Electrophysiological properties of sympathetic preganglionic neurons in the cat spinal cord in vitro

Intracellular recordings were obtained from sympathetic preganglionic neurons of the intermedio-lateral nucleus of the adult cat in slices of upper thoracic spinal cord maintained in vitro. The neurons were identified by their antidromic responses to stimulation of various ipsilateral sites. Sites from which antidromic responses could be evoked were the white ramus, the ventral root, the ventral root exit zone, the white matter between the latter and the outer edge of the tip of the ventral horn, the lateral edge of the ventral horn. Resting membrane potential was –61.3±1.6 mV (mean±SEM), input resistance 67.5±3.7 M, time constant 11.5±1.2 ms. The amplitude of the action potential generated by antidromic or direct stimulation was 77.4±2.3 mV. Threshold for direct spikes was 18.2±1.8 mV. The action potential had an average duration of 3.03±0.16 ms. It showed a prominent hump on the falling phase. The action potential had a tetrodotoxin (TTX)-sensitive and a TTX-resistant component. The latter was abolished by cobalt.Tetraethylammonium, cesium and barium prolonged the action potential duration which acquired a plateau-shape. A prolonged after-hyperpolarization (AHP) followed the sympathetic preganglionic neuron spike. Following a single spike, AHP duration and peak amplitude were 2.8±0.3 s and 16.6±0.7 mV, respectively. The AHP was abolished by cesium or barium, but enhanced by tetraethylammonium. An AHP followed the TTX-resistant spike. EPSPs and IPSPs could be generated by focal stimulation. The EPSP triggered spikes when threshold (15.0±2.0 mV) was reached. The slice of the thoracic spinal cord provides a useful experimental preparation for analysis of cellular properties and synaptic mechanisms of the sympathetic preganglionic neuron.     

Architecture and synaptic relationships in the intermediolateral nucleus of the thoracic spinal cord of the rat: HRP labelling, catecholamine histochemistry and electron microscopic studies

Summary The organization of the intermediolateral nucleus (IML) of the thoracic spinal cord was examined using glyoxylic acid-induced fluorescence histochemistry, retrograde horseradish peroxidase (HRP) labelling and electron microscopy. In serial sections of T2, it was found that the distribution of catecholamine nerve terminals was intimately related to the neuronal perikarya of IML. Potassium permanganate fixation and 5-hydroxydopamine treatment revealed small dense-cored vesicles in axon varicosities with or without synaptic specializations. A gelatinous region, composed of small diameter dendrites and unmyelinated axons, formed a narrow longitudinal bundle in the centre of the nucleus. The population of the axon varicosities in the IML was 0.17 ± 0.02/m² in 75 nm sections. The average size of the axon varicosities with flat synaptic vesicles was 1.44 ± 0.05 m² and that of varicosities with spherical vesicles was 0.97 ± 0.02 m². After HRP injection into the superior cervical ganglion, ipsilateral IML neurons were labelled in T1–T3 segments of the spinal cord. Axon varicosities with flat and others with spherical synaptic vesicles synapsed on the dendrites labelled by HRP. Among axon varicosities synapsing on the preganglionic sympathetic neurons, 74.8 ± 7.1% at axo-somatic synapses and 46.0 ± 6.7% at synapses on proximal dendrites contained flat synaptic vesicles.     

The ciliary ganglion of the cat: a light and electron microscopic study

The ciliary ganglia of eight healthy adult cats were studied by light and electron microscopy. The ganglion, measuring about 2 mm in length, was consistently found to be attached to the branch from the oculomotor nerve supplying the inferior oblique muscle. The number of neurons varied from 2773 to 3794 after applying Abercrombie's correction. The mean of average somal diameter of the neurons was 36.5 m (SD = 5.0 m) and the mean of somal cross-sectional area was 904.2 m² (SD = 262.8 m²). The mean of average nuclear diameter was 13.9 urn (SD = 1.8 m) and the mean of nuclear cross-sectional area was 142.2 m² (SD = 37.1 m²). The mean of the aspect ratios of the soma and nucleus were 1.2 (SD = 0.1) and 1.1 (SD = 0.1) respectively. The frequency distributions of these parameters were all unimodal. Under the light microscope, the Nissl granules in the neurons were prominent and were distributed peripherally, perinuclearly or randomly in the cytoplasm. Under the electron microscope, the rough endoplasmic reticulum showed a similar pattern of distribution in the cytoplasm. In some neurons, glycogen-like granules were present; these were either distributed randomly throughout the cell, or aligned in single rows in relation to sub-surface cisterns and between the cisterns of smooth and rough endoplasmic reticulum. Most of the dendrites were short protrusions from the cell body; some contained glycogen-like granules. Occasionally, the dendritic protrusions were electron-dense. All the synapses encountered were axodendritic. In most axon terminals, the synaptic vesicles were spherical and measured 30–50 nm in diameter; in some, they were flattened, measuring 50 nm by 20 nm. Some axon terminals containing either spherical or flattened synaptic vesicles also contained large dense-cored vesicles that measured 80–100 nm, while their dense core measured 40–60 nm.     

Analysis of synovial fluid from clinically healthy Iranian fat-tailed sheep

In this study synovial fluid from the radiocarpal joints of 100 clinically healthy Iranian sheep (Lori-Bakhtiari) were analyzed. Total nucleated cell count (TNCC) of the synovial fluid was 178.9±75 cells/l (mean±SD). Lymphocytes were the predominant cell type composing 48.34±17.2% of the cells found in the synovial fluid, whereas monocytes, macrophages and neutrophils composed 36.52±3.5%, 12.75±5.9% and 2.28±1.18% of the cells found in the synovial fluid, respectively. The glucose concentration of synovial fluid was 44.9±9 mg/dl. The concentration of total protein, albumin and globulin of the synovial fluid were 2.31±0.55, 1.49±0.38, 0.81±0.28 g/dl, respectively. The albumin to globulin ratio (A/G) was 2.02±0.61. Age and sex had no significant effects on TNCC, percentage of lymphocytes, monocytes, macrophages and neutrophils, concentration of total protein, albumin, globulin, and A/G ratio of fluid from the radiocarpal joint. However, glucose concentration in radiocarpal fluid in sheep less than 1-year-old was significantly (P0.05) higher (48.27±1.4 mg/dl) than 1- to 2-years-old (42.1±1.4 mg/dl) and more than 2-years-old sheep (43.9±1.8 mg/dl). No significant differences were found between right and left limbs for any parameters evaluated in this study.     

Differences in synaptic size in the superficial and deep layers of the molecular layer of the cerebellar cortex of the cat

Summary In a previous study observations in semithin sections of E-PTA-stained cerebellar cortex of the cat revealed differences in size of synaptic grids between the molecular and granular layer (Van der Want et al. 1984). In addition, synaptic size differences were observed between superficial and deep levels in the molecular layer. The present study was an attempt to analyze synapses in ultrathin sections of the cerebellar cortex with special emphasis on size differences of distinct types of synapses at different levels in the molecular layer. Climbing fibers were identified by means of anterograde transport of ³H-leucine injected in the inferior olive and parallel fibers were identified on account of fine structural criteria. Synaptic profiles were measured semi-automatically in the neuropil of the cerebellar cortex at the supra-Purkinje level and the subpial level. Measurements of the trace- and chordlength were obtained from random sections. The frequency distribution of the true diameters of the synapses was reconstructed with a discrete unfolding-procedure. The overall diameter at the superficial level was 390.2±1.5 nm, at the deep level 406.6±1.5 nin. Climbing fibers exhibited mean values of 431.9±4.7 and 461.3±4.1 nm at these levels and parallel fiber terminals mean values of 370.7±2.9 and 395.8±3.0 nm. The frequency distributions showed remarkable and statistically significant differences compared with the overall distributions observed at the superficial and the deep levels respectively. The frequency distributions of synaptic diameters at the superficial and deep levels also differ significantly. The results suggest that synapses are characterized by a specific size which might be related to the region of termination or might be determined by the afferent neuron. This is in agreement with earlier observations in E-PTA treated material.     

Interrelationships between interleukin (IL)-1, IL-6 and IL-8 in synovial fluid of various arthropathies

High levels of many cytokines, including interleukin (IL)-1, IL-6 and IL-8, were found in various arthropathies suggesting that they play a role in the pathogenesis of disease, although their relationship with the type and activity of disease is still not clear. The synovial fluid (SF) of 24 patients with rheumatoid arthritis (RA), 19 with psoriatic arthritis (PA) and 33 with osteoarthritis (OA) was analyzed for IL-1, IL-6 and IL-8. The highest concentration of the three cytokines was found in the SF of RA. IL- detectable levels (>-20 pg/ml) were observed in 8/24 (33.3%) patients with RA, in one patient with PA but in no patient with OA.IL-6 (mean±SD) (1610.37±1781.65 pg/ml) was higher in RA than in PA (672.47±867.40 pg/ml,p=0.043) and OA (89.45±120.52 pg/ml,p=0.0001). IL-8 (1042.72±698.64 pg/ml) was higher in RA than in PA (660.36±625.11 pg/ml,p=0.03) and OA (89.9±45.88 pg/ml,p=0.0001). A correlation between IL-1, IL-6 and IL-8 was found in RA. In all patients a correlation between IL-6 and IL-8 levels was found; moreover, these two cytokines were associated with SF indices of inflammation, such as white blood cells (WBC) count and total protein (TP) concentration.Out findings suggest that these interrelationships play a role in the evolution of more severe erosive arthropathy such as RA.     

Central venous pressure and plasma arginine vasopressin in man during water immersion combined with changes in blood volume

Summary To investigate the influence of central venous pressure (CVP) changes on plasma arginine vasopressin (pAVP), 8 normal male subjects were studied twice before, during and after immersion to the neck in water at 35.1±0.1 C (mean±SE) for 6 h. After 2 h of immersion, blood volume was either expanded (WI_EXP) by intravenous infusion of 2.01 of isotonic saline during 2 h or reduced by loss of 0.51 of blood during 30 min (WI_HEM). The two studies were randomised between subjects. WI_EXP increased CVP, systolic arterial pressure (SAP), diuresis, natriuresis, kaliuresis and osmolar clearance compared to WI_HEM while haematocrit, haemoglobin concentration and urine osmolality decreased. Heart rate, mean arterial (MAP) and diastolic arterial pressure, plasma osmolality, plasma sodium, plasma potassium and free water clearance did not differ significantly in the two studies. pAVP was significantly higher after 6 h in WI_HEM than after 6 h in WI_EXP (2.0±0.2 vs. 1.6±0.2 pg · ml^–1, mean±SE;P<0.05). pAVP values were corrected for changes in plasma volume due to infusion in order properly to reflect AVP secretion. In conclusion, there was a weak, but significant, negative correlation between CVP and pAVP during the two studies, while during recovery from WI_HEM and WI_EXP decrements in SAP and MAP correlated significantly and strongly with increases in pAVP. It is therefore concluded that it is the arterial baroreceptors rather than the cardiopulmonary mechanoreceptors which are of importance in AVP regulation in man.This investigation was supported by the Danish Space Board, grant no. 1112-32/83, 1112-33/83 and 1112-19/84     

Patch-clamp analysis of voltage-gated currents in intermediate lobe cells from rat pituitary thin slices

Ionic currents of hypophyseal intermediate lobe cells were studied using a thin-slice preparation of the rat pituitary in conjunction with conventional and perforated whole-cell patch-clamp recording techniques. A majority (89%) of the cells studied generated Na⁺, Ca²⁺ and K⁺ currents upon depolarizing voltage steps and responded to bath application of -aminobutyric acid (GABA; 20–50 M) with inward currents (in symmetrical chloride, holding potential –80 mV). A small percentage of cells (11%) did not display inward membrane currents upon depolarization and was unresponsive to GABA. In the first type of cells, Ca²⁺ and K⁺ currents were further studied in isolation. Ca²⁺ tail currents showed a biphasic time course upon repolarization, with time constants and amplitudes of 2.07±0.29 ms, 123±22 pA (for the slowly deactivating component) and 0.14±0.06 ms, 437±33 pA (for the fast-deactivating component; means±SD of n=4 cells). Slowly and fast-deactivating conductances were half-maximally activated at around –10 mV and +10 mV respectively. Depolarizing voltage steps elicited two types of K⁺ current, which were separated using a prepulse protocol. A fast-activating, transient component showed half-maximal steadystate inactivation between –65 mV and –45 mV depending on the divalent cation composition of the external solution. Its decay was fitted by single-exponential functions with time constants of 36±11 ms and 3.9±0.9 ms at –20 mV and +40 mV respectively (mean±SD; n=4 cells). Whereas the peak current amplitudes of the transient K⁺ current component remained stable, the amplitude of the second, delayed component increased progressively throughout the course of whole-cell experiments. In cells recorded with the perforated whole-cell technique, bath application of dopamine (10 nM–1 M) induced large hyperpolarizations from a spontaneous membrane potential of –40 mV, but did not consistently affect the amplitude of the voltage-gated K⁺ conductances. These data are compared to previous studies using other preparations of the intermediate lobe, and differences are discussed, thus helping to extend our knowledge of electrical excitability of hypophyseal cells.     

The responses of the catecholamines and β-endorphin to brief maximal exercise in man

Summary The responses to brief maximal exercise of 10 male subjects have been studied. During 30 s of exercise on a non-motorised treadmill, the mean power output (mean±SD) was 424.8±41.9 W, peak power 653.3±103.0 W and the distance covered was 167.3±9.7 m. In response to the exercise blood lactate concentrations increased from 0.60±0.26 to 13.46±1.71 mmol·l^–1 (p<0.001) and blood glucose concentrations from 4.25±0.45 to 5.59±0.67 mmol·l^–1 (p<0.001). The severe nature of the exercise is indicated by the fall in blood pH from 7.38±0.02 to 7.16±0.07 (p<0.001) and the estimated decrease in plasma volume of 11.5±3.4% (p<0.001). The plasma catecholamine concentrations increased from 2.2±0.6 to 13.4±6.4 nmol·l^–1 (p<0.001) and 0.2±0.2 to 1.4±0.6 nmol·l^–1 (p<0.001) for noradrenaline (NA) and adrenaline (AD) respectively. The plasma concentration of the opioid-endorphin increased in response to the exercise from <5.0 to 10.2±3.9 p mol·l^–1. The post-exercise AD concentrations correlated with those for lactate as well as with changes in pH and the decrease in plasma volume. Post-exercise-endorphin levels correlated with the peak speed attained during the sprint and the subjects peak power to weight ratio. These results suggest that the increases in plasma adrenaline are related to those factors that reflect the stress of the exercise and the contribution of anaerobic metabolism. In common with other situations that impose stress,-endorphin concentrations are also increased in response to brief maximal exercise.     

Minimal synaptic delay in the saccadic output pathway of the superior colliculus studied in awake monkey

The synaptic organization of the saccade-related neuronal circuit between the superior colliculus (SC) and the brainstem saccade generator was examined in an awake monkey using a saccadic, midflight electrical-stimulation method. When microstimulation (50–100 A, single pulse) was applied to the SC during a saccade, a small, conjugate contraversive eye movement was evoked with latencies much shorter than those obtained by conventional stimulation. Our results may be explained by the tonic inhibition of premotor burst neurons (BNs) by omnipause neurons that ceases during saccades to allow BNs to burst. Thus, during saccades, signals originating from the SC can be transmitted to motoneurons and seen in the saccade trajectory. Based on this hypothesis, we estimated the number of synapses intervening between the SC and motoneurons by applying midflight stimulation to the SC, the BN area, and the abducens nucleus. Eye position signals were electronically differentiated to produce eye velocity to aid in detecting small changes. The mean latencies of the stimulus-evoked eye movements were: 7.9±1.0 ms (SD; ipsilateral eye) and 7.8±0.9 ms (SD; contralateral eye) for SC stimulation; 4.8±0.5 ms (SD; ipsilateral eye) and 5.1±0.7 ms (SD; contralateral eye) for BN stimulation; and 3.6±0.4 ms (SD; ipsilateral eye) and 5.2±0.8 ms (SD; contralateral eye) for abducens nucleus stimulation. The time difference between SC- and BN-evoked eye movements (about 3 ms) was consistent with a disynaptic connection from the SC to the premotor BNs.     

Evidence for Na/H exchange and Cl/HCO3 exchange in A10 vascular smooth muscle cells

In the present study we used the pH sensitive absorbance of 5(and6)-carboxy-4,5-dimethylfluorescein to investigate intracellular pH (pH_i) regulation in A10 vascular smooth muscle cells: (1) The steady state pH_i in A10 cells averaged 7.01±0.1 (mean±SEM,n=26) at an extracellular pH of 7.4 (28 mM HCO₃/5% CO₂). (2) Removal of extracellular sodium led to an intracellular acidification of 0.36±0.07 pH-units (mean±SEM,n=8). (3) pH_i-Recovery after an acute intracellular acid load (by means of NH₄Cl-prepulse) was reversibly blocked by 1 mM amiloride and was dependent on the presence of sodium. The velocity of pH_i recovery increased with increasing sodium concentrations with an apparentK _m for external sodium of about 30 mM and aV _max of about 0.35 pH units/min. These findings are compatible with a Na/H exchanger being responsible for pH_i recovery after an acid load. (4) Removal of extracellular chioride induced an intracellular alkalinization of 0.23±0.03 pH-units (mean±SEM,n=10). The alkalinization was dependent on the presence of extracellular bicarbonate (5) Removal of chloride during pH_i recovery from an alkaline load (imposed by acetate prepulse) stopped and reversed pH_i backregulation. Chloride removal had no effect in the absence of bicarbonate or in the presence of 10^–4 M DIDS, suggesting that the effects were mediated by a Cl/HCO₃ exchanger. In conclusion we have demonstrated evidence for a Na/H exchanger and a Cl/HCO₃ exchanger in A10 vascular smooth muscle cells.Abbreviations used CDMF 5(and6)-carboxy-4,5-dimethylfluorescein - DIDS 4,4-diisothiocyanostilbene-2,2-disulfonic acid - NMDG N-methyl-d-glucamine; pH_i, intracellular pH - pH_o extracellular pH - Mops 3-[N-Morpholino]propanesulfonic acid - Hepes 2-[4-(2-Hydroxyethyl)-1-piperazinyl]-ethanesulfonic acid - Tris Tris(hydroxymethyl)-aminomethane - EDTA ethylenediamine-tetraacetic acid - EGTA ethyleneglycol-bis-(-amino-ethylether)N,N-tetraacetic acid     

Residual latency (delay at the neuromuscular junction): normative values and heritability in mice

In vertebrates there is a delay in impulse transmission at the neuromuscular junction termed residual latency (RL). RL is composed of synaptic delay proper plus delays due to reduced conduction velocities of fine nerve and muscle fibers. There have been few studies on RL and none under controlled conditions. RL has been determined for 485 HS mice and for 65 male inbred mice in five strains. All measurements were made on tails of awake mice 60–72 days old. The interval between the peak of the compound nerve action potential and the peak of the compound muscle action potential is defined as RL. In 400 HS males the mean (±SE) RL was 0.930±0.005 ms, with a range of 0.726 to 1.375 ms. Inbred means ranged from 0.714±0.024 ms for A/J to 0.0902±0.020 ms for DBA/1J. The inbred means differed very significantly among themselves (F=11.36, df=4, 60,P<0.0001). Nested ANOVA of RL by litter, family, and generation for the HS males and repeated-measures (test-retest) ANOVA for some HS males and inbreds permit estimation of environmental and genetic variances. Corrected for testing error, broad-sense heritability is estimated to be at least one-third and may be appreciably greater. RL may be of interest to behavioral geneticists because of its heritability and its reflection of certain types of CNS synaptic activity.This work was supported by the Natural Sciences and Engineering Research Council of Canada.     

Muscular activity level during pedalling is not affected by crank inertial load

The aim of the present study was to investigate the influence of gear ratio (GR) and thus crank inertial load (CIL), on the activity levels of lower limb muscles. Twelve competitive cyclists performed three randomised trials with their own bicycle equipped with a SRM crankset and mounted on an Axiom ergometer. The power output (80% of maximal aerobic power) and the pedalling cadence were kept constant for each subject across all trials but three different GR (low, medium and high) were indirectly obtained for each trial by altering the electromagnetic brake of the ergometer. The low, medium and high GR (mean±SD) resulted in CIL of 44±3.7, 84±6.5 and 152±17.9 kg·m², respectively. Muscular activity levels of the gluteus maximus (GM), the vastus medialis (VM), the vastus lateralis (VL), the rectus femoris (RF), the medial hamstrings (MHAM), the gastrocnemius (GAS) and the soleus (SOL) muscles were quantified and analysed by mean root mean square (RMS_mean). The muscular activity levels of the measured lower limb muscles were not significantly affected when the CIL was increased approximately four fold. This suggests that muscular activity levels measured on different cycling ergometers (with different GR and flywheel inertia) can be compared among each other, as they are not influenced by CIL.     

Dendritic morphology and retinal distribution of tyrosine hydroxylase-like immunoreactive amacrine cells in Bufo marinus

Summary Tyrosine hydroxylase-like immunoreactive (TH-IR) amacrine cells (ACs) in the retina of metamorphosing and adult Bufo marinus were visualized, and their retinal distribution established, using immunohistochemistry on retinal wholemount and sectioned material. The somata of TH-IR ACs were located in the innermost part of the inner nuclear layer (INL). Their dendrites branched predominantly in the scieral sublamina of the inner plexiform layer (IPL), with sparse branching also in the vitreal sublamina. In the retinae of metamorphosing animals 592 ± 113 (mean ± S.D.) immunoreactive cells and in adult 5,670 ± 528 cells were found. Usually 1, 2 or 3 stem dendrites arose from the somata of TH-IR cells which branched 2 or 3 times. In the adult retinae the dendritic field sizes of immunoreactive cells were in the range of 0.059 ± 0.012 mm², which resulted in a considerable dendritic overlap across the retina. TH-IR cells were unevenly distributed over the retina, with 72 cells/mm² in the central temporal retina, 45–50 cells/mm² along the naso-temporal axis of the retina and 25 cells/mm² in the dorsal and ventral peripheral retina. The average density was 36 ± 6 cells/mm². A considerable number of TH-IR cells (range 52–133, n=4) were displaced into the ganglion cell layer (GCL) of the retina. The mean soma sizes of immunoreactive cells were significantly higher in the low density (95 ± 13 m²) than in the high cell density areas (86 ± 12 m²). There was also a slight but significant increase of the dendritic field sizes of these cells towards the low cell density areas of the retina. These observations show that the retinal distribution of TH-IR ACs parallels the non-uniform distribution of neurons of the INL demonstrated recently in Bufo marinus (Zhu et al. 1990). The class of TH-IR ACs appears to correspond to a subgroup of morphologically distinct dopaminergic ACs found in a number of other vertebrate species.On leave from Department of Anatomy, Zhanjiang Medical College, Guangdong, People's Republic of China     

The relationship between some measures of synaptic ultrastructure as a function of distance from the soma on lamprey reticulospinal neurons

Summary Synaptic junctions located on the dendrites of lamprey (Petromyzon marinus) reticulospinal neurons labelled with intracellularly-injected horseradish peroxidase were studied. The normal ultrastructure of the synaptic junctions was defined and several quantitative measures made from each junction in order to test the hypothesis that distally-located synapses are ultrastructurally different from those located at proximal dendritic sites. A total of 820 contacts from one neuron and 279 from a second neuron ranging from 20 to 340 m from the soma were quantified. The vast majority of the presynaptic endings contained round, clear-cored vesicles and formed an asymmetrical membrane differentiation with the postsynaptic dendrite. A small fraction of the population contained flattened or pleomorphic vesicles and these synapses were equally distributed with respect to distance from the soma. Many of the terminals contained a few large dark- and clear-cored vesicles. Four quantitative measures of each synaptic contact were made. These included vesicle number, length of differentiated membrane, vesicle area and terminal area. Four ratios relating the different quantitative measures were also calculated. Each ratio or measurement from the synaptic junctions was plotted as a function of distance from the soma to determine if differences existed at any distance. It was found that synaptic junctions are uniformly similar and that distal junctions did not differ significantly (P > 0.05) from those at proximal dendritic sites. It is concluded that if distal synapses do compensate for their remote location they do this in some other way, possibly by increasing the number of synaptic contacts made by each presynaptic axon.     

Postsynaptic arch in the frog neuromuscular junction: Paramembranous protuberances coating the inner surface of the postjunctional membrane

Summary The frog neuromuscular junction was fixed and processed for electron microscopy according to the method of rapid freezing followed by freeze-substitution. The synaptic structures, including cleft material, paramembranous cytoplasmic coating on the postsynaptic membrane, and subsynaptic cytoplasmic elements, were examined in thin sections. The basal lamina, about 50 nm thick, was seen to bisect a synaptic cleft 100 nm wide. The lamina consists of two parts: the central dense line and the fine filaments protruding from it in the direction of the apposing postjunctional membrane. Present on the cytoplasmic surface of the postjunctional membrane are electron-dense protuberances, 41 ± 5 nm in width and 27 ± 5 nm in height (top to membrane centre). They are arranged in regular parallel rows, at 54 ± 4nm intervals (centre to centre). The paramembranous protuberance coats the inner surface of the postjunctional membrane at its apex as well as at the middle portion of the junctional process, pointing to its probable hairpin-like course in a transverse plane of the process. From its location and three-dimensional arrangement, this protuberance was termed the postsynaptic arch. A filamentous meshwork is present just beneath the postjunctional membrane and extends into the cell interior. The submembranous meshwork appears to connect to the underlying bundles of cytoskeletal filaments. The possibility is discussed that the postsynaptic, electron-dense arch corresponds to the 43-kDa protein, a major alkaline-extractable protein thought to be associated with the cholinergic receptor molecules in the postsynaptic membrane.     

An intracellular HRP-study of cat tensor tympani motoneurons

Summary The morphology of single tensor tympani motoneurons was investigated following antidromic identification and intracellular injection of horseradish peroxidase. Eight motoneurons were selected for complete reconstruction and quantitative analysis. The mean size of tensor tympani somata (26.3±1.8 m) make this parvocellular cluster of motoneurons below the trigeminal motor nucleus a population of the smallest cranial motoneurons yet described. Axons emerged from either the soma or a primary dendrite. They coursed dorsolaterally frequently through the trigeminal motor nucleus before looping ventrolaterally into the Vth nerve. No collaterals were observed within the brainstem. The 5 primary dendrites of each cell branched heavily and, on average, exhibited 40 terminal branches with an average tree expansion of 1262.5 m. The dendritic arborization extended far beyond the nuclear boundaries described by the distribution of cell bodies. These data suggest that the overall membrane area for synaptic innervation is large and thus it provides morphological evidence for the hypothesis that tensor tympani motoneurons receive divergent multisensory synaptic input. The latter assumption was supported by morphological and electrophysiological evidence including close the proximity of motoneuronal dendrites to auditory (superior olivary complex) and somatosensory (trigeminal) relay centers. Since no dendrite ever entered the trigeminal motor nucleus proper the tensor motoneuron pool is distinct from the trigeminal not only in terms of soma size, location and function, but also the disposition and expansion of the postsynaptic receptive field. Based on these criteria the tensor tympani motoneuron pool should no longer be regarded as an accessory trigeminal nucleus but be recognized in its own right as the tensor tympani motor nucleus of V.Preliminary report of this work has been presented by Friauf and Baker 1983     

GABA-containing neuronal processes in normal and cortically deafferented dorsal lateral geniculate nucleus of the cat: an immunogold and quantitative EM study

Summary The qualitative and quantitative synaptology of flat synaptic vesicle containing F type terminals was analysed in normal and in chronically cortically deafferented dorsal Lateral Geniculate Nucleus (dLGN) of the cat using an electron microscopic immunogold technique for visualization of GABA. A direct correlation was found between the density (number of gold particles) of GABA immunostaining and the number of synaptic vesicles in different F terminals. This suggested a quantitative relationship between transmitter content and the number of vesicles in the labeled terminals. Not only the number but also the size of synaptic vesicles was found to be different in the two main groups of F profiles, i.e. the axonal F1 and dendritic F2 terminals. Measurement of the size of synaptic vesicles in F1 axon terminals revealed two subpopulations of these endings: F1₁ and F1₂ terminals with vesicle diameters of 31.56 ± 0.08 nm and 33.73 ± 0.12 nm (P < 0.01; Chi² test) respectively. The size of synaptic vesicles in axonal F1₂ terminals was identical to that found in F2 dendritic profiles, suggesting that both processes belonged to the same, intrageniculate (interneuronal) cell population. F1₁ terminals, however, appeared to be axonal endings of extrageniculate (most probably of perigeniculate) neurons. Quantitative analysis of the two types of GABAergic axon terminals revealed the geniculocortical relay cells to be the main postsynaptic targets for F1₁ (extrageniculate) terminals while F1₂ axons terminated equally on both interneurons and relay cells. Following chronic decortication of the dLGN, the distribution pattern of both GABAergic axonal types had changed considerably. As a result of a severe loss in relay cells, more F1₁ and F1₂ axon terminals were found on GABA-containing interneuronal processes than on relay cells. An increase in the number of F1 axonal terminals per neuron was also revealed, (particularly on GABAergic interneurons), suggesting a compensatory reactive synaptogenesis by both F axonal types following decortication.     

Anterograde transsynaptic degeneration in the deep cerebellar nuclei of Purkinje cell degeneration (pcd) mutant mice

Summary The genetically-determined loss of Purkinje cells (PCs) in Purkinje cell degeneration (pcd) mutant mice results in the loss of presynaptic afferents to the deep cerebellar nuclei (DCN). This deafferentation takes place between postnatal day (P)17 and P45, i.e. after the maturation of cerebellar circuitry. We examined the DCN of normal and pcd mutant mice by quantitative light microscopic methods to determine whether neuronal atrophy or loss in the DCN take place during and after the loss of their input from the PCs. Neuronal diameters in control mice were 16.4±0.72 m (mean±S.D.) at P23 and 15.6±0.64 m at P300. The respective values in pcd mutant mice were 15.7±0.58 m and 13.5±0.24 m. Diameters in 300-day-old mutants were significantly smaller than those in both age-matched controls and 23-day-old mutants (P< 0.001). Neuronal populations in the DCN of control mice were 10,167± 949 at P23 and 10,429±728 at P300. The respective values in mutants were 9,436±1,366 and 7,424±1,324. There was a significant difference of 29% [95% confidence limits: 9–45%] between 300-day-old mutants and age-matched controls (P<0.01), and a significant loss of 21% [95% confidence limits: 4–36%] in 300-day-old mutants with respect to 23-day-old mutants (P<0.05). The total volume of the DCN was 22% less in 300-day-old mutants in relation to 23-day-old mutants (P< 0.05). These findings support the idea that the stability of DCN neurons in the mature cerebellum depends in part on the synaptic input from PCs.     

Effects of Ba2+ on the mechanical properties of glycerinated heart muscle

At a muscle length, L₀ (just taut), isometric tension and tension transients in response to rapid step stretches in length (mostly less than 1.2% of L₀ within 2 ms) were measured at constant levels of Ba²⁺ activation of varying magnitude in glycerinated cat right-ventricular papillary muscles (2–3 mm long, 130–200 m in diameter). The majority of the experiments were carried out at room temperature (26–27°C) and at a pH of 6.8 The steady isometric tension increased as Ba²⁺ was varied from slightly below pBa 6 to about pBa 4. The concentration range of Ba²⁺-activated muscle was roughly 10 times higher than that of Ca²⁺-activated muscle. Maximum Ba²⁺-activated isometric tension was 79.0±4.2% (mean±SD,n=8) of that activated with Ca²⁺. The tension transients in Ba²⁺-activated muscle were characterized by at least three distinct phases; an immediate tension increase coincident with the stretch, a rapid exponential tension decrease (time constant, ₁ = 7.3 ± 1.0 ms,n = 5) and a delayed exponential tension rise (₂ = 104 ± 5.7 ms,n=5). The profile of tension response was quite similar to that of Ca²⁺-activated muscle. These results suggest that in Ba²⁺-activated glycerinated heart muscle the cross-bridge turnover is taking place as in the Ca²⁺-activated muscle, but the number of active cross-bridges at maximally activated state is smaller than that of Ca²⁺-activated muscle.