Intercellular adhesion can be visualized using fluorescently labeled fibrosarcoma HT1080 cells cocultured with hematopoietic cell lines or CD34(+) enriched human mobilized peripheral blood cells

BACKGROUND

Intercellular contacts between adjacent cells migrating over each other are important in many cellular processes. However, it has been difficult to visualize and identify dynamic intercellular adhesions between migrating cells in situ.

METHODS

Two fluorescent membrane dyes, PKH2 and PKH26 for staining HT1080 and hematopoietic cells and cell lines, and an automated fluorescence microscopy system were used to monitor intercellular adhesion.

RESULTS

Cellular extensions connecting two or more adjacent cells were visualized, showing the intercellular adhesion between migrating cells for minutes and up to hours. After cells adhered to each other, followed by cell migration in different directions, cellular extensions were dragged from the pivotal contact points in different focal planes. CD34(+)-enriched mobilized peripheral blood cells and six hematopoietic cell lines showed intercellular connections in cocultures with HT1080. However, the frequency of intercellular connections was variable in different cocultures. A cell density of about 3.1 x 10(4) cells/cm(2) for both cell lines in cocultures provided an adequate number of cells in each field of view, showing up to four intercellular connections per 100 total cells plated.

DISCUSSION

The tools derived from this study will open new areas of investigation for understanding the mechanism of the intercellular adhesion process.

Extension of osmolality-induced podia is observed from fluorescently labeled hematopoietic cell lines in hyperosmotic medium

BACKGROUND

Since the description of long podia extended by hematopoietic cells and cell lines, the reliable elicitation of podia extensions is needed to study these podia systemically. In this study, hyperosmotic stress was considered as an elicitor.

METHODS

Using two fluorescent membrane dyes PKH2 and PKH26, and an automated fluorescence microscopy system, morphological changes of seven human cell lines (six hematopoietic, one fibrosarcoma) at different osmolalities were monitored. Presence of surface molecules on the hyperosmolality-induced podia (osmopodia) was examined.

RESULTS

In hyperosmotic medium, cells shrank rapidly, followed by osmopodia extension. Cells exhibited variable number (up to five) and length (up to longer than 100 microm) of osmopodia in about 1 h. Dead cells did not extend podia. Frequency, length, and number of podia were variable among cell lines studied. CD44 and CD45 were not present on the osmopodia, although they were present on the cell surface, showing that osmopodia characteristics differ from the podia observed previously in isotonic media. The osmopodia extension process was shown to be reversible upon repeated osmolality changes.

CONCLUSIONS

Osmopodia extended by human hematopoietic cell lines display a newly observed cellular morphology and provide a tool for investigation of dynamic cellular response to environmental changes.

Prevalence and treatment of pressure ulcers in northern New South Wales

This paper reports on a small, cross-sectional study of 18 hospitals in northern New South Wales. The objectives of this study were to collect baseline data on: (i) the prevalence and type of pressure ulcers in a variety of rural hospitals; and (ii) the range of nursing and medical interventions that are used to prevent/treat pressure ulcers. Using a cross-sectional design, the study found that pressure ulcer prevalence, which was 6%, was within the range found by previous reports (4-15%). Pressure ulcer prevention and treatment practices were varied, ranging from turning of the patient and occlusive dressings, to such creative methods as exposure to sunshine and airing the wound. This study demonstrates that despite years of attention to pressure sore prevention and treatment, the prevalence of ulcers is still a significant problem in northern New South, Wales hospitals.

Key adhesion molecules are present on long podia extended by hematopoietic cells

BACKGROUND

We recently reported that CD34(+) hematopoietic cells and the KG1a cell line extend long, thin podia. These podia can dynamically extend and retract, often adhere to the substrate, and appear to connect cells up to 300 microm apart. The surface receptors found on these podia have not been described.

METHODS

By using time-lapse fluorescent microscoscopy and immunostaining techniques, we describe a method for detecting surface receptors on these podia. This includes an in situ antibody staining procedure without fixing cells.

RESULTS

We demonstrate, using CD34 selected mobilized peripheral blood cells and KG1a cells, that adhesion molecules known to play important roles in blood-cell migration and adhesion are present on these podia. These include: CD11a, CD18, CD29, CD34, CD45, CD49d, CD49e, and CD62L. Additionally, CD54 and CD44 were present on the podia extended by KG1a cells, but were not detectable on the primary CD34(+) cells. The integrin CD49d localized at the base of these podia in a time-dependent manner in KG1a cells. The frequency and morphology of these long podia on three myeloid leukemia-cell lines (KG1a, MV4-11, and AML-193) and a CD34-negative T-cell line (CEM) are also compared. KG1a and CEM cell lines extend long, dynamic podia that are similar to the podia on primary CD34(+) cells in morphology and adhesion molecule expression. The AML-193 and MV4-11 cell lines, however, did not extend these long podia.

CONCLUSIONS

We describe a technique that provides a method of detecting surface receptors on thin cell membrane projections. These results support the likely role of these podia in cell migration and cell-cell communication.

Symmetry of initial cell divisions among primitive hematopoietic progenitors is independent of ontogenic age and regulatory molecules

We have developed a time-lapse camera system to follow the replication history and the fate of hematopoietic stem cells (HSC) at a single-cell level. Combined with single-cell culture, we correlated the early replication behavior with colony development after 14 days. The membrane dye PKH26 was used to monitor cell division. In addition to multiple, synchronous, and symmetric divisions, single-sorted CD34(+)/CD38(-) cells derived from fetal liver (FLV) also gave rise to a daughter cell that remained quiescent for up to 8 days, whereas the other daughter cell proliferated exponentially. Upon separation and replating as single cells onto medium containing a cytokine cocktail, 60.6% +/- 9.8% of the initially quiescent cells (PKH26 bright) gave rise again to colonies and 15.8% +/- 7.8% to blast colonies that could be replated. We have then determined the effects of various regulatory molecules on symmetry of initial cell divisions. After single-cell sorting, the CD34(+)/CD38(-) cells derived from FLV were exposed to flt3-ligand, thrombopoietin, stem cell factor (SCF), or medium containing a cytokine cocktail (with SCF, interleukin-3, interleukin-6, granulocyte-macrophage colony-stimulating factor, and erythropoietin). Whereas mitotic rate, colony efficiency, and asymmetric divisions could be altered using various regulatory molecules, the asymmetric division index, defined as the number of asymmetric divisions versus the number of dividing cells, was not altered significantly. This observation suggests that, although lineage commitment and cell proliferation can be skewed by extrinsic signaling, symmetry of early divisions is probably under the control of intrinsic factors.

Phototoxicity of the fluorescent membrane dyes PKH2 and PKH26 on the human hematopoietic KG1a progenitor cell line

BACKGROUND

The phototoxic effects of the well-known fluorescent membrane dyes PKH2 and PKH26 have been unknown, although their use in cell tracking experiments has increased dramatically. To eliminate the phototoxicity-induced alteration in cell function and morphology, it is essential to examine the suspicious phototoxicity of these dyes.

METHODS

Chemical and phototoxic effects of PKH dyes on the human hematopoietic KG1a cell line were examined. To minimize phototoxicity in long-term cell tracking experiments lasting up to 18 h with a fluorescence microscope system, time-lapse monitoring with different time intervals and exposure times was introduced.

RESULTS

There were no significant effects of the two PKH dyes on cell viability and growth when using dye concentrations up to 5 microM. However, when stained cells were exposed to excitation light, cell viability decreased dramatically, showing the phototoxicity of the PKH dyes. More than 60% of cells stained with 5 microM PKH26 died after 5 min of continuous light exposure. The phototoxic effect was more extensive in cells stained with higher concentrations of the dyes.

CONCLUSIONS

We present guidelines for the optimal use of these dyes by using a defined hardware configuration.

Phototoxicity of the fluorescent membrane dyes PKH2 and PKH26 on the human hematopoietic KG1a progenitor cell line

BACKGROUND

The phototoxic effects of the well-known fluorescent membrane dyes PKH2 and PKH26 have been unknown, although their use in cell tracking experiments has increased dramatically. To eliminate the phototoxicity-induced alteration in cell function and morphology, it is essential to examine the suspicious phototoxicity of these dyes.

METHODS

Chemical and phototoxic effects of PKH dyes on the human hematopoietic KG1a cell line were examined. To minimize phototoxicity in long-term cell tracking experiments lasting up to 18 h with a fluorescence microscope system, time-lapse monitoring with different time intervals and exposure times was introduced.

RESULTS

There were no significant effects of the two PKH dyes on cell viability and growth when using dye concentrations up to 5 microM. However, when stained cells were exposed to excitation light, cell viability decreased dramatically, showing the phototoxicity of the PKH dyes. More than 60% of cells stained with 5 microM PKH26 died after 5 min of continuous light exposure. The phototoxic effect was more extensive in cells stained with higher concentrations of the dyes.

CONCLUSIONS

We present guidelines for the optimal use of these dyes by using a defined hardware configuration.

Evaluation and rehabilitation of patients with adult motor neuron disease

Adult motor neuron disease (amyotrophic lateral sclerosis [ALS]) is a neurodegenerative disorder characterized by loss of motor neurons in the cortex, brain stem, and spinal cord, manifested by upper and lower motor neuron signs and symptoms affecting bulbar, limb, and respiratory musculature. Clinically, the disease course is characterized by progressive weakness, atrophy, spasticity, dysarthria, dysphagia, and respiratory compromise, ultimately resulting in death or mechanical ventilation in the vast majority of patients. Patterns of presentation and pathological features of the disease, along with clinical and electrophysiologic criteria for diagnosis, are discussed in this review. Since 8% to 22% of patients survive more than 10 years without ventilator use, meticulous medical and rehabilitation management is extremely important to ensure optimal health and quality of life in these patients. Major issues in the care of individuals with ALS include weakness and spasticity, impairments in activities of daily living and mobility, communication deficits and dysphagia in those with bulbar involvement, respiratory compromise, fatigue and sleep disorders, pain, and psychosocial distress. Research in ALS changes rapidly, but is currently focused on potential etiologic factors such as glutamate excitotoxicity, role of oxidative stress, autoimmunity to calcium channels, and cytoskeletal abnormalities, as well as related treatment initiatives including glutamate modulators, neurotrophic factors, antioxidants, antiapoptotic factors, and gene therapy. Recently, mutations in the gene encoding Cu/Zn superoxide dismutase were identified in a subset of familial ALS patients. Riluzole, a glutamate antagonist and Na-channel blocker, became the only drug currently approved for treatment of ALS after studies showed a small positive effect on survival. Until a definitive treatment or cure for ALS is found, the multifaceted rehabilitation team approach remains the best hope for improving health and survival in this devastating illness.

Two new pseudopod morphologies displayed by the human hematopoietic KG1a progenitor cell line and by primary human CD34(+) cells

A primitive human hematopoietic myeloid progenitor cell line, KG1a, characterized by high expression of the CD34 surface antigen has been observed to extend long, thin pseudopodia. Once extended, these pseudopods may take on one of two newly described morphologies, tenupodia or magnupodia. Tenupodia are very thin and form in linear segments. They adhere to the substrate, can bifurcate multiple times, and often appear to connect the membranes of cells more than 300 micrometer apart. Magnupodia are much thicker and have been observed to extend more than 330 micrometer away from the cell. Magnupods are flexible and can exhibit rapid dynamic motion, extending or retracting in a few seconds. During retraction, the extended material often pools into a bulb located on the pod. Both morphologies can adhere to substrates coated with fibronectin, collagen IV, and laminin as well as plastic. The CD34 and CD44 antigens are also present on the surface of these podia. Primary human CD34(+) cells from fetal liver, umbilical cord blood, adult bone marrow, and mobilized peripheral blood extend these podia as well. The morphology that these pseudopods exhibit suggest that they may play both sensory and mechanical roles during cell migration and homing after bone marrow transplantation.

Effect of acute exercise on plasma homocysteine

BACKGROUND

The aim this work was to study the effects of acute exercise on plasma homocysteine level.

METHODS

Twenty healthy, physically active males aged 24-39 (X = 29) ran on treadmill at an intensity of 70% of their maximal heart for 30 minutes. Blood was taken before, immediately following and 30 minutes following the exercise bout.

RESULTS

There was no statistically significant relationship between pre-exercise plasma homocysteine levels and VO2 max (r = -0.05). Plasma homocysteine significantly increased 11.5% from the pre-exercise to 11.6 +/- 3.3 mumol.L-1 immediate post exercise levels. Thirty minutes postexercise plasma homocysteine was still elevated from pre-exercise levels, however the mean of 11.2 +/- 2.9 mumol.L-1 was not statistically different from pre-exercise values. The increase in homocysteine that occurred with 30 minutes of exercise is thought to be the result of hemoconcentration as indicated by changes in plasma albumin. Plasma albumin likewise paralleled the changes observed for homocysteine. Mean pre-exercise plasma albumin values were 42.9 +/- 2.9 g.L-1. Plasma albumin significantly increased 6.9% to 45.8 +/- 2.4 g.L-1 immediately post-exercise. Thirty minutes post exercise plasma albumin was still elevated from pre-exercise levels at 44.8 +/- 5.4 g.L-1. When the homocysteine plasma levels were adjusted for changes in plasma albumin, there was no statistical difference between any of the time points.

CONCLUSIONS

It was concluded that acute exercise does not have any effect on plasma homocysteine in young healthy men aged 24-39.

Detection of Chlamydia trachomatis cervical infection by urine tests among adolescents clinics

PURPOSE

To compare urine ligase and polymerase chain reaction (LCR, PCR) tests for diagnosis of Chlamydia trachomatis cervical infection with PCR and nucleic acid probe (GPA) on cervical specimens in adolescents, as well as risk factors for C. trachomatis infection and prevalence of infection at enrollment.

METHODS

Urine and cervical specimens were collected from women aged 13-20 years attending adolescent clinics, and interviews were administered. Urine specimens were tested by PCR and LCR, and cervical specimens by GPA and PCR. Prevalence rates of C. trachomatis infection and gonorrhea were compared by demographic, behavioral, and clinical risk factors.

RESULTS

Of 415 women tested, 86 (20.7%) were infected with C. trachomatis as indicated by positive cervical PCR results. A higher prevalence of C. trachomatis infection was seen among adolescents who douched monthly or more frequently, or had gonorrhea; prevalence declined from 25.8% in the first 7 months to 16.3% in the last 14 months of the study (p = .017). A statistically significant protective effect for reported condom use was not observed. Sensitivity of urine PCR was 89.5% and specificity was 100% relative to cervical PCR, compared to 84.9% and 99.4% (urine LCR) and 65.4% and 98.0% (cervical GPA). Sensitivity of urine PCR was higher in women with discharge; urine LCR sensitivity was higher in women < 19 years of age.

CONCLUSIONS

Polymerase chain reaction and LCR assays on urine specimens were sensitive, specific, and noninvasive tests in this population of adolescents with high C. trachomatis infection prevalence. Chlamydia trachomatis infection was associated with douching monthly or more frequently. Prevalence of infection declined over the period during which the study was conducted.

The burden of physical inactivity & cardiovascular heart disease

Heart disease exacts a tremendous toll each year in mortality and health care expenditures. Although physical activity reduces the risk of heart disease, the population remains inactive. The importance of physical activity in risk and health care cost reduction is discussed.

Effective intercellular communication distances are determined by the relative time constants for cyto/chemokine secretion and diffusion

A cell's ability to effectively communicate with a neighboring cell is essential for tissue function and ultimately for the organism to which it belongs. One important mode of intercellular communication is the release of soluble cyto- and chemokines. Once secreted, these signaling molecules diffuse through the surrounding medium and eventually bind to neighboring cell's receptors whereby the signal is received. This mode of communication is governed both by physicochemical transport processes and cellular secretion rates, which in turn are determined by genetic and biochemical processes. The characteristics of transport processes have been known for some time, and information on the genetic and biochemical determinants of cellular function is rapidly growing. Simultaneous quantitative analysis of the two is required to systematically evaluate the nature and limitations of intercellular signaling. The present study uses a solitary cell model to estimate effective communication distances over which a single cell can meaningfully propagate a soluble signal. The analysis reveals that: (i) this process is governed by a single, key, dimensionless group that is a ratio of biological parameters and physicochemical determinants; (ii) this ratio has a maximal value; (iii) for realistic values of the parameters contained in this dimensionless group, it is estimated that the domain that a single cell can effectively communicate in is approximately 250 micron in size; and (iv) the communication within this domain takes place in 10-30 minutes. These results have fundamental implications for interpretation of organ physiology and for engineering tissue function ex vivo.

Responses of melanin-concentrating hormone mRNA to salt water challenge in the rainbow trout

Melanin-concentrating hormone (MCH) is a structurally conserved neuropeptide, produced in the hypothalamus of all vertebrates where it probably serves as a central neurotransmitter/neuromodulator. In teleost fish it is also a neurohypophysial hormone with peripheral effects on skin colour but its central effects are less well understood. In mammals, MCH mRNA abundance changes in response to salt-loading or dehydration, suggesting an involvement in salt or water balance. The present study has used in situ hybridization to investigate the response of the MCH neurons in the rainbow trout (Oncorhynchus mykiss) to progressive changes in ambient salinity. In trout, MCH perikarya are found in two hypothalamic sites: predominantly in the nucleus lateralis tuberis (NLT) and, to a lesser extent, in neurons above the lateral ventricular recess (LVR). Immersion in 50% salt water (SW) for 24 h had no effects on MCH transcripts, plasma osmotic pressure (OP) or cortisol concentrations, but after 24 h in 80% SW, plasma OP and cortisol were raised and MCH transcripts in the NLT were significantly increased (159% of controls, p < 0.01). LVR-MCH neurons remained unaffected. However, after 24 h in 100% SW, MCH mRNA was significantly reduced in both groups of neurons (NLT -62% of controls, p < 0.001; LVR -33% of control, p < 0.001). These responses were transient and were no longer apparent after 6 days in 100% SW, despite the fact that plasma OP and cortisol levels continued to rise. The relative importance of osmotic disturbance and stress on the differential responses of the 2 groups of MCH neurons to changing salinity is discussed, together with a consideration of the potential role of MCH in osmoregulation.

Atypical presentation of Henoch-Schoenlein purpura in two children

Henoch-Schoenlein purpura (HSP) is a common vasculitic disorder of childhood. Patients with this disorder typically present with palpable purpura or petechia associated with one or more of the following signs and symptoms: abdominal pain, arthritis/arthralgias, and nephritis. The diagnosis may be difficult to make, however, when a patient presents with isolated symptoms such as abdominal pain without the typical rash. A high index of suspicion must be maintained to diagnose HSP in this setting and to avoid unnecessary interventions. This report describes two unusual patients with the presenting complaint of abdominal pain who had delayed onset of the purpuric rash, making the diagnosis of HSP difficult.

Physical activity in the prevention of cardiovascular disease

Research during the past several decades confirms the health benefits of regular physical activity, including improved cardiovascular function and quality of life, with reduced risks of morbidity and mortality from cardiovascular heart disease (CHD). Health care professionals, including physical therapists, can assist the public by promoting physical activity and describing the type, quantity, and quality of activity that confers health benefits. Participation in vigorous physical activity for at least 30 minutes a day is recommended for cardiorespiratory fitness, but recent studies suggest that physical activity below this level can have benefits in reducing the risk for CHD. This article addresses the relationship between physical inactivity and the financial burdens on health care, the relationship between physical inactivity and the risks of developing CHD in different age groups, the health benefits associated with moderate levels of physical activity, and the amounts and types of physical activities that are needed to reduce the risk of CHD.

Evidence for the stochastic acquisition of cytokine profile by CD4+ T cells activated in a T helper type 2-like response in vivo

The diversity of cytokine production patterns displayed by T cells activated in vivo was investigated by analyzing short-term antigen-specific CD4+ T cell clones and single CD4+ T cells derived from draining lymph nodes of mice undergoing a T helper 2 (Th2)-like response to keyhole limpet hemocyanin (KLH). On average, 2.7% of CD4+ lymph node cells gave rise to clones in the presence of the immunizing antigen and, of these, about 90% secreted interleukin-4 (IL-4) and 20% secreted interferon-gamma (IFN-gamma) when restimulated after 2 weeks in vitro. Almost all IFN-gamma-producing clones co-produced IL-4. The definition of clones as positive or negative for cytokine synthesis depended on assay sensitivity, however, since their titers were distributed continuously from the threshold of detection over at least a 1000-fold range. Reverse-transcription polymerase chain reaction analysis of 59 clones revealed multiple patterns of co-expression of IL-2, IL-3, IL-4, IL-6, IFN-gamma and granulocyte-macrophage colony-stimulating factor (GM-CSF) mRNA. Although most clones contained detectable IL-4 and IL-6 mRNA and a minority contained IFN-gamma mRNA, only 1 clone expressed the canonical Th2 cytokine profile. The observed frequencies of mRNA co-expression for most of the six cytokines (including IL-4 with IFN-gamma), and the frequency of co-secretion of IL-4 and IFN-gamma, were not significantly different from those predicted for random association. Independent regulation of IL-4 and IFN-gamma mRNA expression was confirmed at the single-cell level in a polyclonal population of KLH-primed CD4+ cells, among which co-expression of these cytokines again occurred at the frequency predicted for a random event. The data suggest that the polarization of this immune response towards a Th2 cytokine profile is achieved by altering the probabilities of expression of the IL-4, IFN-gamma and other cytokine genes at the population level, rather than by selective expansion of a distinct T cell subset.

Developmental changes in melanin-concentrating hormone in Rana temporaria

Melanin-concentrating hormone (MCH) is a vertebrate neuropeptide produced in hypothalamic neurons. In bony fish, such as trout, MCH acts as a neurohypophysial hormone which, once released into the circulation, acts on pigmented skin cells with the result that the fish turns pale to camouflage itself against a light colored background. In other animals the role of MCH is not clearly established but it appears to be a neuromodulator/transmitter within the central nervous system rather than a hormone. The present study examines MCH function in the grass frog, Rana temporaria. Using immunocytochemistry the location and morphology of irMCH neurons were followed, from tadpole to adult frog. In adult R. temporaria a group of MCH neurons appeared to comprise small and large-celled populations located in the ventral and dorsal infundibular regions, respectively. A group of MCH neurons in the preoptic area is proposed, although the perikarya were rarely immunostainable. Immunoreactive fibers were seen in various areas of the brain, including the olfactory lobes, optic tecta, habenular nucleus, and spinal cord. Immunoreactive MCH cells were only visible in midmetamorphic climax stages, and cellular morphology suggested low secretory activity until the animal first emerged onto land at which time nuclear size and granulation increased significantly. No such increase was observed in equivalent stages of the South African clawed toad, Xenopus laevis, an animal which is fully aquatic throughout its life in contrast to R. temporaria which is terrestrial.(ABSTRACT TRUNCATED AT 250 WORDS)

Preparation and characterization of liposomes containing a lipophilic cisplatin derivative for clinical use

Cis-bis-neodecanoato-trans-R,R-1,2 diaminocyclohexane platinum(II) (NDDP) is a lipophilic cisplatin derivative that has been formulated entrapped in multilamellar liposomes composed of dimyristoylphosphatidyl choline (DMPC) and dimyristoylphosphatidyl glycerol (DMPG). A phase I clinical study with liposome-entrapped NDDP (L-NDDP) administered i.v. every 4 weeks has been recently completed. L-NDDP was synthesized, manufactured, and reconstituted for clinical use in our laboratories. L-NDDP was prepared as a lyophilized powder containing the NDDP and the phospholipids (NDDP-lipid weight ratio 1:15; DMPC-DMPG molar ratio 7:3). The liposome suspension was obtained on the day of use just before administration to the patients by adding normal saline (final concentration 1 mg NDDP/ml) and shaking in a water-bath shaker at room temperature according to an established protocol. A total of 54 batches of lyophilized L-NDDP were prepared. Physical appearance, phospholipid content and integrity, and elemental platinum content were determined in all batches and found to be reproducible. All batches contained < 0.24 ng/ml endotoxin. The amount of residual organic solvents was < 0.05 per cent. In all reconstituted doses, drug entrapment was > 90 per cent, and the proportion of liposomes measuring > 5 microns was < 20 per cent. Our results show that reproducible batches of liposomal preparations of new compounds can be prepared in the laboratory facilities of academic institutions, thus allowing for early clinical trials with novel therapeutic agents.

Distribution of ryanodine receptor-like immunoreactivity in mammalian central nervous system is consistent with its role in calcium-induced calcium release

The distributions of ryanodine receptor-like immunoreactivity and Ca-ATPase-like immunoreactivity were identified in the guinea-pig and rat central nervous system using antibodies raised against the rabbit skeletal muscle ryanodine receptor and Ca-ATPase. In both guinea-pig and rat cerebellum, the ryanodine receptor-like immunoreactivity was restricted to the soma and dendrites of Purkinje cells. In the medulla, neuron somata in the hypoglossal nucleus were stained in both species, but in the dorsal motor nucleus of the vagus somata were stained in guinea-pigs but not in rats. This species difference in ryanodine receptor-like immunoreactivity is consistent with the species difference in expression of a ryanodine sensitive, calcium activated potassium conductance in neurons of the dorsal motor nucleus of the vagus. Immunoreactivity to Ca-ATPase was present in vagal motoneurons in both species with denser staining in the guinea-pig. The data further support the idea that, in neurons of the dorsal motor nucleus of the vagus, release of intracellular calcium stores via a ryanodine receptor activates a specific class of potassium channels, thereby modulating cell excitability.