Biomedical subjects

A J Todd

Publications and source records attributed to A J Todd.

At least 19 recordsLinked to original sources

PubMed2005

Clinical features remain important for the diagnosis of infective endocarditis in the modern era.

BACKGROUND: Infective endocarditis (IE) can be difficult to diagnose, due to multiple (often non-specific) presenting features. AIM: To assess the predictive accuracy of classical clinical features and blood investigations readily available at the time of presentation. DESIGN: Cross-sectional analysis. METHODS: We studied 29 IE cases and 79 controls (clinically suspicious contemporaneous cases where IE was subsequently excluded) from a hospital-based group of patients referred to a cardiac department with possible infective endocarditis. Patients were identified from the echocardiography database. Cases were defined by final diagnosis. Symptoms, signs, risk factors for IE and blood investigations were recorded from case notes and examined by univariate and multivariate analyses. RESULTS: The sensitivity, specificity, and positive and negative predictive values of transthoracic echocardiography (TTE) for detection of IE in clinically suspected cases were 71%, 98%, 57% and 99%, respectively. Univariate analyses revealed a significant association between IE and several clinical features. Under multivariate analysis, previous heart valve surgery (OR 13.3, 90%CI 3.2-55.6), positive blood cultures (OR 17.2, 90%CI 4.9-58.8), signs of embolism (OR 11.4, 90%CI 3.0-43.5), a new, altered or changing murmur (OR 10.3, 90%CI 2.8-38.5) and splenomegaly (OR 18.2, 90%CI 3.6-90.9) were independent predictors for IE. DISCUSSION: Clinical features at presentation continue to be important for the diagnosis of IE. Features such as positive blood cultures, signs of embolism and a changing heart murmur should be used to guide investigation and treatment of IE prior to echocardiography, or when TTE is negative.

Adult↗

PubMed2005

P boutons in lamina IX of the rodent spinal cord express high levels of glutamic acid decarboxylase-65 and originate from cells in deep medial dorsal horn.

Presynaptic inhibition of primary muscle spindle (group Ia) afferent terminals in motor nuclei of the spinal cord plays an important role in regulating motor output and is produced by a population of GABAergic axon terminals known as P boutons. Despite extensive investigation, the cells that mediate this control have not yet been identified. In this work, we use immunocytochemistry with confocal microscopy and EM to demonstrate that P boutons can be distinguished from other GABAergic terminals in the ventral horn of rat and mouse spinal cord by their high level of the glutamic acid decarboxylase (GAD) 65 isoform of GAD. By carrying out retrograde labeling from lamina IX in mice that express green fluorescent protein under the control of the GAD65 promoter, we provide evidence that the cells of origin of the P boutons are located in the medial part of laminae V and VI. Our results suggest that P boutons represent the major output of these cells within the ventral horn and are consistent with the view that presynaptic inhibition of proprioceptive afferents is mediated by specific populations of interneurons. They also provide a means of identifying P boutons that will be important in studies of the organization of presynaptic control of Ia afferents.

Afferent Pathways↗

PubMed2005

Fos induction in lamina I projection neurons in response to noxious thermal stimuli.

Lamina I of the spinal cord contains many projection neurons: the majority of these are activated by noxious stimulation, although some respond to other stimuli, such as innocuous cooling. In the rat, approximately 80% of lamina I projection neurons express the neurokinin 1 (NK1) receptor, on which substance P acts. Lamina I neurons can be classified into three main morphological classes: pyramidal, fusiform and multipolar cells. It has been reported that in the cat, pyramidal cells respond to innocuous cooling, and whilst both fusiform and multipolar cells are activated by noxious mechanical and heat stimuli, only cells in the latter group respond to noxious cold [Nat Neurosci 1 (1998) 218]. However, we have previously shown that NK1 receptor-immunoreactive projection neurons belonging to each morphological class are equally likely to up-regulate the transcription factor Fos after noxious chemical stimulation, and that the density of innervation by substance P-containing (nociceptive) afferents is similar for cells of each type [J Neurosci 22 (2002) 4103]. This suggests that the morphological-physiological correlation that has been reported in the cat may not apply in the rat. We have tested this further by examining Fos expression in lamina I spinoparabrachial neurons in the rat after application of noxious heat or noxious cold stimuli under general anesthesia. Following noxious heat, 57-69% of NK1 receptor-immunoreactive spinoparabrachial neurons expressed Fos, and the proportion did not differ significantly between morphological groups. However, after noxious cold stimulation Fos was present in 63% of multipolar neurons, but only 19-26% of fusiform or pyramidal cells. These results suggest that although most NK1 receptor-expressing spinoparabrachial neurons are activated by noxious stimuli, responsiveness to noxious cold is significantly more common in those of the multipolar type. There therefore appears to be a correlation between morphology and function for lamina I projection neurons in the rat.

Animals↗

PubMed2004

Lack of evidence for significant neuronal loss in laminae I-III of the spinal dorsal horn of the rat in the chronic constriction injury model.

Peripheral nerve injury leads to structural and functional changes in the spinal dorsal horn, and these are thought to be involved in the development of neuropathic pain. In the chronic constriction injury (CCI) model, abnormal 'dark' neurons and apoptotic nuclei have been observed in laminae I-III of the dorsal horn in the territory innervated by the injured sciatic nerve. These findings have been taken as evidence that there is significant neuronal death in this model, and it has been suggested that loss of inhibition resulting from death of GABAergic inhibitory interneurons contributes to the neuropathic pain. However, loss of neurons from the dorsal horn has not been directly demonstrated in neuropathic models, even though this issue is of considerable importance for our understanding of the mechanisms that underlie neuropathic pain. In this study, we have looked for evidence of neuronal death by using a stereological method (the optical disector) with NeuN-immunostaining, and examining spinal cords of naïve rats, and of rats that had undergone CCI or sham operations. All of the CCI animals showed clear signs of thermal hyperalgesia. However, the numbers of neurons in laminae I-III of the ipsilateral dorsal horn in these animals did not differ significantly from those on the contralateral side, nor from those of sham-operated or naïve animals. These results do not, therefore, support the suggestion that there is significant neuronal death in the dorsal horn in this model.

Animals↗

PubMed2003

Evidence against cholera toxin B subunit as a reliable tracer for sprouting of primary afferents following peripheral nerve injury.

In order to investigate whether cholera toxin B subunit (CTb) is transported by unmyelinated primary afferents following nerve injury, we transected the sciatic nerves of six rats, and injected the transected nerves (and in three cases also the intact contralateral nerves) with CTb, 2 weeks later. The relationship between CTb and two neuropeptides, vasoactive intestinal peptide (VIP) and neuropeptide Y (NPY), was then examined in neurons in the ipsilateral L4 and L5 dorsal root ganglia, using immunofluorescence staining and confocal microscopy. We also immunostained sections of spinal cord and caudal medulla for CTb, NPY and VIP. Following nerve section, VIP immunoreactivity was increased in laminae I-II of the spinal cord while NPY immunoreactivity was increased in laminae III-IV of the spinal cord and in the gracile nucleus. On the contralateral side, CTb labelling was detected in laminae I and III-V of the dorsal horn of the L4 and L5 spinal segments, as well as in the gracile nucleus. CTb labelling was seen in the same areas on the lesioned side, but with a dramatic increase in lamina II. No VIP or NPY immunoreactivity was observed in L4 and L5 dorsal root ganglia on the side of the intact nerve, but on the lesioned side VIP was detected in many small neurons and NPY in numerous large neurons. In agreement with the report by Tong et al. [J. Comp. Neurol. 404 (1999) 143], we found that while CTb labelling in the dorsal root ganglion on the side of the intact nerve was mainly in large neurons, on the lesioned side CTb was present in dorsal root ganglion neurons of all sizes. The main finding of the present study was that almost all of the VIP- (96%) and NPY- (98%) positive neurons in the dorsal root ganglia on the lesioned side were also CTb-labelled. After nerve injury VIP is upregulated in fine afferents that terminate in laminae I and II, and most of these probably have unmyelinated axons. Since the cell bodies of these neurons were labelled with CTb that had been injected into the transected sciatic nerve, this suggests that many of these fine afferents, which do not normally transport CTb, are capable of doing so after injury.

Afferent Pathways↗

PubMed2003

Selective loss of spinal GABAergic or glycinergic neurons is not necessary for development of thermal hyperalgesia in the chronic constriction injury model of neuropathic pain.

GABA and glycine are inhibitory neurotransmitters used by many neurons in the spinal dorsal horn, and intrathecal administration of GABA(A) and glycine receptor antagonists produces behavioural signs of allodynia, suggesting that these transmitters have an important role in spinal pain mechanisms. Several studies have described a substantial loss of GABA-immunoreactive neurons from the dorsal horn in nerve injury models, and it has been suggested that this may be associated with a loss of inhibition, which contributes to the behavioural signs of neuropathic pain. We have carried out a quantitative stereological analysis of the proportions of neurons in laminae I, II and III of the rat dorsal horn that show GABA- and/or glycine-immunoreactivity 2 weeks after nerve ligation in the chronic constriction injury (CCI) model, as well as in sham-operated and nai;ve animals. At this time, rats that had undergone CCI showed a significant reduction in the latency of withdrawal of the ipsilateral hindpaw to a radiant heat stimulus, suggesting that thermal hyperalgesia had developed. However, we did not observe any change in the proportion of neurons in laminae I-III of the ipsilateral dorsal horn that showed GABA- or glycine-immunoreactivity compared to the contralateral side in these animals, and these proportions did not differ significantly from those seen in sham-operated or nai;ve animals. In addition, we did not see any evidence for alterations of GABA- or glycine-immunostaining in the neuropil of laminae I-III in the animals that had undergone CCI. Our results suggest that significant loss of GABAergic or glycinergic neurons is not necessary for the development of thermal hyperalgesia in the CCI model of neuropathic pain.

Animals↗

PubMed2003

Distribution and colocalisation of glutamate decarboxylase isoforms in the rat spinal cord.

The inhibitory neurotransmitter GABA is synthesized by glutamic acid decarboxylase (GAD), and two isoforms of this enzyme exist: GAD65 and GAD67. Immunocytochemical studies of the spinal cord have shown that whilst both are present in the dorsal horn, GAD67 is the predominant form in the ventral horn. The present study was carried out to determine the pattern of coexistence of the two GAD isoforms in axonal boutons in different laminae of the cord, and also to examine the relation of the GADs to the glycine transporter GLYT2 (a marker for glycinergic axons), since many spinal neurons are thought to use GABA and glycine as co-transmitters. Virtually all GAD-immunoreactive boutons throughout the spinal grey matter were labelled by both GAD65 and GAD67 antibodies; however, the relative intensity of staining with the two antibodies varied considerably. In the ventral horn, most immunoreactive boutons showed much stronger labelling with the GAD67 antibody, and many of these were also GLYT2 immunoreactive. However, clusters of boutons with high levels of GAD65 immunoreactivity were observed in the motor nuclei, and these were not labelled with the GLYT2 antibody. In the dorsal horn, some GAD-immunoreactive boutons had relatively high levels of labelling with either GAD65 or GAD67 antibody, whilst others showed a similar degree of labelling with both antibodies. GLYT2 immunoreactivity was associated with many GAD-immunoreactive boutons; however, this did not appear to be related to the pattern of GAD expression. It has recently been reported that there is selective depletion of GAD65, accompanied by a loss of GABAergic inhibition, in the ipsilateral dorsal horn in rats that have undergone peripheral nerve injuries [J Neurosci 22 (2002) 6724]. Our finding that some boutons in the superficial laminae showed relatively high levels of GAD65 and low levels of GAD67 immunoreactivity is therefore significant, since a reduction in GABA synthesis in these axons may contribute to neuropathic pain.

Amino Acid Transport Systems, Neutral↗

PubMed2003

The expression of vesicular glutamate transporters VGLUT1 and VGLUT2 in neurochemically defined axonal populations in the rat spinal cord with emphasis on the dorsal horn.

Two vesicular glutamate transporters, VGLUT1 and VGLUT2, have recently been identified, and it has been reported that they are expressed by largely nonoverlapping populations of glutamatergic neurons in the brain. We have used immunocytochemistry with antibodies against both transporters, together with markers for various populations of spinal neurons, in an attempt to identify glutamatergic interneurons in the dorsal horn of the mid-lumbar spinal cord of the rat. The great majority (94-100%) of nonprimary axonal boutons that contained somatostatin, substance P or neurotensin, as well as 85% of those that contained enkephalin, were VGLUT2-immunoreactive, which suggests that most dorsal horn neurons that synthesize these peptides are glutamatergic. In support of this, we found that most somatostatin- and enkephalin-containing boutons (including somatostatin-immunoreactive boutons that lacked calcitonin gene-related peptide and were therefore probably derived from local interneurons) formed synapses at which AMPA receptors were present. We also investigated VGLUT expression in central terminals of primary afferents. Myelinated afferents were identified with cholera toxin B subunit; most of those in lamina I were VGLUT2-immunoreactive, whereas all those in deeper laminae were VGLUT1-immunoreactive, and some (in laminae III-VI) appeared to contain both transporters. However, peptidergic primary afferents that contained substance P or somatostatin (most of which are unmyelinated), as well as nonpeptidergic C fibres (identified with Bandeiraea simplicifolia isolectin B4) showed low levels of VGLUT2-immunoreactivity, or were not immunoreactive with either VGLUT antibody. As all primary afferents are thought to be glutamatergic, this raises the possibility that unmyelinated afferents, most of which are nociceptors, express a different vesicular glutamate transporter.

Adjuvants, Immunologic↗

PubMed2003

A quantitative and morphological study of projection neurons in lamina I of the rat lumbar spinal cord.

In the rat lumbar spinal cord the major supraspinal targets for lamina I projection neurons are the caudal ventrolateral medulla (CVLM), lateral parabrachial area (LPb) and periaqueductal grey matter (PAG). In this study we have estimated the number of lamina I neurons retrogradely labelled from each of these sites in the L4 segment, as well as the proportion that can be labelled by injecting different tracers into two separate sites. Our results suggest that this segment contains approximately 400 lamina I projection neurons on each side, and that approximately 85% of these can be labelled from either the CVLM or the LPb on the contralateral side. Around 120 lamina I cells in L4 project to the PAG, and over 90% of these cells can also be labelled from the CVLM or LPb. Most lamina I neurons projecting to CVLM or LPb are located in the contralateral dorsal horn, but in each case some cells were found to have bilateral projections. We also examined horizontal sections to investigate morphology and the expression of the neurokinin 1 (NK1) receptor in cells labelled from CVLM, LPb or PAG. There were no consistent morphological differences between these groups, however, while cells with strong or moderate NK1 receptor-immunostaining were labelled from LPb or CVLM, they seldom projected to the PAG. These results suggest that many lamina I cells project to more than one site in the brain and that those projecting to PAG may represent a distinct subclass of lamina I projection neuron.

Animals↗

PubMed2002

Selective innervation of lamina I projection neurones that possess the neurokinin 1 receptor by serotonin-containing axons in the rat spinal cord.

Axons containing serotonin descend from brainstem to spinal cord and are thought to contribute to stimulation-produced and opioid analgesia, partly by a direct inhibitory action of serotonin on projection neurones. The density of serotoninergic innervation is highest in lamina I, which contains many nociceptive projection neurones. Two sets of anatomical criteria have been used to classify lamina I projection neurones: somatodendritic morphology and presence or absence of the neurokinin 1 receptor. To test whether the strength of serotoninergic innervation of lamina I projection neurones was related to morphology or neurokinin 1 receptor expression, we used confocal microscopy to determine the density of serotoninergic contacts on 60 cells retrogradely labelled from the caudal ventrolateral medulla. The contact density on neurones with the neurokinin 1 receptor was variable, with some cells receiving heavy input and others having few contacts. However, on average they received significantly more contacts (5.64 per 1000 microm(2) plasma membrane +/- 0.47, S.E.M.) than neurones which lacked the receptor (2.49 +/- .36). Among the neurokinin 1 neurones, serotoninergic innervation density was not related to morphology. Since the majority of serotoninergic boutons in lamina I of rat spinal cord do not appear to form synapses, we carried out electron microscopy on three heavily innervated neurokinin 1 receptor-immunoreactive projection neurones. Symmetrical synapses were found at 89% of serotoninergic contacts. These results indicate that serotoninergic innervation of lamina I projection neurones in the rat spinal cord is related to expression of neurokinin 1 receptors, but not to morphology, and that (at least on heavily innervated neurones) most serotonin-containing boutons which are in contact form synapses.

Animals↗

PubMed2002

MOR-1-immunoreactive neurons in the dorsal horn of the rat spinal cord: evidence for nonsynaptic innervation by substance P-containing primary afferents and for selective activation by noxious thermal stimuli.

A direct action of mu-opioid agonists on neurons in the spinal dorsal horn is thought to contribute to opiate-induced analgesia. In this study we have investigated neurons that express the mu-opioid receptor MOR-1 in rat spinal cord to provide further evidence about their role in nociceptive processing. MOR-1-immunoreactive cells were largely restricted to lamina II, where they comprised approximately 10% of the neuronal population. The cells received few contacts from nonpeptidergic unmyelinated afferents, but many from substance P-containing afferents. However, electron microscopy revealed that most of these contacts were not associated with synapses. None of the MOR-1 cells in lamina II expressed the neurokinin 1 receptor; however, the mu-selective opioid peptide endomorphin-2 was present in the majority (62-82%) of substance P axons that contacted them. Noxious thermal stimulation of the foot induced c-Fos expression in approximately 15% of MOR-1 cells in the medial third of the ipsilateral dorsal horn at mid-lumbar level. However, following pinching of the foot or intraplantar injection of formalin very few MOR-1 cells expressed c-Fos, and for intraplantar formalin injection this result was not altered significantly by pretreatment with systemic naloxone. Although these findings indicate that at least some of the neurons in lamina II with MOR-1 are activated by noxious thermal stimulation, the results do not support the hypothesis that the cells have a role in transmitting nociceptive information following acute mechanical or chemical noxious stimuli.

Afferent Pathways↗

PubMed2002

Anatomy of primary afferents and projection neurones in the rat spinal dorsal horn with particular emphasis on substance P and the neurokinin 1 receptor.

The dorsal horn of the spinal cord plays an important role in transmitting information from nociceptive primary afferent neurones to the brain; however, our knowledge of its neuronal and synaptic organisation is still limited. Nociceptive afferents terminate mainly in laminae I and II and some of these contain substance P. Many projection neurones are located in lamina I and these send axons to various parts of the brain, including the caudal ventrolateral medulla (CVLM), parabrachial area, periaqueductal grey matter and thalamus. The neurokinin 1 (NK1) receptor on which substance P acts is expressed by certain neurones in the dorsal horn, including approximately 80 % of lamina I projection neurones. There is also a population of large NK1 receptor-immunoreactive neurones with cell bodies in laminae III and IV which project to the CVLM and parabrachial area. It has been shown that the lamina III/IV NK1 receptor-immunoreactive projection neurones are densely and selectively innervated by substance P-containing primary afferent neurones, and there is evidence that these afferents also target lamina I projection neurones with the receptor. Both types of neurone are innervated by descending serotoninergic axons from the medullary raphe nuclei. The lamina III/IV neurones also receive numerous synapses from axons of local inhibitory interneurones which contain GABA and neuropeptide Y, and again this input shows some specificity since post-synaptic dorsal column neurones which also have cell bodies in laminae III and IV receive few contacts from neuropeptide Y-containing axons. These observations indicate that there are specific patterns of synaptic connectivity within the spinal dorsal horn.

Animals↗

PubMed2001

A population of large lamina I projection neurons with selective inhibitory input in rat spinal cord.

Lamina I of the spinal dorsal horn contains a diverse mixture of neurons. Among these, a group of giant neurons (Waldeyer cells) has long been recognized. In this study we have used immunocytochemistry to characterize a population of Waldeyer cells which were identified by the presence of high levels of the glycine receptor-associated protein gephyrin on their cell bodies and proximal dendrites. Most of these cells (27/29) were retrogradely labelled after injection of cholera toxin B subunit into the parabrachial area, and the majority (26/30) expressed the protein product of immediate-early gene c-fos, Fos, following noxious stimulation. Unlike many lamina I projection neurons, these cells either lacked the neurokinin 1 receptor, or expressed it at a very low level. Most of the gephyrin puncta on the cells were adjacent to axons that contained glutamate decarboxylase (and were therefore presumably GABAergic), which suggests that the cells are under powerful inhibitory control. Only around 35% of the puncta were associated with axons that expressed the glycine transporter GLYT2 (a marker for glycinergic axons); however, the glycine receptor alpha1 subunit was present at all of the gephyrin puncta on these cells. The cells received synapses from axons that contained nitric oxide synthase, most of which were also GABAergic, and in some cases this input was so dense that it outlined the cell bodies and dendrites. The innervation by nitric oxide synthase-containing axons was selective for these cells, compared to other neurons in the dorsal horn. From the results of this study we suggest that the gephyrin-rich cells form a specific population of lamina I projection neurons which convey noxious information to the brain. These cells are under powerful inhibitory control, and the study provides further evidence that inhibitory circuits in the dorsal horn are organized in a specific manner.

Amino Acid Transport Systems, Neutral↗

PubMed2000

Neurokinin 1 receptor expression by neurons in laminae I, III and IV of the rat spinal dorsal horn that project to the brainstem.

Large neurons in laminae III and IV of the spinal cord which express the neurokinin 1 receptor and have dendrites that enter the superficial laminae are a major target for substance P (SP)-containing (nociceptive) primary afferents. Although some of these neurons project to the thalamus, we know little about other possible projection targets. The main aim of this study was to determine whether all cells of this type are projection neurons and to provide information about brainstem sites to which they project. Injections of cholera toxin B subunit were made into four brainstem areas that receive input from the spinal cord, and the proportion of cells of this type in the L4 spinal segment that were retrogradely labelled was determined in each case. The results suggest that most of these cells (>90%) project to the contralateral lateral reticular nucleus (or to a nearby region), while many (>60%) send axons to the lateral parabrachial area and some to the dorsal part of the caudal medulla. However, few of these cells project to the periaqueductal grey matter. As lamina I neurons with the neurokinin 1 receptor appear to be important in the generation of hyperalgesia, we also examined projection neurons in this lamina and found that for each injection site the great majority possessed the receptor. These results demonstrate that dorsal horn neurons which express the neurokinin 1 receptor contribute to several ascending pathways that are thought to be important in pain mechanisms.

Afferent Pathways↗

PubMed1999

The types of neuron which contain protein kinase C gamma in rat spinal cord.

Protein kinase C (PKC) is thought to have a role in sensitization of dorsal horn neurons in certain pain states, and a recent study has reported that mice which lack the gamma isoform (PKCgamma) show reduced neuropathic pain after peripheral nerve injury. Although PKCgamma is present at high levels in the ventral part of lamina II we have limited information concerning the types of neuron in which it is located. In this study we have used immunocytochemistry to characterise the neurons which contain PKCgamma. Immunoreactive neurons were concentrated in ventral lamina II, but were also present in lamina III. Some weakly-immunoreactive neurons were located in the dorsal part of lamina II and in lamina I. The great majority (92%) of cells with PKCgamma were not GABA-immunoreactive, and these cells are likely to be excitatory interneurons. Dual-immunofluorescence labelling showed that PKCgamma was not randomly distributed amongst non-GABAergic neurons, since it was present in 76% of cells with neurotensin and 45% of those with somatostatin, but only 5% of those with the mu-opioid receptor (MOR-1). Cells with the neurokinin 1 receptor are found in lamina I and lamina III, and PKCgamma was present in 22% and 37% of these populations, respectively. These results suggest that excitatory interneurons in laminae II and III which lack the micro-opioid receptor may have a significant role in generating neuropathic pain.

Animals↗

PubMed1999

GABAergic neurons that contain neuropeptide Y selectively target cells with the neurokinin 1 receptor in laminae III and IV of the rat spinal cord.

Neuropeptide Y (NPY) is contained in a population of GABAergic interneurons in the spinal dorsal horn and, when administered intrathecally, can produce analgesia. We previously identified a strong monosynaptic link between substance P-containing primary afferents and cells in lamina III or IV with the neurokinin 1 (NK1) receptor. Because some of these cells belong to the spinothalamic tract, they are likely to have an important role in pain mechanisms. In this study, we used confocal microscopy to examine the input to lamina III/IV NK1 receptor-immunoreactive neurons from NPY-containing axons. All of the cells studied received a dense innervation from NPY-immunoreactive axons, and electron microscopy revealed that synapses were often present at points of contact. Most NPY-immunoreactive boutons were also GABAergic, which supports the suggestion that they are derived from local neurons. The association between NPY-containing axons and NK1 receptor-immunoreactive neurons was specific, because postsynaptic dorsal column neurons (which were located in laminae III-V but did not possess NK1 receptors) and lamina I neurons with the NK1 receptor received significantly fewer contacts from NPY-immunoreactive axons. In addition, the NK1 receptor-immunoreactive lamina III/IV cells received few contacts from nitric oxide synthase-containing axons (which belong to a different population of GABAergic dorsal horn neurons). The NPY-containing axons appeared to be targeted to the NK1 receptor-immunoreactive neurons themselves rather than to their associated substance P-immunoreactive inputs. The dense innervation of these cells by NPY-containing axons suggests that they may possess receptors for NPY and that activation of these receptors may contribute to NPY-mediated analgesia.

Animals↗

PubMed1999

Neurons in laminae III and IV of the rat spinal cord with the neurokinin-1 receptor receive few contacts from unmyelinated primary afferents which do not contain substance P.

We have previously demonstrated that neurons in laminae III and IV of the spinal dorsal horn which possess the neurokinin-1 receptor and have long dorsal dendrites receive a major synaptic input from substance P-containing primary afferents and a more limited input from myelinated afferents. In the present study we have carried out a quantitative analysis of the contacts which cells of this type receive from two other classes of unmyelinated primary afferent: those which contain somatostatin and those without neuropeptides. We found that although boutons belonging to both of these types of afferent do form contacts with neurons of this type, the contacts are far less numerous than those formed by substance P-containing afferents. In laminae I and II, the density of contacts which dendrites of these cells received from somatostatin-containing afferents was 1.2/100 microm and that from non-peptidergic C afferents was 2.0/100 microm, which is far lower than our previous estimate of 18.8/100 microm from substance P-containing fibres in these laminae. These results indicate that although the dendrites of large neurons in laminae III and IV which possess the neurokinin-1 receptor pass through regions of the dorsal horn in which many types of primary afferent terminate, their synaptic input from primary afferents is organized in a highly selective manner.

Animals↗

PubMed1998

A quantitative study of neurons which express neurokinin-1 or somatostatin sst2a receptor in rat spinal dorsal horn.

The neurokinin-1 and somatostatin sst2a receptors have both been identified on spinal cord neurons. In this study we have estimated the proportions of neurons in different parts of the spinal cord which express these receptors, by using a monoclonal antibody against a neuronal nuclear protein named NeuN and combining the optical disector method with confocal microscopy. The NeuN antibody was initially tested on over 3200 neurons identified with antisera against a variety of compounds, including neuropeptides, enzymes and receptors, and also on astrocytes and oligodendrocytes. All of the neurons, but none of the glial cells that were examined possessed NeuN-immunoreactivity, which suggests that NeuN is a reliable marker for all spinal cord neurons. We found that approximately 45% of neurons in lamina I, 23-29% of those in laminae IV-VI and 18% in lamina X possessed the neurokinin-1 receptor, while the receptor was present on a smaller proportion of neurons in laminae II and III (6% and 11%, respectively). Thirteen percent of lamina I neurons and 15% of those in lamina II expressed the sst2a receptor. To provide further information about the types of neuron which possess the sst2a receptor, we searched for possible co-existence with the neurokinin-1 receptor as well as with GABA and glycine. sst2a and neurokinin-1 receptors were not co-localized on neurons in laminae I and II. All of the sst2a-immunoreactive neurons examined were also GABA-immunoreactive, and 83.5% were glycine-immunoreactive, indicating that the receptor is located on inhibitory neurons in the superficial dorsal horn. These results demonstrate the proportions of neurons in each region of the spinal cord which can be directly activated by substance P or somatostatin acting through these receptors. Levels of receptors can change in pathological states, and this method could be used to determine whether or not these changes involve alterations in the number of neurons which express receptors. In addition, the method can be used to estimate the sizes of neurochemically-defined populations of spinal cord neurons.

Animals↗