Close appositions between Tyrosine hydroxylase immunoreactive boutons and respiratory neurons in the rat ventrolateral medulla

Abstract

The extent of the adrenergic input to respiratory neurons in the ventrolateral medulla oblongata of rats was assessed by using a combination of intracellular recording, dye filling, and immunohistochemistry. Twenty-two neurons that displayed a pronounced respiration-related modulation of their membrane potential, and could not be antidromically activated by electrical stimulation of the superior laryngeal, vagus, or facial nerves, were labelled by intracellular injection of biocytin. Three types of respiration-related neurons were labelled: small neurons located in the Bötzinger complex between 0.5 and 1.0 mm caudal to the facial nucleus; medium-sized neurons located in the ventral respiratory group 1.0 to 2.0 mm caudal to the facial nucleus; and large motoneurons located within the nucleus ambiguus 0.5 to 2.0 mm caudal to the facial nucleus. Small Bötzinger neurons [length = 22 +/- 5 microns, width = 13 +/- 3 microns, area = 222 +/- 79 microns2; (mean +/- SD, n = 5)] had membrane potentials of -15 to -27 mV during the recording period. Four of five of these cells had profuse axonal terminations between 50 microns caudal and 450 microns rostral to their somata, suggesting that they may form part of local networks responsible for generating respiratory activity. Medium-sized ventral respiratory group neurons (length = 26 +/- 5 microns, width = 18 +/- 4 microns, area = 377 +/- 141 microns2; n = 5) were found in the vicinity of the nucleus ambiguus dorsal to the lateral reticular nucleus. Three of five of these neurons had an axon that crossed the midline and travelled caudally. One axon had a collateral with varicosities close to its soma. The somata of motoneurons (length = 29 +/- 6 microns, width = 21 +/- 4 microns, area = 485 +/- 142 microns2; n = 12) were located within the nucleus ambiguus, and had axons that could be traced to exist points from the medulla. Tyrosine hydroxylase immunoreactive cells and their terminal fibres within the medulla were localised by immunocytochemistry. Small Bötzinger neurons received the largest number of close appositions from tyrosine hydroxylase immunoreactive boutons (13 +/- 2 appositions/neuron; n = 5). Medium-sized ventral respiratory group neurons received fewer appositions (8 +/- 4 appositions/neuron; n = 5). Most motoneurons (n = 10) received few appositions from tyrosine hydroxylase immunoreactive boutons, while two received none. The average number was 3 +/- 3 appositions/neuron (n = 12).(ABSTRACT TRUNCATED AT 400 WORDS)

B�tzinger neurons project towards bulbospinal neurons in the rostral ventrolateral medulla of the rat

“…In agreement with previous studies (Pilowsky et al, 1990;Bryant et al, 1993;Sun et al, 1994), labelled Bötzinger neurons had small cell bodies, especially those with less negative membrane potentials (Fig. 2).…”

“…Accordingly, it is possible that Bötzinger neurons may interact with neurons modulating sensory neurons as well as with bulbospinal presympathetic neurons. However, the few Bötzinger varicosities seen in the RVLM here and in earlier studies (Bryant et al, 1993;Sun et al, 1994) contrasts with the numerous axon terminals found in the respiratory regions of the ventral medulla, suggesting that the main output from Bötzinger neurons is towards other respiratory neurons.…”

“…Additional doses of sodium pentobarbitone (3 mg/kg) were administered intravenously as required. The surgical techniques involved were as previously described (Pilowsky et al, 1990;Sun et al, 1994). In brief, the right femoral artery and vein were cannulated and a tracheotomy was performed.…”

“…We and others have recently obtained intracellular recordings from neurons in the Bötzinger complex of the adult rat (Pilowsky et al, 1990;Bryant et al, 1993;Sun et al, 1994). One distinction between Bötzinger and many other morphologically identified respiratory neurons is that Bötzinger neurons tend to have extensive intramedullary axon collaterals including some, with varicosities, in the RVLM.…”

Differential Cardiorespiratory and Sympathetic Reflex Responses to Microinjection of Neuromedin U in Rat Rostral Ventrolateral Medulla

“…The RVLM is a functionally heterogeneous region with cardiovascular and respiratory (Bö tzinger and pre-Bö tzinger) regions intermingled (Pilowsky et al, 1990(Pilowsky et al, , 2009Kanjhan et al, 1995). This close relationship, and synaptic input from respiratory neurons to RVLM neurons (Sun et al, 1997), along with close appositions between bulbospinal tyrosine hydroxylase-immunoreactive neurons of the C1 cell group and boutons from identified Bö tzinger neurons (Sun et al, 1994) suggest a possible site of action for the known interactions between the two systems and a possible explanation for the effects of NMU on respiration observed in this study.…”