close apposition to the trochlearis neurons. A dorsomedial and a ventrolateral cell group becomes labeled via the abducens nerve. The former supplies the m. rectus lateralis, while the latter corresponds to the accessorius abducens nucleus which innervates the mm. rectractores. Neurons in this latter nucleus are large and multipolar, resembling the neurons in the ventrolateral motor nuclei. Their axons originate from dorsal dendrites and form a "knee" around the dorsomedial aspect of the abducens nucleus. Cobalt applied to the hypoglossus nerve reaches a dorsomedial cell group (the nucleus proper), spinal motoneurons and sympathetic preganglionic neurons. Of the dorsomedial motor cells, the hypoglossus neurons are the largest, and a branch of their ventral dendrites terminates on the contralateral side. Some functional and developmental biological aspects of the morphological findings, such as the crossing axons and the peculiar morphology of the accessory abducens nucleus, are discussed.     

Strategies of hypoxia and anoxia tolerance in cardiomyocytes from the overwintering common frog, Rana temporaria

Using ventricular cardiomyocytes of the common frog, Rana temporaria, we investigated the metabolic strategies employed by the heart to tolerate 4 mo of hypoxic submergence (overwintering) as well as acute bouts of anoxia. In contrast to what is observed for the whole animal, there was no change in oxygen consumption in cardiomyocytes isolated from normoxic frogs compared with those isolated from 4-mo hypoxic animals. Furthermore, cells from both normoxic and hypoxic frogs were able to completely recover oxygen consumption following 30 min of acute anoxia. From estimates of ATP turnover, it appears that frog cardiomyocytes are capable of a profound, completely reversible metabolic depression, such that ATP turnover is reduced by >90% of control levels during anoxia but completely recovers with reoxygenation. Moreover, this phenomenon is also observed in frogs that have been subjected to 4 mo of extended hypoxia. We found a significant increase in the stress protein, hsp70, after 1 mo of hypoxic submergence, which may contribute to the heart's remarkable hypoxia and anoxia tolerance and may act to defend metabolism during the overwintering period.     

Physiological and biochemical changes in frog sciatic nerve during anoxia and recovery

Frog (Rana pipiens) sciatic nerve was incubated, with and without stimulation, in an oil bath. The correlation between changes in the magnitude of the compound action potential (α and β) and changes in metabolites, particularly energy reserves, during anoxia and recovery from anoxia was studied. The time to extinction of the action potential in anoxia was frequency-dependent. The action potential could not be restored, nor its extinction delayed, by washing the nerve in O₂-free Ringer's solution. Therefore, in this system extracellular K⁺ accumulation was not a significant factor in blocking impulse conduction. At the time of complete nerve block resulting from anoxia (90 min at rest), ATP, P-creatine and glucose were 30, 10 and 10 per cent, respectively, of initial levels. Glycogen did not fall below 42 per cent of control levels even after 5 h of anoxia. Changes in the levels of energy reserves during anoxia were used to calculate the metabolic rate of nerves at rest and during stimulation. In one series of experiments, the resting metabolic rate was 0·12 mequiv. of ‘high-energy phosphate’ (～P)/kg/min. Stimulation increased the metabolic rate to 0·22 mequiv. of ～P/kg/min at 30 Hz and to 0·29 mequiv. of ～P/kg/min at 100 Hz. The change in metabolic rate when the nerve passed from the resting to the stimulated state was quite abrupt, an observation suggesting that the slow transition observed with methods monitoring O₂, consumption was largely instrumental. In nerve stimulated to exhaustion in the absence of O₂, neither ATP nor P-creatine had fully recovered within 60 min after O₂, was readmitted, although the action potential reached supranormal levels 15 min after return to O₂. The ratio of lactate: pyruvate, which increased as expected during anoxia, paradoxically increased even further after O₂, was readmitted. The rate of energy utilization during recovery was 0·30 mequiv. of ～P/kg/min. Nerves stimulated at 100–200 Hz in O₂, exhibited no changes in levels of P-creatine, ATP or lactate, an observation implying that the nerve could not be made to use ～P faster than oxidation of glucose could provide it. This meant that the maximal metabolic rate was not limited by the rate of supply of chemical energy. Instead, the limitation may have arisen as a result of a limited rate at which ionic imbalance can result from stimulation or a limited pump capacity of the axonal membrane. Nerves stimulated at 200 Hz in O₂ for 20 min and then transferred to an O₂-free environment without further stimulation exhibited an increase in the rate of energy utilization (nearly two-fold) over the resting rate, a finding that suggested a metabolic (ionic?) debt as a result of activity which could not be met even though the energy supply was adequate. Therefore, restriction of energy expenditure by a limiting pumping rate seemed to be the most likely explanation. The resting metabolic rate of frog sciatic nerve was only one-quarter to one-third of the rate for rat sciatic nerve, when compared at the same temperature (25°C).     

Chewing disability in older adults attributable to tooth loss and other oral conditions

doi: 10.1111/j.1741‐2358.2010.00412.x Chewing disability in older adults attributable to tooth loss and other oral conditions Background: This study evaluates associations between oral health‐related factors and chewing ability, and quantifies the risk contributed by each factor. Materials and methods: Chewing ability and information on number of teeth, dentures and dental problems over the last 12 months were collected by mailing questionnaires to a random sample of 60‐ to 71‐year‐olds from Adelaide, South Australia. Logistic regression was used to model oral status and oral symptoms as predictors of chewing disability, and to estimate the population‐attributable fraction. Results: A total of 444 persons responded (response rate = 68.8%). Among dentate subjects, 10.3% were chewing‐deficient, with chewing disability more prevalent (p < 0.05) among those with <21 teeth (26.4%), dentures (20.4%), painful aching in the mouth (25.4%), pain in the face (16.7%), broken/chipped teeth (15.6%), sensitive teeth (14.1%), loose teeth (37.1%), and sore gums (18.0%). Adjusted Odds ratios (OR) showed inadequate dentition (OR = 4.20), painful aching in the mouth (OR = 4.88), and presence of loose teeth (OR = 4.70) were associated with chewing disability (p < 0.01), and their population attributable fractions were 18.5%, 15.1% and 7.8% respectively. Conclusions: Loose teeth, number of teeth and pain in the mouth were associated with chewing disability, with an inadequate dentition and pain in the mouth contributing most to chewing disability in this population.