Electrical activity of caudal neurosecretory neurons in seawater and freshwater-adapted Platichthys flesus, in vivo.

This study examined the electrical firing activity of neuroendocrine Dahlgren cells in the caudal neurosecretory system (CNSS) of the euryhaline flounder in vivo. Intracellular recordings revealed generally similar activity patterns and membrane properties to those previously reported in vitro. To investigate the potential role of the CNSS in osmoregulatory adaptation, extracellular, multiunit, recordings compared the activity patterns of Dahlgren cells in fully seawater- and freshwater-adapted fish. The proportion of cells showing bursting (as opposed to phasic or tonic) activity was greater in seawater-than in freshwater-adapted fish, as was the Correlation Index, a measure of the degree of correlation between firing activities of cells recorded simultaneously from the same preparation. Acute transfer of fish from seawater to freshwater gill perfusion led to recruitment of previously silent Dahlgren cells and a reduction in Correlation Index; freshwater to seawater transfer increased the Correlation Index. Severing the spinal cord anterior to the CNSS led to an increase in overall Dahlgren cell activity. Electrical stimulation of branchial nerve branches providing input to the brainstem, or tactile (pinch) stimulation of lips or fins, led to a reduction in CNSS activity lasting up to 500 s, indicating the presence of descending modulatory pathways from the brain. These results are consistent with a role for CNSS neuropeptides, urotensins, in supporting survival in a hypertonic, seawater, environment.

Electrical activity of caudal neurosecretory neurons in seawater- and freshwater-adapted flounder: responses to cholinergic agonists.

The caudal neurosecretory system (CNSS) of the euryhaline flounder is involved in osmoregulatory responses underlying adaptation to seawater and freshwater. This study compared electrophysiological activity and responses to cholinergic agonists in the neuroendocrine Dahlgren cells in an in vitro preparation taken from fully seawater- (SWA) or freshwater-adapted (FWA) fish. Resting membrane and action potential parameters showed few differences between SWA and FWA cells. The hyperpolarisation-activated sag potential and depolarising afterpotential were present under both conditions; however, amplitude of the latter was significantly greater in SWA cells. The proportions of cells within the population exhibiting different firing patterns were similar in both adaptation states. However, bursting parameters were more variable in FWA cells, suggesting that bursting activity was less robust. The muscarinic agonist, oxotremorine, was largely inhibitory in Dahlgren cells, but increased activity in a non-Dahlgren cell population, alpha neurons. Nicotine promoted bursting activity in SWA Dahlgren cells, whereas it inhibited over half of FWA cells.

Bursting properties of caudal neurosecretory cells in the flounder Platichthys flesus, in vitro.

Bursting activity in type 1 Dahlgren cells was studied using intra- and extracellular recording from an in vitro preparation of the caudal neurosecretory system of the euryhaline flounder. 45% of cells showed spontaneous bursts of approximately 120s duration and 380s cycle period. Similar bursts were triggered by short duration (<5s) depolarising or hyperpolarising pulses. Cells displayed a characteristic depolarising after potential, following either an action potential with associated afterhyperpolarisation, or a hyperpolarising current pulse. This depolarising after potential was related to a 'sag' potential, which developed during the hyperpolarising pulse. Both the depolarising after potential and the sag potential occurred only in cells at more depolarised (<60 mV) holding potentials. In addition, the amplitude of the depolarising after potential was dependent on the amplitude and the duration of the hyperpolarising pulse. The depolarising after potential following action potentials may provide a mechanism for facilitating repetitive firing during a burst. Extracellular recording revealed similar bursting in individual units which was not, however, synchronised between units. Spontaneous bursting activity recorded both intra- and extracellularly was inhibited by application of a known neuromodulator of the system, 5-hydroxytryptamine. This study provides a basis for investigating the relationship between physiological status, Dahlgren cell activity and neuropeptide secretion.

Spontaneous modulations of the electric organ discharge in the weakly electric fish, Apteronotus leptorhynchus: a biophysical and behavioral analysis.

Brown ghosts, Apteronotus leptorhynchus, are weakly electric gymnotiform fish whose wave-like electric organ discharges are distinguished by their enormous degree of regularity. Despite this constancy, two major types of transient electric organ discharge modulations occur: gradual frequency rises, which are characterized by a relatively fast increase in electric organ discharge frequency and a slow return to baseline frequency; and chirps, brief and complex frequency and amplitude modulations. Although in spontaneously generated gradual frequency rises both duration and amount of the frequency increase are highly variable, no distinct subtypes appear to exist. This contrasts with spontaneously generated chirps which could be divided into four "natural" subtypes based on duration, amount of frequency increase and amplitude reduction, and time-course of the frequency change. Under non-evoked conditions, gradual frequency rises and chirps occur rather rarely. External stimulation with an electrical sine wave mimicking the electric field of a neighboring fish leads to a dramatic increase in the rate of chirping not only during the 30 s of stimulation, but also in the period immediately following the stimulation. The rate of occurrence of gradual frequency rises is, however, unaffected by such a stimulation regime.

A saccular origin of frequency tuning in myogenic vestibular evoked potentials?: implications for human responses to loud sounds.

Previous research has indicated that an early component of click-evoked myogenic potentials in the sternocleidomastoid muscle is vestibularly mediated, since it can be obtained in subjects with loss of cochlear function, but is absent in subjects with loss of vestibular function (Colebatch et al., 1994). We report here the results of an experiment to investigate whether this response shows any tuning properties. In a sample of 11 subjects, we obtained acoustically evoked EMG from the sternocleidomastoid muscle in response to 110 dB SPL 10 ms tone pips with frequencies of 100 Hz, 200 Hz, 400 Hz, 800 Hz, 1600 Hz and 3200 Hz. The results of this experiment indicate that this response does indeed have a well-defined frequency tuning which may be modelled as a resonance with a maximum response at frequencies between 300-350 Hz. The possible saccular origin of the tuning response and the consequences that this may have in human responses to loud sounds is discussed. Also discussed are the consequences of particular electrode arrangements in relation to the innervation and anatomy of sternocleidomastoid.

Ethanol augments the baroreflex-inhibitory effects of sciatic nerve stimulation in the anaesthetized dog.

Electrical stimulation of somatic afferent fibres in the sciatic nerve has been used as a model of injury in the anaesthetized dog. Stimulation of the sciatic nerve (during reflexly induced periods of apnoea to obviate any respiratory effects of sciatic stimulation) led to a simultaneous increase in arterial blood pressure and heart rate and a decrease in baroreflex sensitivity. Infusion of ethanol sufficient to produce clinically relevant plasma ethanol levels (100-200 mg %) had no consistent effects on baroreflex sensitivity, but enhanced the pressor response and significantly augmented the inhibitory effects of sciatic stimulation on the baroreflex. Since ethanol is commonly associated with injury in man, such changes in the response to 'injury' may modify the patients' cardiovascular response to the injury and complicate diagnosis.

Effect of first-responder automated defibrillation on time to therapeutic interventions during out-of-hospital cardiac arrest. The Multicenter High Dose Epinephrine Study Group.

STUDY OBJECTIVES: The effect of automated defibrillation provided by basic emergency medical technician (EMT) first-responder units on the time intervals to other critical interventions in the management of out-of-hospital cardiac arrests is unknown. The purpose of this study was to define and compare elapsed time intervals to basic CPR, paramedic arrival, initial countershock, endotracheal intubation, IV access, and initial adrenergic drug therapy in first-responder automated defibrillation/paramedic versus basic EMT/paramedic emergency medical services systems. DESIGN: Prospectively collected data from a 15-month multicenter study of out-of-hospital, nontraumatic cardiac arrests were analyzed. The mean time intervals to critical therapeutic interventions between first-responder automated defibrillation/paramedic and basic EMT/paramedic groups were compared using the Student's t-test with Bonferroni correction. SETTING: Three first-responder automated defibrillation/paramedic and three basic EMT/paramedic urban emergency medical services systems. PARTICIPANTS: 1,578 patients with out-of-hospital cardiac arrest. INTERVENTIONS: The first-responder automated defibrillation/paramedic group received initial ECG analysis and/or automated countershock by first-responder/EMTs; the basic EMT/paramedic group received initial ECG analysis and/or manual countershock by paramedics. RESULTS: Elapsed time intervals in minutes +/- SD for first-responder automated defibrillation/paramedic versus basic EMT/paramedic groups, respectively, were as follows: Collapse to CPR, 4.3 +/- 3.9 versus 5.4 +/- 5.2 (P = .017); collapse to countershock, 10.7 +/- 5.9 versus 13.0 +/- 6.0 (P = .017); collapse to paramedic arrival, 13.0 +/- 5.4 versus 10.3 +/- 6.1 (P = .0001); paramedic arrival to IV access, 5.1 +/- 3.9 versus 7.0 +/- 5.0 (P = .0001); paramedic arrival to endotracheal intubation, 4.8 +/- 4.0 versus 6.8 +/- 5.8 (P = .0001); paramedic arrival to initial adrenergic drug therapy, 7.4 +/- 4.5 versus 8.2 +/- 4.7 (P = .015); collapse to IV access, 17.7 +/- 6.1 versus 16.6 +/- 7.4 (P = .10); collapse to endotracheal intubation, 17.3 +/- 6.4 versus 16.6 +/- 7.8 (P = .32); collapse to initial adrenergic drug therapy, 20.4 +/- 6.7 versus 18.1 +/- 7.2 (P = .010). The time intervals from paramedic arrival to IV access, endotracheal intubation, and initial adrenergic drug therapy remained shorter in the first-responder automated defibrillation/paramedic systems despite stratification by presenting cardiac rhythm. CONCLUSION: First-responder automated defibrillation/paramedic systems provide not only shorter times to initial countershock, as compared with basic EMT/paramedic systems, but by having delegated initial countershock to first-responders, they also allow for significantly shorter times from paramedic arrival to IV access, endotracheal intubation, and initial adrenergic drug therapy interventions.

Microbiology of chronic sinusitis in children.

To better understand the factors involved in chronic sinusitis in childhood, we cultured the sinuses, middle meatus, and nasopharynx in 39 children requiring surgical intervention. Sixty-nine percent of these patients had other medical problems, including asthma (49%) and immunologic compromise (18%). We cultured coagulase-negative staphylococcus in 18 patients, Streptococcus viridans in 14 patients, normal flora in 10 patients, Staphylococcus aureus in nine patients, group D streptococcus in five patients, Corynebacterium in five patients, Haemophilus influenzae in three patients, Neisseria in three patients, and Streptococcus pneumoniae, group A streptococcus, Escherichia coli, Pseudomonas aeruginosa, Klebsiella oxytoca, Propionibacterium acnes, Actinomyces, and an anaerobic gram-negative bacillus in one patient each. Cultures yielded no growth in nine patients. A strong association between cultures of the middle meatus obtained ipsilaterally and cultures of the maxillary (83%) and ethmoid sinuses (80%) occurred. A poor correlation was found between cultures of the nasopharynx and maxillary (45%) and ethmoid sinuses (49%). All seven patients who had both maxillary and ethmoid sinus cultures showed the same organisms in both sinuses. Only 41% of organisms were found on both sides when procedures were performed bilaterally. Cultures of the middle meatus appear to be sensitive and specific for organisms within sinuses. The presence of predominantly nonvirulent organisms in low titers suggests that additional factors other than bacterial overgrowth contribute to the pathogenesis of chronic sinusitis in children.

A correlative study of the physiology and morphology of the retinotectal pathway of the perch.

The anatomy and physiology of the retinotectal pathway of the perch was investigated using physiological and histological techniques. Massed responses of the optic nerve to single shocks exhibited five distinct peaks. Single-unit responses to shocks indicate two groups of fast fibers correlating well with peaks I and II of the massed response. The flash-evoked response in nerve and tectum has three major phases (PSPI-III), with a marked low-threshold fast component. Patterns of flash-evoked response from single fibers vary, but the responses of fast transient fibers coincide with the timing of PSPI, and longer latency groups with PSPII-III. Units reflexly activated by efferents were also seen, and 12% of units were photically inexcitable. Surprisingly, few fibers responded well to a scanned spot light, unlike tectal cells, and receptive fields were often large (greater than 70 deg). ON/OFF responses, evoked either by whole field or local illumination, were much commoner than pure ON or OFF responses. Effects of electrical stimulation or cautery of the tectum on the flash-evoked response of fiber bundles, via the efferents were marginal, but repetitive stimulation or section of the optic nerve produced clear-cut deficits in the slow components of the flash-evoked response of the nerve. Stimulation of the eighth nerve produced a complex long-latency, large-amplitude response in the optic nerve. The fiber spectrum of the optic nerve taken from electron micrographs revealed the presence of a relatively small group (less than 1%) of thick fibers with diameters between 3 microns and 10 microns that could be correlated with fast responses recorded from the optic nerve, and the remainder with axon diameters down to 0.2 microns providing the slow responses. The distribution of cell-body diameters from sectioned and wholemount material indicated a marked distinction between small and large ganglion cells. The total number of fibers in the nerve was estimated 868,840.

Motor responses to localized electrical stimulation of the tectum in the freshwater perch (Perca fluviatilis).

The results of localized electrical stimulation of the teleostean tectum indicate the presence within each tectal lobe of separate motor areas mediating ipsilateral turning, contralateral turning, and rolling movements. Stimulation of caudal regions produced larger turning circles than stimulation of rostral sites. Both these sets of observations conflict with the retinotopic map. Stimulation sites connected with turning and rolling movements were mostly located in the upper layer of the tectum. Other kinds of movement including aggressive behaviour, escape movements, head dipping, and forward swimming were obtained by stimulating the deeper tectal sites and subtectal areas. These results suggest that the tectum may be differentiated into areas with specific motor functions and afferent connections. This has important consequences for studies on optic nerve regeneration and neuronal specificity.

Spontaneous histamine release after exposure to hyperosmolar solutions.

Since basophils from certain allergic individuals release histamine spontaneously in aqueous or deuterium oxide-containing buffers, we examined spontaneous release after a brief exposure to hyperosmolar buffers. With leukocytes from 71 normal and allergic volunteers, it was found that 15-minute suspension in 770 mosm/kg Ca++-free buffers caused the cells to release 3% to 83% of cellular histamine (mean 29 +/- 3) when the cells were resuspended in isosmolar buffers containing Ca++. The cells from individuals with a history of food allergy were significantly more easily activated when the cells were compared to cells of normal volunteers (p less than 0.005), but cells from other allergic volunteers were more readily activated as well. Activation was maximal at 770 mosm/kg and occurred in the absence of Ca++, whereas subsequent histamine release was partially Ca++ dependent. Activation could be observed as early as 30 seconds and was maximal at 15 minutes; histamine release from activated cells was almost as rapid. We conclude that the basophils from certain allergic individuals demonstrate unusual "releasability" and that this responsiveness to osmotic activation could play a role in reactions to hyperosmolar radiocontrast media.

The receptive field structure of visual cells from the optic tectum of the freshwater perch (Perca fluviatilis).

Recordings from the intrinsic tectal cells of the perch have allowed a classification of visual units on the basis of receptive field type. Comparisons with retinal and tectal cells in carp, goldfish, pike, trout and in the Anura were made. Most striking are cells with vertical bar-shaped features forming part of the R.F. The relation between the receptive fields of units lying adjacent within the tectum, suggests that parts of the same pattern are derived from cells within the same vertical column.

Chemical and biological properties of B16 murine melanoma cells grown in defined medium containing bovine serum albumin.

The addition of 1 percent (w/v) bovine serum albumin (BSA) to the F12 medium utilized for the growth of the B16 melanoma cells significantly stimulated the growth of this cell line. The synthesis of mucopolysaccharides and sialoglycopeptides in this medium is identical with that in Eagle's minimal essential medium with Earle's balanced salt solution supplemented with 2 mM L-glutamine, twice the recommended concentration of vitamins, nonessential amino acids, sodium pyruvate, and 10 percent (v/v) fetal calf serum. Cell volume and morphology did not change significantly, under the different growth conditions and tumorigenicity, as assayed by injection of cultured cells into syngeneic animals, was not decreased. Analysis of the BSA used indicated the presence of a sialoglycoprotein contaminant. This sialoglycoprotein contaminant was present in all lots examined and contains N-acetyl-and N-glycolylneuraminic acid, mannose, galactose, and glucosamine. The sialoglycoprotein can be removed by chromatography on acetate form anion-exchange resin at pH 4.3. F12 media containing the purified BSA plus selenite and the sodium salts of palmitic, oleic, and linoleic acids supported growth of the melanoma cells to the same extent as did the media containing unpurified BSA, indicating that the sialoglycoprotein has no role in sustaining the growth of the cells.