To characterize mechanisms involved in neurokinin type 1 receptor (NK1R)-mediated
emesis, we investigated the brainstem
emetic signaling pathways following treating least shrews with the selective NK1R agonist
GR73632. In addition to episodes of
vomiting over a 30-min observation period, a significant increase in
substance P-immunoreactivity in the
emetic brainstem dorsal motor nucleus of the vagus (DMNX) occurred at 15 min post an intraperitoneal (i.p.) injection
GR73632 (5 mg/kg). In addition, time-dependent upregulation of phosphorylation of several
emesis -associated
protein kinases occurred in the brainstem. In fact, Western blots demonstrated significant phosphorylations of Ca2+/
calmodulin kinase IIα (CaMKIIα), extracellular signal-regulated
protein kinase1/2 (ERK1/2),
protein kinase B (Akt) as well as α and βII
isoforms of
protein kinase C (PKCα/βII). Moreover, enhanced phospho-ERK1/2 immunoreactivity was also observed in both brainstem slices containing the dorsal vagal complex
emetic nuclei as well as in jejunal sections from the shrew small intestine. Furthermore, our behavioral findings demonstrated that the following agents suppressed
vomiting evoked by
GR73632 in a dose-dependent manner: i) the NK1R antagonist
netupitant (i.p.); ii) the L-type Ca2+ channel (LTCC) antagonist
nifedipine (subcutaneous, s.c.); iii) the
inositol trisphosphate receptor (IP3R) antagonist 2-APB (i.p.); iv) store-operated Ca2+ entry inhibitors
YM-58483 and
MRS-1845, (i.p.); v) the ERK1/2 pathway inhibitor
U0126 (i.p.); vi) the PKC inhibitor
GF109203X (i.p.); and vii) the inhibitor of
phosphatidylinositol 3-kinase (PI3K)-Akt pathway
LY294002 (i.p.). Moreover, NK1R, LTCC, and IP3R are required for
GR73632-evoked CaMKIIα, ERK1/2, Akt and PKCα/βII phosphorylation. In addition, evoked ERK1/2 phosphorylation was sensitive to inhibitors of PKC and PI3K. These findings indicate that the LTCC/IP3R-dependent PI3K/PKCα/βII-ERK1/2 signaling pathways are involved in NK1R-mediated
vomiting.