Medicine & Health

Publication Search Results

Now showing 1 - 10 of 17
  • (1998) Bradley, Peter; Rozenfeld, Anatoly; Lee, Kevin; Jamieson, Dana; Heiser, Gernot; Satoh, S
    Journal Article
    The first results obtained using a SOI device for microdosimetry applications are presented. Microbeam and broadbeam spectroscopy methods are used for determining minority carrier lifetime and radiation damage constants. A spectroscopy model is presented which includes the majority of effects that impact spectral resolution. Charge collection statistics were found to substantially affect spectral resolution. Lateral diffusion effects significantly complicate charge collection

  • (1998) Bertrand, P. P; Kunze, W. A.; Bornstein, J. C.; Furness, J. B.
    Journal Article
    The patterns of innervation of the mucosa by axons of individual primary afferent neurons with cell bodies in the myenteric plexus were studied by mapping sites from which electrical stimulation of the mucosa elicited action potentials (APs) in their cell bodies. Segments of guinea-pig ileum were dissected to reveal the myenteric plexus over half of the intestinal circumference, leaving the mucosa intact over the other half. Intracellular recordings were taken from myenteric neurons located within 1 mm of the intact mucosa. Focal electrical stimuli were applied to the mucosa at multiple locations separated by about 1 mm. Neurons that responded had round or oval cell bodies with several long processes (Dogiel type II) and APs that had an inflection on the falling phase (AH-neurons). Responses consisted of single APs or bursts of APs. Maps of the mucosal projections of 30 neurons were generated. The maximum distances from which individual neurons responded were 7 mm circumferential and 2 mm oral or anal to the cell body with a higher proportion of responses from the oral regions. The areas of intact mucosa calculated to be innervated ranged from 1 mm2 up to approximately 15 mm2 (mean 3.9 mm2; median 2.5 mm2). It is estimated that the areas innervated would be two to three times larger under conditions where part of the mucosa is not removed. Some neurons also responded to a chemical or a mechanical stimulus applied to the mucosa within the electrically mapped area. It is concluded that intrinsic primary afferent neurons have overlapping receptive fields with 230 to 350 neurons innervating the same region of mucosa.

  • (1998) Kunze, W. A.; Furness, J. B.; Bertrand, P. P; Bornstein, J. C.
    Journal Article
    1. Isolated longitudinal muscle-myenteric plexus preparations from guinea-pig ileum were used to investigate the activity of myenteric neurons when the tissue was stretched in the circumferential direction. Membrane potentials were recorded via flexibly mounted intracellular recording electrodes containing Neurobiotin in 1 M KCl. The preparations were stretched to constant widths (+20% and +40% beyond slack width). 2. Multipolar neurons (Dogiel type II morphology) discharged spontaneous action potentials and proximal process potentials during maintained stretching, three of twenty-one at +20% stretch and seven of nine at +40% stretch. At the maximum extent of stretch tried, +40% beyond slack tissue width, action potentials in Dogiel type II neurons occurred at 10-33 Hz. Neurons with other morphologies were all uniaxonal. Some displayed spontaneous fast EPSPs or action potentials, three of forty one at +20% stretch and seven of nineteen at +40% stretch. 3. In seven of eight Dogiel type II neurons, action potentials or proximal process potentials persisted when membrane hyperpolarization was imposed via the recording electrode. Action potential discharge was abolished by hyperpolarization in seven of nine uniaxonal neurons; the exceptions were two orally projecting neurons. 4. Dogiel type II and uniaxonal neurons were classified as rapidly accommodating if they discharged action potentials only at the beginning of a 500 ms intracellular depolarizing pulse and slowly accommodating if they discharged for more than 250 ms. For Dogiel type II neurons, three of thirteen were slowly accommodating at +20% stretch and two of four at 40% stretch. For uniaxonal neurons the corresponding data were twelve of twenty-six and fifteen of nineteen neurons. The slowly accommodating state was associated with increased cell input resistance in uniaxonal neurons. 5. The spontaneous action potential discharge in Dogiel type II and uniaxonal neurons ceased when the muscle was relaxed pharmacologically by nicardipine (3 microM) or isoprenaline (1 microM), although the applied stretch was maintained. At the same time, evoked spike discharge became rapidly accommodating. 6. We conclude that many Dogiel type II neurons, and possibly some orally projecting uniaxonal neurons, are intrinsic, stretch-sensitive, primary afferent neurons that respond to muscle tension with sustained action potential discharge.

  • (1999) Lomax, A. E.; Sharkey, K. A.; Bertrand, P. P; Low, A. M.; Bornstein, J. C.; Furness, J. B.
    Journal Article
    Intracellular recordings were made from myenteric neurons of the guinea-pig distal colon to determine their electrical behaviour in response to intracellular current injection and stimulation of synaptic inputs. The recording microelectrode contained the intracellular marker biocytin, which was injected into impaled neurons so that electrophysiology, shape and immunohistochemistry could be correlated. Myenteric neurons in the distal colon were divided into four morphological groups based on their shapes and projections. One group (29 of the 78 that were characterized electrophysiologically, morphologically and immunohistochemically) was the multiaxonal Dogiel type II neurons, the majority (25/29) of which were calbindin immunoreactive. Each of these neurons had an inflection on the falling phase of the action potential that, in 24/29 neurons, was followed by a late afterhyperpolarizing potential (AHP). Slow excitatory postsynaptic potentials were recorded in 20 of 29 Dogiel type II neurons in response to high frequency internodal strand stimulation and two neurons responded with slow inhibitory postsynaptic potentials. Low amplitude fast excitatory postsynaptic potentials occurred in 3 of 29 Dogiel type II neurons. Neurons of the other three groups were all uniaxonal: neurons with Dogiel type I morphology, filamentous ascending interneurons and small filamentous neurons with local projections to the longitudinal or circular muscle or to the tertiary plexus. Dogiel type I neurons were often immunoreactive for nitric oxide synthase or calretinin, as were some small filamentous neurons, while all filamentous ascending interneurons tested were calretinin immunoreactive. All uniaxonal neurons exhibited prominent fast excitatory postsynaptic potentials and did not have a late AHP following a single action potential, that is, all uniaxonal neurons displayed S type electrophysiological characteristics. However, in 6/19 Dogiel type I neurons and 2/8 filamentous ascending interneurons, a prolonged hyperpolarizing potential ensued when more than one action potential was evoked. Slow depolarizing postsynaptic potentials were observed in 20/29 Dogiel type I neurons, 6/8 filamentous ascending interneurons and 8/12 small filamentous neurons. Six of 29 Dogiel type I neurons displayed slow inhibitory postsynaptic potentials, as did 2/8 filamentous ascending interneurons and 4/12 small filamentous neurons. These results indicate that myenteric neurons in the distal colon of the guinea-pig are electrophysiologically similar to myenteric neurons in the ileum, duodenum and proximal colon. Also, the correlation of AH electrophysiological characteristics with Dogiel type II morphology and S electrophysiological characteristics with uniaxonal morphology is preserved in this region. However, filamentous ascending interneurons have not been encountered in other regions of the gastrointestinal tract and there are differences between the synaptic properties of neurons in this region compared to other regions studied, including the presence of slow depolarizing postsynaptic potentials that appear to involve conductance increases and frequent slow inhibitory postsynaptic potentials.

  • (1998) Sharkey, K. A.; Lomax, A. E.; Bertrand, P. P; Furness, J. B.
    Journal Article
    BACKGROUND & AIMS: Prevertebral sympathetic ganglia receive inputs from intestinofugal neurons, with cell bodies located in the wall of the bowel. Intestinofugal neurons are part of the afferent limbs of intestino-intestinal reflexes. The aim of this study was to define the properties of intestinofugal neurons using intracellular recordings. METHODS: Intestinofugal neurons of the distal colon were retrogradely labeled from the inferior mesenteric ganglia. In whole mounts of the myenteric plexus/longitudinal muscle of the distal colon, labeled neurons were identified by their fluorescence and recordings were made using biocytin-filled electrodes. Labeled nerves were characterized immunohistochemically and morphologically. RESULTS: Intestinofugal neurons were uniaxonal neurons with multiple dendrites that had lamellar expansions. They were immunoreactive for choline acetyltransferase. Stimulation of nerve fiber tracts elicited large-amplitude excitatory postsynaptic potentials in all labeled neurons. Some received spontaneous fast excitatory postsynaptic potentials. Those cells that fired action potentials fired only one or two at the start of a depolarizing current pulse. No intestinofugal neurons had Dogiel type II morphology or a late afterhyperpolarizing potential. CONCLUSIONS: Intestinofugal neurons are likely to be activated by other neurons in the gut wall. They are not AH or Dogiel type II neurons. Thus they seem to be second order neurons in afferent pathways of intestino-intestinal reflexes.

  • (1998) Lomax, A. E.; Bertrand, P. P; Furness, J. B.
    Journal Article
    Simultaneous immunofluorescence labelling was used to investigate the patterns of colocalisation of the NK1 tachykinin receptor with other neuronal markers, and hence determine the functional classes of neuron that bear the NK1 receptor in the guinea-pig ileum. In the myenteric plexus, 85% of NK1 receptor-immunoreactive (NK1r-IR) nerve cells had nitric oxide synthase (NOS) immunoreactivity and the remaining 15% were immunoreactive for choline acetyltransferase (ChAT). Of the latter group, about 50% were immunoreactive for both neuropeptide Y (NPY) and somatostatin (SOM), and had the morphologies of secretomotor neurons. Many of the remaining ChAT neurons were immunoreactive for calbindin or tachykinins (TK), but not both. These calbindin immunoreactive neurons had Dogiel type II morphology. No NK1r-IR nerve cells in the myenteric plexus had serotonin or calretinin immunoreactivity. In the submucosal ganglia, 84% of NK1r-IR nerve cells had neuropeptide Y immunoreactivity and 16% were immunoreactive for TK. It is concluded that NK1r-IR occurs in five classes of neuron; namely, in the majority of NOS-immunoreactive inhibitory motor neurons, in ChAT/TK-immunoreactive excitatory neurons to the circular muscle, in all ChAT/NPY/SOM-immunoreactive secretomotor neurons, in a small proportion of ChAT/calbindin myenteric neurons, and in about 50% of ChAT/TK submucosal neurons.

  • (1998) Bertrand, P. P; Kunze, W. A.; Bornstein, J. C.; Furness, J. B.
    Conference Paper
    There are similarities between the mechanisms of sensory transduction by chemoreceptors in the gastrointestinal (GI) tract and by those in the oral cavity. Dissociated rat taste receptor cells have been shown to contain vesicular 5-HT and are excited by exogenous application of 5-HT. Likewise, in the GI tract, enterochromaffin (EC) cells are well known to contain 5-HT and are excited by its exogenous application. Both the taste receptor cell and the EC cell apparently make reciprocal synaptic connections with their extrinsic and (in the case of the gut) intrinsic afferent innervation. However, while the taste receptor cell is known to participate in gustation, the EC cell's role in the initiation of enteric reflexes remains unclear. Thus it may be that common transduction mechanisms are utilized in both systems and it is in this sense that the gut may be said to 'taste' the contents of the lumen. These studies were designed to investigate the sensory transduction mechanisms underlying responses of myenteric sensory neurons to chemical stimulation of the mucosa and with particular attention to the possible interactions between the EC cell and the surrounding afferent innervation. Intracellular electrophysiological recordings were taken from chemosensory myenteric neurons which had AH type electrophysiological characteristics and Dogiel type II morphological characteristics. Short segments of guinea pig ileum were dissected to reveal the myenteric plexus over one half the circumference of the preparation. Focal stimulating electrodes and fine glass pipettes containing chemical substances were used to stimulate the mucosa in the intact half of the preparation. Movement of the smooth muscle was reduced with the addition of scopolamine and nicardipine. In general, stimulation of the mucosa generated bursts of one or more action potentials (APs) recorded at the cell soma. Puffs of 5-HT (3 - 30 M) or 2-methyl 5-HT (0.1 to 1 mM - a 5-HT3 agonist) applied locally to the mucosa were effective in eliciting bursts of APs while puffs of -methyl 5-HT (0.1 to 1 mM - a 5-HT2 agonist) or 5-methoxytryptamine (1 to 10 M - a general 5-HT agonist) were not. Single, electrical stimuli applied to the mucosa elicited a single antidromic AP and a later burst of APs. Spontaneous bursts of APs were also recorded in some cells which were indistinguishable from the electrically evoked late burst of APs. In one instance, initiation of an antidromic AP by electrical stimulation of the mucosa or a single AP by somatic current injection elicited a late AP which appeared to be the result of synaptic interaction at or near the nerve terminal in the mucosa. In cells with spontaneous bursts of APs or where 5-HT elicited a burst of APs, application of tropisetron (10 M - 5-HT3/4 antagonist) reduced the occurrence of bursts and/or the number of APs in a burst. The electrically evoked late burst of APs was only blocked by higher concentrations of tropisetron (30 M) and was not desensitized during repeated applications of 5-HT to the mucosa. The early, antidromic AP was never blocked. In preliminary experiments, granisetron (10 M - 5-HT3 antagonist) reduced the number of APs in response to 5-HT but not to electrical stimulation. These results are consistent with the idea that 5-HT participates in chemosensory transduction, but also suggest that other substances may play a similar role. In addition, anecdotal evidence suggest that the mucosa and its afferent innervation can interact in a positive, reciprocal fashion.

  • (1999) Gosbell, Iain; Ross, Alfred; Turner, Ian
    Journal Article

  • (1999) Bertrand, P. P; Bornstein, J. C.
    Conference Paper

  • (1998) Furness, J. B.; Kunze, W. A.; Bertrand, P. P; Clerc, N.; Bornstein, J. C.
    Journal Article
    After a long period of inconclusive observations, the intrinsic primary afferent neurons of the intestine have been identified. The intestine is thus equipped with two groups of afferent neurons, those with cell bodies in cranial and dorsal root ganglia, and these recently identified afferent neurons with cell bodies in the wall of the intestine. The first, tentative, identification of intrinsic primary afferent neurons was by their morphology, which is type II in the terminology of Dogiel. These are multipolar neurons, with some axons that project to other nerve cells in the intestine and other axons that project to the mucosa. Definitive identification came only recently when action potentials were recorded intracellularly from Dogiel type II neurons in response to chemicals applied to the lumenal surface of the intestine and in response to tension in the muscle. These action potentials persisted after all synaptic transmission was blocked, proving the Dogiel type II neurons to be primary afferent neurons. Less direct evidence indicates that intrinsic primary afferent neurons that respond to mechanical stimulation of the mucosal lining are also Dogiel type II neurons. Electrophysiologically, the Dogiel type II neurons are referred to as AH neurons. They exhibit broad action potentials that are followed by early and late afterhyperpolarizing potentials. The intrinsic primary afferent neurons connect with each other at synapses where they transmit via slow excitatory postsynaptic potentials, that last for tens of seconds. Thus the intrinsic primary afferent neurons form self-reinforcing networks. The slow excitatory postsynaptic potentials counteract the late afterhyperpolarizing potentials, thereby increasing the period during which the cells can fire action potentials at high rates. Intrinsic primary afferent neurons transmit to second order neurons (interneurons and motor neurons) via both slow and fast excitatory postsynaptic potentials. Excitation of the intrinsic primary afferent neurons by lumenal chemicals or mechanical stimulation of the mucosa appears to be indirect, via the release of active compounds from endocrine cells in the epithelium. Stretch-induced activation of the intrinsic primary afferent neurons is at least partly dependent on tension generation in smooth muscle, that is itself sensitive to stretch. The intrinsic primary afferent neurons of the intestine are the only vertebrate primary afferent neurons so far identified with cell bodies in a peripheral organ. They are multipolar and receive synapses on their cell bodies, unlike cranial and spinal primary afferent neurons. They communicate with each other via slow excitatory synaptic potentials in self reinforcing networks and with interneurons and motor neurons via both fast and slow EPSPs.