Glutamic acid decarboxylase-immunoreactivity of bulbar respiratory neuronsidentified by intracellular recording and labeling in rats

To distinguish the GABAergic neuron in the ventral respiratory group (VRG) of rats, immunohistochemical staining of glutamic acid decarboxylase (GAD) was performed in neurons that had been individually identified by in vivo i ntracellular recording and labeling with neurobiotin. A total of five types of respiratory neurons were identified and labeled; augmenting inspiratory (aug-I, n=12), decrementing or early inspiratory (early-I, n=3), inspirati on-expiration phase spanning or late inspiratory (late-I,n=3), decrementing expiratory or postinspiratory (PI, n=8), and augmenting or stage 2 expirat ory (E2, n=3). In addition, expiration-inspiration phase-spanning or pre-in spiratory neurons (pre-I, n=2) were recorded, but not labeled. The membrane potential trajectory of each neuron type resembled that previously describ ed in cat, suggesting a comparable neuronal organization between the two sp ecies. According to the axonal arborization, those labeled neurons were fur ther classified as propriobulbar (6 aug-I, all early-I, all late-I, and 3 P I), bulbospinal (2 aug-I and all E2) and cranial-motor neurons (4 aug-I and 5 PI). GAD-immunoreactivity was consistently detected in the propriobulbar neurons, while it was not seen in cranial-motor and bulbospinal neurons. I n addition, GAD-immunoreactive varicosities were found surrounding the soma tic and dendritic surface of all labeled neurons. The present results illus trate that the propriobulbar types of early-I, aug-I, late-I and PI neurons are GABAergic inhibitory neurons and virtually all types of respiratory ne urons receive GABAergic inputs in the rat's VRG. (C) 2001 Elsevier Science BY. All rights reserved.