Anatomical characteristics of tonic and phasic postganglionic neurons in guinea pig bronchial parasympathetic ganglia

Abstract

Anatomical characteristics of principal parasympathetic ganglia neurons on the guinea pig primary bronchus were analyzed, and the procedure for localizing the ganglia without the aid of staining for in vitro physiological studies is described. The neurons were tightly packed within a perineural sheath, and the cell bodies formed a homogeneous population based on size and shape. By using intracellular electrophysiological recordings, unstained neurons within these ganglia were characterized with suprathreshold depolarizing stimuli as having either accommodating action potential patterns (phasic neurons) or repetitive action potential patterns (tonic neurons). After determining whether a cell was tonic or phasic, it was injected with either horseradish peroxidase or Neurobiotin for characterization of its dendrites. There were no differences between tonic and phasic neurons, and both exhibited the following: (1) dendrites were multiple and branching; (2) all processes (axon and dendrites) arose from a circumscribed area on the somatic surface; (3) the initial direction of the processes was usually toward the center of the ganglion, creating a very dense intraganglionic neuropil; (4) tapering processes (presumed dendrites) extended beyond the border of the perineural sheath; and (5) many processes terminated with bouton‐like swellings near the somatic surfaces of neighboring neurons within the same ganglion. Electron microscopic examination of dendritic and cell body membranes revealed that greater than 90% of the synapses occurred on dendrites. Based on immunohistochemical staining, all neurons were calbindin negative. These results indicate a relatively homogeneous population of neurons in bronchial parasympathetic ganglia displaying dendritic characteristics compatible with complex integrative properties. J. Comp. Neurol. 419:439–450, 2000. © 2000 Wiley‐Liss, Inc.

Nerve growth factor acutely potentiates synaptic transmission in vitro and induces dendritic growth in vivo on adult neurons in airway parasympathetic ganglia

“…Intracellular recordings of passive and active membrane properties were made from the cell bodies of neurons located in tracheal and bronchial parasympathetic ganglia. Consistent with previous studies of guinea pig airway parasympathetic neurons (5,30), resting membrane potential and membrane resistance ranged from Ϫ38 to Ϫ70 mV and 38 to 66 M⍀, respectively, and did not change significantly during the course of experimentation or in the presence of or following NGF-␤ (1-100 ng/ml, n ϭ 5-11) exposure. In control phasic neurons (29,30), a prolonged, suprathreshold depolarizing pulse (500 ms, 1.0 nA) elicited 3.3 Ϯ 0.7 (n ϭ 6) action potentials, followed by accommodation to the stimulus.…”

“…No differences in dendritic length or number for control neurons was observed using these two methods of Neurobiotin development (not shown). Previously (30), sprouting of dendritic terminals (dendrites that terminate with 3 or more short, Ͻ5 m branches) was not seen in control neurons. Three-dimensional measurements of dendrites were made from whole mount preparations of injected neurons at a magnification of ϫ200 using deconvoluted images with length-and volume-rendering analysis program (IPLab, Biovision Technologies, Exton, PA).…”

“…The tissue was then fixed in 4% formaldehyde in PBS for 2 h at 4°C and rinsed in PBS. Once injected, the Neurobiotin was either developed for histochemical (avidin-biotin peroxidase complex and diaminobenzidine kits, Vector Laboratories) or fluorescence (avidin-D fluorescein, Vector Laboratories) staining, and the somal size, length of dendritic processes, and dendritic branching and "sprouting" were measured (30). No differences in dendritic length or number for control neurons was observed using these two methods of Neurobiotin development (not shown).…”

“…The tissue was dissected in flowing (5 ml/min) Krebs bicarbonate buffer at 20 -22°C for up to 1 h before equilibration and electrophysiological experimentation. Unstained ganglia were exposed in the trachea and bronchus by fine dissection with the aid of a stereomicroscope at magnifications of ϫ25-80, using reflected transmitted light as previously described (30). Tracheal ganglia were located on or within the trachealis smooth muscle by following inlet nerves arising from the recurrent laryngeal nerves.…”

Parasympathetic control of airway submucosal glands: Central reflexes and the airway intrinsic nervous system

“…Hence, the most thoroughly studied airway neurons are the large neurons closely associated with the longitudinal nerve trunks in ferrets (Coburn and Kalia 1986), and the presumably corresponding neurons in rat pups (Allen and Burnstock 1990), the peribronchial nerve ganglia in guinea pigs (Myers and Undem 1993;Myers and Undem 1995;Myers 2000;Kajekar, Rohde et al 2001;Myers 2001;Canning, Reynolds et al 2002;Myers, Goldie et al 2005), and corresponding neurons in cats (Mitchell, Herbert et al 1987), and humans (Kajekar, Rohde et al 2001).…”