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Differential intrinsic chemosensitivity of brainstem neurons from the locus coeruleus (LC), the nucleus tractus solitarius (NTS) and the retrotrapezoid nucleus (RTN)
Author(s) -
Putnam Robert W.,
Hartzler Lynn K.,
Conrad Susan C.,
Ritucci Nick A.,
Dean Jay B.
Publication year - 2006
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.20.4.a785-d
Subject(s) - brainstem , locus coeruleus , nucleus , chemistry , neuron , electrophysiology , medicine , endocrinology , neuroscience , biophysics , biology
We studied the CO 2 ‐sensitivity of neurons from LC, NTS and RTN. Firing rate and intracellular pH (pHi) responses to hypercapnic acidosis (HA) were studied in neurons from neonatal rat brainstem slices (300 μm) using whole cell patch and fluorescence imaging techniques. In response to HA, >90% of LC, 46% of NTS and 42% of RTN neurons increased their firing rate. The magnitude of the HA‐induced increase in firing rate, calculated as the chemosensitivity index (CI), was 137±5% (n=17), 153±6% (52), and 248±30% (18) for LC, NTS and RTN neurons, respectively. Upon exposure to synaptic block medium (SNB) (11.4 mM Mg 2+ ; 0.2 mM Ca 2+ ), the spontaneous firing rate of LC neurons increased from 0.9±0.1 to 2.2±0.5 Hz (10) (p<0.05), but the firing rate of NTS neurons decreased from 1.4±0.3 to 0.6±0.1 Hz (10) (p<0.05). In 10 LC neurons, CI in response to HA was 140±5% in normal solution and 143±10% in SNB (NS). In 10 NTS neurons, CI in response to HA was 169±19% in normal solution and increased to 235±20% in SNB (p<0.05). HA induced a sustained acidification of 0.26, 0.19 and 0.15 pH unit for LC, NTS and RTN neurons, respectively. Neurons from these 3 areas define a range of neurons with low (LC), intermediate (NTS) and high (RTN) chemosensitivity. In LC and NTS the vast majority of CO 2 ‐sensitive neurons are intrinsically chemosensitive. Since pHi responses to HA are similar in neurons from these areas, the differences in their intrinsic chemosensitivity must reside in differences in their ion channels. [Supported by NIH grants RO1 HL56683 and F32 HL80877.]