Participation of GABA in establishing behavioral hierarchies in the terrestrial snail

GABA-immunoreactive fibers were observed in the neuropile of each ganglion of Helix lucorum, while GABA-immunoreactive neural somata were found only in the buccal, cerebral, and pedal ganglia. Bath application of 10(-5) M GABA to the preparation "buccal mass-buccal ganglia" elicited a sequence of radula movements characteristic of feeding behavior. Corresponding bursts of activity were recorded in the buccal nerves under GABA application and in the buccal neurons recorded optically. In preparations of isolated central nervous system, the bath applications of GABA (10(-5) to 10(-4) M) elicited no changes in synaptic input of the premotor interneurons involved in the withdrawal behavior. However, a significant decrease in amplitude of the synaptic input and in the number of spikes in responses elicited by the test nerve stimulation was observed in metacerebral serotonergic neurons involved in modulating the feeding behavior. GABA application inhibited the spontaneous spike activity in some pedal serotonergic neurons involved in the network underlying withdrawal responses and evoked bursting activity in the other neurons of this functional group. The effects of GABA application on mechanically isolated serotonergic neurons suggest that the primary effect of GABA is inhibition. Thus, our results give evidence of the putative role of GABA in activating the feeding behavior and in the synergistic suppression of serotonergic modulation of the withdrawal behavior and serotonergic modulation of feeding, which has corresponded to the observed behavioral suppression of withdrawal reactions during feeding.     

Functions of Peptide CNP4, Encoded by the HCS2 Gene, in the Nervous System of Helix Lucorum

The aims of the present work were to study the role of neuropeptide CNP4, encoded by the HCS2 gene (which is expressed mainly in parietal command interneurons), in controlling the activity of the respiratory system, and also to study the effects of this neuropeptide on isolated defensive behavior neurons in prolonged culture. The influence of the command interneuron on the pneumostoma included a direct effect consisting of closure and a delayed effect consisting of intensification of respiratory movements. Application of neuropeptide CNP4 produced a pattern similar to the delayed effects seen on stimulation of the command interneuron, i.e., significant increases in the frequency and intensity of pneumostoma movements and strengthening of the rhythmic activity of the pneumostoma motoneuron. Studies of the effects of neuropeptide CNP4 on isolated neurons after prolonged culture showed that neuron process growth correlated with the presence of the neuropeptide in the medium. Identification of the location of the HCS2 precursor protein and neuropeptide CNP4 in isolated command interneurons after prolonged culture showed that that only those parts of the cell showing active process growth were immunopositive. Thus, neuropeptide CNP4 appears to be a secreted neuropeptide controlling respiratory system activity, which may also be involved in rearrangements of the network controlling defensive behavior in Helix snails __________ Translated from Zhurnal Vysshei Nervnoi Deyatel'nosti imeni I. P. Pavlova, Vol. 55, No. 1, pp. 91–99, January–February, 2005.     

Identification of mechanoafferent neurons in terrestrial snail: response properties and synaptic connections

In this study, we describe the putative mechanosensory neurons, which are involved in the control of avoidance behavior of the terrestrial snail Helix lucorum. These neurons, which were termed pleural ventrolateral (PlVL) neurons, mediated part of the withdrawal response of the animal via activation of the withdrawal interneurons. Between 15 and 30 pleural mechanosensory neurons were located on the ventrolateral side of each pleural ganglion. Intracellular injection of neurobiotin revealed that all PlVL neurons sent their axons into the skin nerves. The PlVL neurons had no spontaneous spike activity or fast synaptic potentials. In the reduced "CNS-foot" preparations, mechanical stimulation of the skin covering the dorsal surface of the foot elicited spikes in the PlVL neurons without any noticeable prepotential activity. Mechanical stimulus-induced action potentials in these cells persisted in the presence of high-Mg(2+)/zero-Ca(2+) saline. Each neuron had oval-shaped receptive field 5-20 mm in length located on the dorsal surface of the foot. Partial overlapping of the receptive fields of different neurons was observed. Intracellular stimulation of the PlVL neurons produced excitatory inputs to the parietal and pleural withdrawal interneurons, which are known to control avoidance behavior. The excitatory postsynaptic potentials (EPSPs) in the withdrawal interneurons were induced in 1:1 ratio to the PlVL neuron spikes, and spike-EPSP latency was short and highly stable. These EPSPs also persisted in the high-Mg(2+)/high-Ca(2+) saline, suggesting monosynaptic connections. All these data suggest that PlVL cells were the primary mechanosensory neurons.     

Selective blockade of gene expression in a single identified snail neuron

In the present study, the applicability of antisense morpholino oligos for loss-of-function experiments in neurobiology was investigated. The identified withdrawal interneurons of the parietal ganglia expressing helix command neuron-specific 2 (HCS2) gene were pressure injected with HCS2 antisense or control morpholino oligo solution at a final concentration 1-4 microM. No toxic or side effects for the neural functioning were noted immediately or several hours after injection. The changes in the concentration of HCS2-encoded protein in neurons after injection were monitored by two methods, Western blotting and immunostaining of the brain. The amount of the peptide immunoreactive with the HCS2 antibody started to decline in the injected cells at day 2 post-injection, decreased four- to five-fold at day 4, and stayed at this low level thereafter. Similar results obtained by both methods suggest significant selective blockade of production of the HCS2-encoded peptide. In contrast, no substantial decrease of the HCS2-encoded polypeptide was observed after injection with control oligos. Due to the high stability of the morpholino oligos in the cell, they represent a highly efficient tool for a specific long-term blockade of gene expression in molluscan neurons.     

In vitro formation and activity-dependent plasticity of synapses between Helix neurons involved in the neural control of feeding and withdrawal behaviors

Short-term activity-dependent synaptic plasticity has a fundamental role in short-term memory and information processing in the nervous system. Although the neuronal circuitry controlling different behaviors of land snails of the genus Helix has been characterized in some detail, little is known about the activity-dependent plasticity of synapses between identified neurons regulating specific behavioral acts. In order to study homosynaptic activity-dependent plasticity of behaviorally relevant Helix synapses independently of heterosynaptic influences, we sought to reconstruct them in cell culture. To this aim, we first investigated in culture the factors regulating synapse formation between Helix neurons, and then we studied the short-term plasticity of in vitro-reconstructed monosynaptic connections involved in the neural control of salivary secretion and whole-body withdrawal. We found that independently of extrinsic factors, cell-cell interactions are seemingly sufficient to trigger the formation of electrical and chemical synapses, although mostly inappropriate--in their type or association--with respect to the in vivo synaptic connectivity. The presence of ganglia-derived factors in the culture medium was required for the in vitro reestablishment of the appropriate in vivo-like connectivity, by reducing the occurrence of electrical connections and promoting the formation of chemical excitatory synapses, while apparently not influencing the formation of inhibitory connections. These heat-labile factors modulated electrical and chemical synaptogenesis through distinct protein tyrosine kinase signal transduction pathways. Taking advantage of in vitro-reconstructed synapses, we have found that feeding interneuron-efferent neuron synapses and mechanosensory neuron-withdrawal interneuron synapses display multiple forms of short-term enhancement-like facilitation, augmentation and posttetanic potentiation as well as homosynaptic depression. These forms of plasticity are thought to be relevant in the regulation of Helix feeding and withdrawal behaviors by inducing dramatic activity-dependent changes in the strength of input and output synapses of high-order interneurons with a crucial role in the control of Helix behavioral hierarchy.     

Synaptic contact between mechanosensory neuron and withdrawal interneuron in terrestrial snail is mediated by L-glutamate-like transmitter

The properties of the monosynaptic input from mechanosensory neurons to withdrawal interneurons were examined in Helix lucorum. The instantaneous I-V relation of the excitatory postsynaptic current in withdrawal interneurons was nonlinear, having a plateau region between -40 and -60 mV. On application of the blocker of vertebrate N-methyl-D-aspartate (NMDA) receptors AP5, or reduction of the Mg(2+) concentration, the current-voltage relation became more linear, suggesting that Mg(2+) may partially block the ion channel underlying the EPSC at voltages ranging from -40 to around -60 mV and the involvement of NMDA-like receptors. DNQX and 6-cyano-7-nitroquinoxaline-2,3-dione, which are known to block the glutamate non-NMDA receptors in mammals, significantly depress in a dose-dependent manner the actions of the natural transmitter. Exogenous L-glutamate applications mimicked the action of the mechanosensory neuron transmitter.     

Ontogenesis of the snail, Helix aspersa: embryogenesis timetable and ontogenesis of GABA-like immunoreactive neurons in the central nervous system

Late stages of embryogenesis in the terrestrial snail Helix aspersa L. were studied and a developmental timetable was produced. The distribution of gamma-aminobutyric acid-like immunoreactive (GABA-ir) elements in the CNS of the snail was studied from embryos to adulthood in wholemounts. In adults, approximately 226 GABA-ir neurons were located in the buccal, cerebral and pedal ganglia. The population of GABA-ir cells included four pairs of buccal neurons, three neuronal clusters in the pedal ganglia, two clusters and six single neurons in the cerebral ganglia. GABA-ir fibers were observed in all ganglia and in some nerves. The first detected pair of GABA-ir cells in the embryos appeared in the buccal ganglia at about 63–64% of embryonic development. Five pairs of GABA-ir cell bodies were observed in the cerebral ganglia at about 64–65% of development. During the following 30% of development three more pairs of GABA-ir neurons were detected in the buccal ganglia and over fifteen cells were detected in each cerebral ganglion. At the stage of 70% of development, the first pair of GABA-ir neurons was found in the pedal ganglia. In the suboesophageal ganglion complex, GABA-ir fibers were first detected at about 90% of embryonic development. In the posthatching period, the quantity of GABA-ir neurons reached the adult status in four days in the cerebral ganglia, and in three weeks in the pedal ganglia. In juveniles, transient expression of GABA was found in the pedal ganglia (fourth cluster).     

Enhancement of N-methyl- D-aspartate receptor-mediated excitatory postsynaptic potentials in the neostriatum after methamphetamine sensitization. An in vitro slice study

It has been suggested that behavioral methamphetamine sensitization involves changes in cortical excitatory synaptic inputs to neostriatal (Str) projection neurons. To test this, we performed blind whole-cell recording of medium spiny neurons in Str slice preparations. In Str neurons of naive rats, the amplitude of the subcortical white matter stimulation-induced N-methyl- D-aspartate receptor-mediated excitatory postsynaptic potentials (NMDA-EPSPs) was decreased upon hyperpolarization, owing to the voltage-dependent Mg(2+) blockade of NMDA receptor channels. In contrast, the amplitude of the NMDA-EPSPs in Str neurons of rats undergoing methamphetamine withdrawal (MW) did not show the Mg(2+) blockade and was nearly voltage independent over the membrane potential range of -70 to -110 mV. Application of the specific protein kinase C (PKC) activator, phorbol 12, 13- DL-acetate, blocked the voltage-dependent Mg(2+) blockade of NMDA receptor channels in Str neurons of naive rats. Application of the specific activator of cAMP-dependent protein kinase A (PKA), Sp-cAMPS-triethylamine salt, increased the amplitude of the NMDA receptor-mediated EPSPs at the rest but not at hyperpolarized potentials. Coapplication of the PKC and PKA activators yielded NMDA-EPSPs similar to those seen in Str neurons of MW rats. In Str slices of naive rats, tetanic subcortical white matter stimulation induced long-term depression of field potentials. In Str slices treated with the PKC and/or PKA, the same stimulation induced long-term potentiation of field potentials similar to those observed in slices obtained from MW rats. These results suggest that the enhancement of the NMDA receptor-mediated corticostriatal synaptic transmission plays an important role in behavioral methamphetamine sensitization. This enhancement is probably associated with phosphorylation of NMDA receptors mediated by the simultaneous activation of PKC and PKA.     

Nitric oxide increases excitability by depressing a calcium activated potassium current in snail neurons

In gastropods, the interneuronal messenger, nitric oxide (NO), modulates spike frequency and synaptic transmission. We have characterized the effect of NO on ion currents underlying neuronal excitability, using current-clamp and two-electrode voltage-clamp techniques. Identified neurons of the pulmonate snail, Helix pomatia, respond to the NO donor sodium nitroprusside (SNP) by increasing the firing frequency and decreasing the latency. Voltage-clamp experiments revealed that SNP or S-nitro-N-acetylpenicillamine (SNAP) depressed the macroscopic outward current, while the control compound N-acetylpenicillamine (NAP) had no effect. Current voltage curves generated from voltage steps to different membrane potentials ranging from -40 to +180 mV showed an N-shaped outward current. Superfusion of ganglia with Ca(2+) free Helix solution abolished the N-shape, indicating the contribution of a Ca(2+) activated K(+) current (I(K,Ca)). Exposure of neurons to SNP or SNAP diminished the N-shape, indicating that NO affects I(K,Ca). The depressing effect of SNP on the outward current was slow and reached steady state in about 5 min. In conclusion, our findings indicate that NO enhances excitability in Helix nervous system by decreasing I(K,Ca).     

Alterations of AQP2 expression in trigeminal ganglia in a murine inflammation model

Aquaporins (AQPs) are small membrane channel proteins involved in osmoregulation. To date, only AQP1, AQP2, AQP4 and AQP9 have been found in the nervous system. Generally, they are involved in water movement in nervous tissue, nevertheless, recent data would suggest the involvement of AQPs in neurotransmission. In this work, we have evaluated the expression of AQP1 and AQP2 in the trigeminal ganglia of mice in an animal model of perioral acute inflammatory pain using immunohistochemistry and immunoblotting analysis. Our data have shown for the first time, the alteration of AQP2 expression in trigeminal ganglia in acute inflammatory pain showing increased and intracellular redistribution of AQP2 mainly in small-sized neurons and Schwann cells. Apart from this, the AQP1 expression remained unaltered. On the whole, these data support the hypothesis that AQP2 is involved in pain transmission in the peripheral nervous system.     

Repeated cocaine administration suppresses HVA-Ca2+ potentials and enhances activity of K+ channels in rat nucleus accumbens neurons

The nucleus accumbens (NAc) is an important forebrain area involved in sensitization, withdrawal effects, and self-administration of cocaine. However, little is known about cocaine-induced alterations in the neuronal excitability and whole cell neuroplasticity in this region that may affect behaviors. Our recent investigations have demonstrated that repeated cocaine administration decreases voltage-sensitive sodium and calcium currents (VSSCs and VSCCs, respectively) in freshly dissociated NAc neurons of rats. In this study, current-clamp recordings were performed in slice preparations to determine the effects of chronic cocaine on evoked Ca(2+) potentials and voltage-sensitive K(+) currents in NAc neurons. Repeated cocaine administration with 3-4 days of withdrawal caused significant alterations in Ca(2+) potentials, including suppression of Ca(2+)-mediated spikes, increase in the intracellular injected current intensity required for generation of Ca(2+) potentials (rheobase), reduced duration of Ca(2+) plateau potentials, and abolishment of secondary Ca(2+) potentials associated with the primary Ca(2+) plateau potential. Application of nickel (Ni(2+)), which blocks low-voltage activated T-type Ca(2+) channels, had no impact on evoked Ca(2+) plateau potentials in NAc neurons, indicating that these Ca(2+) potentials are high-voltage activated (HVA). In addition, repeated cocaine pretreatment also hyperpolarized the resting membrane potential, increased the amplitude of afterhyperpolarization in Ca(2+) spikes, and enhanced the outward rectification observed during membrane depolarization. These findings indicate that repeated cocaine administration not only suppressed HVA-Ca(2+) potentials but also significantly enhanced the activity of various K(+) channels in NAc neurons. They also demonstrate an integrative role of whole cell neuroplasticity during cocaine withdrawal, by which the subthreshold membrane excitability of NAc neurons is significantly decreased.     

Identification and modulation of voltage-gated Ca2+ currents in zebrafish Rohon-Beard neurons

Electrically excitable cells have voltage-dependent ion channels on the plasma membrane that regulate membrane permeability to specific ions. Voltage-gated Ca(2+) channels (VGCCs) are especially important as Ca(2+) serves as both a charge carrier and second messenger. Zebrafish (Danio rerio) are an important model vertebrate for studies of neuronal excitability, circuits, and behavior. However, electrophysiological properties of zebrafish VGCCs remain largely unexplored because a suitable preparation for whole cell voltage-clamp studies is lacking. Rohon-Beard (R-B) sensory neurons represent an attractive candidate for this purpose because of their relatively large somata and functional homology to mammalian dorsal root ganglia (DRG) neurons. Transgenic zebrafish expressing green fluorescent protein in R-B neurons, (Isl2b:EGFP)(ZC7), were used to identify dissociated neurons suitable for whole cell patch-clamp experiments. Based on biophysical and pharmacological properties, zebrafish R-B neurons express both high- and low-voltage-gated Ca(2+) current (HVA- and LVA-I(Ca), respectively). Ni(+)-sensitive LVA-I(Ca) occur in the minority of R-B neurons (30%) and ω-conotoxin GVIA-sensitive Ca(V)2.2 (N-type) Ca(2+) channels underlie the vast majority (90%) of HVA-I(Ca). To identify G protein coupled receptors (GPCRs) that modulate HVA-I(Ca), a panel of neurotransmitters was screened. Application of GABA/baclofen or serotonin produced a voltage-dependent inhibition while application of the mu-opioid agonist DAMGO resulted in a voltage-independent inhibition. Unlike in mammalian neurons, GPCR-mediated voltage-dependent modulation of I(Ca) appears to be transduced primarily via a cholera toxin-sensitive Gα subunit. These results provide the basis for using the zebrafish model system to understanding Ca(2+) channel function, and in turn, how Ca(2+) channels contribute to mechanosensory function.     

Serotonin-immunoreactive varicosities in the cell body region and neural sheath of the snail, Helix pomatia, ganglia: an electron microscopic immunocytochemical study

The distribution and connections of serotonin-immunoreactive fibers in the cell body region and neural sheath of the central ganglia of the snail, Helix pomatia, have been examined. The cell body region of the ganglia is supplied by an extremely dense network of varicose serotonin-immunoreactive fibers which surround neuronal perikarya in the ganglia. Immunoreactive processes also run to the neural sheath of both the ganglia and the peripheral nerve roots, forming a dense network. Electron microscopy revealed five different connections of serotonin-immunoreactive varicosities, according to their target: (i) non-specialized contacts with neuronal perikarya; (ii) non-specialized contacts with axon processes on the surface of the peripheral nerve roots; (iii) non-specialized neuromuscular connections with smooth muscle fibers in the neural sheath; (iv) varicosities engulfed by glial processes in both the cell body region and neural sheath; (v) varicosities embedded in the connective tissue elements of the sheath either partly or completely free of glial processes. In all cases of appositions no membrane specializations could be observed on either site of the contacts. These observations provide morphological evidence for non-synaptic regulatory actions of serotonin-containing neurons in Helix central nervous system: (i) modulation of the activity of neuronal perikarya; (ii) involvement in neuromuscular regulation; (iii) neurohormonal modulation of peripheral processes by release through the neural sheath.     

Hydrogen peroxide induces transient dephosphorylation of tau protein in cultured rat oligodendrocytes

In brainstem slices of guinea pigs perfused with artificial cerebro-spinal fluid (ACSF), the discharge of all the spontaneously active neurons of the medial vestibular nucleus (MVN) is regular. It has been reported that prolonged exposure to a low Ca(2+) medium could induce these neurons to fire bursts of spikes. In this study, we performed a systematic exploration of the spontaneous activity of the guinea pig MVN neurons by extracellular recordings in slices perfused either with a low Ca(2+)-high Mg(2+) medium, or with ACSF added with omega-agatoxin-IVA and with omega-conotoxin-GVIA. The percentage of recorded neurons which fired bursts, was 67% in low Ca(2+)-high Mg(2+) medium and 34% under the action of Ca(2+) channel blockers. These results show that the sensitivity of the firing properties to divalent cations is not shared by all of the MVN neurons and that the regularity of firing of a class of MVN neurons depends on the Ca(2+) channels they express in their membranes.     

Age-associated changes in distribution of the P2X2 receptor in the major pelvic ganglion of the male rat

P2X purinoceptors constitute a group of ligand-gated ion channels one of which, the P2X2 receptor has previously been described in neurons within autonomic ganglia, including the major pelvic ganglion (MPG). Earlier work strongly suggests that age-associated attrition of sympathetic but not parasympathetic MPG neurons occurs but there have been no investigations of age-related changes in P2X2 receptor expression in autonomic ganglia or to determine whether the receptor is localised in one or both of the two MPG neuronal subpopulations. In the current study, immunocytochemistry was employed to label cells expressing the P2X2 receptor in the MPG from young and aged male Wistar rats. By combining P2X2 receptor immunocytochemistry with the immunolocalisation of tyrosine hydroxylase (TH), the numbers of sympathetic (TH+) and parasympathetic (TH-) neurons expressing the P2X2 receptor were determined. In young rats P2X2 receptor expression was found in 93.08+/-3.2% of TH- (parasympathetic) neurons. In aged rats a similar analysis revealed no significant difference in the number of TH- neurons expressing the P2X2 receptor. In contrast a significant increase in the number of TH+ sympathetic neurons expressing P2X2 was observed in the MPG of aged rats (10.70+/-2.26%) in comparison to the young group (2.38+/-0.78%). Age-related changes in the numbers of small intensely fluorescent (SIF) cells which were highly P2X2 positive were also quantified, revealing a small reduction in number with age. This study has demonstrated the preferential localisation of P2X2 receptors to parasympathetic MPG neurons and suggests that purinergic transmission in the pelvic organs maybe largely unaffected by ageing.     

Lithium slows neuronal calcium regulation in the snail Helix pomatia

Steady-state and transient changes in intracellular calcium concentrations ([Ca2+]i) of snail neurons (Helix pomatia) were measured by the Ca2+ indicator Arsenazo(III) following manipulation of the extracellular concentration of lithium chloride (LiCl). Application of LiCl in concentrations equivalent to those used in the treatment of manic-depressive illness produces slowing in Ca2+ reequilibration after Ca2+-influx during depolarization, concomitantly with steady-state elevation of [Ca2+]i of about 100 nM, suggesting a change in Ca2+ reequilibration as a prominent action of LiCl. This mechanism may be relevant to the therapeutic effects of LiCl.     

The presence and distribution of pituitary adenylate cyclase activating polypeptide and its receptor in the snail Helix pomatia

The aim of this study was to show the presence, distribution and function of the pituitary adenylate cyclase activating polypeptide (PACAP) and its receptors in the CNS and peripheral nervous system of the mollusk, Helix pomatia. PACAP-like and pituitary adenylate cyclase activating polypeptide receptor (PAC1-R)-like immunoreactivity was abundant both in the CNS and the peripheral nervous system of the snail. In addition several non-neuronal cells also revealed PACAP-like immunoreactivity. In inactive animals labeled cell bodies were mainly found and in the neuropile of active animals dense immunostained fiber system was additionally detected suggesting that expression of PACAP-like peptide was affected by the behavioral state of the animal. RIA measurements revealed the existence of both forms of PACAP in the CNS where the 27 amino acid form was found to be dominant. The concentration of PACAP27 was significantly higher in samples from active animals supporting the data obtained by immunohistochemistry. In Western blot experiments PACAP27 and PACAP38 antibodies specifically labeled protein band at 4.5 kDa both in rat and snail brain homogenates, and additionally an approximately 14 kDa band in snail. The 4.5 kDa protein corresponds to PACAP38 and the 14 kDa protein corresponds to the preproPACAP or to a PACAP-like peptide having larger molecular weight than mammalian PACAP38. In matrix-assisted laser desorption ionization time of flight (MALDI TOF) measurements fragments of PACAP38 were identified in brain samples suggesting the presence of a large molecular weight peptide in the snail. Applying antibodies developed against the PACAP receptor PAC1-R, immunopositive stained neurons and a dense network of fibers were identified in each of the ganglia. In electrophysiological experiments, extracellular application of PACAP27 and PACAP38 transiently depolarized or increased postsynaptic activity of neurons expressing PAC1-R. In several neurons PACAP elicited a long lasting hyperpolarization which was eliminated after 1.5 h continuous washing. Taken together, these results indicate that PACAP may have significant role in a wide range of basic physiological functions in snail.     

Chronic constriction injury induces aquaporin-2 expression in the dorsal root ganglia of rats

Aquaporins are a family of water channel proteins involved in water homeostasis in several tissues. Current knowledge of aquaporin expression in the nervous system is very limited. Therefore the first aim of this study was to assess, by immunohistochemistry and immunoblotting analysis, the presence and localization of aquaporin-2 in the spinal cord and dorsal root ganglia of naïve adult rats. In addition, we evaluated aquaporin-2 expression in response to chronic constriction injury of the sciatic nerve, a model of neuropathic pain. Our results showed that aquaporin-2 expression was not detectable either in the spinal cord or the dorsal root ganglia of naïve rats. However, we showed for the first time an increase of aquaporin-2 expression in response to chronic constriction injury treatment in small-diameter dorsal root ganglia neurons but no expression in the lumbar spinal cord. These data support the hypothesis that aquaporin-2 expression is involved in inflammatory neuropathic nerve injuries, although its precise role remains to be determined.