Embryonic geniculate ganglion neurons in culture have neurotrophin-specific electrophysiological properties

Geniculate ganglion neurons provide a major source of innervation to mammalian taste organs, including taste buds in the soft palate and in fungiform papillae on the anterior two thirds of the tongue. In and around the fungiform papillae, before taste buds form, neurotrophin mRNAs are expressed in selective spatial and temporal patterns. We hypothesized that neurotrophins would affect electrophysiological properties in embryonic geniculate neurons. Ganglia were explanted from rats at gestational day 16, when growing neurites have entered the papilla core, and maintained in culture with added brain-derived neurotrophic factor (BDNF), neurotrophin 4 (NT4), nerve growth factor (NGF) or neurotrophin 3 (NT3). Neuron survival with BDNF or NT4 was about 80%, whereas with NGF or NT3 less than 15% of neurons survived over 6 days in culture. Whole cell recordings from neurons in ganglion explants with each neurotrophin condition demonstrated distinctive neurophysiological properties related to specific neurotrophins. Geniculate neurons cultured with either BDNF or NT4 had similar passive-membrane and action potential properties, but these characteristics were significantly different from those of neurons cultured with NGF or NT3. NGF-maintained neurons had features of increased excitability including a higher resting membrane potential and a lower current threshold for the action potential. About 70% of neurons produced repetitive action potentials at threshold. Furthermore, compared with neurons cultured with other neurotrophins, a decreased proportion had an inflection on the falling phase of the action potential. NT3-maintained neurons had action potentials that were of relatively large amplitude and short duration, with steep rising and falling slopes. In addition, about 20% responded with a repetitive train of action potentials at threshold. In contrast, with BDNF or NT4 repetitive action potential trains were not observed. The data demonstrate different neurophysiological properties in developing geniculate ganglion neurons maintained with specific neurotrophins. Therefore, we suggest that neurotrophins might influence acquisition of distinctive neurophysiological properties in embryonic geniculate neurons that are fundamental to the formation of peripheral taste circuits and a functioning taste system.     

Contributions of placodal and neural crest cells to avian cranial peripheral ganglia

The method of embryonic tissue transplantation was used to confirm the dual origin of avian cranial sensory ganglia, to map precise locations of the anlagen of these sensory neurons, and to identify placodal and neural crest-derived neurons within ganglia. Segments of neural crest or strips of presumptive placodal ectoderm were excised from chick embryos and replaced with homologous tissues from quail embryos, whose cells contain a heterochromatin marker. Placode-derived neurons associated with cranial nerves V, VII, IX, and X are located distal to crest-derived neurons. The generally larger, embryonic placodal neurons are found in the distal portions of both lobes of the trigeminal ganglion, and in the geniculate, petrosal and nodose ganglia. Crest-derived neurons are found in the proximal trigeminal ganglion and in the combined proximal ganglion of cranial nerves IX and X. Neurons in the vestibular and acoustic ganglia of cranial nerve VIII derive from placodal ectoderm with the exception of a few neural crest-derived neurons localized to regions within the vestibular ganglion. Schwann sheath cells and satellite cells associated with all these ganglia originate from neural crest. The ganglionic anlagen are arranged in cranial to caudal sequence from the level of the mesencephalon through the third somite. Presumptive placodal ectoderm for the VIIIth, the Vth, and the VIIth, IXth, and Xth ganglia are located in a medial to lateral fashion during early stages of development reflecting, respectively, the dorsolateral, intermediate, and epibranchial positions of these neurogenic placodes.     

The origins of the afferent fibers to the lingual muscles of the dog, a retrograde labelling study with horseradish peroxidase

The origin of the afferent fibers to the lingual muscles of the dog was investigated by means of retrograde transport of horseradish peroxidase (HRP) from injection sites in the tongue and the extrinsic lingual muscles. Intralingual injections were not satisfactory because the enzyme diffused beyond the intrinsic lingual muscles to include virtually all tissues within the tongue. Thus, the resultant retrograde labeling of cell bodies of the trigeminal, geniculate, glossopharyngeal, vagal, and first cervical (C1) spinal ganglia represented a composite of lingual sensory innervation. In order to confine HRP uptake to intramuscular nerve endings, injections were limited to surgically isolated extrinsic lingual muscles, i.e., the genioglossus, hyoglossus, and styloglossus. After these intramuscular injections, labeled neurons appeared ipsilaterally in the C1 spinal ganglion, the proximal vagal (jugular) ganglion, and trigeminal ganglion. Earlier suggestions that the lingual proprioceptive neurons of the dog reside in the distal vagal (nodose) ganglion and hypoglossal ganglia were not confirmed. The mesencephalic nucleus of the trigeminal nerve failed to label after enzyme injections into the tongue or the extrinsic lingual muscles. The retrograde labeling of cell bodies in the C1 spinal ganglion was abolished when HRP injections into the extrinsic lingual muscles were preceded by surgical interruption of the ansa cervicalis or distal section of the hypoglossal nerve. Retrograde labeling of neurons in the proximal vagal ganglion persisted after hypoglossal nerve transections.     

Biophysical properties and responses to neurotransmitters of petrosal and geniculate ganglion neurons innervating the tongue

The properties of afferent sensory neurons supplying taste receptors on the tongue were examined in vitro. Neurons in the geniculate (GG) and petrosal ganglia (PG) supplying the tongue were fluorescently labeled, acutely dissociated, and then analyzed using patch-clamp recording. Measurement of the dissociated neurons revealed that PG neurons were significantly larger than GG neurons. The active and passive membrane properties of these ganglion neurons were examined and compared with each other. There were significant differences between the properties of neurons in the PG and GG ganglia. The mean membrane time constant, spike threshold, action potential half-width, and action potential decay time of GG neurons was significantly less than those of PG neurons. Neurons in the PG had action potentials that had a fast rise and fall time (sharp action potentials) as well as action potentials with a deflection or hump on the falling phase (humped action potentials), whereas action potentials of GG neurons were all sharp. There were also significant differences in the response of PG and GG neurons to the application of acetylcholine (ACh), serotonin (5HT), substance P (SP), and GABA. Whereas PG neurons responded to ACh, 5HT, SP, and GABA, GG neurons only responded to SP and GABA. In addition, the properties of GG neurons were more homogeneous than those of the PG because all the GG neurons had sharp spikes and when responses to neurotransmitters occurred, either all or most of the neurons responded. These differences between neurons of the GG and PG may relate to the type of receptor innervated. PG ganglion neurons innervate a number of receptor types on the posterior tongue and have more heterogeneous properties, while GG neurons predominantly innervate taste buds and have more homogeneous properties.     

The origins of the afferent fibers to the lingual muscles of the dog,a retrograde labeling study with horseradish peroxidase

The origin of the afferent fibers to the lingual muscles of the dog was investigated by means of retrograde transport of horseradish peroxidase (HRP) from injection sites in the tongue and the extrinsic lingual muscles. Intralingual injections were not satisfactory because the enzyme diffused beyond the intrinsic lingual muscles to include virtually all tissues within the tongue. Thus, the resultant retrograde labeling of cell bodies of the trigeminal, geniculate, glossopharyngeal, vagal, and first cervical (C₁) spinal ganglia represented a composite of lingual sensory innervation. In order to confine HRP uptake to intramuscular nerve endings, injections were limited to surgically isolated extrinsic lingual muscles, i.e., the genioglossus, hyoglossus, and styloglossus. After these intramuscular injections, labeled neurons appeared ipsilaterally in the C₁ spinal ganglion, the proximal vagal (jugular) ganglion, and trigeminal ganglion. Earlier suggestions that the lingual proprioceptive neurons of the dog reside in the distal vagal (nodose) ganglion and hypoglossal ganglia were not confirmed. The mesencephalic nucleus of the trigeminal nerve failed to label after enzyme injections into the tongue or the extrinsic lingual muscles. The retrograde labeling of cell bodies in the C₁ spinal ganglion was abolished when HRP injections into the extrinsic lingual muscles were preceded by surgical interruption of the ansa cervicalis or distal section of the hypoglossal nerve. Retrograde labeling of neurons in the proximal vagal ganglion persisted after hypoglossal nerve transections.     

Voltage dependence of membrane properties of trigeminal root ganglion neurons

1. Membrane potentials of trigeminal root ganglion neurons were varied systematically by intracellular injections of long-lasting step currents to determine the voltage dependence of their membrane electrical properties. The complex impedance and impedance magnitude functions were first determined using oscillatory input currents superimposed on these step currents. 2. Systematic step variations in the membrane potential led to qualitative changes in the impedance magnitude functions. Depolarization of neurons exhibiting resonance at their initial resting membrane potentials resulted in a reduction in the resonance behavior. Hyperpolarization of these neurons to membrane potentials of about -80 to -90 mV led to a disappearance of the resonant peak but increased the maximum of the impedance magnitude. 3. The complex impedance data were fitted with a neuronal model derived from linearized Hodgkin-Huxley-like equations, yielding estimates for the membrane properties. The four parameters of the model were 1) a time invariant, resting membrane conductance, Gr, 2) a voltage- and time-dependent conductance, GL, 3) a time constant, tau u, for the unknown ionic channels that are activated by the 2- to 5-mV oscillatory perturbation of the stepped membrane potential, and 4) Ci, the input capacitance. 4. The results of the curve-fitting procedures suggested that all parameters depended on membrane voltage. The most voltage-dependent parameters were GL and tau u throughout a 25- to 30-mV range that was subthreshold to the production of action potentials. Both Gr and GL increased with subthreshold depolarization. 5. These impedance data suggest the very important role of the membrane potential of the trigeminal root ganglion neurons on their abilities to synthesize and filter inputted electrical signals.     

Neuronal cell death and population dynamics in the developing rat geniculate ganglion

In contrast to many neuronal systems, the pattern of developmental neuronal degeneration in the rat geniculate ganglion has remained undefined. To address this issue sectioned geniculate ganglia from embryonic day 13 to postnatal day 3 have been examined using standard histological techniques, TdT-mediated dUTP-digoxigenin nick end labeling to verify apoptotic activity, bromo-deoxyuridine incorporation to monitor neuronal precursor proliferation, and anti-beta-neurotubulin III to verify the neuronal identity of pycnotic cells. Results summed from alternate (embryonic day 13) or every third (embryonic day 14-postnatal day 3) section show that neuronal degeneration occurs as early as embryonic day 13 (6.8% of neurons counted), well before geniculate innervation of lingual taste buds at embryonic day 16. A degenerative peak occurs at embryonic day 17 (9.5%) followed by a decline (1.7% at embryonic day 18) and leveling off (0.1%-0.2% at embryonic day 22-postnatal day 3). Thus, geniculate neuronal degenerative pattern includes both innervation-associated histogenetic and morphogenetic cell death. Corresponding counts of mean neuronal numbers in the sections showed a continual rise from embryonic day 13 through embryonic day 18 (approx. 330-760) followed by a slight decline at embryonic day 19 (to approx. 630) and then a final leveling off at 800-825 by embryonic day 20. This pattern differs from many other developing neural systems which show a major population crash during initial target contact. It likely reflects different but slightly overlapping neuronal precursor proliferation and degeneration patterns in multiple geniculate neuronal subpopulations.     

Neurotrophin-induced rapid enhancement of membrane potential oscillations in mesencephalic trigeminal neurons

We have proposed that neurotrophins, in addition to their trophic actions, act as neuromodulators in the adult central nervous system. As a first step to test this hypothesis, we examined in the adult rat slice preparation whether nerve growth factor and neurotrophin-3 are capable of altering the excitability of neurons of the mesencencephalic trigeminal nucleus. In contrast to vehicle pressure microapplication, which did not evoke changes in the electrophysiological properties of these neurons, neurotrophin application produced a significant increase in amplitude of the membrane potential oscillatory activity that is observed in these cells and a significant decrease in their threshold current. The latency of these effects ranged from 2 to 80 s and the duration ranged from 2 to 11 min. Neurotrophin-3 induced a decrease in input resistance and resting membrane potential in 58% of the cells; nerve growth factor induced a decrease in input resistance and resting membrane potential in 35% of the neurons. The spike configuration and action potential afterhyperpolarization potential remained unchanged following neurotrophin application. Tetrodotoxin blocked the membrane potential oscillatory activity of trigeminal mesencephalic neurons. Neurotrophin-induced effects were not blocked by the tyrosine kinase inhibitor K-252a, whereas IgG-192, an antibody directed to the neurotrophin low-affinity receptor, enhanced excitability, as did neurotrophins. These results demonstrate that neurotrophins are capable of producing a rapid increase in the excitability of trigeminal mesencephalic neurons and suggest that their effects may be mediated by low-affinity neurotrophin receptors.     

Primary involvement of K+ conductance in membrane resonance of trigeminal root ganglion neurons

1. The complex impedances and impedance magnitude functions were obtained from neurons in in vitro slices of trigeminal root ganglia using frequency-domain analyses of intracellularly recorded voltage responses to specified oscillatory input currents. A neuronal model derived from linearized Hodgkin-Huxley-like equations was used to fit the complex impedance data. This procedure yielded estimates for membrane electrical properties. 2. Membrane resonance was observed in the impedance magnitude functions of all investigated neurons at their initial resting membrane potentials and was similar to that reported previously for trigeminal root ganglion neurons in vivo. Tetrodotoxin (10(-6) M), a Na+-channel blocker, applied in the bathing medium for 20 min produced only minor changes, if any, in the resonance, although gross impairment of Na+-spike electrogenesis was apparent in most of the neurons. Brief applications (1-5 min) of a K+-channel blocker, tetraethylammonium (TEA; 10(-2) M), increased the impedance magnitude and abolished, in a reversible manner, the resonant behavior. In all cases, the resonant frequency was decreased by TEA administration prior to total blockade of resonance. 3. The TEA-induced blockade of resonance was associated with decreases in the estimates of the membrane conductances, without significant alterations of input capacitance. A particularly large decrease was observed in Gr, the time-invariant resting conductance that includes a lumped leak conductance component. The voltage- and time-dependent conductance, GL, and associated relaxation time constant, tau u, also declined progressively during administration of TEA. 4. Systematic variations in the membrane potentials of trigeminal root ganglion neurons were produced by intracellular injections of long-lasting step currents with superposition of the oscillatory current stimuli, in order to assess the effects of TEA on the relationship of the electrical properties to the membrane potential. Applications of TEA led to a depolarizing shift in the dependence of the membrane property estimates, suggesting voltage-dependence of the effects of TEA on presumed K+ channels in the membrane. 5. These data suggest a primary involvement of K+ conductance in the genesis of membrane resonance. This electrical behavior or its ionic mechanism is a major modulator of the subthreshold electrical responsiveness of trigeminal root ganglion neurons.     

Neurotrophin-induced rapid enhancement of membrane potential oscillations in mesencephalic trigeminal neurons

We have proposed that neurotrophins, in addition to their trophic actions, act as neuromodulators in the adult central nervous system. As a first step to test this hypothesis, we examined in the adult rat slice preparation whether nerve growth factor and neurotrophin-3 are capable of altering the excitability of neurons of the mesencencephalic trigeminal nucleus. In contrast to vehicle pressure microapplication, which did not evoke changes in the electrophysiological properties of these neurons, neurotrophin application produced a significant increase in amplitude of the membrane potential oscillatory activity that is observed in these cells and a significant decrease in their threshold current. The latency of these effects ranged from 2 to 80 s and the duration ranged from 2 to 11 min. Neurotrophin-3 induced a decrease in input resistance and resting membrane potential in 58% of the cells; nerve growth factor induced a decrease in input resistance and resting membrane potential in 35% of the neurons. The spike configuration and action potential afterhyperpolarization potential remained unchanged following neurotrophin application. Tetrodotoxin blocked the membrane potential oscillatory activity of trigeminal mesencephalic neurons. Neurotrophin-induced effects were not blocked by the tyrosine kinase inhibitor K-252a, whereas IgG-192, an antibody directed to the neurotrophin low-affinity receptor, enhanced excitability, as did neurotrophins.These results demonstrate that neurotrophins are capable of producing a rapid increase in the excitability of trigeminal mesencephalic neurons and suggest that their effects may be mediated by low-affinity neurotrophin receptors.     

Temperature neurons in the crotaline trigeminal ganglia.

1. Intrasomal recordings were made with microelectrodes from 153 warm (infrared) neurons in the trigeminal ganglia of 36 crotaline snakes, Trimeresurus flavoviridis. Background discharges were observed at room temperature. The 153 warm neurons were classified into two groups: 81 were sensitive to less than or equal to 10 mg of von Frey hair mechanical stimulation (warm T + M neuron), and 72 were insensitive to up to 100 mg or more of mechanical stimulation (warm T neuron). For T + M and T neurons the receptive fields were all located in the pit organ. The mechanically sensitive field of warm T + M neurons located within the infrared receptive field on the pit membrane was less than 1 mm in diameter, and there was only one field per neuron. 2. Electrophysiological parameters were measured. These measurements included membrane potential, action potential amplitude, time of peaking, time duration at the resting membrane potential level, afterhyperpotential (AHP) height and AHP time to half-decay, and maximum rates of depolarization and repolarization. No difference in action potential parameters between the means of these two submodality groups was observed. 3. Intracellular horseradish peroxidase (HRP) labeling was used for defining the warm neuron profile. The somata of warm T and warm T + M neurons and T- or Y-shaped bifurcations of the axon were observed in the ganglion. At the bifurcation point, nodes of Ranvier were observed, but without broad triangular expansion. Diameters of the central axons were thinner than those of the peripheral or stem axons. There were no differences between the mean diameters of the two submodalities. 4. The central axons of warm T and T + M neurons projected to the lateral descending nucleus of the trigeminal nerve (LTTD). Their synaptic boutons were found in the LTTD. No branching of the axons to the principal sensory nucleus or the descending nucleus of the trigeminal nerve was found. These results were the same for six warm T and eight warm T + M neurons. 5. Conduction velocities of the peripheral fibers were measured by stimulating superficial branches of the maxillary nerve electrically. Three groups of conduction velocity were identified in the compound potentials. The conduction velocity of the peak action potential of the warm T fibers was 6.9 +/- 1.2 (SD) m/s (n = 18), that of the T + M fibers 6.7 +/- 0.9 m/s (n = 23). These fell into the second group of the compound potentials.(ABSTRACT TRUNCATED AT 400 WORDS)     

Maturation of opioid sensitivity of fetal mouse dorsal root ganglion neuron perikarya in organotypic cultures: regulation by spinal cord

Opioid agonists selectively decrease the duration of the Ca2+ component of the action potential recorded from embryonic dorsal root ganglion neurons in dissociated cell cultures. In contrast, no significant alterations in the action potentials generated by adult dorsal root ganglion neurons in vivo were detected during opioid exposure. In the present study, the perikaryal opioid sensitivity of fetal mouse dorsal root ganglion neurons was analyzed during maturation in organotypic explant cultures. To determine whether spinal cord might influence this sensitivity, neuron perikarya were tested in ganglia grown: (a) in isolation; (b) attached to spinal cord explants; and (c) attached to spinal cord, but decentralized by a dorsal root transection in mature explants 1-2 weeks before the tests. After 2-8 weeks in culture, the duration of the Ba2+-enhanced Ca2+ component of intracellularly recorded action potentials was measured prior to and during bath exposure to the opioid, [D-Ala2, D-Leu5]enkephalin. Sensitive neurons were characterized by a marked, reversible reduction (averaging about 50%) in the duration of the Ca2+ component (which was antagonized by naloxone). The fraction of opioid-sensitive neuron perikarya in dorsal root ganglia grown attached to cord explants was significantly lower (48%) than in ganglia grown isolated (78%) or decentralized in vitro (79%). The mean duration of the Ca2+ component was significantly shorter in ganglion cells which had been grown attached to cord, or subsequently decentralized, compared to cells grown in isolated ganglia (by 24 and 38%, respectively). This difference was even larger in the opioid-insensitive groups. Although opioid-sensitive perikarya in ganglia grown attached to cord had a significantly longer Ba2+-enhanced Ca2+ component than that of insensitive neurons, some of the insensitive perikarya in all 3 types of explant paradigms displayed Ca2+ components which were as prolonged as those of sensitive cells. The results obtained in this study support the hypothesis that the observed decrease in the fraction of opioid-sensitive perikarya during development of fetal mouse dorsal root ganglia is due to regulation by interactions with their central target tissue, the spinal cord. The developmental decrease in the duration of the Ca2+ component of the action potential of these ganglion cells is also enhanced by the presence of the spinal cord. However, regulation of functional opiate receptors and Ca2+ component duration of the ganglion cell perikarya appear to be independent processes.     

Functional similarities and differences of AMPA and kainate receptors expressed by cultured rat sensory neurons

Dorsal root ganglion neurons express functional AMPA and kainate receptors near their central terminals. Activation of these receptors causes a decrease in glutamate release during action potential evoked synaptic transmission. Due to differences in kinetic properties and expression patterns of these two families of glutamate receptors in subpopulations of sensory neurons, AMPA and kainate receptors are expected to function differently. We used embryonic dorsal root ganglion (DRG) neurons maintained in culture to compare functional properties of kainate and AMPA receptors. Most DRG neurons in culture expressed kainate receptors and about half also expressed AMPA receptors. Most AMPA and kainate receptor-expressing DRG neurons were sensitive to capsaicin, suggesting involvement of these glutamate receptors in nociception. When activated by kainate, AMPA receptors were capable of driving a sustained train of action potentials while kainate receptors tended to activate action potential firing more transiently. Glutamate elicited more action potentials and a larger steady-state depolarization in neurons expressing both AMPA and kainate receptors than in neurons expressing only kainate receptors. Adding to their more potent activation properties, AMPA receptors recovered from desensitization much more quickly than kainate receptors. Activation of presynaptic receptors by low concentrations of kainate, but not ATPA, caused a tetrodotoxin-sensitive increase in the frequency of spontaneous EPSCs recorded in dorsal horn neurons. By recording synaptic pairs of DRG and dorsal horn neurons, we found that activation of presynaptic kainate and AMPA receptors decreased evoked glutamate release from terminals of DRG neurons in culture. Our data suggest that the endogenous ligand, glutamate, will cause a different physiological impact when activating these two types of non-NMDA glutamate receptors at central or peripheral nerve endings of sensory neurons.     

Developmental expression of Bdnf,Ntf4/5, and TrkB in the mouse peripheral taste system

Brain‐derived neurotrophic factor (BDNF), neurotrophin‐4 (NT4), and their TrkB receptor regulate taste system development. To determine where and when gustatory neurons come in contact with these important factors, temporospatial expression patterns of Bdnf, Ntf4/5, and TrkB in the peripheral taste system were examined using RT‐PCR. In the lingual epithelium, Ntf4/5 mRNA expression was higher than that of Bdnf at embryonic day 12.5 (E12.5), and the expression of both factors decreased afterwards. However, Ntf4/5 expression decreased at an earlier age than Bdnf. Bdnf and Ntf4/5 are expressed in equal amounts at E12.5 in geniculate ganglion, but Bdnf expression increased from E14.5 to birth, whereas Ntf4/5 expression decreased. These findings indicate that NT4 functions at early embryonic stages and is derived from different sources than Bdnf. TrkB expression in the geniculate ganglion is robust throughout development and is not a limiting factor for neurotrophin function in this system. Developmental Dynamics 239:2637–2646, 2010. © 2010 Wiley‐Liss, Inc.     

Electrophysiological and morphological diversity of mouse sympathetic neurons

We have used multiple-labeling immunohistochemistry, intracellular dye-filling, and intracellular microelectrode recordings to characterize the morphological and electrical properties of sympathetic neurons in the superior cervical, thoracic, and celiac ganglia of mice. Neurochemical and morphological characteristics of neurons varied between ganglia. Thoracic sympathetic ganglia contained three main populations of neurons based on differential patterns of expression of immunoreactivity to tyrosine hydroxylase, neuropeptide Y (NPY) and vasoactive intestinal peptide (VIP). In the celiac ganglion, nearly all neurons contained immunoreactivity to both tyrosine hydroxylase and NPY. Both the overall size of the dendritic tree and the number of primary dendrites were greater in neurons from the thoracic and celiac ganglia compared with those from the superior cervical ganglion. The electrophysiological properties of sympathetic neurons depended more on their ganglion of origin rather than their probable targets. All neurons in the superior cervical ganglion had phasic firing properties and large afterhyperpolarizations (AHPs). In addition, 34% of these neurons displayed an afterdepolarization preceding the AHP. Superior cervical ganglion neurons had prominent I(M), I(A), and I(H) currents and a linear current-voltage relationship between -60 and -110 mV. Neurons from the thoracic ganglia had significantly smaller action potentials, AHPs, and apparent cell capacitance compared with superior cervical ganglion neurons, and only 18% showed an afterdepolarization. All neurons in superior cervical ganglia and most neurons in celiac ganglia received at least one strong preganglionic input. Nearly one-half the neurons in the celiac ganglion had tonic firing properties, and another 15% had firing properties intermediate between those of tonic and phasic neurons. Most celiac neurons showed significant inward rectification below -90 mV. They also expressed I(A), but with slower inactivation kinetics than that of superior cervical or thoracic neurons. Both phasic and tonic celiac ganglion neurons received synaptic inputs via the celiac nerves in addition to strong inputs via the splanchnic nerves. Multivariate statistical analysis revealed that the properties of the action potential, the AHP, and the apparent cell capacitance together were sufficient to correctly classify 80% of neurons according to their ganglion of origin. These results indicate that there is considerable heterogeneity in the morphological, neurochemical, and electrical properties of sympathetic neurons in mice. Although the morphological and neurochemical characteristics of the neurons are likely to be related to their peripheral projections, the expression of particular electrophysiological traits seems to be more closely related to the ganglia within which the neurons occur.     

铃蟾肽对交感神经节细胞的易化作用及离子机制探讨

目的：观察铃蟾肽（BOM）对豚鼠离体交感神经节细胞膜电位和膜电阻的影响及初步离子机制。方法：细胞内生物电记录技术。结果：BOM在大部分细胞上引起的缓慢去极化与剂量相关，可为特异性受体阻断剂Tyr^4,[D-phel2]BOM所阻断；BOM使去极化电位幅度增大并转化为动作电位（AP），并使电刺激突触前神经所致的使兴奋性突触后电位（f-EPSP)转化为AP。多数细胞膜电阻的减小及离子替换等显示Na^ 、K^ 可能参与该反应。结论：BOM通过相应受体对交感神经节内神经元兴奋性起易化作用；非单一离子参与该作用。     

Differential distribution of calcitonin gene-related peptide and its receptor components in the human trigeminal ganglion

Calcitonin gene related peptide (CGRP) has a key role in migraine and recently CGRP receptor antagonists have demonstrated clinical efficacy in the treatment of migraine. However, it remains unclear where the CGRP receptors are located within the CGRP signaling pathway in the human trigeminal system and hence the potential antagonist sites of action remain unknown. Therefore we designed a study to evaluate the localization of CGRP and its receptor components calcitonin receptor-like receptor (CLR) and receptor activity modifying protein (RAMP) 1 in the human trigeminal ganglion using immunohistochemistry and compare with that of rat. Antibodies against purified CLR and RAMP1 proteins were produced and characterized for this study. Trigeminal ganglia were obtained at autopsy from adult subjects and sections from rat trigeminal ganglia were used to compare the immunostaining pattern. The number of cells expressing CGRP, CLR and RAMP1, respectively, were counted. In addition, the glial cells of trigeminal ganglion, particularly the satellite glial cell, were studied to understand a possible relation. We observed immunoreactivity for CGRP, CLR and RAMP1, in the human trigeminal ganglion: 49% of the neurons expressed CGRP, 37% CLR and 36% RAMP1. Co-localization of CGRP and the receptor components was rarely found. There were no CGRP immunoreactions in the glial cells; however some of the glial cells displayed CLR and RAMP1 immunoreactivity. Similar results were observed in rat trigeminal ganglia. We report that human and rat trigeminal neurons store CGRP, CLR and RAMP1; however, CGRP and CLR/RAMP1 do not co-localize regularly but are found in separate neurons. Glial cells also contain the CGRP receptor components but not CGRP. Our results indicate, for the first time, the possibility of CGRP signaling in the human trigeminal ganglion involving both neurons and satellite glial cells. This suggests a possible site of action for the novel CGRP receptor antagonists in migraine therapy.     

Analysis of passive and active electrophysiologic properties of neurons in mammalian nodose ganglia maintained in vitro.

1. We studied the passive and active electrical properties of the soma membrane of neurons in nodose ganglia removed from cats and rabbits and maintained in vitro. The ganglia were superfused at 37 degrees C with a solution formulated to approximate the extracellular fluid of each species. The solution was buffered to pH 7.34, continuously equilibrated with 95% O2 and 5% CO2, and contained dialyzed calf serum and glucose. We also examined these properties in nodose ganglion neurons in vivo. Intracellular recordings were obtained with glass micropipettes filled with either 3 M KCl or 5 M K acetate. 2. We determined mean values for a variety of passive and active electrophysiologic properties. Values obtained in vitro did not differ significantly from those obtained in vivo. Based on the passive electrical properties of the soma membrane, neurons in the nodose ganglion appear to be a uniform population, despite the different sensory modalities conveyed by the afferent fibers. 3. Cell bodies of neurons generated action potentials in response to impulses in their afferent fibers. Somatic spikes could be evoked by stimulation of either the supranodose or infranodose vagus nerve, and an inflection point could be seen on their rising phase. When the vagus nerve was stimulated at frequencies greater than 10-20 Hz, the generation of somatic spikes often became progressively delayed and then failed completely, leaving a smaller potential (IS spike) which was apparently generated in the initial complex. The afterhyperpolarization was associated only with the somatic spike. 4. Many neurons, both in vitro and in vivo, developed a persistent hyperpolarization when repetitive action potentials occurred in the soma. This hyperpolarization was apparent at frequencies as low as 1-2 Hz, persisted for up to 5 s after the occurrence of the last somatic spike, and sometimes caused failure of somatic spikes to be generated. 5. Neurons in both species differed in their responses to suprathreshold depolarization applied through the recording electrode. Some neurons produced a train of action potentials which lasted for the duration of the depolarizing pulse, the frequency of the train being related to the magnitude of depolarization. The trains were characterized by gradually decreasing spike amplitudes and increasing interspike intervals. Other neurons responded with only a single spike or brief burst of action potentials at the beginning of depolarization to threshold. 6. It is suggested that the adaptive properties of the soma membrane of a peripheral sensory neuron are similar to those of its sensory ending, and that electrophysiological studies of the soma membrane may provide an opportunity to examine mechanisms of receptor adaptation.     

Postnatal maturational changes in rat pelvic autonomic ganglion cells: a mixture of steroid-dependent and -independent effects

Androgens have potent effects on the maturation and maintenance of a number of neural pathways involved in reproductive behaviors in males. Most studies in this area have focused on central pathways, but androgen receptors are expressed by many peripheral neurons innervating reproductive organs, and previous studies have demonstrated structural and chemical changes in these neurons at puberty and after castration. We have performed the first electrophysiological comparison of pelvic autonomic ganglion neurons in male rats before and after puberty and following pre- or postpubertal castration. Studies were performed in vitro on intact ganglia with hypogastric and pelvic nerves attached to allow synaptic activation of sympathetic or parasympathetic neurons, respectively. Pelvic ganglion neurons underwent many changes in their passive and active membrane properties over the pubertal period, and some of these changes were dependent on exposure to circulating androgens. The most pronounced steroid-dependent effects were on membrane capacitance (soma size) in sympathetic neurons and duration of the action potential afterhyperpolarization in tonic neurons. Our study also showed that rat pelvic ganglion cells and their synaptic inputs were more diverse than previously reported. In conclusion, this study demonstrated that rat pelvic ganglion neurons undergo considerable postnatal changes in their electrophysiological properties. The steroid dependence of some of these changes indicates that circulating androgens may influence reproductive behaviors at many locations within the nervous system not just in the brain and spinal cord.