Biomedical subjects

S M Miller

Publications and source records attributed to S M Miller.

At least 73 records · Page 4Linked to original sources

PubMed1998

Rapid reduction of Hg(II) by mercuric ion reductase does not require the conserved C-terminal cysteine pair using HgBr2 as the substrate.

Conditions are described under which the nonphysiological substrate mercuric bromide (HgBr2) is rapidly turned over, both by the wild type (CCCC) and by an active site double mutant (CCAA) of mercuric reductase in which the C-terminal cysteines 557' and 558' are replaced by alanine and only the redox-active pair Cys135 and Cys140 are available for catalysis. A maximum rate of turnover kcatapp of approximately 18 s-1 (at 3 degreesC) for both enzymes is observed, and at high [HgBr2]/[enzyme] ratios, inhibition is found. The UV-vis spectral changes during turnover are closely similar in both enzymes, indicating that catalysis follows the same enzymatic mechanism. Single-turnover analysis of the mutant enzyme shows that after binding of HgBr2, two further rapid events ensue, followed by reduction of the metal ion (kobs approximately 23.5 s-1). It is shown that under multiple-turnover conditions, completion of the catalytic cycle must occur via an ordered mechanism where rapid binding of a new molecule of HgBr2 to EH2.NADP+ precedes exchange of the pyridine nucleotide. Binding of HgBr2 to the active site triple mutant C135A/C557A/C558A (ACAA) is ca. 100-fold slower compared to that of the CCAA mutant and results in no detectable turnover. It is concluded that in the reducible enzyme.Hg(II) complex, the metal ion is coordinated to Cys135 and Cys140 and that for efficient catalysis both residues are required. Furthermore, the data imply that binding to EH2.NADPH occurs via initial rate-limiting attack of Cys135, followed by reaction with Cys140.

Alanine↗

PubMed1998

The three-dimensional structure of myenteric neurons in the guinea-pig ileum.

Myenteric neurons of the guinea-pig ileum were intracellularly filled with the fluorescent dye Lucifer Yellow, optically sectioned with a confocal microscope and volume reconstructed to recreate 3-D images of the cells. The resulting images provide information not evident from regular microscopy. The somata varied in cross-section from flat-oval to nearly circular, and their surface membranes were marked by invaginations and protrusions significantly increasing the surface area of the somatic membrane. The neurons could be divided into four morphological classes: Dogiel type I, Dogiel type II, filamentous, and intermediate. There was no clear correlation between cell class and the shape of the soma in cross-section. The dendritic processes of all the neurons studied extended in an orad-caudad or circumferential direction of the bowel wall. When the filled neurons were viewed edge-on, the spatial arrangement of the processes was confined to a plane that had a thickness less than the thickness of the parent soma. The broad, short dendrites of Dogiel type I neurons were oval or nearly circular in cross-section. Directly measured quantitative data were obtained for the volume and surface area of the somata and visible processes. The structural details reported herein are likely to have important implications regarding the functional properties of individual enteric ganglion neurons and circuits of enteric ganglion neurons.

Animals↗

PubMed1998

Visualization of interstitial cells of Cajal in the mouse colon by vital staining.

Interstitial cells of Cajal (ICCs) are believed to be a major element in generating the spontaneous rhythm of the gastrointestinal tract. A prominent problem in the study of these cells has been the difficulty in observing them in intact tissues. We used the lipophilic dye DiI to stain ICCs in the submucosal-circular muscle border of freshly dissected mouse colon. The placement of small DiI crystals in this area resulted in the labeling of ICC-like cells. Two main morphological cell types, viz., bipolar and multipolar, were noted. Bipolar cells had two primary processes emerging from the poles of an elongated soma. The mean length of these processes was 78.7 microm. These cells constituted 42.3% of the sample (n=105). Multipolar cells (54.3% of total) had a less elongated soma and extended 3-6 main processes whose mean length was 56.3 microm. These processes showed no preferred direction. The length of the primary processes of bipolar cells was 40% greater than that of multipolar cells (P<0.02). Three cells (2.9%) had only one primary process. The DiI stain could be converted into a stable electron-opaque product. Electron-microscopic observations showed that these cells had the typical appearance of ICCs reported in previous studies. This staining method should be useful for physiological investigations of ICCs in gastrointestinal tissues.

Animals↗

PubMed1998

Bradycardia induced by intravascular versus direct stimulation of the vagus nerve.

BACKGROUND: Electrical stimulation of the parasympathetic nervous system results in slowing of the heart. We sought to determine whether cardiac vagal efferent axons can be stimulated adequately to induce bradycardia without disturbing the integrity of the thorax. METHODS: Cardiodepressor effects elicited by direct stimulation of a vagus nerve in anesthetized dogs and pigs were compared with those generated when the same nerve was stimulated indirectly through bipolar electrodes placed in the adjacent superior vena cava. RESULTS: The heart rate of dogs decreased by about 80% when electrical stimuli were delivered to the right thoracic vagus at the level of the thoracic outlet through bipolar electrodes placed either in the adjacent superior vena cava (intravascular method) or directly on the nerve (direct method). Maximal responses were achieved with 10-V, 5-ms, and 20-Hz stimuli. In anesthetized pigs, similar bradycardia occurred when the right cervical vagus or the right cranial thoracic vagus was stimulated either directly or indirectly through the intravascular method. Atrial dysrhythmias occurred when the stimulating electrodes were placed by either method within 1 cm of the right atrium in both animal models. CONCLUSIONS: Controlled bradycardia can be induced during operation without the risk of generating cardiac dysrhythmias using electrical stimuli (10 V, 5 ms, and 10 to 20 Hz) delivered to the right cervical vagus nerve or the right cranial thoracic vagus nerve through adjacent intravascular electrodes.

Animals↗

PubMed1998

Heme oxygenase 2 is present in interstitial cell networks of the mouse small intestine.

BACKGROUND & AIMS: The interstitial cell (IC) network may be of fundamental importance in regulating gastrointestinal motility. Intestinal smooth muscle cells are depolarized in the absence of ICs, and there are no spontaneous slow waves. The messenger molecules between IC network and smooth muscle are unknown. Exogenous administration of CO relaxes the opossum internal anal sphincter and the guinea pig ileum, and it modulates potassium current and membrane potential of circular smooth muscle cells of the human jejunum. The aim of this study was to determine whether heme oxygenase (HO)-1 and HO-2, enzymes that catalyze the production of CO, are present in the IC network of the mouse small intestine. METHODS: Antibodies specific for c-Kit, HO-1, and HO-2 were used for immunohistochemistry. Confocal images were obtained and were volume rendered, and the images were converted into three-dimensional images. RESULTS: HO-2-like but not HO-1-like immunoreactivity was found in IC networks associated with the myenteric plexus and the deep muscular plexus. CONCLUSIONS: HO-2 but not HO-1 is present in the IC cell network of the mouse small intestine. The enzymatic activity of HO-2 will result in the endogenous production of CO in IC networks of the mouse small intestine.

Animals↗

PubMed1998

Patch-clamp recordings of membrane currents evoked during natural synaptic activity in sympathetic neurons.

Membrane currents elicited by colonic distension and by electrical stimulation of the intermesenteric nerve containing colonic afferent nerve fibres were recorded from neurons of the mouse superior mesenteric ganglion at 20 degrees C with the whole-cell patch-clamp method. Electrically-evoked excitatory postsynaptic currents reversed at -3.5 mV. At membrane holding voltages of -70 mV and -110 mV, the excitatory postsynaptic currents were characterized by a single exponential decay with a mean (+/- S.E.M.) time-constant of 17.5 +/- 1.3 ms and 15.5 +/- 2.3 ms, respectively. Colonic distension evoked a series of the excitatory postsynaptic currents which ranged in amplitude from 10 to 700 pA (at a membrane holding voltage of -70 mV). Hexamethonium (100 microM) applied only to the ganglion abolished both electrically- and distension-evoked excitatory postsynaptic currents, suggesting activation of nicotinic acetylcholine receptors. The decay time-course of distension-evoked single excitatory postsynaptic currents was characterized by one, or, less commonly, by two exponentials. The decay time-constant histograms of distension-evoked single excitatory postsynaptic currents exhibited main kinetic components of 8.1 +/- 2.3 ms and 8.2 +/- 2.5 ms (peak +/- S.D.) at -70 and -110 mV membrane holding voltages, respectively. Longer time-constants ranging up to 51 ms were also observed. The number of the distension-evoked excitatory postsynaptic currents with a decay time-constant higher than 20 ms, as well as their mean amplitude, were significantly lower at -110 mV than at -70 mV membrane potential levels, in contrast to the currents with a decay time-constant lower than or equal to 20 ms. The results suggest that colonic afferent nerve fibres activate in the mouse superior mesenteric ganglion neurons a few populations of the postsynaptic nicotinic acetylcholine receptors with different channel kinetics, which are characterized by a lack of voltage sensitivity within -70 to -110 mV membrane potential range, except those with comparatively slow channel kinetics, which are possibly blocked by membrane hyperpolarization.

Animals↗

PubMed1998

Distribution of heme oxygenase and effects of exogenous carbon monoxide in canine jejunum.

Carbon monoxide (CO) has been postulated to be a messenger in the gastrointestinal tract. The aims of this study were to determine the distribution of heme oxygenase (HO), the source for endogenous CO in the canine jejunum, and to determine the effects of CO on jejunal circular smooth muscle cells. HO-2 isoform was present in a population of myenteric and submucosal neuronal cell bodies, in nerve fibers innervating the muscle layers, and in smooth muscle cells. HO-1 isozyme was not detected in the canine jejunum. Exogenous CO increased whole cell current by 285 +/- 86%, hyperpolarized the membrane potential by 8.5 +/- 2.9 mV, and increased guanosine 3',5'-cyclic monophosphate (cGMP) levels in smooth muscle cells. 8-Bromo-cGMP also increased the whole cell current. The data suggest that endogenous activity of HO-2 may be a source of CO in the canine jejunum and that exogenously applied CO can modulate intestinal smooth muscle electrical activity. It is therefore reasonable to suggest a role for endogenously produced CO as a messenger in the canine jejunum.

Alkaloids↗

PubMed1998

Diabetes: targeting an old adversary.

For the first time in almost 20 years, new recommendations on diagnosis, classification, and testing strategies for diabetes have been issued. For clinical labs, combatting this old enemy under the new guidelines will include expanded patient screening and closer monitoring. Learn about the high-risk groups in the U.S. population, the long-term effects of diabetes, and how changes in testing approaches can improve disease management and patient outcomes.

Clinical Laboratory Techniques↗

PubMed1998

Procedural considerations in the real-ear measurement of completely-in-the-canal instruments.

Conventional procedures for measurement of the real-ear aided response (REAR) of hearing aids are performed by placing the probe tube 5 mm beyond the medial tip of the canal portion of the earmold or shell and within 5 mm of the tympanic membrane. Completely-in-the-canal (CIC) instruments insert more deeply into the ear canal, and thus may make adherence to conventional probe-microphone procedures impossible. The REAR was measured at several probe tube insertion depths, using two insertion methods: through a probe vent and alongside the CIC shell. Results indicated that conventional probe insertion depth is not necessary for CIC instruments and may place some clients at risk for discomfort due to contact of the probe tube with the tympanic membrane. Placement of the probe tube along-side the CIC shell rather than through a probe vent resulted in slit leak venting effects that were highly variable across subjects. A probe tube placement protocol for use with CIC instruments is suggested.

Adult↗

PubMed1997

Selective disruption of neurotransmission by acetylcholinesterase antibodies in sympathetic ganglia examined with intracellular microelectrodes.

Antibodies to acetylcholinesterase (AChE) induce adrenergic dysfunction in rats by selective, complement-mediated destruction of preganglionic sympathetic nerve terminals. To analyze this phenomenon at the neuronal level, monoclonal antibodies to AChE (1.6 mg) were injected via the tail vein, and superior cervical ganglia (SCG) or inferior mesenteric ganglia (IMG) were studied in vitro. In control SCG, all impaled neurons generated action potentials during direct injection of depolarizing current or indirect stimulation through the preganglionic nerve. Current injection remained effective in ganglia from treated rats, but preganglionic stimulation was greatly impaired: at 12 h and 3 d, less than 10% of the neurons responded, even to a maximal stimulus (150 V); at 9 d, only 25% responded. By contrast, in IMG, synaptic transmission was much less affected by antibody exposure: 60% or more of examined neurons responded to preganglionic stimulation. Differences in antibody access did not explain differing sensitivities of SCG and IMG since immunohistochemistry showed rapid accumulation of IgG deposits in both ganglia. These results are believed to reflect widespread but subtotal preganglionic sympathectomy by AChE antibodies. Current information indicates that paravertebral ganglia are all antibody-sensitive, but some prevertebral ganglia are resistant, suggesting immunochemical differences between them.

Acetylcholinesterase↗

PubMed1997

Enhancing adherence following abnormal Pap smears among low-income minority women: a preventive telephone counseling strategy.

BACKGROUND: Although the incidence of precancerous conditions of the cervix has recently been increasing, prompt initial and long-term follow-up care can effectively reduce unnecessary morbidity and mortality. For example, the 4-year survival rates among those individuals at greatest risk for cervical cancer (i.e., minority women of low socioeconomic status) approach 95% with early detection. Women who present with advanced disease have a much poorer outlook (0%-39% survival). Yet, high-risk individuals are least likely to adhere to recommended diagnostic regimens. PURPOSE: We tested the effectiveness of a brief telephone counseling intervention directed to low-income, inner-city women after they had received an abnormal Pap smear result. The women were counseled on the importance of having an initial and 6-month repeat follow-up diagnostic procedure (i.e., colposcopic examination of the cervix). METHODS: A randomized trial design was used to compare the effects on these women of telephone counseling with (n = 192) or without (n = 203) a booster counseling telephone call prior to the appointment for a repeat colposcopy 6 months later, with a telephone appointment confirmation/reminder call (n = 216) and with standard care (i.e., no telephone contact) (n = 217). The telephone counseling protocol probed for and addressed three psychologic barriers to adherence (i.e., attendance at appointment for colposcopy examination): 1) encoding/expectancy (e.g., did the patient understand her risk of developing cervical cancer?); 2) affective/emotional (e.g., was the woman worried about the condition and its consequences?); and 3) self-regulatory/practical (e.g., was the woman likely to forget medical appointments?). Logistic regression was used to analyze the effects of the intervention group and the type of psychologic barriers elicited on colposcopy adherence. RESULTS: The results of logistic regression analysis (using those who received an appointment confirmation/reminder telephone call as the comparison group) revealed that telephone counseling produced significantly higher adherence rates to the initial colposcopy visit compared with telephone confirmation (300 [76%] of 395 women versus 147 [68%] of 216; odds ratio [OR] = 1.50; 95% confidence interval [CI] = 1.04-2.17). Additionally, standard care resulted in significantly lower adherence rates than did telephone confirmation (109 [50%] of 217 women versus 147 [68%] of 216; OR = 0.47; 95% CI = 0.32-0.73). Regarding attendance at the 6-month repeat colposcopy appointments, the 80 patients who had received telephone counseling prior to the initial visit (and were recommended for follow-up colposcopy) were significantly more likely to adhere than were the 47 patients who had received telephone confirmation (49 [61%] of 80 women versus 17 [36.2%] of 47; OR = 2.70; 95% CI = 1.15-6.51). The 6-month adherence rates for patients in the telephone confirmation group and the standard care group (n = 30) were low and did not differ significantly (17 [36.2%] of 47 women versus nine [30.0%] of 30; OR = 1.08; 95% CI = 0.40-2.89). Forgetting medical appointments (OR = 0.31; 95% CI = 0.19-0.51) and having scheduling conflicts (OR = 0.45; 95% CI = 0.28-0.72) were also associated with lower rates of adherence. CONCLUSION: The use of telephone counseling appears to be an effective strategy for enhancing initial and long-term adherence to a follow-up cervical diagnostic procedure in a traditionally underserved population. Patients who respond to a positive Pap test result with a particular profile of psychologic barriers may require more intensive and targeted counseling interventions.

Colposcopy↗

PubMed1997

Protection of nitrergic neurotransmission by and colocalization of neural nitric oxide synthase with copper zinc superoxide dismutase.

This study examined in the rat anococcygeus muscle the tissue distribution of copper zinc superoxide dismutase, the activity of CuZn SOD, and the role of CuZn SOD in protecting nitric oxide from destruction by superoxide anion. Immunohistochemical studies revealed intense staining for CuZn SOD in neuronal nitric oxide synthase-containing nerves. Muscle strips contained 1081 +/- 300 units SOD g-1 wet tissue (mean +/- S.E.M., n = 5). Diethyldithiocarbamate (2 mM) inhibited CuZn SOD activity in supernatant fractions of muscle homogenates by 34% (P < 0.01, n = 5), an effect reversed by CuCl2 (2 mM). In control conditions, electrical field stimulation of nitrergic inhibitory nerves evoked a 61.5 +/- 10.5% (n = 10) relaxation against guanethidine (30 microM)-induced tone. Relaxation evoked by nitrergic inhibitory nerves was neither potentiated by exogenous CuZn SOD (10-1000 U ml-1) nor reduced by the O-2-generator, pyrogallol (30 microM). When diethyldithiocarbamate (2 mM) was present, stimulation of nitrergic inhibitory nerves evoked a 51.7 +/- 10.8% (P < 0.05, n = 10) relaxation against guanethidine (30 microM)-induced tone. Addition of pyrogallol (30 microM) to diethyldithiocarbamate-treated (2 mM for 30 min) muscle strips further reduced nerve-evoked relaxation to 30.7 +/- 7.6% (P < 0.01, n = 10). The inhibitory effect of pyrogallol was reversed by exogenous CuZn SOD (100 U ml-1). Diethyldithiocarbamate (2 mM) had no effect on relaxation evoked by exogenous NO (1 microM). The data indicate that CuZn SOD is present in rat anococcygeus muscle, that it is colocalized with nNOS in the nitrergic nerves, and that it protects NO from destruction by O-2.

Animals↗

PubMed1997

The use of propofol for induction of anaesthesia in dogs premedicated with acepromazine, butorphanol and acepromazine-butorphanol.

Cardiovascular, pulmonary and anaesthetic-analgesic responses were evaluated in 18 male and female dogs to determine the effect of the injectable anaesthetic propofol used in conjuction with acepromazine and butorphanol. The dogs were randomly divided into three groups. Dogs in Group A were premeditated with 0.1 mg/kg of intramuscular acepromazine followed by an induction dose of 4.4 mg/kg of intravenous propofol; Group B received 0.2 mg/kg of intramuscular butorphanol and 4.4 mg/kg of intravenous propofol; dogs in Group AB were administered a premeditation combination of 0.1 mg/kg of intramuscular acepromazine and 0.2 mg/kg of intramuscular butorphanol, followed by induction with 3.3 mg/kg of intravenous propofol. The induction dose of propofol was given over a period of 30-60 seconds to determine responses and duration of anaesthesia. Observations recorded in the dogs included heart and respiratory rates, indirect arterial blood pressures (systolic, diastolic and mean), cardiac rhythm, end-tidal CO, tension, oxygen saturation, induction time, duration of anaesthesia, recovery time and adverse reactions. The depth of anaesthesia was assessed by the response to mechanical noxious stimuli (tail clamping), the degree of muscle relaxation and the strength of reflexes. Significant respiratory depression was seen after propofol induction in both groups receiving butorphanol with or without acepromazine. The incidence of apnea was 4/6 dogs in Group B, and 5/6 dogs in Group AB. The incidence of apnea was also correlated to the rate of propofol administration. Propofol-mediated decreases in arterial blood pressure were observed in all three groups. Moderate bradycardia (minimum value > 55 beats/min) was observed in both Groups B and AB. There were no cardiac dysrhythmias noted in any of the 18 dogs. The anaesthetic duration and recovery times were longer in dogs premeditated with acepromazine/butorphanol.

Journal Article↗

PubMed1997

Colonic mechanosensory afferent input to neurons in the mouse superior mesenteric ganglion.

Electrical activity and synaptic responses were recorded intracellularly in 415 neurons of the mouse superior mesenteric ganglion (SMG) attached to a segment of distal colon in vitro. Eighty-seven percent of neurons tested received ongoing nicotinic cholinergic fast excitatory postsynaptic potentials (fEPSPs). Colonic distension caused an initial transient followed by a sustained, slowly adapting increase in fEPSP activity. Application of hexamethonium only to the colon reduced, but did not completely abolish, distension-evoked responses, suggesting direct projection of some distension-sensitive fibers. Ongoing fEPSPs were abolished when nerve trunks connecting the SMG to the colon were transected or blocked with tetrodotoxin applied to the colon. Intracellular labeling with horseradish peroxidase or lucifer yellow revealed that about 90% of neurons receiving colonic synaptic input had a caudally projecting axon; about 60% that did not receive colonic input had a rostrally projecting axon. The latter neurons were found only in the cephalad ganglion region. These results show that mouse SMG neurons receive colonic mechanosensory afferent synaptic input and thus may participate in sympathetic intestinal reflexes.

Animals↗

PubMed1997

In vivo detection of calcium from dicalcium phosphate dihydrate dentifrices in demineralized human enamel and plaque.

A series of studies was conducted to clarify the role of DCPD in improving the effects of fluoride in the mouth. We performed plaque fluid studies to see if the use of DCPD dentifrices increases the levels of free Ca2+ ions and the DSenamel in plaque fluid. The results of these studies showed that plaque fluid was undersaturated with respect to DCPD; therefore, DCPD would dissolve in the mouth. The Ca2+ activity in plaque fluid measured 12 hours post-treatment was significantly elevated with the use of DCPD dentifrices in comparison with silica dentifrices. The use of DCPD dentifrices also increased the DSenamel of plaque fluid in comparison with a NaF/silica dentifrice. To determine whether Ca from DCPD could be detected in demineralized enamel and whole plaque after in vivo usage of a DCPD/ fluoride dentifrice, we conducted a 44Ca labeling study. Secondary Ion Mass Spectrometry (SIMS) was used to detect and measure changes in 44Ca levels in enamel before and after 6 days of in vivo treatment with a 44DCPD/fluoride dentifrice. The results showed that 44Ca from DCPD was incorporated into enamel and detected in plaque 18 hours post-treatment. The findings from these studies show that brushing with a DCPD dentifrice introduces additional, exogenous Ca into the oral environment, which fosters improved remineralization of teeth in combination with fluoride.

Calcium↗

PubMed1997

Successful aging in America, Part I. Nutrition, the elderly, and the laboratory.

Laboratory testing should be integral to nutrition-related services, including screening, assessment, and monitoring for both inpatient and outpatient geriatric populations. Find out how the laboratory can contribute to the improved health of seniors and reduce overall healthcare costs through nutritional status assessment and monitoring.

Aged↗

PubMed1996

Light, electron, and confocal microscopic study of the mouse superior mesenteric ganglion.

The superior mesenteric ganglion (S.m.g.), a sympathetic prevertebral ganglion, is an integrating center for gastrointestinal reflexes. Many details of its structure are still lacking. In the present study, mouse S.m.g. neurons were studied by light, electron, and confocal microscopy. Neurons had an average of 5-6 primary dendrites. Total dendritic length averaged 963 microns. Confocal microscopy and three-dimensional reconstructed images revealed cell body surface features, precise location where axons and dendrites emerged from it, cell body size, and extent of dendritic projection in three axes. Cell body diameter and dendritic projections were less in the dorsoventral than in the rostrocaudal or mediolateral axes. Cell body surface area and volume averaged 4,271 microns 2 and 4,908 microns 3, respectively. Dendritic surface areas and volumes were 5-6 times larger. Two main neuron types (projecting caudally or rostrally) were distinguished. The former were found throughout the S.m.g., whereas the latter were found only in the cephalad region, comprising about 40% of neurons found there. Rostrally projecting neurons had fewer primary dendrites, fewer total dendritic branches, and shorter total dendritic length than caudally projecting neurons. There were regional differences in percentage of neurons responding to electrical stimulation of left or right hypogastric, lumbar colonic, or left splanchnic nerves but not in nerve fibers connecting the S.m.g. and celiac ganglion. A greater percentage of caudally than rostrally projecting cephalad neurons responded to stimulation of any nerve trunk. These results indicate that the mouse S.m.g. contains at least two distinct types of neurons that differ in their morphology and their source of preganglionic synaptic input.

Animals↗

PubMed1996

Morphology of diaphragm neuromuscular junctions on different fibre types.

We hypothesize that the morphology of the neuromuscular junction on different muscle fibre types varies, reflecting differences in activation history. In the rat diaphragm muscle, we used a three-colour fluorescent immunocytochemical technique to simultaneously visualize (1) innervating axons and presynaptic nerve terminals, (2) motor endplates, and (3) myosin heavy chain isoform expression (muscle fibre type). Laser-scanning confocal microscopy was then used to optically section the triple-labelled muscle fibres, and create three-dimensional views of the neuromuscular junction. Type I fibres were innervated by the smallest axons, and type IIa, IIx and IIb fibres by progressively larger axons. Absolute planar areas of nerve terminals and endplates progressively increased from type I, IIa, IIx to IIb fibres. When normalized for fibre diameter, planar areas of nerve terminals were largest on type I fibres, with no difference among type II fibres. The normalized planar area of endplates were larger for type I and IIb fibres, compared to type IIa and IIx fibres. The three-dimensional surface area of endplates was largest on type I fibres, with no differences across type II fibres. When normalized for fibre diameter, endplate surface areas increased progressively from type I, IIa, IIx to IIb fibres. The branching patterns of both nerve terminals and endplates varied across fibre types. The number of nerve terminal and endplate branches increased progressively from type I, IIa, IIx to IIb fibres. Conversely, individual branch length was longest on type I fibres, and shortest on type IIb fibres. The extent of overlap of pre- and postsynaptic elements of the neuromuscular junction decreased progressively on type I, IIa, IIx and IIb fibres. We conclude that these morphological differences at the neuromuscular function of different fibre types reflect differences in activation history and may underlie phenotypic differences in neuromuscular transmission.

Animals↗