Glutamic acid as a synpatic transmitter candidate in the dorsal sensory neuron: reconsiderations

Glutamate pharmacology and metabolism in peripheral primary afferents: physiological and pathophysiological mechanisms

In addition to using glutamate as a neurotransmitter at central synapses, many primary sensory neurons release glutamate from peripheral terminals. Primary sensory neurons with cell bodies in dorsal root or trigeminal ganglia produce glutaminase, the synthetic enzyme for glutamate, and transport the enzyme in mitochondria to peripheral terminals. Vesicular glutamate transporters fill neurotransmitter vesicles with glutamate and they are shipped to peripheral terminals. Intense noxious stimuli or tissue damage causes glutamate to be released from peripheral afferent nerve terminals and augmented release occurs during acute and chronic inflammation. The site of action for glutamate can be at the autologous or nearby nerve terminals. Peripheral nerve terminals contain both ionotropic and metabotropic excitatory amino acid receptors (EAARs) and activation of these receptors can lower the activation threshold and increase the excitability of primary afferents. Antagonism of EAARs can reduce excitability of activated afferents and produce antinociception in many animal models of acute and chronic pain. Glutamate injected into human skin and muscle causes acute pain. Trauma in humans, such as arthritis, myalgia, and tendonitis, elevates glutamate levels in affected tissues. There is evidence that EAAR antagonism at peripheral sites can provide relief in some chronic pain sufferers.

Glutamate and metabotropic glutamate receptors associated with innervation of the uterine cervix during pregnancy: Receptor antagonism inhibits c-fos expression in rat lumbosacral spinal cord at parturition

Dorsal root ganglia (DRG) neurons connect the spinal cord and uterine cervix, and are activated at parturition with subsequent stimulation of secondary neurons in the spinal dorsal horn and autonomic areas. Neuropeptide neurotransmitters and receptors have been studied in these areas, but amino acid transmitters, e.g., glutamate, an excitatory neurotransmitter involved in sensory and nociceptive processing, have not been characterized. To determine if glutamate is involved in innervation of the cervix, rats were examined for markers of glutamatergic neurons in the L6-S1 spinal cord, DRG and cervix. Metabotropic glutamate receptors mGluR5 in the spinal dorsal horn and their expression over pregnancy were examined in pregnant rats and pregnant rats treated continuously with an antagonist of mGluR5, 2-methyl-6-(phenylethynyl) pyridine (MPEP). Rats were allowed to deliver pups to determine if the antagonist altered the expression of an early response gene protein, Fos, in the L6-S1 cord. Immunohistochemistry showed glutamate- and vesicular glutamate transporter1 (VGluT1)-positive fibers in the cervix, glutamate- and VGluT1-expressing neurons in the DRG, some of which also exhibited retrograde tracer from cervical injections, and VGluT1 and mGluR5 immunoreactivities in the L6-S1 spinal dorsal horns. Expression of mGluR5 receptors increased over pregnancy. Fos-positive neurons were present among mGluR5-immunoreactivity in the spinal dorsal horn. Parturition-induced Fos-positive neurons in the spinal cords were abundant in control rats, but were reduced by 70% in MPEP-treated animals. These results suggest that glutamate is likely involved in the transmission of sensory signals, possibly pain, from the cervix to the spinal cord at parturition.

Neurotrophins in spinal cord nociceptive pathways

Neurotrophins are a well-known family of growth factors for the central and peripheral nervous systems. In the course of the last years, several lines of evidence converged to indicate that some members of the family, particularly NGF and BDNF, also participate in structural and functional plasticity of nociceptive pathways within the dorsal root ganglia and spinal cord. A subpopulation of small-sized dorsal root ganglion neurons is sensitive to NGF and responds to peripheral NGF stimulation with upregulation of BDNF synthesis and increased anterograde transport to the dorsal horn. In the latter, release of BDNF appears to modulate or even mediate nociceptive sensory inputs and pain hypersensitivity. We summarize here the status of the art on the role of neurotrophins in nociceptive pathways, with special emphasis on short-term synaptic and intracellular events that are mediated by this novel class of neuromessengers in the dorsal horn. Under this perspective we review the findings obtained through an array of techniques in naïve and transgenic animals that provide insight into the modulatory mechanisms of BDNF at central synapses. We also report on the results obtained after immunocytochemistry, in situ hybridization, and monitoring intracellular calcium levels by confocal microscopy, that led to hypothesize that also NGF might have a direct central effect in pain modulation. Although it is unclear whether or not NGF may be released at dorsal horn endings of certain nociceptors in vivo, we believe that these findings offer a clue for further studies aiming to elucidate the putative central effects of NGF and other neurotrophins in nociceptive pathways.

The effect of glutamate antagonists on c-fos expression induced in spinal neurons by irritation of the lower urinary tract

Chemical irritation of the lower urinary tract (LUT) of the rat increases the expression of c-fos in neurons in the dorsal horn, dorsal commissure and intermediolateral region of the spinal cord. The role of glutamatergic synapses in this response was examined using two glutamate receptor antagonists, MK-801 (an NMDA antagonist) and CNQX (an AMPA antagonist). In rats with an intact spinal cord, MK-801 (3.5 mg/kg, i.v.) administered 15 min before bladder irritation decreased (50-60%) the number of c-fos-positive cells in all regions of the cord. A smaller dose of MK-801 (0.8 mg/kg, i.v.) was ineffective. In spinal transected rats (4-7 days prior to the experiment) MK-801 (3.5 mg/kg, i.v.) decreased c-fos expression only in the medial dorsal horn. CNQX (1.2 mg/kg, i.v.) was ineffective in both preparations. These results indicate that activation of NMDA receptors at glutamate synapses in the central nervous system may play a role in the processing of nociceptive input from the LUT and may also be involved in reflex pathways mediating micturition.

Antinociceptive actions of different classes of excitatory amino acid receptor antagonists in mice

Intrathecal (i.t.) injection of the competitive and selective N-methyl-D-aspartate (NMDA) receptor antagonists DL-2-amino-5-phosphonopentanoic acid (AP5), D-2-amino-7-phosphonoheptanoic acid (AP7), beta-D-aspartylaminomethyl phosphonic acid (Asp-AMP), 3-((+/-)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP) and gamma-D-glutamylaminomethyl phosphonic acid (Glu-AMP) produced dose-dependent and reversible analgesic effects in the mouse hot-plate and formalin tests of nociception. They were slightly more potent in the formalin test but had no or negligible effects in the tail-flick test. The non-selective or non-NMDA receptor antagonists 6-cyano-7-nitro-quinoxalinedione (CNQX), 6,7-dinitro-quinoxalinedione (DNQX), gamma-D-glutamylglycine (gamma DGG), gamma-glutamylaminomethyl sulphonic acid (GAMS), kynurenic acid, cis-2,3-piperidine dicarboxylic acid (cis-PDA; partial agonist) and p-bromobenzoyl piperazine dicarboxylic acid (pBB-PzDA) had the same efficacy in the mouse hot-plate, tail-flick and formalin tests (gamma DGG and pBB-PzDA were not tested in the formalin test). This heterogeneous group of antagonists was somewhat more potent in the tail-flick test and slightly less potent in the formalin test than in the hot-plate test. Of the two glycine site antagonists tested, 7-chlorokynurenic acid (7-Cl-Kyn) and (+/-)-3-amino-1-hydroxy-2-pyrrolidone (HA-966), the effect of the latter was compatible with selective action at the NMDA receptor complex while the action of the former was comparable to those of non-selective excitatory amino acid (EAA) receptor antagonists.(ABSTRACT TRUNCATED AT 250 WORDS)

Glutamate-immunoreactivity in the trigeminal and dorsal root ganglia, and intraspinal neurons and fibres in the dorsal horn of the rat

Putative aspartergic and glutamatergic sensory neurons in the rat were identified by autoradiography and immunocytochemistry respectively. Approximately 3% of large L4 dorsal root ganglion neurons (diameter 18-52 microns) accumulated radiolabelled aspartate, whereas all satellite glia had high affinity for the amino acid. Glutamate-immunofluorescent (Glu-FITC) dorsal root ganglia neurons comprised 38.3% at S1, 35.6% at L2, 33.9% at C5 and 28.8% at T6. Numbers of immunoreactive neurons were higher with the more sensitive peroxidase-anti-peroxidase (Glu-PAP) method; and the cell counts totalled 42% (S1), 41.2% (L4), 35% (C5) and 34.6% (T6). The trigeminal ganglion (TG) contained 24% Glu-FITC and 32.3% Glu-PAP positive cells. The majority of glutamate-immunoreactive sensory neurons were small, ranging from 10-35 microns with median diameters of 17.5 microns (C5), 21 microns (S1), 24.2 microns (TG) and 28.5 microns (L2). It is evident therefore, that a subgroup of class B cells are glutamatergic. Glutamate immunoreactivity in the spinal cord was similar in all segments and was localized in the superficial lamina and substantia gelatinosa of the dorsal horn. Stained interneurons were located among the immunoreactive fibres. The dorsolateral funiculus contained dense plexus of immunoreactive fibres which increased in prominence after intraperitoneal injection of L-gluatamate, but penetration of exogenous glutamate into the grey matter was limited. Instead, the meninges and basal layers of the spinal blood vessels were intensely immunoreactive. The studies describe the subtypes of acidic amino acidergic neurons and relates the immunohistochemistry to a functional subclass.

Heterogeneous astroglial response in the rat spinal cord to long-term portacaval shunt: an immunohistochemical study

Glial fibrillary acidic protein (GFAP) immunoreactivity has been used to study the astroglial response in the rat spinal cord to long-term portacaval shunt (PCS). The astroglial response in PCS rats is heterogeneous. In general, astrocytes show a loss of GFAP immunoreactivity, as well as shrinking and pyknosis in their nuclei; however, while GFAP reactivity was unchanged in the periependymal region, it was strongly increased in the dorsolateral region of the spinal cord (lateral spinal nucleus, dorsal root entry zone, and the most dorsal region of the dorsal horn). Three possibilities are postulated to explain how astrocytes, in the periependymal and dorsolateral regions, can support the effects of PCS: a) astrocytes related to glutamatergic pathways ought to possess a more efficient ammonia uptake and detoxification system, b) long-term PCS can activate nociceptive pathways (substancePergic fibers), and c) astrocytes located in periependymal and dorsolateral regions can be exposed to lower concentrations of ammonia because of its diffusion into the cerebro-spinal fluid close to these regions.

Ultrastructural visualization of glutamate and aspartate immunoreactivities in the rat dorsal horn, with special reference to the co-localization of glutamate, substance P and calcitonin-gene related peptide

Antisera raised against the fixation products of L-glutamate and L-aspartate were used, singly or in combination, to study the ultrastructural localization of the amino acids in the rat dorsal horn, with post-embedding immunogold techniques. Immunostaining for each of the amino acids was also combined with immunolocalization of GABA, an important inhibitory neurotransmitter in the spinal cord, or synaptophysin, a synaptic vesicle glycoprotein. In addition, we examined the localization of glutamate immunoreactivity in relation to that of calcitonin-gene related peptide and substance P, two neuropeptides present in high concentrations in the dorsal horn. Glutamate- and aspartate-immunoreactive neuronal cell bodies, dendrites, axons and terminals were apparent in the first three laminae of the dorsal horn. In somatic and dendritic profiles, the immunolabel was present over the general cytoplasm and mitochondria; in the terminals, it was found over small, agranular vesicles, mitochondria and, at times, synaptic densities. Quantitative estimation indicated that the colloidal gold density in the glutamate-immunoreactive terminals was five-fold more than in any other neuronal profile. Both glutamate- and aspartate-immunopositive terminals made asymmetric synaptic contacts onto unlabelled dendrites; glutamate-positive terminals often formed the core of type I and II glomeruli. After double labelling of the same sections, glutamate and aspartate immunoreactivities consistently occurred in different axonal and terminal profiles. In these preparations, it was clearly seen that glutamate-immunoreactive terminals were far more numerous than (more than 10-fold) those immunoreactive for aspartate. Double labelling for glutamate or aspartate and GABA also revealed distinct staining of different terminals. Simultaneous immunolocalization of each of the amino acids and synaptophysin showed the amino acid and glycoprotein immunoreactivities co-localized in small, agranular vesicles in immunoreactive terminals. Finally, triple labelling of the same sections for glutamate, calcitonin gene-related peptide and substance P revealed that glutamate was often co-localized with either of the two neuropeptides in the same axonal boutons; terminals that showed simultaneous labelling for glutamate, calcitonin gene-related peptide and substance P were also noted. In all cases, the glutamate immunoreactivity was restricted to small, clear vesicles whereas the neuropeptide immunoreactivities were present in larger, dense-cored vesicles. Our observations demonstrate that there is an abundant glutamate immunoreactivity in the superficial layers of the rat dorsal horn, localized in neuronal profiles distinct from those containing aspartate or GABA.(ABSTRACT TRUNCATED AT 400 WORDS)

Colocalization of fixative-modified glutamate and glutaminase but not GAD in rubrospinal neurons

In an attempt to identify putative neurotransmitters of rubrospinal neurons, immunocytochemical procedures were utilized in combination with retrograde tracing techniques in 15 adult male rats. Following injections of horseradish peroxidase (HRP) or wheat germ agglutinin conjugated to HRP (WGA-HRP) into the spinal cord, midbrain sections were processed with a combined procedure that allowed visualization of both the retrograde tracer and one or more antigens including glutamate, glutaminase, and glutamatic acid decarboxylase (GAD). Initial colocalization studies demonstrated that glutamatelike and glutaminaselike immunoreactivities were cocontained within the same neurons. Following injections of HRP or WGA-HRP into the spinal cord approximately 53% of retrogradely labeled neurons contained glutamate immunoreactivity. Triple-labeling experiments indicated that glutamatelike immunoreactivity was colocalized with glutaminase immunoreactivity in retrogradely labeled rubrospinal neurons. Retrogradely labeled neurons did not contain GAD immunoreactivity. Moreover, triple labeling experiments verified that glutamatelike immunoreactive retrogradely labeled cells did not cocontain GAD immunoreactivity. These studies demonstrate that glutamate and its synthesizing enzyme, glutaminase, are present in some rubrospinal neurons and raise the possibility that a component of the rubrospinal projection may be glutamatergic. GAD, on the other hand, is not present in rubrospinal neurons. This finding supports the hypothesis that GABAergic neurons play a role as interneurons in the red nucleus.

Organization of glutamate-like immunoreactivity in the rat superficial dorsal horn: light and electron microscopic observations

Glutamate has been shown to be a neurotransmitter in the central nervous system of vertebrates, and it has been hypothesized that glutamate is functional as a neurotransmitter in the spinal cord dorsal horn. A monoclonal antibody to fixative-modified glutamate was used in this study to examine the light microscopic and ultrastructural profiles of glutamate-like immunoreactivity in the superficial dorsal horn of the rat spinal cord. Glutamate-like immunoreactivity was observed in neurons, fibers, and terminals of both laminae I and II. Marginal zone immunoreactive neurons ranged from 10 to 30 micron in diameter and received many nonimmunoreactive somatic synapses. In substantia gelatinosa, immunoreactive neurons were observed in both inner and outer layers, ranged 5 to 10 micron in diameter, and received few nonimmunoreactive somatic synapses. Glutamate-like immunoreactive dendrites were observed in both laminae and were contacted primarily by nonimmunoreactive synaptic terminals that generally contained small clear vesicles. Both myelinated and unmyelinated immunoreactive axons were observed in Lissauer's tract. Immunoreactive terminals contained small (40 nm) clear vesicles and generally formed simple synaptic contacts with nonimmunoreactive dendrites in laminae I and II. The results of this study corroborate the importance of glutamate as a neurotransmitter in spinal sensory mechanisms.

Central transport and distribution of labelled glutamic and aspartic acids to the cochlear nucleus in cats: an autoradiographic study

The use of Gd-DTPA in nondegenerative spinal lesions is described. Thirty consecutive patients were examined by MR with and without Gd-DTPA. The information obtained with unenhanced T1- and T2-weighted spin-echo images was compared with that obtained with Gd-DTPA T1-weighted images. The results showed that, according to the criteria used, more information was present on the MR images with Gd-DTPA in 18 of 30 patients. In six of 30 patients, the improved quality of the images led to a change in the neurosurgical or neurologic approach. Gd-DTPA proved to be a safe contrast medium; no side effects or adverse reactions were observed.

It is recommended that Gd-DTPA be used in nondegenerative lesions involving the spinal cord to obtain the same or more information in a shorter acquisition time.

Immunocytochemical localizations of cytosolic and mitochondrial glutamic oxaloacetic transaminase isozymes in rat primary sensory neurons as a marker for the glutamate neuronal system

The localization of cytosolic (s-) and mitochondrial (m-) glutamic oxaloacetic transaminase (GOT) was examined in the rat trigeminal, jugular and dorsal root ganglia by means of an indirect immunofluorescence method using antibodies specific for s- and m-GOT. Staining of s-GOT-like immunoreactivity was seen in giant, large, medium and small cells in these ganglia. On the other hand, m-GOT-like immunoreactivity was not seen in them. The distribution of GOT suggests that glutamate may be a transmitter released from primary sensory neurons.

Co-localization of fixative-modified glutamate and glutaminase in neurons of the spinal trigeminal nucleus of the rat: an immunohistochemical and immunoradiochemical analysis

The spinal trigeminal nucleus (STN) is involved in processing orofacial sensory information, including tactile, thermal and nociceptive input, and relaying this information to higher brain centers, such as the thalamus. Very little information is available regarding the major excitatory neurotransmitters of this nucleus. The amino acid glutamate has been proposed as a major excitatory neurotransmitter in the central nervous system. In the present study, a novel monoclonal antibody, specific for fixative-modified glutamate, was utilized in conjunction with polyclonal antisera against glutaminase and aspartate aminotransferase (AATase) in an attempt to identify and map the locations of possible glutamatergic neurons in the STN. Co-localization experiments were performed by radiolabeling our monoclonal antibody and using this antibody in conjunction with the polyclonal antisera against glutaminase and AATase to evaluate the possible coexistence of glutamate with glutaminase or AATase in STN neurons. In all three subnuclei of the STN, immunohistochemically labeled neuronal profiles were observed with both of the polyclonal antisera and with the monoclonal antibody. Subnucleus caudalis contained the greatest number of labeled profiles per coronal section followed by subnucleus interpolaris and subnucleus oralis. The number and the distribution of immunoreactive profiles observed after the use of the glutaminase antiserum was comparable to that obtained with the monoclonal antibody. Co-localization experiments demonstrated that all glutaminase-like immunoreactive neurons also contained fixative-modified glutamate-like immunoradioactivity. These results suggest that glutamatergic neurons are present in the spinal trigeminal nucleus. The AATase antiserum labeled more neuronal profiles in each of the three subnuclei than did the glutaminase antiserum or the monoclonal antibody. In addition, co-localization experiments indicated that glutamate-like immunoreactivity was present in only two-thirds of AATase-like immunoreactive neuronal profiles. These findings suggest that glutaminase may be a more reliable marker of glutamatergic function than AATase.

The development of responsiveness to substance P and glutamate in the spinal motoneurons of rat fetuses

The development of responsiveness of motoneurons to substance P (SP) and glutamate was investigated in the isolated spinal cord of the rat fetus at embryonic days 13.5-21.5. The motoneurons at embryonic day 14.5 first responded to SP with a slow depolarization. The responsiveness to SP increased by embryonic days 19.5-21.5. In a low Ca2+ solution, responsiveness was reduced after embryonic day 17.5. Glutamate caused a slow depolarization of motoneurons from embryonic day 13.5. The responsiveness increased until embryonic day 17.5 and decreased thereafter.

Decreased uptake and release of D-aspartate in the guinea pig spinal cord after dorsal root section

This study attempts to determine if L-glutamate and/or L-aspartate may be transmitters of dorsal sensory neurons. The uptake and the electrically evoked release of D-[3H]aspartate, a putative marker for L-glutamate and L-aspartate, were measured in the cervical enlargement (segments C4-T1) of the guinea pig spinal cord before and after cutting dorsal roots C5-T1 on the right side. The uptake and the release of gamma-aminobutyric acid (GABA) also were measured as indices of the integrity of GABAergic neurons in the spinal cord. The cervical enlargement was excised and divided into left and right halves, then into dorsal and ventral quadrants. Quadrants from unlesioned animals took up D-aspartate and GABA, achieving concentrations in the tissues which were 14-25 times that in the medium. Subsequently, electrical stimulation evoked a Ca2+-dependent release of D-aspartate and of GABA. The uptake and release of D-aspartate and GABA were similar in tissues taken from intact and sham-operated animals. However, dorsal rhizotomy, without damage to dorsal radicular or spinal blood vessels, depressed the uptake (by 22-29%) and the release (by 50%) of D-aspartate only in quadrants ipsilateral to the lesion. The uptake and the release of GABA were unchanged. In transverse sections of the cervical enlargement, stained to reveal degenerating fibers, by far the heaviest loss of axons occurred in the cuneate fasciculus and in the gray matter ipsilateral to the cut dorsal roots. These findings suggest that the synaptic endings of dorsal sensory neurons probably mediate the uptake and the release of D-aspartate and, therefore, may use L-glutamate or L-aspartate as a transmitter. When spinal blood vessels were damaged during dorsal rhizotomy, the deficits in D-aspartate uptake and release were larger than those in the absence of vascular damage and were accompanied by deficits in GABA uptake and release. These findings imply that vascular damage results in the loss of intraspinal neurons, some of which probably mediate the uptake and release of D-aspartate and, therefore, may use L-glutamate and/or L-aspartate as a transmitter.

Effects of glutamate and aspartate on sympathetic preganglionic neurons in the upper thoracic intermediolateral nucleus of the cat

Glutamate and aspartate excited all spontaneously active sympathetic preganglionic neurons (SPNs) tested in the intermediolateral nucleus of spinal segments T1-T3. Most silent neurons could be induced to discharge but the remainder showed only a decrease in antidromic spike amplitude. These effects were typically fast (on, off less than 1 s). D,L-Homocysteic acid also produced excitation; this effect was typically slower. Glutamate and aspartate were usually equipotent; 20% were differentially sensitive to aspartate, 10% to glutamate.

Inhibitory actions of a novel endogenous tripeptide, methyionyl-tyrosyl-lysine, on proprioceptive neurons in the lumbar spinal cord of the cat

The actions of a tripeptide, methionyl-tyrosyl-lysine (Met-Tyr-Lys), isolated from spinal cord and dorsal root ganglia have been investigated by iontophoretic application to single neurones in the spinal cord of the cat. Met-Tyr-Lys inhibited a group of neurons located mainly in laminae V and VI of the lumbar dorsal horn: excitation was never observed. The inhibition was rapid in onset and was not mimicked by the action of the constituent amino acids. Neurons inhibited by Met-Tyr-Lys received proprioceptive inputs as shown by their excitation or inhibition from stimulation of deep receptors and by their responses to leg or foot movement. Bicuculline and strychnine separately, at doses which antagonized responses to gamma-aminobutyric acid and glycine, respectively, had no or little effect both on responses to Met-Tyr-Lys and on the inhibition evoked in the same neurons by low-intensity (1.5-4T) stimulation of the tibial or common peroneal nerves. Thus receptors for Met-Tyr-Lys are different from those for glycine or gamma-aminobutyrate. In addition it is possible that there is a component of the inhibition evoked by peripheral nerve stimulation which is not mediated by either glycine or gamma-aminobutyrate. Met-Tyr-Lys may have an inhibitory role in relation to proprioception.

Capsaicin does not change tissue levels of glutamic acid, its uptake, or release in the rat spinal cord

Capsaicin treatment (50 mg/kg, subcutaneous) of newborn rats resulted in 1 75% decrease of substance P immunoreactivity in the dorsal spinal cord of the adult animal, but failed to affect levels of the proposed sensory neurotransmitter glutamic acid or to alter high-affinity uptake of [3H]glutamic acid into synaptosomes of the same tissue. Furthermore, capsaicin (30 microM) in vitro had no influence on the release of [3H]glutamic acid from spinal cord P2 fractions of untreated adult rats, but induced a marked release of substance P. The results suggest that, in contrast to substance P fibers, neurons containing glutamic acid are not sensitive to capsaicin. Eleven other neurochemical parameters measured in the spinal cord did not appear to be changed by the treatment with capsaicin, suggesting a considerable neurochemical selectivity of the lesion.

Circling behavior following unilateral kainic acid injections into rat striatum

Unilateral injection of kainic acid (2.5-25 nmol) into rat anterior caudate putamen induced dose-related circling behaviour. Kainic acid (10 nmol) consistently caused initial weak ipsiversive circling lasting 1 h followed by prolonged strong contraversive rotation lasting in excess of 10 h. Unilateral intrastriatal administration of L-glutamic acid, or of monosodium L-glutamate, to normal rats, or administration of monosodium L-glutamate to rats with extensive decortication, did not induce circling behaviour. The simultaneous unilateral injection of monosodium L-glutamate (1 mumol) with kainic acid (10 nmol) did not modify circling behaviour induced by kainic acid. However, extensive decortication greatly reduced circling induced by unilateral intrastriatal kainic acid (10 nmol), and effect not reversed by the simultaneous administration of monosodium L-glutamate (1 mumol). Unilateral 6-hydroxydopamine lesions of the left nigrostriatal pathway abolished the initial ipsiversive rotation and potentiated the subsequent contraversive rotation for up to 4 h after intrastriatal injection of kainic acid (10 nmol). Peripheral administration of haloperidol (1 mg/kg i.p.) also abolished initial ipsiversive rotation and decreased the subsequent contraversive rotation. Electro-coagulation of the ipsilateral strio-nigral pathway prolonged the initial ipsiversive rotation produced by kainic acid, but markedly attenuated contraversive rotation. These findings suggest that circling induced by intrastriatal administration of kainic acid depends on intact corticostriate pathways, but it cannot be reproduced or modified by intrastriatal administration of glutamate. Kainic acid circling appears to be mediated via strio-nigral pathways, and to be modulated by dopaminergic function.

Pharmacology of pain and analgesia

Physiological events involved in nociception and pain perception are examined. Substance P could be a primary afferent transmitter of certain nociceptive information. Transmission of this information can be modulated within the spinal cord by intrinsic and descending mechanisms. The intrinsic mechanism involves inhibitory opiate effects within substantia gelatinosa. Centres for descending systems are located in medulla and periaqueductal gray matter. They are activated by exogenous narcotic agonists, and by regional connections. Descending inhibitory pathways are serotonergic and noradrenergic. GABA and glycine are also possibly involved in antinociception. Narcotics have been shown to produce analgesia when administered to the intrathecal or epidural spaces of humans. These routes are still experimental. The place of clinical modification of transmitter system is discussed, but no conclusions or recommendations can be made at this early stage.