Colocalization of GABA and glycine in the rat dorsal column nuclei

Modulation of tactile feedback for the execution of dexterous movement

[Figure: see text].

Morphological and neurochemical characterization of glycinergic neurons in laminae I-IV of the mouse spinal dorsal horn

A growing body of experimental evidence shows that glycinergic inhibition plays vital roles in spinal pain processing. In spite of this, however, our knowledge about the morphology, neurochemical characteristics, and synaptic relations of glycinergic neurons in the spinal dorsal horn is very limited. The lack of this knowledge makes our understanding about the specific contribution of glycinergic neurons to spinal pain processing quite vague. Here we investigated the morphology and neurochemical characteristics of glycinergic neurons in laminae I-IV of the spinal dorsal horn using a GlyT2::CreERT2-tdTomato transgenic mouse line. Confirming previous reports, we show that glycinergic neurons are sparsely distributed in laminae I-II, but their densities are much higher in lamina III and especially in lamina IV. First in the literature, we provide experimental evidence indicating that in addition to neurons in which glycine colocalizes with GABA, there are glycinergic neurons in laminae I-II that do not express GABA and can thus be referred to as glycine-only neurons. According to the shape and size of cell bodies and dendritic morphology, we divided the tdTomato-labeled glycinergic neurons into three and six morphological groups in laminae I-II and laminae III-IV, respectively. We also demonstrate that most of the glycinergic neurons co-express neuronal nitric oxide synthase, parvalbumin, the receptor tyrosine kinase RET, and the retinoic acid-related orphan nuclear receptor β (RORβ), but there might be others that need further neurochemical characterization. The present findings may foster our understanding about the contribution of glycinergic inhibition to spinal pain processing.

TRPV1-Like Immunoreactivity in the Human Locus K, a Distinct Subregion of the Cuneate Nucleus

The presence of transient receptor potential vanilloid type-1 receptor (TRPV1)-like immunoreactivity (LI), in the form of nerve fibres and terminals, is shown in a set of discrete gray matter subregions placed in the territory of the human cuneate nucleus. We showed previously that those subregions share neurochemical and structural features with the protopathic nuclei and, after the ancient name of our town, collectively call them Locus Karalis, and briefly Locus K. TRPV1-LI in the Locus K is codistributed, though not perfectly overlapped, with that of the neuropeptides calcitonin gene-related peptide and substance P, the topography of the elements immunoreactive to the three markers, in relation to each other, reflecting that previously described in the caudal spinal trigeminal nucleus. Myelin stainings show that myelinated fibres, abundant in the cuneate, gracile and trigeminal magnocellular nuclei, are scarce in the Locus K as in the trigeminal substantia gelatinosa. Morphometric analysis shows that cell size and density of Locus K neurons are consistent with those of the trigeminal substantia gelatinosa and significantly different from those of the magnocellular trigeminal, solitary and dorsal column nuclei. We propose that Locus K is a special component of the human dorsal column nuclei. Its functional role remains to be determined, but TRPV1 appears to play a part in it.

Immunocytochemistry for Drugs Containing an Aliphatic Primary Amino Group in the Molecule, Anticancer Antibiotic Daunomycin as a Model

An immunocytochemistry (ICC) for the anticancer antibiotic daunomycin (DM) was developed using a combination of anti-DM serum produced against N-(gamma-male-imidobutyryloxy)succinimide (GMBS)-conjugated DM, and DM-uptake human melanoma BD cells. The antiserum was demonstrated to be specific for DM and the structurally related analogs adriamicin and epirubicin by an ICC model system of the enzyme immunoassay (EIA) using glutaraldehyde (GA)-conjugated DM as a solid phase antigen. No cross-reaction occurred with any of the other antibiotics tested such as bleomycin, pepleomycin, and mitomycin C. Successful DM ICC required a series of processes prior to the immunocytochemical reaction: the cells were first fixed with GA, then reduced with NaBH4, treated with hydrochloric acid, and finally digested with protease. The cell specimens were then subjected to immunoreaction with anti-DM serum followed by peroxidase-labeled goat anti-rabbit IgG/Fab', and in both immune reagents the detergent Triton X-100 was contained as well. The present ICC covering all these processes successfully stained for DM in the nucleus and in the perinuclear Golgi region of the cytoplasm of the BD cells, consistent with the results obtained by the DM autofluorescence method. This ICC was found to be three times as sensitive as the cytofluorometric method and applicable to the paraffin sections of the liver of rats 24 hr after an IV injection of DM. The principle used in the present study for developing DM ICC might be applied to other drugs containing the primary amino group(s) in the molecule. Thus, these ICCs for drugs are direct, precise and easy new methods that should have potential for pharmacology and toxicology studies of drugs, revealing the localization of a drug in cells and tissues.

The human cuneate nucleus contains discrete subregions whose neurochemical features match those of the relay nuclei for nociceptive information

The present paper is aimed at defining distinctive subdivisions of the human cuneate nucleus (Cu), evident from prenatal to old life, whose occurrence has never been clearly formalized in the human brain, or described in other species so far. It extends our early observations on the presence of gray matter areas that host strong substance P (SP) immunoreactivity in the territory of the human Cu and adjacent cuneate fascicle. Here we provide a three-dimensional reconstruction of the Cu fields rich in SP and further identify those areas by means of their immunoreactivity to the neuropeptides SP, calcitonin gene-related peptide, methionine- and leucine-enkephalin, peptide histidine-isoleucine, somatostatin and galanin, to the trophins glial cell line-derived neurotrophic factor and brain-derived neurotrophic factor, and to the neuroplasticity proteins polysialylated neural cell adhesion molecule and growth-associated protein-43. The presence, density and distribution of immunoreactivity for each of these molecules closely resemble those occurring in the superficial layers of the caudal spinal trigeminal nucleus (Sp5C). Myelin and Nissl stainings suggest that those Cu subregions and the Sp5C superficial layers share a similar histological aspect. This work establishes the existence of definite subregions, localized within the Cu territory, that bear the neurochemical and histological features of sensory nuclei committed to the neurotransmission of protopathic stimuli, including pain. These findings appear of particular interest when considering that functional, preclinical and clinical studies show that the dorsal column nuclei, classical relay station of fine somatic tactile and proprioceptive sensory stimuli, are also involved in pain neurotransmission.

Immunocytochemistry for vancomycin using a monoclonal antibody that reveals accumulation of the drug in rat kidney and liver

We prepared monoclonal antibodies against N-(γ-maleimidobutyryloxy)succinimide-conjugated vancomycin (VM). The monoclonal antibody was specific for conjugated or free VM. The monoclonal antibody enabled us to develop an immunocytochemical method for detecting the uptake of VM in the rat kidney and liver. Three hours after a single intravenous (i.v.) injection of VM at the therapeutic dose, the immunocytochemistry revealed that VM accumulated in large amounts in both the S1 and S2 segments and in much smaller amounts in the S3 segment of the proximal tubules as well as in the distal tubules and collecting ducts. The drug was detected in the cytoplasm, cytoplasmic irregular granules, nuclei, and microvilli of the proximal tubule cells. The distal tubules and collecting ducts contained scattered swollen cells in which both the nuclei and cytoplasm were heavily immunostained. Twenty-four hours after injection, most of the swollen cells returned back to normal size and had somewhat decreased immunostaining. Also, significant amounts of VM remained accumulated for as long as 8 days postadministration. In the liver, similar drug accumulation was observed in the Kupffer cells and the endothelial cells of the hepatic sinusoids but not in the hepatocytes, suggesting that vancomycin cannot be eliminated via the liver. Immunoelectron microscopic studies demonstrated that in the collecting ducts, uptake of VM occurred exclusively in the lysosomes and cytoplasm of the principal cells and scarcely in the intercalated cells. Furthermore, double fluorescence staining using rats simultaneously administered with VM and gentamicin strongly suggests that both drugs colocalized in lysosomes in the proximal tubule cells of kidneys.

Estrogen in cycling rats alters gene expression in the temporomandibular joint, trigeminal ganglia and trigeminal subnucleus caudalis/upper cervical cord junction

Females report temporomandibular joint (TMJ) pain more than men and studies suggest estrogen modulates this pain response. Our goal in this study was to determine genes that are modulated by physiological levels of 17β-estradiol that could have a role in TMJ pain. To complete this goal, saline or complete Freund's adjuvant was injected in the TMJ when plasma 17β-estradiol was low or when it was at a high proestrus level. TMJ, trigeminal ganglion, and trigeminal subnucleus caudalis/upper cervical cord junction (Vc/C(1-2) ) tissues were isolated from the treated rats and expression of 184 genes was quantitated in each tissue using real-time PCR. Significant changes in the amount of specific transcripts were observed in the TMJ tissues, trigeminal ganglia, and Vc/C(1-2) region when comparing rats with high and low estrogen. GABA A receptor subunit α6 (Gabra6) and the glycine receptor α2 (Glra2) were two genes of interest because of their direct function in neuronal activity and a >29-fold increase in the trigeminal ganglia was observed in proestrus rats with TMJ inflammation. Immunohistochemical studies showed that Gabrα6 and Glrα2 neuronal and not glial expression increased when comparing rats with high and low estrogen. Estrogen receptors α and β are present in neurons of the trigeminal ganglia, whereby 17β-estradiol can alter expression of Gabrα6 and Glrα2. Also, estrogen receptor α (ERα) but not ERβ was observed in satellite glial cells of the trigeminal ganglia. These results demonstrate that genes associated with neurogenic inflammation or neuronal excitability were altered by changes in the concentration of 17β-estradiol.

GABA and glycine immunolabeling in the chicken tangential nucleus

In the vestibular nuclei, GABAergic and glycinergic neurons play important roles in signal processing for normal function, during development, and after peripheral vestibular lesions. The chicken tangential nucleus is a major avian vestibular nucleus, whose principal cells are projection neurons with axons transmitting signals to the oculomotor nuclei and/or cervical spinal cord. Antibodies against GABA, glycine and glutamate were applied to study immunolabeling in the tangential nucleus of 5-7 days old chicken using fluorescence detection and confocal imaging. All the principal cells and primary vestibular fibers were negative for GABA and glycine, but positive for glutamate. GABA is the predominant inhibitory neurotransmitter in the tangential nucleus, labeling most of the longitudinal fibers in transverse tissue sections and more than 50% of all synaptic terminals. A large fraction of GABAergic terminals were derived from the longitudinal fibers, with fewer horizontal GABAergic fibers detected. GABA synapses terminated mainly on dendrites in the tangential nucleus. In contrast, glycine labeling represented about one-third of all synaptic terminals, and originated from horizontally-coursing fibers. A distinct pool of glycine-positive terminals was found consistently around the principal cell bodies. While no GABA or glycine-positive neuron cell bodies were found in the tangential nucleus, several pools of immunopositive neurons were present in the neighboring vestibular nuclei, mainly in the descending vestibular and superior vestibular nuclei. GABA and glycine double-labeling experiments revealed little colocalization of these two neurotransmitters in synaptic terminals or fibers in the tangential nucleus. Our data support the concept of GABA and glycine playing critical roles as inhibitory neurotransmitters in the tangential nucleus. The two inhibitory neurotransmitters have distinct and separate origins and display contrasting subcellular termination patterns, which underscore their discrete roles in vestibular signal processing.

Processing afferent proprioceptive information at the main cuneate nucleus of anesthetized cats

Medial lemniscal activity decreases before and during movement, suggesting prethalamic modulation, but the underlying mechanisms are largely unknown. Here we studied the mechanisms underlying proprioceptive transmission at the midventral cuneate nucleus (mvCN) of anesthetized cats using standard extracellular recordings combined with electrical stimulation and microiontophoresis. Dual simultaneous recordings from mvCN and rostroventral cuneate (rvCN) proprioceptive neurons demonstrated that microstimulation through the rvCN recording electrode induced dual effects on mvCN projection cells: potentiation when both neurons had excitatory receptive fields in muscles acting at the same joint, and inhibition when rvCN and mvCN cells had receptive fields located in different joints. GABA and/or glycine consistently abolished mvCN spontaneous and sensory-evoked activity, an effect reversed by bicuculline and strychnine, respectively; and immunohistochemistry data revealed that cells possessing strychnine-sensitive glycine receptors were uniformly distributed throughout the cuneate nucleus. It was also found that proprioceptive mvCN projection cells sent ipsilateral collaterals to the nucleus reticularis gigantocellularis and the mesencephalic locomotor region, and had slower antidromic conduction speeds than cutaneous fibers from the more dorsally located cluster region. The data suggest that (1) the rvCN-mvCM network is functionally related to joints rather than to single muscles producing an overall potentiation of proprioceptive feedback from a moving forelimb joint while inhibiting, through GABAergic and glycinergic interneurons, deep muscular feedback from other forelimb joints; and (2) mvCN projection cells collateralizing to or through the ipsilateral reticular formation allow for bilateral spreading of ascending proprioceptive feedback information.

Glycinergic mediation of tactile allodynia induced by platelet-activating factor (PAF) through glutamate-NO-cyclic GMP signalling in spinal cord in mice

Our previous study showed that intrathecal (i.t.) injection of platelet-activating factor (PAF) induced tactile allodynia, suggesting that spinal PAF is a mediator of neuropathic pain. The present study further examined the spinal molecules participating in PAF-induced tactile allodynia in mice. I.t. injection of L-arginine, NO donor (5-amino-3-morpholinyl-1,2,3-oxadiazolium (SIN-1) or 3,3-bis(aminoethyl)-1-hydroxy-2-oxo-1-triazene (NOC-18)) or cGMP analog (8-(4-chlorophenylthio)-guanosine 3',5'-cyclic monophosphate; pCPT-cGMP) induced tactile allodynia. PAF- and glutamate- but not SIN-1- or pCPT-cGMP-induced tactile allodynia was blocked by an NO synthase inhibitor. NO scavengers and guanylate cyclase inhibitors protected mice against the induction of allodynia by PAF, glutamate and SIN-1, but not by pCPT-cGMP. cGMP-dependent protein kinase (PKG) inhibitors blocked the allodynia induced by PAF, glutamate, SIN-1 and pCPT-cGMP. To identify signalling molecules through which PKG induces allodynia, glycine receptor alpha3 (GlyR alpha3) was knocked down by spinal transfection of siRNA for GlyR alpha3. A significant reduction of GlyR alpha3 expression in the spinal superficial layers of mice treated with GlyR alpha3 siRNA was confirmed by immunohistochemical and Western blotting analyses. Functional targeting of GlyR alpha3 was suggested by the loss of PGE(2)-induced thermal hyperalgesia and the enhancement of allodynia induced by bicuculline, a GABA(A) receptor antagonist in mice after GlyR alpha3 siRNA treatment. pCPT-cGMP, PAF, glutamate and SIN-1 all failed to induce allodynia after the knockdown of GlyR alpha3. These results suggest that the glutamate-NO-cGMP-PKG pathway in the spinal cord may be involved in the mechanism of PAF-induced tactile allodynia, and GlyR alpha3 could be a target molecule through which PKG induces allodynia.

Neurochemical characterization of neuronal populations expressing protein kinase C gamma isoform in the spinal cord and gracile nucleus of the rat

Protein kinase C gamma (PKCgamma) is widely distributed throughout the CNS and is thought to play a role in long term hyper-excitability in nociceptive neurones. Here, we provide the first report of PKCgamma cells in the dorsal column nuclei of the adult rat. Retrograde labeling of PKCgamma cells from the thalamus with choleragenoid revealed that 25% of the PKCgamma positive gracile cells projected to the thalamus. Further, we have characterized the distribution of PKCgamma within gracile nucleus in terms of colocalization with various neurotransmitter receptors or enzymes and calcium binding proteins, and compared this with PKCgamma colocalization in cells of laminae I-III of the spinal cord. We show that approximately 90% of the PKCgamma cells in the gracile nucleus and 60% in the dorsal horn were immuno-positive for the AMPA receptor subunit glutamate 2/3 (GluR2/3). Little coexpression was seen with neurokinin 1 receptor, nitric oxide synthase (NOS) and the AMPA receptor subunit GluR1, markers of distinct neuronal subpopulations. In the spinal cord, a quarter of PKCgamma cells expressed calbindin, but very few cells did so in the gracile nucleus. Electrical stimulation at c-fiber strength of the normal or injured sciatic nerve was used to induce c-fos as a marker of postsynaptic activation in the spinal cord and gracile nucleus. Quantitative analysis of the number of PKCgamma positive gracile cells that expressed also c-fos increased from none to 24% after injury, indicating an alteration in the sensory activation pattern in these neurones after injury. C-fos was not induced in inner lamina II following c-fiber electrical stimulation of the intact or axotomized sciatic nerve, indicating no such plasticity at the spinal cord level. As dorsal column nuclei cells may contribute to allodynia after peripheral nerve injury, pharmacological modulation of PKCgamma activity may therefore be a possible way to ameliorate neuropathic pain after peripheral nerve injury.

Distribution of anticancer antibiotic daunomycin in the rat heart and kidney revealed by immunocytochemistry using monoclonal antibodies

Two monoclonal antibodies (ADM-1-11 and 79-31 mAbs) were raised against daunomycin (DM) conjugated to bovine serum albumin via the cross-linker N-(gamma-maleimidobutyryloxy)succinimide. The monoclonal antibodies (mAbs) specifically detected DM as well as its analogs doxorubicin and epirubicin, but did not react with other anticancer antibiotics, including pepleomycin, mitomycin C, and actinomycin D. The mAbs reacted strongly with glutaraldehyde-conjugated DM in an enzyme linked immunosorbent assay (ELISA) used as a model system for immunocytochemistry as well as in appropriately pretreated sections of tissues from animals injected with DM. No staining occurred in tissues from uninjected animals. In order to perform DM ICC a number of tissue treatment conditions critical to the detection of low molecular weight substances were employed. Uptake of DM was studied in rats after a single i.v. or i.p. administration of the drug. In the heart, accumulation of DM occurred in nuclei and in the cytoplasm. In the kidney, DM immunoreactivity accumulated in all segments of the nephron except for the proximal tubules. Since the proximal tubules are known to be where a variety of transport systems including P-glycoprotein (Pgp) and organic anion-transporting polypeptides (OATPs) in drug interactions occur, the absence of DM accumulation in these segments may reflect a transport phenomenon depending upon such transporters. The availability of methods to study sites of accumulation of DM offers possibilities for understanding toxic side effects of this drug on the heart and kidney. Moreover, the immunocytochemical methodology developed may prove useful for the localization of other low molecular weight drugs that can be fixed in situ by glutaraldehyde.

Spontaneous bursting and rhythmic activity in the cuneate nucleus of anaesthetized rats

Spontaneous and rhythmic neuronal activity in dorsal column nuclei has long been identified in anesthetized cats. Here, we have studied the spontaneous behavior of cuneate cells in anesthetized rats through extracellular recording, showing that most cuneate neurones recorded (155 of 185) fired spontaneously. Overall, 74% of these spontaneously firing neurones were single-spiking and 26% were bursting. Cells were considered "bursting" when more than 50% of the spontaneous spikes belonged to bursts. Nevertheless, occasional bursts were seen in 33% of spontaneous cuneate cells which were classified as single-spiking. Rhythmic firing was observed in about 14% of both spontaneously bursting and single-spiking cells, and these cells were located close to the obex (+/-0.5 mm). Although the spike-frequency was mostly in the range 0-15 spikes/s, spontaneous rhythmic activity was circumscribed mainly to the alpha/beta-like range, both in single-spiking (26.1+/-3.6 Hz, n=16) and bursting cells (19.5+/-4.1 Hz, n=6). Lemniscal stimulation often activated several antidromic units with the same latency. About 65% of cuneolemniscal cells were spontaneously active and of these, 83% were single-spiking and 11% rhythmic (all single-spiking). In cells that were not antidromically activated from the medial lemniscus, short latency orthodromic responses consistent with excitation by recurrent lemniscal collaterals were often observed following lemniscal activation. Interestingly, only cells completely unresponsive to lemniscal stimulation showed rhythmic bursting. Most spontaneous cells responded with a burst to natural receptive field stimulation, while rhythmic cells became temporally arrhythmic. These results demonstrate, for the first time, that rat cuneate neurones can fire bursts spontaneously. Besides, this bursting activity can be rhythmic. These two properties, and the fact that groups of cuneolemniscal cells share the same conduction velocity, probably imply the reinforcement of temporal and spatial summation at their targets when they are synchronously recruited by the stimulation of overlapping receptive fields.

Neuron numbers in the sensory trigeminal nuclei of the rat: A GABA- and glycine-immunocytochemical and stereological analysis

The volume, total neuron number, and number of GABA- and glycine-expressing neurons in the sensory trigeminal nuclei of the adult rat were estimated by stereological methods. The mean volume is 1.38+/-0.13 mm3 (mean+/-SD) for the principal nucleus (Vp), 1.59+/-0.06 for the n. oralis (Vo), 2.63+/-0.34 for the n. interpolaris (Vip), and 3.73+/-0.11 for the n. caudalis (Vc). The total neuron numbers are 31,900+/-2,200 (Vp), 21,100+/-3,300 (Vo), 61,600+/-8,300 (Vip), and 159,100+/-25,300 (Vc). Immunoreactive (-ir) neurons were classified as strongly stained or weakly stained, depending on qualitative criteria, cross-checked by a densitometric analysis. GABA-ir cells are most abundant in Vc, in an increasing rostrocaudal gradient within the nucleus. Lower densities are found in Vip and Vp. The mean total number of strongly labeled GABA-ir neurons ranges between 1,800 in Vp to 7,800 in Vip and 22,900 in Vc, and varies notably between subjects. Glycine-ir neurons are more numerous and display more homogeneous densities in all nuclei. Strongly labeled Gly-ir cells predominate in all nuclei, their total number ranging between 9,400 in Vp to 24,300 in Vip and 34,200 in Vc. A substantial fraction of immunolabeled neurons in all nuclei coexpress GABA and glycine. In general, all neurons strongly immunoreactive for GABA are small, while weakly GABA-ir cells which coexpress Gly are larger. In Vc, one-third of all neurons are immunoreactive: 16.6% of them are single-labeled for GABA and 31.6% are single-labeled for glycine. The remaining 51.8% express GABA and glycine in different combinations, with those showing strong double labeling accounting for 22.6%.

Neurons in the dorsal column nuclei of the rat emit a moderate projection to the ipsilateral ventrobasal thalamus

The dorsal column nuclei (DCN; gracile and cuneate nuclei) give rise to the medial lemniscus, the fibre system that provides an organised somatosensory input to the thalamus. Unlike the spinothalamic and trigeminothalamic tracts that project, also to the ipsilateral thalamus, the medial lemniscus system is believed to be entirely crossed. We demonstrate that DCN emit a small number of axons that reach the ipsilateral thalamus. As retrograde fluorescent neuronal tracer Fluoro-gold was stereotaxically injected in the ventrobasal thalamus of nine young adult Wistar rats. The injection foci were voluminous and encroached upon adjacent nuclei, but the periphery of the injection halo never spilled over to the contralateral thalamus. All sections of the contralateral gracile and cuneate nuclei and the midline nucleus of Bischoff contained abundant retrogradely labelled neurons. The comparison with the Nissl-stained parallel sections suggests that approximately 70-80% of the DCN neurons project to the contralateral thalamus. Counting of retrogradely labelled neurons in two cases revealed 4,809 and 4,222 neurons in the contralateral and 265 and 214 in the ipsilateral DCN, respectively. Thus, although less prominent than the ipsilateral spinothalamic tract, the lemniscal system also emits an ipsilateral projection that accounts for about 5% of the neuronal population in DCN that innervates the ventrobasal thalamus.

Chemoarchitecture of the dorsal column nucleus of the larval sea lamprey

We studied the organization of the dorsal column nucleus (DCN) of larval sea lamprey with immunohistochemical and tract-tracing techniques. Texas red-coupled dextran amine was injected into the spinal cord, which allowed tracing the dorsal column fibers and characterizing the DCN. The dorsal column fibers formed a dense tract coursing adjacent to the dorsal midline of the spinal cord to the caudal rhombencephalon alar plate. In larvae, most spinal cord dorsal cells and spinal ganglion perikarya, and many dorsal column fibers, were calretinin-immunoreactive. We delineated the DCN in the dorsomedial portion of the obex and preobecular alar plate. It consists of a periventricular neuronal cell layer and neurons scattered in the lateral neuropil and receives dorsal column fibers. After immunohistochemistry with antibodies against glutamate, glycine, and GABA numerous immunoreactive perikarya were observed in the DCN. In addition to glutamate-, glycine-, and GABA-immunoreactive processes, serotonin- and dopamine-immunoreactive fibers coursed in the neuropil of this nucleus. A few small calretinin-immunoreactive perikarya were also observed in the DCN. Our results reveal the presence of inhibitory and excitatory transmitters in neurons of the DCN, and suggest that dopamine and serotonin modulate the activity of this nucleus.

GABAergic and glycinergic presympathetic neurons of rat medulla oblongata identified by retrograde transport of pseudorabies virus and in situ hybridization

Electron microscopy suggests that up to half the synaptic input to sympathetic preganglionic neurons (SPGNs) is GABAergic or glycinergic. A proportion of this input is suspected to originate from neurons located within the medulla oblongata. The present study provides definitive evidence for the existence of these supraspinal presympathetic (PS) neurons with inhibitory phenotypes. PS neurons were identified by retrograde trans-synaptic migration of pseudorabies virus (PRV) injected into the adrenal gland. GABAergic or glycinergic cell bodies were identified by the presence of glutamate decarboxylase (GAD)-67 mRNA or glycine transporter (GlyT)-2 mRNA detected with in situ hybridization (ISH). Neither GABAergic nor glycinergic PS neurons were tyrosine hydroxylase (TH)-immunoreactive (ir). GABAergic PS neurons were located within the ventral gigantocellular nucleus, gigantocellular nucleus alpha, and medial reticular formation, mostly medial to the TH-ir PS neurons. About 30% of GABAergic PS neurons were serotonergic cells located in the raphe pallidus (RPa) and parapyramidal region (PPyr). Glycinergic PS neurons had the same general distribution as the GABAergic cells, except that no glycinergic neurons were located in the RPa or PPyr and none were serotonergic. PRV immunohistochemistry combined with ISH for both GlyT2 and GAD-67 mRNAs showed that at least 63% of midline medulla GABAergic PS neurons were also glycinergic and 76% of glycinergic PS neurons were GABAergic. In conclusion, the rostral ventromedial medulla contains large numbers of GABAergic and glycinergic neurons that innervate adrenal gland SPGNs. Over half of these PS neurons may release both transmitters. The physiological role of this medullary inhibitory input remains to be explored.

GABA, in some cases together with glycine, is used as the inhibitory transmitter by pump cells in the Hering-Breuer reflex pathway of the rat

The Hering-Breuer reflex is one of the fundamental respiratory reflexes and is mediated by second-order relay neurons of the slowly adapting lung stretch receptors. These neurons, which are called pump cells, are located in the nucleus tractus solitarii and include a population of inhibitory neurons. We aimed to determine which transmitter, GABA or glycine, the inhibitory pump cells use. In addition, we examined whether or not second-order relay neurons of the rapidly-adapting lung stretch receptors (RAR-cells), whose excitatory or inhibitory nature is not known, use these inhibitory neurotransmitters. In Nembutal-anesthetized, neuromuscularly blocked and artificially ventilated rats, we labeled pump cells (n=33) and RAR-cells (n=26) with Neurobiotin and processed the tissues for detection of mRNA encoding either glutamic acid decarboxylase isoform 67 (GAD67) or glycine transporter 2 (GLYT2) using in situ hybridization. The pump cells were located in the interstitial nucleus and its vicinity and the RAR-cells in the commissural subnucleus. The majority (64%) of the pump cells examined for GAD67 mRNA and many (26%) of the pump cells examined for GLYT2 mRNA expressed respective mRNAs. Of the eight pump cells in which both mRNAs were double-detected, three expressed both mRNAs and one expressed GAD67 mRNA but not GLYT2 mRNA, the other four expressing neither mRNAs. On the other hand, RAR-cells expressed neither GAD67 mRNA nor GLYT2 mRNA. The results suggest that the inhibitory pump cells are basically GABAergic and some of them may corelease GABA and glycine, and that RAR-cells are neither GABAergic nor glycinergic. These findings expand our understanding of the networks of lung receptor-mediated reflexes including the Hering-Breuer reflex.

Intracuneate mechanisms underlying primary afferent cutaneous processing in anaesthetized cats

The cutaneous primary afferents from the upper trunk and forelimbs reach the medial cuneate nucleus in their way towards the cerebral cortex. The aim of this work was twofold: (i) to study the mechanisms used by the primary afferents to relay cutaneous information to cuneate cuneolemniscal (CL) and noncuneolemniscal (nCL) cells, and (ii) to determine the intracuneate mechanisms leading to the elaboration of the output signal by CL cells. Extracellular recordings combined with microiontophoresis demonstrated that the primary afferent cutaneous information is communicated to CL and nCL cells through AMPA, NMDA and kainate receptors. These receptors were sequentially activated: AMPA receptors participated mainly during the initial phase of the response, whereas kainate- and NMDA-mediated activity predominated during a later phase. The involvement of NMDA receptors was confirmed by in vivo intracellular recordings. The cutaneous-evoked activation of CL cells was decreased by GABA and increased by glycine acting at a strychnine-sensitive site, indicating that glycine indirectly affects CL cells. Two subgroups of nCL cells were distinguished based on their sensitivity to iontophoretic ejection of glycine and strychnine. Overall, the results support a model whereby the primary afferent cutaneous input induces a centre-surround antagonism in the cuneate nucleus by activating (via AMPA, NMDA and kainate receptors) and disinhibiting (via serial glycinergic-GABAergic interactions) a population of CL cells with overlapped receptive fields that at the same time inhibit (via GABAergic cells) other neighbouring CL cells with different receptive fields.

Overall distribution of GLYT2 mRNA-containing versus GAD67 mRNA-containing neurons and colocalization of both mRNAs in midbrain, pons, and cerebellum in rats

We aimed to clarify the overall distribution of glycinergic neurons in the midbrain, pons, and cerebellum in rats, using in situ hybridization for mRNA encoding glycine transporter 2 (GLYT2), which reliably detects glycinergic cell bodies. We combined this method with in situ hybridization for mRNA encoding glutamic acid decarboxylase isoform 67 (GAD67), and have presented for the first time global and detailed views of the distribution of glycinergic neurons in relation to GABAergic neurons. In addition to this single-detection study, we performed double-detection of GLYT2 mRNA and GAD67 mRNA to determine the distribution of neurons co-expressing these mRNAs. We have shown that many areas of the brainstem and cerebellum, not only areas where previous immunohistochemical studies have specified, involve double-labeled neurons with GLYT2 and GAD67 mRNAs. In particular, when lightly labeled GLYT2 mRNA-positive neurons were distributed within the area of GAD67 mRNA-positive neurons, almost all such GLYT2 mRNA-positive neurons were GAD67 mRNA-positive. Areas or neuron groups expressing exclusively GLYT2 mRNA or GAD67 mRNA were rather limited, such as the superior colliculus, nucleus of the trapezoid body, and Purkinje cells. The present study suggests that the corelease of glycine and GABA from single neurons is more widespread than has been reported.

Primary somatosensory cortex modulation of tactile responses in nucleus gracilis cells of rats

Corticofugal influences from the primary somatosensory cortex to the gracilis nuclei were studied with single unit recordings performed in urethane-anaesthetized rats. Two types of neurons were identified: low firing rate (LF) neurons, which could be activated antidromically by medial lemniscus stimulation; and high firing rate (HF) neurons. The effects of electrically stimulating the contralateral primary somatosensory cortex were studied in two situations: when the stimulated cortical area and specific gracilis cells had overlapping receptive fields and when the receptive fields of the cells and primary somatosensory cortex did not overlap. Cortical stimulation facilitated cortical and tactile responses in most gracilis neurons (68% and 58% for LF and HF neurons, respectively) with overlapping receptive fields. When receptive fields were different, cortical stimulation inhibited tactile response in most LF neurons (58%) and some HF neurons (20%). Trains of cortical shocks during sensory stimulation demonstrated that the facilitatory and inhibitory effects outlasted the stimulation period by 5 min. The facilitatory effect was decreased by iontophoretic application of the N-methyl-D-aspartate (NMDA) receptor antagonist APV (50 mm). However, APV did not modify the intensity of the tactile response inhibition in cells with nonoverlapping receptive fields, although, its duration was decreased (<5 min). Iontophoretic application of the gamma-aminobutyric acid (GABA)(A) antagonist bicuculline (20 mm) blocked the cortically evoked inhibition in cells with nonoverlapping receptive fields. The results indicate that the somatosensory cortex precisely controls somatosensory transmission throughout the gracilis nucleus by means of NMDA and GABA(A) receptor activation.

Quantitative stereological evaluation of the gracile and cuneate nuclei and their projection neurons in the rat

Stereological methods were employed to estimate the volume and neuron numbers of the rat dorsal column nuclei (DCN). These methods were applied to Nissl-stained sections from control animals and cases that received injections of horseradish peroxidase in the thalamus, the cerebellum, or the spinal cord. Additional cases received combinations of fluorescent tracers in the same structures, to examine whether some of the retrogradely labeled neurons sent collaterals to different targets. The mean volume of the DCN is 0.81 mm(3) (range 0.65-1.10 mm(3)), of which 3%, 39%, and 59% correspond, respectively, to the nucleus of Bischoff (Bi), the gracile (Gr), and the cuneate (Cu) nuclei. Within Cu, the middle division (CuM) is the largest (42%), followed by the rostral (CuR; 36%) and caudal (CuC; 22%) divisions. The mean total number of neurons in the DCN is 16,000 (range 12,400-19,500), of which 2.4%, 34.0% and 63.6% correspond, respectively, to Bi, Gr, and Cu. Within Cu, CuM contains 48% of all neurons, and 27% correspond to CuR and 25% to CuC. Interanimal variability is moderate for the whole DCN and Cu but increases when individual nuclei are considered. About 80% of DCN neurons project to the thalamus, 3% to the spinal cord, and 7% to the cerebellum. Thalamic-projecting cells are more numerous in CuM and Gr (83%), and relatively less common in Bi and CuC (72-74%). Most of the DCN neurons projecting to the spinal cord appear in CuC and CuM. Two-thirds of the neurons projecting to the cerebellum are located in CuR, 20% in CuM, and 15% in Gr. A small fraction of neurons projects simultaneously to spinal cord and thalamus.

New corticocuneate cellular mechanisms underlying the modulation of cutaneous ascending transmission in anesthetized cats

The ascending cutaneous transmission through the middle cuneate nucleus is subject to cortico-feedback modulation. This work studied the intracuneate cellular mechanisms underlying the corticocuneate influence. Single unit extracellular records combined with iontophoresis showed that the corticocuneate input activates cuneo-lemniscal (CL) and noncuneo-lemniscal (nCL) cells via N-methyl-D-aspartate (NMDA) and non-NMDA receptors as shown by the decrease of the cortical-induced activation on ejection of CNQX and APV, either alone or in combination. These results were confirmed by in vivo intracellular recordings. Two subgroups of nCL cells were distinguished according to their sensitivity to iontophoretic ejection of glycine and its antagonist, strychnine. Finally, the corticalevoked activation of CL cells was decreased by GABA and increased by glycine acting at a strychnine-sensitive site, indicating that glycine indirectly affects the cuneo-lemniscal transmission. A model is proposed whereby the cortex influences CL cells through three different mechanisms, producing 1) activation via non-NMDA and NMDA receptors, 2) inhibition through GABAergic nCLs, and 3) disinhibition via serial glycinergic-GABAergic nCL cells. These corticocuneate feedback effects serve to potentiate the activity of CL cells topographically aligned through direct activation and disinhibition, while inhibiting, via GABAergic cells, other CL neurons not topographically aligned.

The chemo- and somatotopic architecture of the Galago cuneate and gracile nuclei

The pattern of peripheral nerve inputs into the dorsal column nuclei, cuneate and gracile, was investigated in the prosimian Galago garnetti. The major findings were, that there is a greater segregation of the inputs from the fingers/hand within the cuneate compared with input form the toes/foot within the gracile. In both nuclei, cell clusters can be identified as cytochrome oxidase dense blotches, reactive also for the activity-dependent enzyme nitric oxide synthase. In the cuneate, cell clusters were apparent as six main cytochrome oxidase/nitric oxide synthase-reactive ovals arranged in a medial to lateral sequence. In contrast in the gracile, a higher degree of parcellation was noted and several cytochrome oxidase/nitric oxide synthase blotches were distributed along the rostrocaudal axis of the nucleus. This different architecture parallels differences in the organization of the inputs from the hand and from the foot. In the cuneate, cholera toxin B subunit conjugated to horseradish peroxydase labeled terminals from the glabrous and hairy skin of digits d1 to d5 segregated in each of the five most lateral cytochrome oxidase/nitric oxide synthase blotches. Afferents from the thenar, palmar pads and hypothenar overlapped with those from digit 1, digit 2 to digit 4 and digit 5, respectively. Inputs from wrist arm and shoulder were segregated in the most medial blotch. In the gracile, multiple foci of cholera toxin B subunit conjugated to horseradish peroxydase labeled terminals were observed upon injections of single sites in the toes or plantar pads. Although in multiple foci, inputs from different toes segregated from one another as well. Terminals from the plantar pads appeared to converge on the same cytochrome oxidase/nitric oxide synthase blotches targeted by inputs from the toes. In both the cuneate and the gracile, cytochrome oxidase/nitric oxide synthase blotches also presented intense immunoreactivity for GABA, calbindin, parvalbumin, and brain derived neurotrophic factor. Finally, in the cuneate the cell cluster region presented similarities in prosimian galagos and four species of New World monkeys, whereas it appeared more differentiated and complex in the Old Word macaque monkeys. In conclusion, the different pattern of segregation of the inputs from the hand and from the foot can be related to the different metabolic organization of the cuneate and of the gracile, respectively.

The lemniscal-cuneate recurrent excitation is suppressed by strychnine and enhanced by GABAA antagonists in the anaesthetized cat

In the somatosensory system, cuneolemniscal (CL) cells fire high frequency doublets of spikes facilitating the transmission of sensory information to diencephalic target cells. We studied how lemniscal feedback affects ascending transmission of cutaneous neurons of the middle cuneate nucleus. Electrical stimulation of the contralateral medial lemniscus and of the skin at sites evoking responses with minimal threshold induced recurrent activation of CL cells at a latency of 1-3.5 ms. The lemniscal feedback activation was suppressed by increasing the stimulating intensity at the same sites, suggesting recurrent-mediated lateral inhibition. The glycine antagonist strychnine blocked the recurrent excitatory responses while GABAA antagonists uncovered those obscured by stronger stimulation. CL cells sharing a common receptive field (RF) potentiate one another by recurrent activation and disinhibition, the disinhibition being produced by serial interactions between glycinergic and GABAergic interneurons. Conversely, CL cells with different RFs inhibit each other through recurrent GABA-mediated inhibition. The lemniscal feedback would thus enhance the surround antagonism of a centre response by increasing the spatial resolution and the transmission of weak signals.

Costorage and coexistence of neuropeptides in the mammalian CNS

The term neuropeptides commonly refers to a relatively large number of biologically active molecules that have been localized to discrete cell populations of central and peripheral neurons. I review here the most important histological and functional findings on neuropeptide distribution in the central nervous system (CNS), in relation to their role in the exchange of information between the nerve cells. Under this perspective, peptide costorage (presence of two or more peptides within the same subcellular compartment) and coexistence (concurrent presence of peptides and other messenger molecules within single nerve cells) are discussed in detail. In particular, the subcellular site(s) of storage and sorting mechanisms within neurons are thoroughly examined in the view of the mode of release and action of neuropeptides as neuronal messengers. Moreover, the relationship of neuropeptides and other molecules implicated in neural transmission is discussed in functional terms, also referring to the interactions with novel unconventional transmitters and trophic factors. Finally, a brief account is given on the presence of neuropeptides in glial cells.

The distribution and characterization of NADPH-d/NOS-IR neurons in the rat cuneate nucleus

Nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemistry and nitric oxide synthase (NOS) immunohistochemistry have been used to characterize the nitric oxide (NO)-containing neurons in the rat cuneate nucleus. The present results showed that NADPH-d-positive/NOS-immunoreactive (-IR) neurons were distributed in the entire rostrocaudal extent of the nucleus. In the caudal region (approximately 1-2 mm caudal to the obex), NADPH-d/NOS-IR neurons were aggregated along the dorsal area of the nucleus notably in the lateral aspect. When traced rostrally, labeled neurons were progressively reduced and the cells were randomly distributed. The labeled neurons varied from round, ovoid to spindle-shaped with a mean profile area of about 140.1+/-1.7 microm(2) (n=720). They made up 7-10% of the neuronal population in the cuneate nucleus. By immunoelectron microscopy, the immunoreaction product was deposited throughout the cytoplasm extending from the soma to the proximal and distal dendrites. Results of NADPH-d staining paralleled that of NOS immunohistochemistry. Furthermore, NADPH-d reactivity and NOS-IR were colocalized in the same neurons following double labeling. Using NADPH-d histochemistry along with anti-gamma-aminobutyric acid (GABA) and -glycine postembedding immunolabeling for identification of GABA- and glycine-IR neurons, respectively, about 33% of the NADPH-d-positive neurons contained both GABA and glycine, 26% of them contained only glycine, while 41% of them showed neither GABA nor glycine labeling. Cuneothalamic neurons (CTNs) were identified by injecting the retrograde tracer Fluorogold (FG) into the ventrobasal complex of the thalamus. Numerous FG-labeled neurons were present in the contralateral cuneate nucleus, but none were reactive for NADPH-d. The present results suggest that approximately 60% of the NADPH-d/NOS-IR neurons in the cuneate nucleus are interneurons containing GABA and/or glycine.

Afferent synaptic contacts on glycine-immunoreactive neurons in the rat cuneate nucleus

This study was aimed to clarify whether the primary afferent terminals (PATs), GABAergic terminals, and glutamatergic terminals made direct synaptic contacts with glycine-IR neurons in the cuneate nucleus of rats. In this connection, injection of the anterograde tracer WGA-HRP into brachial plexus, antiglycine preembedding immunoperoxidase, and anti-GABA, along with antiglutamate postembedding immunogold labeling, were used to identify the PATs, glycine-IR neurons, GABA-IR terminals, and glutamate-IR terminals, respectively. The present results showed that HRP-labeled PATs, immunoperoxidase-labeled glycine-IR terminals, immunogold-labeled GABA-IR, and glutamate-IR terminals made axodendritic synaptic contacts with immunoperoxidase-labeled glycine-IR neurons. The latter three presynaptic elements also formed axosomatic synapses with glycine-IR neurons. Statistical analysis has shown that the minimum diameter of the glycine-IR dendrites postsynaptic to the above-mentioned four presynaptic elements did not differ significantly. In addition, the synaptic ratio of the glutamate-IR terminals on the glycine-IR dendrites was higher than that of GABA-IR terminals. The synaptic ratio of the GABA-IR terminals on glycine-IR dendrite was in turn higher than that of the PATs and glycine-IR terminals. It is suggested that the PATs and glutamate-IR terminals on the glycine-IR neurons may be involved in subsequent postsynaptic inhibition for spatial precision of lateral inhibition. On the other hand, the GABA-IR and glycine-IR terminals which make synaptic contacts with the dendrites of glycine-IR neurons may provide a putative means for disinhibition or facilitation to maintain the baseline neuronal activity in the rat cuneate nucleus. The results of quantitative analysis suggest that glutamate act as the primary excitatory neurotransmitter, while GABA, when compared with glycine, may serve as a more powerful inhibitory neurotransmitter on glycine-IR neurons in the rat cuneate nucleus.

Rhythmic neuronal interactions and synchronization in the rat dorsal column nuclei

Single-unit and multiunit activities were recorded from dorsal column nuclei of anesthetized rats in order to study the characteristics of the oscillatory activity expressed by these cells and their neuronal interactions. On the basis of their firing rate characteristics in spontaneous conditions, two types of dorsal column nuclei cell have been identified. Low-frequency cells (74%) were silent or displayed a low firing rate (1.9+/-0.48 spikes/s), and were identified as thalamic-projecting neurons because they were activated antidromically by medial lemniscus stimulation. High-frequency cells (26%) were characterized by higher discharge rates (27.2+/-5.1 spikes/s). None of them was antidromically activated by medial lemniscus stimulation. Low-frequency neurons showed a non-rhythmic discharge pattern spontaneously which became rhythmic under sensory stimulation of their receptive fields (48% of cases; 4.8+/-0.23Hz). All high-frequency neurons showed a rhythmic discharge pattern at 13.8+/- 0.68Hz either spontaneously or during sensory stimulation of their receptive fields. The shift predictor analysis indicated that oscillatory activity is not phase-locked to the stimulus onset in either type of cell, although the stimulus can reset the phase of the rhythmic activity of high-frequency cells. Cross-correlograms between pairs of low-frequency neurons typically revealed synchronized rhythmic activity when the overlapping receptive fields were stimulated. Rhythmic synchronization of high-frequency discharges was rarely observed spontaneously or under sensory stimulation. High-frequency neuronal firing could be correlated with the low-frequency neuronal activity or more often with the multiunit activity during sensory stimulation. Moreover, the presence of oscillatory activity modulated the sensory responses of dorsal column nuclei cells, favoring their responses. These findings indicate that thalamic-projecting and non-projecting neurons in dorsal column nuclei exhibited distinct oscillatory characteristics. However, both types of neuron may be entrained into an oscillatory rhythmic pattern when their overlapping receptive fields are stimulated, suggesting that in those conditions the dorsal column nuclei generate a populational oscillatory output to the somatosensory thalamus which could modulate and amplify the effectiveness of the somatosensory transmission.

GABA, 5-HT and amino acids in the rotifers Brachionus plicatilis and Brachionus rotundiformis

gamma-Aminobutyric acid (GABA) and 5-hydroxytryptamine (5-HT) have been shown to increase the reproduction of the Brachionus plicatilis (NH3L strain). In the present study, the endogenous presence of GABA and 5-HT in the rotifers B. plicatilis (NH3L and Kamiura strains) and Brachionus rotundiformis (Langkawi strain) were confirmed by dot blot immunoassay and high-performance liquid chromatography (HPLC). HPLC showed that GABA and 5-HT concentrations in the three rotifer strains range from 71 to 188 pmol/mg and from 12 to 64 pmol/mg, respectively. A total of 33 amino acids were also detected in B. plicatilis and B. rotundiformis, with glutamic acid, serine, glycine, taurine, threonine, alanine, arginine, proline, valine and isoleucine in high concentrations relative to other amino acids.

Somatostatin-IR neurons are a major subpopulation of the cuneothalamic neurons in the rat cuneate nucleus

This study was aimed to localize and characterize the somatostatin-immunoreactive (SOM-IR) neurons in the rat cuneate nucleus (CN). By immuno-histochemistry, the SOM-IR neurons, which were widely distributed in the nucleus, were round, spindle or multiangular in shape (mean area = 226.1 +/ -3.1 microm(2), n = 1016). By electron microscopy, the neurons shared all the ultrastructural features of the cuneothalamic neurons (CTNs) which showed a slightly indented nucleus and a fairly rich cytoplasm containing well-developed Golgi apparatuses and rough endoplasmic reticulum (rER). The SOM immunoreaction product filled the cytoplasm of the neurons extending from the soma to the proximal and distal dendrites, which were postsynaptic to unlabeled boutons. In addition to soma and dendrites, SOM-IR boutons were also identified which made axodendritic synaptic contacts with SOM-IR dendrites. The SOM-IR neurons were characterized by using anti-SOM pre-embedding immunolabeling coupled with horseradish peroxidase (HRP) retrograde method, or SOM immunolabeling along with anti-glutamate, gamma-aminobutyric acid (GABA) or glycine post-embedding immunolabeling for identification of CTNs, glutamate-IR, GABA-IR and glycine-IR neurons, respectively. It was shown that more then 80% of the CTNs contained SOM and, furthermore, they contained glutamate but not GABA or glycine. On the basis of present findings, it is suggested the majority of the SOM-IR neurons in the rat CN are CTNs and that they may be involved in modulation of somatosensory synaptic transmission.

Cuneothalamic relay neurons are postsynaptic to glycine-immunoreactive terminals in the rat cuneate nucleus

This study was aimed to clarify whether the cuneothalamic relay neurons (CTNs) in the rat cuneate nucleus contained glycine or whether the neurons were modulated directly by presynaptic glycine-IR terminals. For this purpose, retrograde transport of wheat germ agglutinin conjugated with horseradish peroxidase (WGA-HRP) and immunoperoxidase labelling for glycine have been used to ascertain if the CTNs in the rat are glycine-immunoreactive (glycine-IR). Our results have shown that the WGA-HRP-labelled CTNs (mean area = 318 +/- 6.5 microm(2)) were not reactive for glycine. Glycine immunoreactivity, however, was localized in some small-sized neurons (mean area = 210 +/- 6.2 microm(2)) and axon terminals associated with the CTNs. The synaptic organization between the glycine-IR terminals and CTNs was further analyzed using anti-glycine postembedding immunogold labelling. By electron microscopy, the immunogold-labelled glycine-IR terminals containing pleomorphic synaptic vesicles formed symmetrical synaptic contacts with the dendrites, dendritic spines, and somata of CTNs. Quantitative estimation showed that the mean ratios of glycine-IR terminals to total terminals associated with the soma, proximal dendrites and distal dendrites of the CTN were 49.5, 45.2, and 45.8%, respectively. The higher incidence of glycine-IR terminals on the soma, however, was not significantly different from that of the proximal and distal dendrites. Notwithstanding the above, this study has shown a large number of glycine-IR terminals making direct synaptic contacts with CTNs, suggesting that glycine is one of the important neurotransmitters involved in postsynaptic inhibition on the cuneothalamic relay neurons to modulate incoming somatosensory information from forelimb areas in the rat.

Lemniscal recurrent and transcortical influences on cuneate neurons

Intracellular recordings were obtained from cuneate neurons of chloralose-anesthetized, paralysed cats to study the synaptic responses induced by electrical stimulation of the contralateral medial lemniscus. From a total of 178 cells sampled, 109 were antidromically fired from the medial lemniscus, 82 of which showed spontaneous bursting activity. In contrast, the great majority (58/69) of the non-lemniscal neurons presented spontaneous single spike activity. Medial lemniscus stimulation induced recurrent excitation and inhibition on cuneolemniscal and non-lemniscal cells. Some non-lemniscal neurons were activated by somatosensory cortex and inhibited by motor cortex stimulation. Some other non-lemniscal cells that did not respond to medial lemniscus stimulation in control conditions were transcortically affected by stimulating the medial lemniscus after inducing paroxysmal activity in the sensorimotor cortex. These findings indicate that different sites in the sensorimotor cortex can differentially influence the sensory transmission through the cuneate, and that the distinct available corticocuneate routes are selected within the cerebral cortex. From a total of 92 cells tested, the initial effect induced by low-frequency stimulation of the sensorimotor cortex was inhibition on most of the cuneolemniscal neurons (32/52) and excitation on the majority of the non-lemniscal cells (25/40). The fact that a substantial proportion of cuneolemniscal and non-lemniscal cells was excited and inhibited, respectively, suggests that the cerebral cortex may potentiate certain inputs by exciting and disinhibiting selected groups of cuneolemniscal cells. Finally, evidence is presented demonstrating that the tendency of the cuneolemniscal neurons to fire in high-frequency spike bursts is due to different mechanisms, including excitatory synaptic potentials, recurrent activation through lemniscal axonal collaterals, and via the lemnisco-thalamo-cortico-cuneate loop.A corticocuneate network circuit to explain the results is proposed.

Sensorimotor cortical influences on cuneate nucleus rhythmic activity in the anesthetized cat

This work aimed to study whether the sensorimotor cerebral cortex spreads down its rhythmic patterns of activity to the dorsal column nuclei. Extracellular and intracellular recordings were obtained from the cuneate nucleus of chloralose-anesthetized cats. From a total of 140 neurons tested (106 cuneolemniscal), 72 showed spontaneous rhythmic activity within the slow (< 1 Hz), delta (1-4 Hz), spindle (5-15 Hz) and higher frequencies, with seven cells having the delta rhythm coupled to slow oscillations. The spindle activity recorded in the cuneate was tightly coupled to the thalamo-cortico-thalamic spindle rhythmicity. Bilateral or contralateral removal of the frontoparietal cortex abolished the cuneate slow and spindle oscillations. Oscillatory paroxysmal activity generated by fast electrical stimulation (50-100 Hz/1-2 s) of the sensorimotor cortex induced burst firing synchronized with the paroxysmal cortical "spike" on all the non-lemniscal neurons, and inhibitory responses also coincident with the cortical paroxysmal "spike" in the majority (71%) of the cuneolemniscal cells. The remaining lemniscal-projecting neurons showed bursting activity (11%) or sequences of excitation-inhibition (18%) also time-locked to the cortical paroxysmal "spike". Additionally, the cerebral cortex induced coherent oscillatory activity between thalamic ventroposterolateral and cuneate neurons. Electrolytic lesion of the pyramidal tract abolished the cortically induced effects on the contralateral cuneate nucleus, as well as on the ipsilateral medial lemniscus. The results demonstrate that the sensorimotor cortex imposes its rhythmic patterns on the cuneate nucleus through the pyramidal tract, and that the corticocuneate network can generate normal and abnormal patterns of synchronized activity, such as delta waves, spindles and spike-and-wave complexes. The cuneate neurons, however, are able to generate oscillatory activity above 1 Hz in the absence of cortical input, which implies that the cerebral cortex probably imposes its rhythmicity on the cuneate by matching the intrinsic preferred oscillatory frequency of cuneate neurons.

In vitro electrophysiological properties of rat dorsal column nuclei neurons

The dorsal column nuclei include the gracile and cuneate nuclei, which receive somatosensory information from the periphery and project to the ventroposterior nucleus of the contralateral thalamus. The aim of this study was to determine the electrophysiological and morphological characteristics of the neurons of the dorsal column nuclei and to identify synaptic events evoked by electrical stimulation of the dorsal column, using an in vitro slice preparation. The results show two types of neurons, termed type I and II. A repolarizing sag distinguished type I cells during hyperpolarizing current injection, suggesting the activation of a Q-current. Moreover, type I cells, but not type II cells, were capable of maintaining spontaneous rhythmic activity at 9-15 Hz. Both types of cells displayed a delay in their return to the resting membrane potential following hyperpolarizing current pulses, indicating the existence of an A-current. Electrical stimuli applied to the dorsal column elicited brief EPSPs and IPSPs in both cell types. EPSPs were abolished by 6-cyano-7-nitroquinoxaline-2,3-dione, indicating that they were mediated through non-NMDA receptors. IPSPs were blocked by picrotoxin, implying the activation of GABAA receptors. Intracellular staining with carboxyfluoresceine revealed that type I neurons had elongated somas and primary dendrites that extended radially. Type II cells were smaller and had round somas with few primary dendrites, most of them emerging from one pole of the soma. The axon of many type I neurons was stained and could be followed running ventrally and in rostral direction.

Corticofugal action on somatosensory response properties of rat nucleus gracilis cells

Single unit recordings were performed in the nucleus gracilis (Gr) of anesthetized rats to study the influences of the sensorimotor corticofugal projections on sensory responses of those cells. The effects of electrical stimulation of contralateral primary sensory cortex were studied in two conditions: when the receptive fields of the stimulated cortical area and the gracilis cells overlapped (matched) or when they were completely different (unmatched). Cortical stimulation at low intensities (<50 microA) evoked spike firing only in gracilis neurons with matched receptive fields. When the receptive fields were unmatched, the intensity of the stimulation had to be increased above 50 microA to elicit spike firing. To study the corticofugal actions on the responses of Gr neurons, the onset of peripheral stimulation was likened to a single cortical shock in the sensorimotor cortex. When receptive fields matched, cortical stimulation facilitated the cellular responses to the natural sensory stimulation of their RF in most of the Gr neurons (86%). In the unmatched receptive fields, cortical stimulation could either inhibit (66.7%), facilitate (20.8%) or did not modify (12.5%) the sensory response at all. Trains of cortical shocks during sensory stimulation demonstrated that the facilitatory and inhibitory effects on Gr neurons outlasted the period of stimulation by 30-60 s. Results indicate that the sensorimotor cortex exercises a very precise control of sensory transmission throughout the Gr nucleus and suggest that the corticofugal projection may play an important role in the plasticity of the sensorimotor system.

Electron microscopic analysis of gamma-aminobutyric acid and glycine colocalization in rat trigeminal subnucleus caudalis

Postembedding immunogold methods were used to examine the distribution of gamma-aminobutyric acid (GABA) and glycine and especially their colocalization in glomerular neuronal profiles adjacent to trigeminal primary afferent profiles in lamina II of rat subnucleus caudalis. We found that 60% of the profiles adjacent to the trigeminal primary afferent terminals exhibited colocalization of GABA and glycine. GABA alone was found to localize in 17% of the adjacent profiles. Glycine alone was found to localize in 18% of the adjacent profiles. Of interest, 10% of the trigeminal primary afferent fibers showed glycine localization. All the profiles with colocalization of GABA and glycine were identified as presynaptic axonal terminals, suggesting a possible cumulative effect by these two inhibitory neurotransmitters in presynaptic inhibition. These findings show that GABA and glycine colocalize in a subpopulation of presynaptic axonal terminals within lamina II of the subnucleus caudalis. The possible origins of these axons are discussed, as well as their potential involvement in presynaptic inhibition of orofacial nociception.

Evidence for a possible glycinergic inhibitory neurotransmission in the midbrain and rostral pons of the rat studied by gephyrin

The data on the glycinergic transmission in the rostral brainstem are both few and controversial. The present report provides evidence for a possible glycinergic transmission in Sprague-Dawley rats, based on observations of immunocytochemical labeling for gephyrin, a 93 kDa protein and a component of the functional glycine receptor. A monoclonal antibody against gephyrin was used, and the reaction product was visualized by means of avidin-biotin-peroxidase procedure. The reaction product in midbrain and rostral pons was found in neuronal perikarya and in proximal dendrites but in some cases the most distal dendritic branches were also labeled. The neuropil usually displayed a moderate staining with finely granulated reaction product. The most significant immunocytochemical signal was mainly encountered in large and medium-sized neuronal populations of the motor cranial nerve nuclei (III, IV, V), in the reticular formation (laterodorsal tegmental nucleus, pedunculopontine tegmental nucleus, deep mesencephalic nucleus), in the red nucleus, in the intermediate and deep gray strata of the superior colliculus. Only in the substantia nigra and the inferior colliculus the parvocellular cell populations were mainly labeled. The present data suggest a significant inhibitory glycinergic neurotransmission in the rostral brainstem, probably mediated by interneurons.

Immunocytochemical localization of the AMPA receptor subunits in the mesencephalic trigeminal nucleus of the rat

The mesencephalic trigeminal nucleus is composed of large (35-50 microns) pseudo-unipolar neurons. Closely associated with them are small (< 20 microns) multipolar neurons. An unique peculiarity of the pseudo-unipolar perikarya is that they receive synaptic input from various sources, which sets them apart from the dorsal root and cranial nerves sensory ganglia neurons. Whereas glutamate is the best neurotransmitter candidate in pseudo-unipolar neurons, glutamatergic input into them has not yet been reported. AMPA glutamate receptors are implicated in fast excitatory glutamatergic synaptic transmission. They have been localized ultrastructurally at postsynaptic sites. This study demonstrates that the pseudo-unipolar neurons of the mesencephalic trigeminal nucleus express AMPA glutamate receptor subunits, which indicates that these neurons receive glutamatergic input. Serial sections from the rostral pons and midbrain of Sprague-Dawley rats were immunostained with antibodies against C-terminus of AMPA receptor subunits: GluR1, GluR2/3, and GluR4. The immunoreaction was visualized with avidin-biotin-peroxidase/DAB for light and electron microscopy. With GluR1 antibody only the smallest multipolar neurons were recognized as immunopositive within the mesencephalic trigeminal nucleus. GluR2/3 stained the pseudo-unipolar neurons intensely within the entire rostro-caudal extent of the nucleus. In addition the former antibody stained small multipolar neurons within the mesencephalic trigeminal nucleus, though with somewhat larger dimensions than those immunoreactive for GluR1. Whereas the overall staining with GluR4 antibody was scant, those pseudo-unipolar neurons that were stained, were strongly stained. Furthermore, a considerable number of microglial cells within and surrounding the mesencephalic trigeminal nucleus displayed very intense immunoreactivity for GluR4. These results are discussed in the light of the glutamate receptor subunit composition.

Simultaneous determination of total and extracellular concentrations of the amino acid neurotransmitters in cat visual cortex by microbore liquid chromatography and electrochemical detection

To investigate the influence of a partial sensory deprivation on the total and extracellular concentration of the amino acid neurotransmitters in cat visual cortex, two microbore HPLC methods were developed for the simultaneous determination of aspartate, glutamate, glycine, taurine and gamma-aminobutyric acid in cat brain extracts or microdialysis samples. For the determination of the total neurotransmitter concentrations in the visual cortex, the brains were quickly frozen and 200-microns cryostat sections were made. From these sections tissue samples of 2 x 2 mm2 containing the six cortical layers were dissected out of the central and peripheral parts of area 17. After homogenisation and centrifugation, the supernatants were used for quantitative amino acid analysis using an o-phthalaldehyde-tert.-butylthiol pre-column derivatisation HPLC gradient elution method on a microbore column (100 x 1 mm I.D.; C8) and single electrochemical detection. Microdialysis samples from area 17 were obtained every 15 min using 2-mm probes perfused with synthetic cerebrospinal fluid at a flow-rate of 1 microliter/min. After o-phthalaldehyde-tert.-butylthiol derivatisation they were analysed on a microbore column by isocratic elution and dual electrochemical detection. The instrumentation and the different separation parameters were optimised and standard curve, recovery, analytical precision and detection limits for each neurotransmitter were determined.

Synaptic relationships between corticocuneate terminals and glycine-immunoreactive neurons in the rat cuneate nucleus

The present study describes the ultrastructural synaptic relationships between corticocuneate terminals (CCTs) and glycine-immunoreactive (glycine-IR) neurons in the cuneate nucleus of rats using anterograde tract-tracing of wheatgerm agglutinin conjugated with horseradish peroxidase (WGA-HRP) and anti-glycine immunoperoxidase labeling methods. The HRP-labeled CCTs made axodendritic synapses preferentially in the ventral part of the cuneate nucleus near the obex. In a total of 182 CCTs surveyed, 14 of them made direct synaptic contacts with immunoperoxidase-labeled glycine-IR dendrites. The present results suggest that cortical modulation on the sensory transmission of cuneate nucleus may be mediated through glycine-IR neurons.

Morphometric study of glycine-immunoreactive neurons and terminals in the rat cuneate nucleus

The distribution of glycine-immunoreactive (glycine-IR) neurons and their associated axon terminals in the rat cuneate nucleus was studied using antiglycine postembedding immunoperoxidase labelling and immunogold staining, respectively. The immunoperoxidase-labelled glycine-IR neurons were widely distributed in the entire rostrocaudal extent of the nucleus. They made up 30.8% (9671/31368) of the neurons surveyed. Quantitative evaluation showed that the percentage of glycine-IR neurons in the caudal level was significantly higher than that in the middle and rostral levels. The glycine-IR neurons were small cells (mean area = 198+/-1.9 microm2, n = 2862) with ovoid or spindle-shaped somata. Statistical analysis showed that the size of the glycine-IR neurons in the rostral level was significantly smaller than that in the middle and caudal levels. Immunogold labelled glycine-IR terminals which contained predominantly pleomorphic synaptic vesicles were mostly small (mean area = 1.24+/-0.03 microm2, n = 286) and they constituted 24.7% (286/1158) of the total terminals surveyed. They formed axodendritic, axosomatic and axoaxonic synapses with unlabelled elements. It is suggested from this study that glycine is one of the major neurotransmitters involved in the depression of synaptic transmission in the cuneate nucleus.

Heterogeneity of AMPA receptors in the dorsal column nuclei of the rat

We have combined immunocytochemistry with retrograde tracing to demonstrate that projecting neurons in the gracile and cuneate nuclei express predominantly the GluR3 subunit of the AMPA receptor while interneurons in these nuclei express predominantly the GluR1 subunit. Interneurons expressing the GluR2 subunit are also present. It is speculated that the two classes of interneurons may release different inhibitory transmitters.

Electrophysiological effects of temporary deafferentation on two characterized cell types in the nucleus gracilis of the rat

Single- and multiunit recordings were made in the nucleus gracilis of anaesthetized rats in order to study the characteristics of the responses to natural cutaneous stimulation before and during local anaesthetic-induced deafferentation. Two types of cells were found which exhibited different electrophysiological features at rest and in response to stimulation of their receptive fields (RFs). Low-frequency (LF) neurons (77%) had very low spontaneous activity, and most could be antidromically activated from the medial lemniscus. High-frequency (HF) cells (23%) had a much higher spontaneous discharge rate, with shorter spike duration, and did not project through the lemniscus. Both cell types generated phasic responses with similar latencies following cutaneous stimulation. Recordings of lemniscal axons had similar characteristics to those of LF neurons. Within minutes after anaesthetizing the functional centre of the RF, the LF and HF cells displayed new RFs, and enhanced responses to stimuli delivered at the periphery of the original fields. Firing rates increased during anaesthesia, but only in LF cells. Using a paired-stimulation paradigm, many LF neurons displayed during anaesthesia a decrease of the normal inhibition that the conditioning stimulus evoked on the responses to the test stimulus; the opposite effect was observed in all HF cells. These results suggest that (i) LF neurons correspond to thalamic projection cells, and HF neurons may be inhibitory interneurons; (ii) by disinhibiting LF (but not HF) cells, temporary deafferentation may increase neuronal responsiveness to peripheral stimulation, and thus contribute to reveal new RFs, and (iii) these changes in the nucleus gracilis may partly account for the reorganization of representational maps at higher levels of the somatosensory pathways.

Distribution of GABAergic and glycinergic premotor neurons projecting to the facial and hypoglossal nuclei in the rat

The distribution of inhibitory premotor neurons for the facial and hypoglossal nuclei was examined in the lower brainstem of the rat. A retrograde axonal tracing method with the fluorescent tracer, tetramethylrhodamine dextran amine (TMR-DA), was combined with immunofluorescence histochemistry for glutamic acid decarboxylase (GAD), i.e., the enzyme involved in gamma-aminobutyric acid synthesis, or glycine. In the rats injected with TMR-DA unilaterally into the facial or hypoglossal nucleus, the distribution of TMR-DA-labeled neurons showing GAD-like immunoreactivity (GAD/TMR-DA neurons) was essentially the same as that of TMR-DA-labeled neurons displaying glycine-like immunoreactivity (Gly/TMR-DA neurons). The distributions of GAD/TMR-DA and Gly/TMR-DA neurons in the rats injected with TMR-DA into the facial nucleus were also similar to those in the rats injected with TMR-DA into the hypoglossal nucleus. These neurons were seen most frequently in the lateral aspect of the pontine reticular formation, the supratrigeminal region, the dorsal aspect of the lateral reticular formation of the medulla oblongata, and the reticular regions around the raphe magnus nucleus and the gigantocellular reticular nucleus pars alpha, bilaterally with a slight dominance on the side ipsilateral to the injection site. A number of GAD/TMR-DA and Gly/TMR-DA neurons were also seen in the oral and interpolar subnuclei of the spinal trigeminal nucleus, bilaterally with a slight ipsilateral dominance. In the rats injected with TMR-DA into the facial nucleus, GAD/TMR-DA and Gly/TMR-DA neurons were also encountered in the paralemniscal zone of the midbrain tegmentum bilaterally with an apparent dominance on the side contralateral to the injection site. A large part of these inhibitory premotor neurons for the facial and hypoglossal nuclei and the excitatory ones may constitute premotor neuron pools common to the orofacial motor nuclei implicated in the control of integrated orofacial movements.