Biomedical subjects

T Preuss

Publications and source records attributed to T Preuss.

11 recordsLinked to original sources

PubMed2006

Representation of auditory signals in the M-cell: role of electrical synapses.

The teleost Mauthner (M-) cell mediates a sound-evoked escape behavior. A major component of the auditory input is transmitted by large myelinated club endings of the posterior VIIIth nerve. Paradoxically, although nerve stimulations revealed these afferents have mixed electrical and glutamatergic synapses on the M-cell's distal lateral dendrite, paired pre- and postsynaptic recordings indicated most individual connections are chemically silent. To determine the sensory information encoded and the relative contributions of these two transmission modes, M-cell responses to acoustic stimuli in air were recorded intracellularly. Excitatory postsynaptic potentials (EPSPs) evoked by both short 100- to 900-Hz "pips" and longer-lasting amplitude- and frequency-modulated sounds were dominated by fast, repetitive EPSPs superimposed on an underlying slow depolarization. Fast EPSPs 1) have kinetics comparable to presynaptic action potentials, 2) are maximal on the distal lateral dendrite, and 3) are insensitive to GluR antagonists. They presumably are coupling potentials, and power spectral analysis indicated they constitute a high-pass signal that accurately tracks sound frequency and amplitude. The spatial profile of the slow EPSP suggests both proximal and distal dendritic sources, a result supported by predictions of a multicompartmental model and the effects of AMPAR antagonists, which preferentially reduced the proximal component. Thus a second class of afferents generates a portion of the slow EPSP that, with sound stimuli, demonstrate that the dominant mode of transmission at LMCE synapses is electrical. The slow EPSP is a dynamic, low-pass representation of stimulus strength. Accordingly, amplitude and phase information, which are segregated in other systems, are faithfully represented in the M-cell.

Acoustic Stimulation↗

PubMed2000

Effects of temperature on escape jetting in the squid Loligo opalescens.

In Loligo opalescens, a sudden visual stimulus (flash) elicits a stereotyped, short-latency escape response that is controlled primarily by the giant axon system at 15 C. We used this startle response as an assay to examine the effects of acute temperature changes down to 6 C on behavioral and physiological aspects of escape jetting. In free-swimming squid, latency, distance traveled and peak velocity for single escape jets all increased as temperature decreased. In restrained squid, intra-mantle pressure transients during escape jets increased in latency, duration and amplitude at low temperature. Recordings of stellar nerve activity revealed repetitive firing of the giant motor axon accompanied by increased activity in the non-giant motor axons that run in parallel. Selective stimulation of giant and non-giant motor axons in isolated nerve-muscle preparations failed to show the effects seen in vivo, i.e. increased peak force and increased neural activity at low temperature. Taken together, these results suggest that L. opalescens is able to compensate escape jetting performance for the effects of acute temperature reduction. A major portion of this compensation appears to occur in the central nervous system and involves alterations in the recruitment pattern of both the giant and non-giant axon systems.

Animals↗

PubMed2000

Role of prey-capture experience in the development of the escape response in the squid Loligo opalescens: a physiological correlate in an identified neuron.

Although extensively used for biophysical studies, the squid giant axon system remains largely unexplored in regard to in vivo function and modulation in any biologically relevant context. Here we show that successful establishment of the recruitment pattern for the giant axon in the escape response elicited by a brief electrical stimulus depends on prey-capture experience early in life. Juvenile squid fed only slow-moving, easy-to-capture prey items (Artemia salina) develop deficits in coordinating activity in the giant axon system with that of a parallel set of non-giant motor axons during escape responses. These deficits are absent in cohorts fed fast-moving, challenging prey items (copepods). These results suggest that the acquisition of inhibitory control over the giant axon system is experience-dependent and that both prey-capture and escape behavior depend on this control.

Animals↗

PubMed1997

Comparison of two different methods for inactivation of viruses in serum.

In order to compare protocols for inactivation of viruses potentially present in biological specimens, three different model viruses were treated in bovine serum by two different inactivation methods: samples were subjected either to chemical inactivation with ethylenimine (El) at concentrations of 5 and 10 mM at 37 degrees C for periods up to 72 h or to electron-beam irradiation in frozen and liquid form with doses varying between 11 and 46 kGy. The chemical inactivation resulted in nonlinear tailing curves in a semilogarithmic plot of virus titer versus inactivation time showing non-first-order kinetics with respect to virus titer. The time for inactivation of 7 log10 units of porcine parvovirus (PPV) was about 24 h for both El concentrations, whereas 5 log10 units of bovine viral diarrhea virus (BVDV) was inactivated in 2 h for both El concentrations and 6 log10 units of porcine enterovirus (PEV) was inactivated within 3 h. The inactivation with electron-beam irradiation resulted in almost linear curves in a semilogarithmic plot of virus titer versus irradiation dose, reflecting a first-order inactivation. The rate of inactivation was almost twice as fast in the liquid samples compared to the rate in frozen ones, giving values of the doses needed to reduce virus infectivity 1 log10 unit for inactivation of PPV of 11.8 and 7.7 kGy for frozen and liquid samples, respectively, whereas the corresponding values for BVDV were 4.9 and 2.5 kGy, respectively, and those for PEV were 6.4 and 4.4 kGy, respectively. The nonlinear inactivation with El makes it impossible to extrapolate the curves beyond the virus detection limit and thereby predict the necessary time for complete inactivation, i.e., to a level beyond the detection limit, of virus in a given sample. The first-order inactivation obtained with electron-beam irradiation makes such a prediction possible and justifiable. The two methods are discussed with respect to their different kinetics and applicability under different circumstances and criteria for inactivation, and considerations for choice of method are discussed.

Animals↗

PubMed1997

Visual field representation in striate and prestriate cortices of a prosimian primate (Galago garnetti).

Microelectrode mapping techniques were used to study the visuotopic organization of the first and second visual areas (V1 and V2, respectively) in anesthetized Galago garnetti, alorisiform prosimian primate. 1) V1 occupies approximately 200 mm2 of cortex, and is pear shaped, rather than elliptical as in simian primates. Neurons in V1 form a continuous (1st-order) representation of the visual field, with the vertical meridian forming most of its perimeter. The representation of the horizontal meridian divides V1 into nearly equal sectors representing the upper quadrant ventrally, and the lower quadrant dorsally. 2) The emphasis on representation of central vision is less marked in Galago than in simian primates, both diurnal and nocturnal. The decay of cortical magnification factor with increasing eccentricity is almost exactly counterbalanced by an increase in average receptive field size, such that a point anywhere in the visual field is represented by a compartment of similar diameter in V1. 3) Although most of the cortex surrounding V1 corresponds to V2, one-quarter of the perimeter of V1 is formed by agranular cortex within the rostral calcarine sulcus, including area prostriata. Although under our recording conditions virtually every recording site in V2 yielded visually responsive cells, only a minority of those in area prostriata revealed such responses. 4) V2 forms a cortical belt of variable width, being narrowest (approximately 1 mm) in the representation of the area centralis and widest (2.5-3 mm) in the representation of the midperiphery (>20 degrees eccentricity) of the visual field. V2 forms a second-order representation of the visual field, with the area centralis being represented laterally and the visual field periphery medially, near the calcarine sulcus. Unlike in simians, the line of field discontinuity in Galago V2 does not exactly coincide with the horizontal meridian: a portion of the lower quadrant immediately adjacent to the horizontal meridian is represented at the rostral border of ventral V2, instead of in dorsal V2. Despite the absence of cytochrome oxidase stripes, the visual field map in Galago V2 resembles the ones described in simians in that the magnification factor is anisotropic. 5) Receptive field progressions in cortex rostral to dorsal V2 suggest the presence of a homologue of the dorsomedial area, including representations of both quadrants of the visual field. These results indicate that many aspects of organization of V1 and V2 in simian primates are shared with lorisiform prosimians, and are therefore likely to have been present in the last common ancestor of living primates. However, some aspects of organization of the caudal visual areas in Galago are intermediate between nonprimates and simian primates, reflecting either an intermediate stage of differentiation or adaptations to a nocturnal niche. These include the shape and the small size of V1 and V2, the modest degree of emphasis on central visual field representation, and the relatively large area prostriata.

Animals↗

PubMed1997

Post-hatching development of circular mantle muscles in the squid Loligo opalescens.

Post-hatching development of the circular muscles in the mantle of squid was studied morphometrically to identify structural changes and to quantify hyperplasia and hypertrophy of the muscle fibers. Superficial, mitochondria-rich (SMR) fibers and central, mitochondria-poor (CMP) fibers are present at hatching. Although both fiber types increase in size and, even more so, in number during post-hatching development, CMP fibers increase at a much higher rate than do SMR fibers. As a result, the relative proportion of SMR to CMP fibers shifts from about 1:1 in a hatchling to about 1:6 in an 8-week-old animal; it then apparently remains constant to adulthood. These structural changes are consistent with developmental changes in muscular activity. During slow, jet-propelled swimming, 1-week-old animals show mantle contractions that have twice the relative amplitude and frequency of those in adults. The presence of Na-channel protein in mantle muscle was detected bio-chemically by using site-directed antibodies; the protein was found to be preferentially expressed in CMP fibers. These results suggest that SMR fibers are an important source of locomotory power at hatching, but become progressively less important during the first 8 weeks of development as CMP fibers assume the dominant role in jet locomotion.

Animals↗

PubMed1996

Activity of antibodies against Salmonella dublin, Toxoplasma gondii, or Actinobacillus pleuropneumoniae in sera after treatment with electron beam irradiation or binary ethylenimine.

Viral contamination of biological material may constitute a risk when samples are exchanged between countries, and it may be necessary to subject the material to an inactivation treatment. The present study investigated possible adverse effects on antibody activity subsequent to either electron beam irradiation or binary ethylenimine (BEI) treatment. The treatments were performed with sera obtained from pigs or cattle. For each treatment level, the posttreatment activity was plotted against the pretreatment activity, and regression analyses were carried out. The slope of the regression line was used as an estimate for the relative posttreatment activity. For a Toxoplasma gondii indirect enzyme-linked immunosorbent assay (ELISA) and agglutination assay as well as for a Salmonella dublin indirect ELISA, the posttreatment activity was more than 89% of the pretreatment activity when the samples were irradiated in the frozen state (on dry ice) with up to 46. kGy or when they were treated with 5 or 10 mM BEI for up to 48 h. The samples were more sensitive to irradiation in the liquid state. Thus, samples irradiated with 22.6 kGy retained 98% of their activity in the indirect ELISA when they were irradiated in the frozen state on dry ice but only 35% of their activity when they were irradiated in the liquid state at 0 degrees C. The patterns seen in an S. dublin blocking ELISA and an Actinobacillus pleuropneumoniae complement fixation assay differed in that samples with a low level of pretreatment activity were subject to a relatively greater decrease in activity than samples with a high level of pretreatment activity. The complement fixation assay was particularly sensitive to irradiation of serum. It is concluded that serum samples retain sufficient activity by both methods of virus inactivation, especially when used in indirect ELISA or in the T. gondii agglutination assay.

Actinobacillus pleuropneumoniae↗

PubMed1996

All-or-none contraction and sodium channels in a subset of circular muscle fibers of squid mantle.

Motor function in squid (Loligo) mantle reflects the highly coordinated activity of two motor pathways associated with giant and non-giant motor axons that respectively produce all-or-none and graded contractions in mantle muscle. Whereas both types of axons innervate circular mantle muscle fibers, precise nerve-muscle relationships remain unclear. Are squid like most invertebrates, in which single muscle fibers receive dual innervation from giant and non-giant motor axons, or is squid mantle configured more like vertebrates, in which parallel motor axon systems innervate distinct fast and slow muscle fibers? In this report, we describe giant and nongiant motor pathways that appear to control different pools of circular muscle fibers in squid. A subset of circular muscle fibers possesses large Na currents, and these fibers are proposed to employ Na-dependent action potentials to produce fast, all-or-none muscle twitches associated with giant axon stimulation.

Animals↗

PubMed1995

Proprioceptive hair cells on the neck of the squid Lolliguncula brevis: a sense organ in cephalopods for the control of head-to-body position.

Decapod cephalopods, such as cuttlefishes and squids, have a distinct neck region that allows movements (roll, pitch and yaw) of the head relative to the body. This paper describes the structure, innervation and central pathways of proprioceptive hair cells on the neck of the squid Lolliguncula brevis that sense such movements and control head-to-body position. These hair cells exist on the dorsal side of the neck underneath the nuchal cartilage, close to the animal's midline on either side of the nuchal crest. On each side, the hair cells can be divided into an anterior and a posterior group of 25-35 and 70-80 cells, respectively. An individual hair cell carries up to 300 kinocilia of equal length (about 30 microns), arranged in up to seven rows. The hair cells of the left and right anterior group are morphologically polarized in the medial direction, whereas the hair cells of the left and right posterior group are polarized in the anterior direction. The hair cells are primary sensory cells. They are innervated by a branch of the postorbital nerve and project ipsilaterally into the ventral part of the ventral magnocellular lobe. Efferent synaptic contacts are present at the base of the hair cells. In behavioural tests the influence of the neck hair cells on head position control was investigated. During imposed body rolls, a unilateral deafferentation of the cells caused an asymmetric change of the compensatory head roll response and elicited a head roll offset to the operated side. Bilateral deafferentation of the cells elicited a downward head pitch offset. This offset was superimposed on the compensatory head pitch response during imposed body pitch. These morphological and behavioural findings show that the neck hair cells and the associated nuchal cartilage structures of Lolliguncula brevis form a neck receptor organ that, together with statocyst and visual inputs, controls the position of the animal's head and body.

Animals↗

PubMed1995

A dorsal light reflex in a squid.

A dorsal light reflex is described in the squid Lolliguncula brevis. When illuminated from the side in visually homogeneous surroundings, a free-swimming squid rolls the dorsal side of its head and trunk 10-20 degrees towards the light. With the trunk restricted in a holder, the squid rolls its head 4-5 degrees towards the light; this reaction increases by about 50% when the statocysts are bilaterally removed and increases further when the neck receptor organ is also destroyed. The results indicate a multi-modal interaction of visual, statocyst and proprioceptive inputs during postural control.

Animals↗

PubMed1984

Serial monitoring of T-cell subset ratios with monoclonal antibodies in steroid- and antithymocyte globulin-treated patients with renal allotransplants.

Sequential changes in T-cell subsets or their ratios were employed to predict severity of rejection crises and to identify those patients who might require future antirejection therapy. Forty-two percent of the transplant recipients had a pretransplant OKT4:8 ratio in the range of 1.3 +/- 0.5. By contrast, only 11% had a OKT4:8 ratio of 2.9 or greater. Examination of the entire study group demonstrated that the mean OKT4:8 ratios fell (P less than 0.01) in the first week following the transplant procedure. All patients had at least one episode of acute rejection. There was a marked increase (P less than 0.05) in the OKT4:8 ratio between the first week value and the value immediately preceding (within 3 days) the start of the rejection episode which was 2.64 +/- 0.27. The mean OKT4:8 ratio in the 15 patients leaving the hospital with a functioning transplant was 1.18 +/- 0.35. Three months post-transplant, the OKT4:8 ratio was 1.98 +/- 0.39 in the 12 patients with functioning allografts. This value was not different from those patients' initial pretransplant values. Clinically, the rejection episodes could be divided into two groups based on their response to intravenous methylprednisolone therapy. The first group (n = 9) had milder rejection crises which responded rapidly to administration of one course of methylprednisolone. The second group of patients (n = 9) were also treated initially with methylprednisolone, to which they did not respond, and subsequently received antithymocyte globulin in an attempt to control their ongoing rejection crises. Following the transplant procedure, the OKT4:8 ratio decreased in patients who were destined to have steroid-responsive rejection episodes (P less than 0.01). The OKT4:8 ratio however, failed to fall in those who required ATG for control of their transplant rejection episodes. The onset of rejection episodes was associated with an increase in OKT4:8 ratio in both groups. Following steroid administration, two patterns of OKT4:8 cell responses were observed. Those in whom renal function improved demonstrated a decline in OKT4:8 ratio from 2.4 +/- 0.4 to 1.4 +/- 0.4 (P less than 0.05). However, no change occurred in the OKT4:8 ratios with steroid therapy (2.6 to 2.4 +/- 0.33, P greater than 0.05) in individuals in whom the serum creatinine concentration failed to decline. The patients who failed to respond to steroid therapy were treated with antithymocyte globulin (ATG).(ABSTRACT TRUNCATED AT 400 WORDS)

Acute Disease↗