Patterns of spontaneous unit preoptic neurosecretory cell discharges in the rainbow trout, Salmo gairdneri

Extracellular antidromic potentials recorded from the neurosecretory cell body were characterized by the following criteria: constant latency, the ability to follow a high frequency rate of stimulation and the collision test. The latency of the antidromic potentials ranged from 12 to 24 ms (17.46 +/- 3.10 SD) which gave a mean conduction velocity of 0.19 m/s, typical of unmyelinated nerve fibers. Two components could be clearly distinguished in the antidromic potential. A small "A" spike which showed constant latency and a large "B" spike with a variable latency and amplitude. A delay of 6.5 ms between the two spikes could occur and sometimes the "B" spike was blocked leaving only the "A" spike. Four patterns of spontaneous activity seem to emerge: Type I (26% of units, M +/- SD = 0.77 +/- 0.32 sp/s) corresponds to a slow and irregular pattern of activity; Type II (28% of units, M = 1.58 +/- 0.47 sp/s) is hard to classify and may be related to an irregular bursting pattern of activity; Type III (28% of units, M = 2.59 +/- 1.19 sp/s) corresponds to a continuous pattern of activity; Type IV (18% of units) represents a rhythmic pattern of activity with an active phase of about 3 min (M = 2.42 +/- 0.90 min), a silent phase of about 4 min (M = 3.89 +/- 3.02 min) and a maximal frequency of unit discharge in the range 2-18 sp/s. No statistical differences exist for the mean dorsal aortic pressure (DAP) between the four types of neurosecretory cell activity.     

beta-Receptor agonist activity of phenylephrine in the human forearm.

Phenylephrine is generally regarded as a "pure" alpha(1)-agonist. However, after treatment of the forearm with the alpha-adrenergic-blocking drug phentolamine, brachial artery infusion of phenylephrine can cause transient forearm vasodilation. To determine whether this response was beta-receptor mediated, phenylephrine, phentolamine, and propranolol were infused into the brachial arteries of six healthy volunteers. Forearm vascular conductance (FVC) was also calculated and expressed as arbitrary units (units). Infusion of phenylephrine by itself (0.5 microg. dl forearm volume(-1). min(-1)) caused a sustained decrease (P < 0.05) in FVC from 3.5 +/- 0.7 to 0.9 +/- 0.2 units (P < 0.05). Infusion of the alpha-blocker phentolamine increased (P < 0.05) baseline FVC to 5.7 +/- 1.3 units. Subsequent infusion of phenylephrine after alpha-blockade caused FVC to increase (P < 0.05) for ~1 min from 5.7 +/- 1.3 to a peak of 13.1 +/- 1.8 units. Propranolol had no effect on baseline flow, and subsequent phenylephrine infusion after alpha- and beta-blockade caused a small, but significant, sustained decrease in FVC from 5.1 +/- 1.0 to 3.6 +/- 0.8 units. There were no systemic effects from the infusions, and saline infusion at the same rate (1-2 ml/min) had no forearm vasoconstrictor or dilator effects. These data indicate that in humans phenylephrine can exert transient beta(2)-vasodilator activity when its predominant alpha-constrictor effects are blocked.     

D-Lactic acid-induced neurotoxicity in a calf model

Lactic acidosis (DAC) occurs as a complication of short-bowel syndrome in humans and in a variety of other gastrointestinal disorders in monogastrics and ruminants. DAC is associated with signs of impaired central nervous system (CNS) function including ataxia and coma. The objective of this experiment was to determine whether either acidification of nervous tissue or d-lactic acid is responsible for decreased neurological function. Eight Holstein calves (32 +/- 11 days, 70 +/- 10 kg) were surgically catheterized with indwelling intravenous jugular and atlanto-occipital space cerebrospinal fluid (CSF) catheters and infused for 6 h in random order with isomolar dl-lactic acid (dl-LA), l-lactic acid (l-LA), hydrochloric acid (HCl), or saline. dl-LA induced ataxia after 4 h of infusion and produced the greatest obtunding of CNS function (at 7 h, score 8.0 +/- 0.4), whereas the other infusions caused neither ataxia nor scores over 1.5 (P < 0.01 from dl-LA). dl-LA induced significantly less acidemia than HCl (at 6 h pH 7.13 +/- 0.06 and 7.00 +/- 0.04, base excess -16 +/- 1 and -23 +/- 3 mmol/l, bicarbonate 11 +/- 1 and 8 +/- 1 mmol/l respectively, all P < 0.01) but greater than l-LA and saline (P < 0.01). CSF changes followed a similar but less pronounced pattern. Although HCl infusion produced a severe acidemia and CSF acidosis, only minor effects on neurological function were evident suggesting that d-lactate has a direct neurotoxic effect that is independent of acidosis. Conversely, l-LA produced only minor neurological changes.     

Characterization of Na+/H+ exchange in a rabbit corneal epithelial cell line (SIRC)

Continuous intracellular pH (pHi) measurements were performed in SIRC rabbit corneal epithelial cells using the pH-sensitive absorbance of intracellularly trapped 5(and 6)-carboxy-4',5'-dimethylfluorescein. Steady-state pHi in nominally bicarbonate free Ringer's solution averaged 6.87 +/- 0.02 (mean +/- S.E., n = 53). After intracellular acidification induced by the NH4Cl-prepulse technique, there was a sodium-dependent pHi recovery towards the normal steady-state pHi. The initial pHi recovery rate was a saturable function of extracellular sodium concentration with an apparent Km for external sodium of about 25 mM and a Vmax of about 0.28 pH units/min. Virtually no pHi recovery was observed in the absence of extracellular sodium. Sodium removal during steady state acidified the cells by 0.36 +/- 0.05 pH units (mean +/- S.E., n = 13) within 5 min. There was a dose-dependent inhibition of pHi recovery after NH4Cl prepulse by amiloride with an IC50 of about 15 microM. Amiloride in a concentration of 1 mM almost completely abolished pHi recovery. Amiloride (1 mM) applied during steady state induced an intracellular acidification of 0.2 +/- 0.03 pH units (mean +/- S.E., n = 7) within 5 min. These findings suggest that a Na+/H+ exchange is present in SIRC rabbit corneal epithelial cells. Na+/H+ exchange seems to be the major process involved in pHi recovery in SIRC cells after an intracellular acid load. Na+/H+ exchange also plays a role in the maintenance of steady-state pHi.     

Isobolographic analysis of the dual-site synergism in the antinociceptive response of tramadol in the formalin test in rats

Tramadol is an atypical opioid with a complex mechanism of action including a synergistic interaction between the parent drug and an active metabolite. The local action of the parent drug is poorly documented. This study was designed to evaluate the site-site interaction of the antinociception produced by tramadol given by two different routes. The effects of individual and fixed-ratio combinations of intraplantar (i.pl.) and intraperitoneal (i.p.) tramadol were evaluated using the formalin test in rats. Isobolographic analysis was employed to identify the synergy produced by combinations. In both first and second phases of the formalin test, tramadol was active not only by the systemic (ED50 10.2+/-2.1 and 7.1+/-0.5 mg/kg i.p.) but also by the local route (ED50 171.0+/-44.8 and 134.6 microg/paw i.pl.). The isobolographic analysis revealed a "self-synergism" in the antinociceptive effect between the two routes of administration, as the experimental ED50 (211.1+/-13.6 and 45.9+/-3.9 "dose units" phase 1 and 2, respectively) of the combination was significantly lower than the theoretical ED50 (422.2+/-50.5 and 138.5+/-9.2 "dose units"). The mechanism underlying this self-synergism appears to be partially opioid since systemic but not local naloxone reversed the potentiation. The observed dual-site interaction in the antinociceptive action of tramadol provides insights for alternatives in the management of pain.     

Mucus secretion from single submucosal glands of pig. Stimulation by carbachol and vasoactive intestinal peptide

Secretion rates of >700 individual glands in isolated tracheal mucosa from 56 adult pigs were monitored optically. "Basal" secretion of 0.7 +/- 0.1 nl x min(-1) gland(-1) was observed 1-9 h post-harvest but was near zero on day 2. Secretion to carbachol (10 microm) peaked at 2-3 min and then declined to a sustained phase. Peak secretion was 12.4 +/- 1.1 nl x min(-1) gland(-1); sustained secretion was approximately one-third of peak secretion. Thapsigargin (1 microm) increased secretion from 0.1 +/- 0.05 to 0.7 +/- 0.2 nl x min(-1) gland(-1); thapsigargin did not cause contraction of the trachealis muscles. Isoproterenol and phenylephrine (10 microm each) were ineffective, but vasoactive intestinal peptide (1 microm) and forskolin (10 microm) each produced sustained secretion of 1.0 +/- 0.5 and 1.7 +/- 0.2 nl x min(-1) gland(-1), respectively. The density of actively secreting glands was 1.3/mm(2). Secretion to either carbachol or forskolin was inhibited (approximately 50%) by either bumetanide or HCO(3)(-) removal and inhibited approximately 90% by the combined treatments. Mucus secreted in response to carbachol or forskolin was acidic by approximately 0.2 pH units relative to the bath and remained acidic by approximately 0.1 pH units after bumetanide. The strong secretory response to vasoactive intestinal peptide, the acidity of [cAMP](i)-stimulated mucus, and its inhibition by bumetanide were unexpected.     

Baroreflex control of muscle sympathetic nerve activity during skin surface cooling.

Skin surface cooling improves orthostatic tolerance through a yet to be identified mechanism. One possibility is that skin surface cooling increases the gain of baroreflex control of efferent responses contributing to the maintenance of blood pressure. To test this hypothesis, muscle sympathetic nerve activity (MSNA), arterial blood pressure, and heart rate were recorded in nine healthy subjects during both normothermic and skin surface cooling conditions, while baroreflex control of MSNA and heart rate were assessed during rapid pharmacologically induced changes in arterial blood pressure. Skin surface cooling decreased mean skin temperature (34.9 +/- 0.2 to 29.8 +/- 0.6 degrees C; P < 0.001) and increased mean arterial blood pressure (85 +/- 2 to 93 +/- 3 mmHg; P < 0.001) without changing MSNA (P = 0.47) or heart rate (P = 0.21). The slope of the relationship between MSNA and diastolic blood pressure during skin surface cooling (-3.54 +/- 0.29 units.beat(-1).mmHg(-1)) was not significantly different from normothermic conditions (-2.94 +/- 0.21 units.beat(-1).mmHg(-1); P = 0.19). The slope depicting baroreflex control of heart rate was also not altered by skin surface cooling. However, skin surface cooling shifted the "operating point" of both baroreflex curves to high arterial blood pressures (i.e., rightward shift). Resetting baroreflex curves to higher pressure might contribute to the elevations in orthostatic tolerance associated with skin surface cooling.     

Temporal distribution of rapid eye movements and related monophasic potentials in the brain stem following injection of an anticholinesterase.

The temporal distribution of the horizontal rapid eye movements and the related monophasic potentials recorded from the ascending MLF following intravenous injection of o.i mg/kg of anticholinesterase has been investigated in precollicular decerebrate animals. In particular the intervals between individual MLF potentials occurring during successive REM episodes have been evaluated over a total period of 2000 sec on each experiment. 2. There was a bimodal distribution of intervals due to the fact that all the rapid eye movements and the related MLF potentials were grouped in bursts which occurred at quite regular intervals. 3. During the cholinergically induced episodes of REM, there were usually bursts of REM in one direction followed by bursts of REM in the opposite direction. The mean number of individual eye movements within each burst was 4.67 +/- 0.84, S.D., while the average interval between the individual eye movements corresponded to 167 +/- 36 msec, S.D. 4. There was a great regularity in the periodic occurrence of the bursts of REM. In particular the mean interval between the beginning of a burst of REM in one direction (i.e., towards the left side) and that of the next train oriented in the opposite direction (i.e., towards the right side) was 1.97 +/- 0.47 sec, S.D., while the mean interval between the beginning of this last train and that of the successive train oriented in the former direction corresponded to 2.97 +/- 0.48 sec, S.D. Moreover, the duration of the whole period corresponding to the interval between two successive bursts of REM oriented in the same direction (i.e., towards left or towards right) corresponded on average to 4.94 +/- 0.55 sec S.D. and 4.99 +/- 0.52 sec, S.D. respectively. 5. In addition to these "simple bursts" of rapid eye movements oriented in one direction, there were "complex bursts" in which an alternation of the individual eye movements within each burst was observed. In these instances the mean number of spikes was greater (5.35 +/- 1.20, S.D.) and the mean interval shorter 119 +/- 44 msec, S.D.) than those observed in the "simple bursts", About 10-15% of the bursts occurring during the cholinergically induced REM episodes were of the complex type. 6. These findings obtained from an individual experiment were confirmed in all the decerebrate animals treated with the same dose of anticholinesterase; only slight quantitative differences were detected from case to case. 7. Since the bursts of REM induced by the anticholinesterase depend upon the activity of the vestibular nuclei, it is postulated that cholinergic reticular neurons activate structures which show waxing and waning in their activity before acting on the vestibulo-oculomotor system. This system probably contains the inhibitory interneurons which transform the regularly modulated input into a rhythmic vestibular output...     

Regulation of intracellular pH in human platelets. Effects of thrombin, A23187, and ionomycin and evidence for activation of Na+/H+ exchange and its inhibition by amiloride analogs

Intracellular pH (pHi) of human platelets was measured with the fluorescent dye 2',7'-bis(carboxyethyl)5,6-carboxyfluorescein under various conditions. Stimulation by thrombin at 23 degrees C caused a biphasic change in pHi (initial pHi 7.09); a rapid fall of 0.01-0.04 units (correlated with the rise of [Ca2+]i measured with quin2) followed after 10-15 s by a sustained rise of 0.1-0.15 units pHi. The fall of pHi and [Ca2+]i mobilization was reduced by early (5 s) addition of hirudin, but the later elevated pHi was not reversed by hirudin added after 30 s, although this strips thrombin from receptors and rapidly returns [Ca2+]i to basal levels. In Na+-free medium, or in presence of the Na+/H+ antiport inhibitors, 5-(N,N-dimethyl)amiloride (DMA) or 5-(N-ethyl-N-isopropyl)amiloride (EIPA), thrombin caused a greater fall of pHi (0.22-0.26 units) that was sustained. DMA or EIPA could also reverse the alkalinization response to thrombin. Ca2+ ionophores (ionomycin, A23187) decreased platelet pHi by 0.02-0.15 units, but without an increase of pHi comparable to that following thrombin; DMA and EIPA enhanced the fall of pHi (0.14-0.33 units). Cytoplasmic acidification produced by nigericin (K+/H+ ionophore) was followed by return towards normal that was abolished by Na+/H+ antiport inhibitors. The phorbol diester phorbol 12-myristate 13-acetate had little effect on resting pHi but increased the rate of recovery 2-3-fold after cytoplasmic acidification by nigericin, ionomycin, or sodium propionate. These results indicate that elevation of [Ca2+]i by thrombin enhances H+ production, but the subsequent alkalinization is independent of receptor occupancy or elevated [Ca2+]i and stimulation of the Na+/H+ antiporter by thrombin probably involves some mechanism apart from regulation by H+ and protein kinase C.     

Age of the intronic GAA triplet repeat expansion mutation in Friedreich ataxia

Friedreich ataxia (FRDA), the most frequently inherited ataxia, is due in the vast majority of cases to a large expansion of an intronic GAA repeat. Using linkage disequilibrium analysis based on haplotype data of seven polymorphic markers close to the frataxin gene, the age of FRDA founding mutational event(s) is estimated to be at least 682+/-203 generations (95% confidence interval: 564-801 g), a dating which is consistent with little or no negative selection and provides further evidence for an ancient spread of a pre-mutation (at-risk alleles) in western Europe.     

Effect of a Deficiency of Thiamine on Brain Pyruvate Dehydrogenase: Enzyme Assay by Three Different Methods

A simple and rapid method based on the NADH-linked reduction of a tetrazolium dye was described for the determination of pyruvate dehydrogenase activity in rat brain homogenates. The method (method 3) gave a value of 36.06 +/- 1.24 nmol of pyruvate utilised/min/mg of whole brain protein. This value was higher than that obtained by measurement of the rate of decarboxylation of [1-14C]pyruvate (15.10 +/- 0.88 nmol/min/mg of protein; method 1) and was comparable with the rate of transfer of acetyl groups to an arylamine (39.04 +/- 1.32 nmol/min/mg of protein; method 2). A critique of the values reported by others by different methods was given. The pyruvate dehydrogenase activity in the mitochondria isolated from rat brain was in the "active" (nonphosphorylated) form. A deficiency of thiamine in rats was produced by treatment with pyrithiamine, an antagonist of thiamine. This treatment resulted in abnormal neurological signs, such as ataxia and convulsions. The measurement of the total activity of pyruvate dehydrogenase in the brain by all three methods showed no significant change in the enzymic activity in thiamine-deficient rats after treatment with pyrithiamine. The activities of the enzyme in the brains of pair-fed animals were similar to those in the controls.     

Influence of bronchial arterial PO2 on pulmonary vascular resistance

In six anesthetized and mechanically ventilated adult sheep, the bronchial artery was perfused with blood from an oxygenator-pump circuit. When the lungs were ventilated with 100% O2 and the bronchial O2 tension (PbrO2) was approximately 600 Torr, the mean of the pulmonary vascular resistances (PVR) measured at the beginning (3.32 +/- 0.29 units) and end (3.17 +/- 0.13 units) of the experiment was 3.24 +/- 0.20 units. When the PbrO2 was changed to 58 +/- 1 Torr, the PVR (2.99 +/- 0.14 units) did not change significantly. However, when the lungs were ventilated with air as PbrO2 was decreased to 91 +/- 4, 77 +/- 3, 56 +/- 2, and 42 +/- 1 Torr, the PVR increased to 3.67 +/- 0.18, 4.03 +/- 0.16, 4.79 +/- 0.19, and 4.71 +/- 0.35 units, respectively. However, when the PbrO2 was decreased further to 26 +/- 1 and 13 +/- 1 Torr, the PVR decreased to 3.77 +/- 0.28 and 3.91 +/- 0.30 units, respectively. In contrast, the bronchial vascular resistance decreased monotonically as PbrO2 decreased. The bronchial circulation supplies vasa vasorum to the walls of all but the smallest pulmonary arteries, and it is therefore suggested that the PO2 of the bronchial circulation is responsible for the bimodal response of the pulmonary vasculature, with stimulation of hypoxic pulmonary vasoconstriction at moderate hypoxemia and of hypoxic pulmonary vasodilation at profound hypoxemia. The physiological and pathophysiological significance of the influence of systemic PO2 on pulmonary vascular tone is discussed.     

Isolation and properties of cytoplasmic alpha-glycerol 3-phosphate dehydrogenase from the pectoral muscle of the fruit bat,Eidolon helvum

Cytoplasmic alpha-glycerol-3-phosphate dehydrogenase from fruit-bat-breast muscle was purified by ion-exchange and affinity chromatography. The specific activity of the purified enzyme was approximately 120 units/mg of protein. The apparent molecular weight of the native enzyme, as determined by gel filtration on Sephadex G-100 was 59,500 +/- 650 daltons; its subunit size was estimated to be 35,700 +/- 140 by SDS-polyacrylamide gel electrophoresis. The true Michaelis-Menten constants for all substrates at pH 7.5 were 3.9 +/- 0.7 mM, 0.65 +/- 0.05 mM, 0.26 +/- 0.06 mM, and 0.005 +/- 0.0004 mM for L-glycerol-3-phosphate, NAD(+), DHAP, and NADH, respectively. The true Michaelis-Menten constants at pH 10.0 were 2.30 +/- 0.21 mM and 0.20 +/- 0.01 mM for L-glycerol-3-phosphate and NAD(+), respectively. The turnover number, k(cat), of the forward reaction was 1.9 +/- 0.2 x 10(4)s(-1). The treatment of the enzyme with 5,5'-dithiobis-2-nitrobenzoic acid (DTNB) under denaturing conditions indicated that there were a total of eight cysteine residues, while only two of these residues were reactive towards DTNB in the native enzyme. The overall results of the in vitro experiments suggest that alpha-glycerol-3-phosphate dehydrogenase of the fruit bat preferentially catalyses the reduction of dihydroxyacetone phosphate to glycerol-3-phosphate.     

Adherence of peripheral blood neutrophils in X-ray operators.

The studies were conducted among 39 people (29 women and 10 men) operating X-ray equipment in radiology institutes and comparisons were made in the following schemes: A/ Group of persons operating the X-ray equipment (39 persons) and control group (18 persons). B/ A subgroup of persons that had been operating radiology equipment for > 5 years (29 workers was separated) and the results were compared with those for the subgroup of persons working < 5 years (10 workers). C/ Among the workers a subgroup of women (29) was separated and the results were compared with those for the subgroup of men (10 men). The following investigations were carried out: 1./ The absolute number of neutrophils in peripheral blood. 2./ Neutrophil adherence to fibres. 3./ Evaluation of CD 11b/CD 18 adhesion molecules expression on the surface of neutrophils. 4./ Evaluation of fibronectin concentration in serum. In the group A of the employees examined who operated X-ray units compared with the control group, the statistically significant decrease in the percentage of peripheral blood neutrophils showing adherence was observed and statistically significant decrease in median value and decrease of "Peak" value from the curve of the CD 18 adhesion molecule expression was detected and amounted to respectively: 91.0 +/- 4.26% adhering neutrophils in workers operating X-ray units and 94.8 +/- 2.98% in control group; values of median 120 +/- 4 in workers and 123 +/- 3 in control group in logarithmic scale; values of "Peak" 120 +/- 4 in workers and 123 +/- 3 in control group in logarithmic scale. Our own testing results show that the adherence properties of the peripheral blood neutrophils taken from X-ray operators are independent of the length of employment period and of the sex of the persons tested.     

Interaction of the voltage-sensing fluorescent probe diS-C3-(5) with dipalmitoylphosphatidylcholine liposomes

The interaction of the probe diS-C3-(5) with dipalmitoylphosphatidylcholine (DPPC) liposomes has been studied using fluorescence and differential scanning calorimetry (DSC). The partition coefficients (K) of the probe for the lipid and the aqueous phase (in terms of molar part units) were (1.20 +/- 0.4) X 10(6) at 45 degrees C and (0.50 +/- 0.07) X 10(6) at 23 and 36 degrees C. In terms of volume concentration units, these values correspond to Kp = (2.88 +/- 0.10) X 10(4) and Kp = (1.20 +/- 0.17) X 10(4), respectively. DSC thermograms were practically identical both for large unilamellar and multilamellar liposomes. The main transition peak remained practically unchanged over the entire range of the probe concentrations used. The pretransition could be observed up to maximal probe concentrations applied and it widened and shifted from 35.4 degrees C in pure DPPC to approximately 32 degrees C at a probe/lipid ratio of 0.027. These results suggest that in both quasicrystalline and liquid crystalline lipid bilayers the probe molecules are included in "defects" between structurally ordered microregions (microdomains or clusters). The dependence of the fluorescence response on the transmembrane potential in a suspension of unilamellar DPPC vesicles suggest that the equilibrium thermodynamic model is valid for liquid crystalline bilayers.     

Studies on the growth of the fetal sheep. The effects of reduction of placental size on hormone concentration in fetal plasma

Intrauterine growth retardation was induced in sheep by removal of endometrial caruncles before pregnancy. At a second operation catheters were implanted into the ewe and fetus at 105-135 days of pregnancy. Three groups of fetuses: low birthweight-for-dates (small caruncle) normal birthweight-for dates (normal sized caruncle) and controls have been compared. The concentration of ACTH (60 +/- 6.9 pg/ml) in the normal-sized caruncle fetuses were lower in the controls (144 +/- 4.7 pg/ml) or small caruncle fetuses (142 +/- 53 pg/ml). Basal cortisol concentrations were similar in the controls (7.3 +/- 1.2 ng/ml) and normal-sized caruncle fetuses (6.5 +/- 0.5 ng/ml) but those in the small caruncle fetuses were significantly higher (12.7 +/- 1.0 ng/ml, P less than 0.001). The concentration of insulin correlated with plasma glucose and the mean concentrations were 19.2 +/- 1.6 mu units/ml (controls), 8.4 +/- 2.6 mu units/ml (normal-sized caruncle) and 3.9 +/- 1.6 mu units/ml (controls), 8.4 +/- 2.6 mu units/ml (normal-sized caruncle) and 3.9 +/- 1.6 mu units/ml (small caruncle). Prolactin was significantly lower in the small caruncle fetuses (2.1 +/- 0.3 ng/ml) compared to the controls (66.6 19.4 ng/ml) or normal-sized caruncles (76.1 +/- 38 ng/ml) but growth hormone concentrations in the small caruncle.     

Arrangement of myosin heads in relaxed thick filaments from frog skeletal muscle

The distribution of myosin heads on the surface of frog skeletal muscle thick filaments has been determined by computer processing of electron micrographs of isolated filaments stained with tannic acid and uranyl acetate. The heads are arranged in three strands but not in a strictly helical manner and so the structure has cylindrical symmetry. This accounts for the "forbidden" meridional reflections seen in diffraction patterns. Each layer-line therefore represents the sum of terms of Bessel orders 0, +/- 3, +/- 6, +/- 9 and so on. These terms interact so that, unlike a helical object without terms from overlapping Bessel orders, as the azimuth is changed, the amplitude on a layer-line at a particular radius varies substantially and its phase does not alter linearly. Consequently, a three-dimensional reconstruction cannot be produced from a single view. We have therefore used tilt series of three individual filaments to decompose the data on layer-lines 0 to 6 into terms of Bessel orders up to +/- 9 using a least-squares procedure. These data had a least-squares residual of 0.32 and enabled a three-dimensional reconstruction to be obtained at a nominal resolution of 6 nm. This showed, at a radius of about 10 nm, three strands of projecting morphological units with three units spaced along each strand every 42.9 nm axially. We have identified these units with pairs of myosin heads. Successive units along a strand are perturbed axially, azimuthally and radially from the positions expected if the structure was perfectly helical. This may simply be a consequence of steric restrictions in packing the heads on the thick filament surface, but could also reflect an underlying non-helical arrangement of myosin tails, which would be consistent with the thick filament shaft being constructed from three subfilaments in which the tails were arranged regularly. There was also material at a radius of about 6 nm spaced 42.9 nm axially, which we tentatively identified with accessory proteins. The filament shaft had a pronounced pattern of axial staining.     

A linkage study of hereditary ataxias and related disorders

Genetic markers controlled by 21 genetic systems were studied in 13 families containing members suffering from various hereditary disorders involving ataxia. Classical cerebellar ataxia was present in four, Friedreich ataxia in two, hereditary spastic paraplegia in four, and the Charcot-Marie-Tooth syndrome in three families. In each family, every available member above the lowest age at onset observed in that family, was subjected to a thorough clinical investigation and blood was sampled for investigation of genetic markers.The families with cerebellar ataxia and with Charcot-Marie-Tooth syndrome contained enough informative relatives to allow a formal linkage study using the lodscore method. Three of the pedigress with cerebellar ataxia gave evidence of linkage between the disease and the HLA system with a combined lodscore of 2.128 at a recombination fraction of 0.05 for both sexes combined. The recombination fraction was considerably higher in females than in males, although the difference between the two sexes was not statistically significant.Negative lodscores were obtained for the remaining family with cerebellar ataxia, which might be due to the fact that this family only provided information on recombination in females. However, the clinical features in this family differed from those in the other three families by a significantly higher frequency of dementia and pyramidal tract lesions. Based on these observations and on contradictory results in the literature concerning linkage between cerebellar ataxia and HLA, we suggest that there are two forms of cerebellar ataxia: One (CA¹) linked to HLA with symptoms restricted to lesions in the cerebellum and spinocerebellar system and another (CA²) not linked to HLA with symptoms from more wide-spread lesions of the CNS.None of the other genetic markers (except perhaps GLO) showed linkage to the cerebellar ataxias. Negative lodscores throughout with all 21 genetic markers were found in the families with Charcot-Marie-Tooth syndrome.There was no evidence for linkage between HLA on the one hand and Friedreich ataxia or hereditary spastic paraplegia on the other.List of Abbreviations HA Hereditary ataxias - HLA Major histocompatibility system - CA Cerebellar ataxia - FA Friedreich ataxia - HSP Hereditary spastic paraplegia - CMT Charcot-Marie-Tooth syndrome - MS Multiple sclerosis - Hp Haptoglobin - Gc Group-specific component - PGM Phosphoglucomutase, locus 1 - SP (AcP) Acid phosphatase - AK Adenylatekinase - PGD 6-phosphogluconatedehydrogenase - ADA Adenosinedeaminase - GPT Glutamate pyruvat transaminase - GT Galaktose-1-phosphat uridylyltransferase - EsP Carboxylesterase D - GLO Glyoxylase I This study was aided by grants from Warwara Larsen's Foundation, the Danish Multiple Sclerosis Society and the Medical Research Council