The removal of acetylcholine by diffusion at nicotinic synapses in the rat otic ganglion

Pharmacological properties of P2 receptors on rat otic parasympathetic ganglion neurons

To elucidate the pharmacological profile of P2X receptors and the probable expression of P2Y receptors in otic ganglion neurons from 17-day-old rats, single neurons were enzymatically isolated and maintained in tissue culture for up to 30 h. Whole-cell voltage-clamp recording was carried out at a holding potential of -60 mV. Most otic ganglion neurons responded to adenosine 5'-triphosphate (ATP), 2-methylthio ATP (2-MeSATP) and alpha,beta-methylene ATP (alphabeta-meATP) with sustained currents and EC(50) values of 19 microM, 47 microM and 94 microM, respectively. 2',3'-O-trinitrophenyl-ATP (TNP-ATP) inhibited the response to alphabeta-meATP and ATP with an IC(50) values of 3.9 nM and 18.3 nM, respectively, which was closed to that observed in nodose neurons. The response to ATP was antagonized by suramin and cibacron blue. The dose-response curve of suramin against ATP response at a pH of 6.5 was shifted to the left compared to that at a pH of 7.4. Diinosine pentaphosphate (Ip(5)I), which blocks P2X(3), but not P2X(2/3)-mediated responses, had no effect on the currents evoked by ATP or alphabeta-meATP. In some neurons, uridine 5'-triphosphate (UTP) induced a tiny, but long-lasting current with a mean amplitude of 0.034+/-0.011 nA. Reverse transcriptase-polymerase chain reaction (RT-PCR) confirmed the expression of mRNAs for P2X(2), P2X(3), P2X(4), P2X(6) and P2X(7), but not for P2X(1) and P2X(5) receptors in otic ganglion. In conclusion, in rat otic ganglion neurons, P2X(2/3) heteromultimer receptors dominate, but P2X(7) and P2Y(2) or P2Y(4) receptors also play roles.

Differential expression of P2X receptors on neurons from different parasympathetic ganglia

Whole-cell patch clamp recording and immunohistochemistry were used to investigate the expression of P2X receptors on rat parasympathetic ganglion neurons of the otic, sphenopalatine, submandibular, intracardiac and paratracheal ganglia. Neurons from all five ganglia responded to ATP with a rapidly activating, sustained inward current. Neurons of intracardiac and paratracheal ganglia were insensitive to alphabeta-meATP, while all neurons in the otic and some neurons of sphenopalatine and submandibular ganglia responded. Lowering pH potentiated ATP responses in neurons from all five ganglia. Co-application of Zn(2+) potentiated ATP responses in intracardiac, paratracheal and submandibular ganglion neurons. Immunohistochemistry revealed strong and specific staining for the P2X(2) subunit in all five ganglia and strong P2X(3) staining in otic, sphenopalatine and submandibular ganglia. In conclusion, there is heterogeneity in P2X receptor expression in different parasympathetic ganglia of the rat, but the predominant receptor subtypes involved appear to be homomeric P2X(2) and heteromeric P2X(2/3).

Inhibition of cholinesterase elicits muscarinic receptor-mediated synaptic transmission in the rat adrenal medulla

To determine the role of acetylcholinesterase in cholinergic synaptic transmission in the adrenal medulla in vivo, we applied a dialysis technique to the adrenal medulla of anesthetized rats and examined the effect of acetylcholinesterase inhibitor on the contribution of nicotinic and muscarinic receptors to catecholamine release. Exogenous acetylcholine-induced epinephrine release was inhibited by atropine (a muscarinic receptor antagonist) as well as hexamethonium (a nicotinic receptor antagonist). Endogenous acetylcholine (nerve stimulation)-induced epinephrine release was inhibited by hexamethonium but not atropine. In the presence of neostigmine (an acetylcholinesterase inhibitor), both exogenous and endogenous acetylcholine-induced catecholamine release was enhanced. In either case, epinephrine release was inhibited by atropine as well as hexamethonium. In the presence of eserine (another acetylcholinesterase inhibitor), endogenous acetylcholine-induced epinephrine release was also inhibited by atropine. Exogenous or endogenous acetylcholine-induced norepinephrine release was primarily inhibited by hexamethonium regardless of whether neostigmine was absent or present. In the rat adrenal medulla, the inhibition of acetylcholinesterase not only enhanced cholinergic synaptic transmission but also elicited muscarinic receptor-mediated synaptic transmission for epinephrine release.

Hard metal-induced disease: effects of metal cations in vitro on guinea pig isolated airways

Inhalation of dust from hard metal (HM), a mixture of tungsten carbide, cobalt, and other metals, can cause interstitial alveolitis, fibrosis, and asthma in the workplace. Some effects of HM could occur after the metals dissolve in the lung. We examined whether chloride salts of metals in HM alloys can elicit responses or modify reactivity to methacholine (MCh) or responses to electric field stimulation (EFS) in guinea pig tracheal strips. In unstimulated strips, Co(2+), Cd(2+), and Ni(2+) evoked contractions (>3 x 10(-6) M), while Ta(5+), Zn(2+), Cr(2+), and Cr(3+) caused weak relaxations (>10(-5) M). In strips contracted with MCh (3 x 10(-7) M), Co(2+) and Ni(2+) also caused relaxation in lower concentrations while the other metals caused weak relaxation only in high concentrations (>10(-4) M). The metals were generally without effect on reactivity to MCh, except that Cd(2+) inhibited and Ni(2+) potentiated some responses. The effects of selected metals (10(-6) M; Cr(3+), Ni(2+), Cd(2+), and Co(2+)) on EFS-induced contractile and relaxant responses were examined (+/-MCh; +/-10(-6) M indomethacin (Indo), 30 min). No metal had any effect on the excitatory nonadrenergic, noncholinergic-mediated contraction phase. Cd(2+) and Ni(2+) inhibited cholinergically mediated contractions of unstimulated strips (+Indo), whereas Cr(3+) both inhibited (-MCh, -Indo) and potentiated (-Indo,+MCh; +Indo, +MCh) contractile responses. Cr(3+) was the only metal to inhibit the inhibitory nonadrenergic, noncholinergic-mediated relaxation phase (+/-MCh; -Indo). Co(2+) had no effect at all. The results suggest that smooth muscle tone and nerves in the airways could be targets of cationic metals after they dissolve in the lung.

Neuronal morphology and the synaptic organisation of sympathetic ganglia

In this article, we provide a short review of the structure and synaptic organisation of the final motor neurons in the sympathetic ganglia of mammals. Combinations of pathway tracing, multiple-labelling immunofluorescence and intracellular dye injection have shown that neurons in different functional pathways differ not only in their patterns of neuropeptide expression, but also in the size of their cell bodies and dendritic fields. Thus, vasoconstrictor neurons consistently are smaller than any other major functional class of neurons. Serial section ultrastructural analysis of dye filled neurons, together with electron microscopic and confocal microscopic analysis of immunolabelled synaptic inputs to sympathetic final motor neurons indicate that synapses are rare and randomly distributed over the surface of the neurons. The total number of synapses is simply proportional to the total surface area of the neurons. Many terminal boutons of peptide-containing preganglionic neurons do not make conventional synapses with target neurons. Furthermore, there is a spatial mismatch in the distribution of peptide-containing terminals and neurons expressing receptors for the corresponding peptides. Together, these results suggest that there are likely to be significant differences in the ways that the final sympathetic motor neurons in distinct functional pathways integrate their synaptic inputs. In at least some pathways, heterosynaptic actions of neuropeptides probably contribute to subtle modulation of ganglionic transmission.

Cochlear nerve projections to the small cell shell of the cochlear nucleus: the neuroanatomy of extremely thin sensory axons

Labeling cochlear nerve fibers in the inner ear of chinchillas with biotinylated dextran polyamine was used to trace the thin fibers (Type II), which likely innervate outer hair cells. These axons, 0. 1-0.5 microm in diameter, were distinguished from the thicker Type I, fibers innervating inner hair cells, and traced to small-cell clusters in the cochlear nucleus. This study provided two major new insights into the outer hair cell connections in the cochlear nucleus and the potential significance of very thin axons and synaptic nests, which are widespread in the CNS. 1) EM serial reconstructions of labeled and unlabeled material revealed that Type II axons rarely formed synapses with conventional features (vesicles gathered at junctions). Rather, their endings contained arrays of endoplasmic reticulum and small spherical vesicles without junctions. 2) Type II axons projected predominantly to synaptic nests, where they contacted other endings and dendrites of local interneurons (small stellate and mitt cells, but not granule cells). Synaptic nests lacked intrinsic glia and, presumably, their high-affinity amino acid transporters. As functional units, nests and their Type II inputs from outer hair cells may contribute to an analog processing mode, which is slower, more diffuse, longer-lasting, and potentially more plastic than the digital processors addressed by inner hair cells.