Biomedical subjects

A I Basbaum

Publications and source records attributed to A I Basbaum.

At least 73 records · Page 4Linked to original sources

PubMed1997

Neurokinin-1 receptor-immunoreactive sympathetic preganglionic neurons: target specificity and ultrastructure.

Substance P is involved in cardiovascular control at the spinal cord level, where it acts through neurokinin-1 receptors. In this study we used immunocytochemistry and retrograde tracing to investigate the presence of the neurokinin-1 receptor and its ultrastructural localization in rat sympathetic preganglionic neurons that project to the superior cervical ganglion or the adrenal medulla. Immunofluorescence for the neurokinin-1 receptor outlined the somatic and dendritic surfaces of neurons in autonomic subnuclei of spinal cord segments T1-T12, whereas immunofluorescence for the tracer, cholera toxin B subunit, filled retrogradely labelled cells. There was a significant difference in the proportion of neurokinin-1 receptor-immunoreactive sympathetic preganglionic neurons supplying the superior cervical ganglion and the adrenal medulla. Thirty-eight percent of the neurons that projected to the superior cervical ganglion were immunoreactive for the neurokinin-1 receptor compared to 70% of neurons innervating the adrenal medulla. Of neurons projecting to the superior cervical ganglion, significantly different proportions showed neurokinin-1 receptor immunoreactivity in spinal cord segment T1 (15%) versus segments T2 T6 (45%). At the ultrastructural level, neurokinin-1 receptor staining occurred predominantly on the inner leaflets of the plasma membranes of retrogradely labelled sympathetic preganglionic neurons. Deposits of intracellular label were often observed in dendrites and in the rough endoplasmic reticulum and Golgi apparatus of cell bodies. Neurokinin-1 receptor immunoreactivity was present at many, but not all, synapses as well as at non-synaptic sites, and occurred at synapses with substance P-positive as well as substance P-negative nerve fibres. Only 37% of the substance P synapses occurred on neurokinin-1-immunoreactive neurons in the intermediolateral cell column. These results show that presence of the neurokinin-1 receptor in sympathetic preganglionic neurons is related to their target. The ultrastructural localization of the receptor suggests that sympathetic preganglionic neurons may be affected (i) by substance P released at neurokinin-1 receptor-immunoreactive synapses, (ii) by other tachykinins (e.g., neurokinin A), which co-localize in substance P fibres in the intermediolateral cell column, acting through other neurokinin receptors, and (iii) by substance P that diffuses to neurokinin-1 receptors from distant sites.

Adrenal Medulla↗

PubMed1997

The contribution of supraspinal, peripheral and intrinsic spinal circuits to the pattern and magnitude of Fos-like immunoreactivity in the lumbar spinal cord of the rat withdrawing from morphine.

Withdrawal from morphine evokes increases in Fos-like immunoreactivity in the spinal cord, particularly in the superficial dorsal horn, laminae I/II. To determine the origin of the increased Fos-like immunoreactivity, we selectively targeted central or peripheral opioid receptors with naloxone-methiodide, an antagonist that does not cross the blood-brain barrier, or induced withdrawal after eliminating possible sources of input to the superficial dorsal horn. To induce tolerance, we implanted rats with morphine or placebo pellets (75 mg, six pellets over three days). On day 4, withdrawal was precipitated and after 1 h, the rats were killed, their spinal cords removed and 50 microm transverse sections of the spinal cord immunoreacted with a rabbit polyclonal antiserum directed against the Fos protein. In placebo-pelleted rats, none of the different procedures, viz. spinal transection, unilateral dorsal rhizotomy (L4-S2), neonatal capsaicin treatment or direct intrathecal opioid antagonist injection, induced expression of the Fos protein. However, both spinally transected and rhizotomized withdrawing animals showed significant increases in Fos-like immunoreactivity in laminae I/II, compared to intact withdrawing rats. Neonatal treatment with capsaicin, which eliminates C-fibres, did not alter Fos-like-immunoreactivity. Selective withdrawal of morphine from peripheral opioid receptors by naloxone-methiodide did not induce Fos-like immunoreactivity in the lumbar spinal cord greater than that recorded in nonwithdrawing rats. However, intrathecal injection of naloxone-methiodide increased Fos-like immunoreactivity in laminae I/II and the ventral horn to a greater extent than did subcutaneous injection of naloxone. We hypothesize that the increased Fos expression after systemic withdrawal in spinally-transected rats results from a loss of descending inhibitory control that is activated during withdrawal. The increase in withdrawal-induced Fos-like immunoreactivity after rhizotomy may be secondary to loss of inhibitory controls exerted by large diameter primary afferents or to deafferentation-induced reorganization in the dorsal horn. Since capsaicin did not alter the magnitude of Fos-like immunoreactivity in withdrawing rats, we conclude that hyperactivity of opioid receptor-laden C-fibres is not a necessary contributor to the withdrawal-induced increase in Fos-like immunoreactivity in laminae I and II. Taken together with the results recorded after intrathecal injection of naloxone-methiodide in tolerant rats, we conclude that the pattern of lumbar spinal cord Fos expression following systemic withdrawal is primarily a consequence of increased activity in opioid receptor-containing circuits intrinsic to the dorsal horn and that the magnitude of Fos expression is normally dampened by supraspinal and primary afferent-derived inhibitory inputs.

Animals↗

PubMed1997

Early nociceptive events influence the temporal profile, but not the magnitude, of the tonic response to subcutaneous formalin: effects with remifentanil.

Injection of dilute formalin into the hindpaw produces brief (phase 1) and persistent (phase 2) nociceptive responses in the rat. We recently reported that ongoing peripheral nerve input is required for the expression of behavioral and cardiovascular responses during phase 2. Here we evaluated the contribution of central and peripheral sensitization mechanisms, generated during phase 1, to the magnitude and temporal profile of phase 2. During phase 1, we administered analgesic doses of an ultrashort-acting opioid, remifentanil (i.v. administration from 0-5 min after 5.0% formalin injection), or anesthetic concentrations of halothane (2.1%). Inhibition of phase 1 did not reduce the magnitude of flinching and cardiovascular responses during phase 2, but it did delay their onset and/or termination. Longer remifentanil infusions (0-15 or 0-30 min) produced even longer delays (up to 30 min) in the onset and termination of flinching during phase 2; however, when remifentanil was administered during the early part of phase 2 (15-30 or 15-45 min), it did not prolong the time to termination of phase 2. Continuous infusion (10 mg/kg/hr i.v.) of a peripherally acting opiate antagonist, naloxone methiodide, did not reduce the antinociception produced by remifentanil during phase 1 but almost completely reversed the delay in the onset and termination of phase 2. We conclude that central sensitization mechanisms during phase 1 do not influence the magnitude of phase 2. We also hypothesize that remifentanil interacts with peripheral opioid receptors to impede the formalin-evoked synthesis and/or release of proinflammatory compounds during phase 1 and thus delay phase 2.

Analgesics, Opioid↗

PubMed1996

Inhibition of noxious stimulus-evoked pain behaviors and neuronal fos-like immunoreactivity in the spinal cord of the rat by supraspinal morphine.

In previous studies, we reported that supraspinally administered DAMGO, a mu-opioid agonist, produces a dose-related, naloxone-reversible inhibition of formalin-evoked pain behaviors and spinal cord Fos-like immunoreactivity (FLI) in the rat spinal cord. Although these results support the hypothesis that activation of supraspinal mu-opioid receptors produces antinociception by increasing the activity of bulbospinal inhibitory pathways, other studies suggest that supraspinal morphine decreases rather than increases descending inhibitory control. In the present study, we specifically examined the effect of intracerebroventricular (i.c.v.) injection of morphine in the rat. Supraspinal morphine produced a dose-related, naloxone-reversible inhibition of both formalin-evoked behaviors nd spinal cord FLI. Although the magnitude of the antinociception produced by i.c.v. morphine in the formalin test was significantly correlated with the numbers of FLI neurons in the spinal cord, the lowest dose of i.c.v. morphine tested (0.70 nmol) produced a significant reduction of FLI in the superficial laminae without producing behavioral antinociception, which is consistent with our hypothesis that noxious stimulus-evoked Fos expression in the superficial laminae is a poor predictor of the magnitude of pain behavior. These data support the hypothesis that the antinociceptive effects of supraspinally administered morphine result from an increase in descending inhibitory control.

Analgesics↗

PubMed1996

Spinal cord substance P receptor immunoreactivity increases in both inflammatory and nerve injury models of persistent pain.

Numerous studies have implicated the primary afferent derived neuropeptide, substance P, which exerts its effects via the neurokinin-1/substance P receptor, in the transmission of nociceptive messages at the level of the spinal cord. Immunocytochemical studies demonstrate that the substance P receptor is concentrated in neurons of lamina I of the superficial dorsal horn. Since alterations in the number and distribution of the receptor may underlie persistent pain conditions, we have used immunocytochemistry to study the distribution of the receptor in two very different rat models of persistent pain: chronic inflammation, which is associated with increased levels of substance P, and sciatic nerve section, which is associated with decreased levels of substance P in the dorsal horn. Inflammation was produced by unilateral hindpaw injection of complete Freund's adjuvant. We report that there is an up-regulation of substance P receptor immunoreactivity in the superficial laminae of the dorsal horn in both injury models. The increase was found at all time points studied (up to one week after induction of inflammation and up to two weeks after sciatic nerve section). The increase in substance P receptor immunoreactivity was not only present in the medial part of the dorsal horn at segment L4, which is the region of input of the afferents from the hindpaw, but also in the lateral parts of the dorsal horn, and at segments rostral (L1) and caudal (S1) to the afferent input from the hindpaw. These results indicate that the up-regulation of the receptor is not predictable merely by the change in the concentration of substance P in the dorsal horn. Furthermore, the non-topographic up-regulation of substance P receptor in these different conditions may contribute to the central sensitization of dorsal horn nociceptors under conditions of persistent pain.

Animals↗

PubMed1996

Spinal cord mechanisms of opioid tolerance and dependence: Fos-like immunoreactivity increases in subpopulations of spinal cord neurons during withdrawal [corrected].

Tolerance to the analgesic effects of morphine results in part from the development of a compensatory response in neurons that express the opioid receptor or of neural circuits in which those neurons participate. According to this formulation, withdrawal of morphine results in an overshoot of several neuronal properties because of the unopposed action of the compensatory response system. To identify the population of spinal cord neurons that underlies this state, we monitored expression of Fos-like immunoreactivity, after naltrexone-precipitated abstinence in normal and morphine-tolerant rats. After daily (five days) implantation of morphine or placebo pellets, the rats received an injection of saline or naltrexone and behavior was monitored for 1 h. The rats were then killed, their spinal cords removed and 50-microns transverse sections of the lumbar cord were immunostained with a rabbit polyclonal antiserum directed against Fos. Naltrexone injection in the placebo group did not increase spinal cord Fos expression. Naltrexone-precipitated abstinence resulted in an increase in Fos expression at all levels of the spinal cord; the greatest increase and densest staining was in laminae I through VI. Importantly, when withdrawal was precipitated in anesthetized rats, we recorded a significant reduction in Fos expression, particularly in laminae III through VI, but there was persistent expression in the superficial dorsal horn, particularly in lamina I. These results suggest that spinal cord nociresponsive neurons are sensitized during the development of tolerance. This sensitization is unmasked by the administration of naltrexone and is manifested by fos induction in laminae I/II in awake or anesthetized withdrawing animals. The underlying mechanisms of tolerance development may be similar to those that underlie injury-induced central sensitization and hyperalgesia.

Analgesics, Opioid↗

PubMed1996

Differential contribution of descending controls to the antinociceptive actions of kappa and mu opioids: an analysis of formalin-evoked C-fos expression.

In this study, the effect of intracerebroventricular (icv) administration of (5R)-(5 alpha, 7 alpha, 8 beta)-N-methyl-N-[7-(1-pyrrolindinyl)-1- oxaspiro[4,5]dec-8-yl]-4-benzofurnacetamide monohydrochloride (Cl-977) on pain behaviors and on spinal cord fos-like immunoreactivity (FLI) evoked by unilateral formalin injection into the hindpaw of rats was examined. Intracerebroventricular administration of Cl-977 (0.13-13.00 nmol) produced a dose-dependent inhibition of formalin-evoked pain behaviors, with significant inhibition after 1.30, 4.40 and 13.00 nmol. The estimated ED50 for icv Cl-977 inhibition of formalin-evoked behaviors was 0.95 nmol and the Emax was 53%. The inhibitory effect of 4.40 nmol of icv Cl-977 on formalin-evoked behaviors was prevented by either pretreatment with the kappa selective antagonist nor-binaltorphimine (10 or 100 nmol) or coadministration of the opiate receptor antagonist, naloxone (30 nmol). The lowest dose of icv Cl-977 tested (0.13 nmol) produced a 50% reduction in FLI in the superficial laminae but did not inhibit the expression of FLI in any other regions of the spinal cord. The fos-inhibitory effect of low-dose icv Cl-977 in the superficial cord was reversed by coadministration of naloxone (30 nmol). Higher doses of icv Cl-977 that suppressed formalin-evoked behaviors did not inhibit the expression of FLI in any region of the spinal cord. Finally, neither the inhibitory effect of 4.40 nmol Cl-977 on formalin-evoked behaviors nor the formalin-evoked pattern of FLI expression in the spinal cord of rats treated with this dose of Cl-977 was affected by lesions of the dorsolateral funiculus. These results provide the first evidence that supraspinal kappa receptor-mediated antinociception is not dependent on the integrity of the dorsolateral funiculus and may be mediated exclusively at the supraspinal level, suggesting that there are multiple mechanisms through which opioids can evoke antinociceptive effects.

Analgesics, Opioid↗

PubMed1995

Exaggerated cardiovascular and behavioral nociceptive responses to subcutaneous formalin in the spontaneously hypertensive rat.

Spontaneously hypertensive rats (SHRs) are typically less responsive to phasic noxious stimuli than are their normotensive controls. Here, we used the formalin test to compare behavioral and cardiovascular responses to persistent noxious stimuli. Hindpaw formalin injection produced exaggerated flinching, arterial pressure and heart rate responses in SHRs, suggesting that abnormalities in blood pressure control systems increase nociceptive responses to persistent noxious stimuli.

Animals↗

PubMed1995

Relationship between analgesia and extracellular morphine in brain and spinal cord in awake rats.

Extracellular concentrations of morphine from the dorsal spinal cord, the periaqueductal gray (PAG) including the dorsal raphé, and the lateral hypothalamus were measured by microdialysis in awake rats after intraperitoneal (i.p.) administration of 2.5, 5.0 and 10 mg/kg morphine. Morphine concentrations in all areas showed similar time courses: morphine was detected in the first dialysate sample (13-15 min) and maximal concentrations were reached at 45 min after injection. When in vivo recoveries of morphine from the spinal cord and brain areas were taken into account, no significant differences between morphine concentrations in the various areas were found. The relationship between extracellular morphine concentrations and morphine-induced analgesic behavior was investigated by simultaneously measuring morphine in the dialysate and its analgesic effect in the paw-withdrawal and tail-flick tests. In all areas sampled, the extracellular concentrations of morphine at different times after i.p. injection, significantly correlated with the magnitude of behavioral analgesia assessed by either test. The highest correlation was obtained between extracellular concentrations of morphine in the spinal cord and PAG and behavioral analgesia assessed in the paw-withdrawal test. Our data indicate that, after systemic injection, morphine is evenly distributed throughout the spinal cord and brain including potential anatomical sites of morphine's analgesic action. We estimate that the minimal extracellular morphine concentration in spinal cord that is required to produced a significant increase in nociceptive threshold is approximately 100 pg/25 microl, which corresponds to a tissue concentration of about 100 mg/g of morphine.

Analgesia↗

PubMed1995

Receptor endocytosis and dendrite reshaping in spinal neurons after somatosensory stimulation.

In vivo somatosensory stimuli evoked the release of substance P from primary afferent neurons that terminate in the spinal cord and stimulated endocytosis of substance P receptors in rat spinal cord neurons. The distal dendrites that showed substance P receptor internalization underwent morphological reorganization, changing from a tubular structure to one characterized by swollen varicosities connected by thin segments. This internalization and dendritic structural reorganization provided a specific image of neurons activated by substance P. Thus receptor internalization can drive reversible structural changes in central nervous system neurons in vivo. Both of these processes may be involved in neuronal plasticity.

Animals↗

PubMed1995

Morphological characterization of substance P receptor-immunoreactive neurons in the rat spinal cord and trigeminal nucleus caudalis.

Although there is considerable evidence that primary afferent-derived substance P contributes to the transmission of nociceptive messages at the spinal cord level, the population of neurons that expresses the substance P receptor, and thus are likely to respond to substance P, has not been completely characterized. To address this question, we used an antibody directed against the C-terminal portion of the rat substance P receptor to examine the cellular distribution of the receptor in spinal cord neurons. In a previous study, we reported that the substance P receptor decorates almost the entire dendritic and somatic surface of a subpopulation of spinal cord neurons. In the present study we have taken advantage of this labeling pattern to identify morphologically distinct subpopulations of substance P receptor-immunoreactive neurons throughout the rostral-caudal extent of the spinal cord. We observed a dense population of fusiform substance P receptor-immunoreactive neurons in lamina I at all segmental levels. Despite having the highest concentration of substance P terminals, the substantia gelatinosa (lamina II) contained almost no substance P receptor-immunoreactive neurons. Several distinct populations of substance P receptor-immunoreactive neurons were located in laminae III-V; many of these had a large, dorsally directed dendritic arbor that traversed the substantia gelatinosa to reach the marginal layer. Extensive labeling was also found in neurons of the intermediolateral cell column. In the ventral horn, we found that labeling was associated with clusters of motoneurons, notably those in Onuf's nucleus in the sacral spinal cord. Finally, we found no evidence that primary afferent fibers express the substance P receptor. These results indicate that relatively few, but morphologically distinct, subclasses of spinal cord neurons express the substance P receptor. The majority, but not all, of these neurons are located in regions that contain neurons that respond to noxious stimulation.

Afferent Pathways↗

PubMed1995

Rapid endocytosis of a G protein-coupled receptor: substance P evoked internalization of its receptor in the rat striatum in vivo.

Studies on cultured cells have shown that agonists induce several types of G protein-coupled receptors to undergo internalization. We have investigated this phenomenon in rat striatum, using substance P (SP)-induced internalization of the SP receptor (SPR) as our model system. Within 1 min of a unilateral striatal injection of SP in the anesthetized rat, nearly 60% of the SPR-immunoreactive neurons within the injection zone display massive internalization of the SPR--i.e., 20-200 SPR+ endosomes per cell body. Within the dendrites the SPR undergoes a striking translocation from the plasma membrane to endosomes, and these dendrites also undergo a morphological reorganization, changing from a structure of rather uniform diameter to one characterized by large, swollen varicosities connected by thin fibers. In both cell bodies and dendrites the number of SPR+ endosomes returns to baseline within 60 min of SP injection. The number of neurons displaying substantial endosomal SPR internalization is dependent on the concentration of injected SP, and the SP-induced SPR internalization is inhibited by the nonpeptide neurokinin 1 receptor antagonist RP-67,580. These data demonstrate that in the central nervous system in vivo, SP induces a rapid and widespread SPR internalization in the cell bodies and dendrites and a structural reorganization of the dendrites. These results suggest that many of the observations that have been made on the internalization and recycling of G protein-coupled receptors in in vitro transfected cell systems are applicable to similar events that occur in the mammalian central nervous system in vivo.

Analysis of Variance↗

PubMed1995

Neurochemical characterization of extracellular serotonin in the rostral ventromedial medulla and its modulation by noxious stimuli.

Using in vivo microdialysis, we have characterized serotonin release from the rostral ventromedial medulla of the freely moving rat. Addition of tetrodotoxin or removal of calcium from the dialysis solution diminished the dialysate serotonin content, suggesting that spontaneous, calcium channel- and sodium channel-dependent neuronal release mechanisms contribute to the extracellular serotonin collected from the rostral ventromedial medulla. Extracellular serotonin concentration was increased by depolarization (with 100 mM potassium) and by the local administration of either a reuptake blocker (citalopram), a monoamine oxidase inhibitor (pargyline), or amphetamine. Serotonin release was reduced significantly by 8-hydroxy-2-(di-n-propylamino)tetralin, suggesting that serotonin1A receptors may regulate release from rostral ventromedial medulla neurons. Because the basal serotonin concentration in the rostral ventromedial medulla was approximately twofold higher than that collected from the rostral ventrolateral medulla, a region that contains serotonin terminals but many fewer cell bodies, the possibility of release of serotonin from rostral ventromedial medulla neurons is discussed. Finally, intraplantar formalin injection significantly increased serotonin release, suggesting that this neurotransmitter contributes to nociceptive modulation by regulating the outflow of the rostral ventromedial medulla neurons.

8-Hydroxy-2-(di-n-propylamino)tetralin↗

PubMed1995

Co-injection of wheat germ agglutinin-HRP and choleragenoid-HRP into the sciatic nerve of the rat blocks transganglionic transport.

We report on the surprising loss of transganglionic and retrograde labeling in the spinal cord of the rat after co-injection of the tracers wheat germ agglutinin-HRP (WGA-HRP) and choleragenoid toxin-HRP (CTB-HRP) into the sciatic nerve. Injection of WGA-HRP alone produced a pattern of transganglionic label consistent with transport by small-diameter primary afferent fibers. Small cell bodies were labeled in the ipsilateral dorsal root ganglion (DRG) and there was dense terminal labeling in the superficial dorsal horn of the lumbar spinal cord. Injection of CTB-HRP alone produced a pattern of transganglionic labeling consistent with transport by large-diameter primary afferent fibers. Large cell bodies were labeled in the DRG and there was dense terminal labeling in the nucleus proprius (Laminae III-V) in the spinal cord. CTB-HRP also produced extensive retrograde labeling of ventral horn motor neurons. When the two tracers were co-injected, we found few labeled cells in the ipsilateral DRG and there was almost complete loss of transganglionic terminal labeling in the lumbar spinal cord. Retrograde labeling of motor neurons was also significantly reduced. Even when one of the tracers (e.g., WGA-HRP) was injected 24 hr after and up to 10 mm proximal to the site of the first tracer (e.g., CTB-HRP), an inhibitory interaction was detected. The labeling pattern was always characteristic of the first tracer injected.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1995

Persistent cardiovascular and behavioral nociceptive responses to subcutaneous formalin require peripheral nerve input.

Hindpaw injection of formalin produces acute (Phase 1) and persistent (Phase 2) nociceptive behaviors. This model has provided critical evidence supporting a contribution of central sensitization (hyperexcitability of spinal neurons) to the expression of persistent pain. Here, we evaluated the contribution of ongoing peripheral nerve inputs to Phase 2 pain responses. In addition to pain behavior (flinching), we measured formalin-evoked increases in arterial pressure and heart rate; these cardiovascular responses were also biphasic in nature. The arterial pressure response correlated highly with behavior, and was dependent on formalin concentration (0.625-5.0%), indicating that it was largely driven by noxious input. Lightly anesthetized (0.7% halothane) rats exhibited robust increases in blood pressure in the absence of pain behavior, indicating cardiovascular responses did not reflect somatomotor-cardiovascular coupling. Animals obtained from Charles River exhibited slightly larger Phase 2 flinching and heart rate responses compared to those obtained from Bantin and Kingman, suggesting cardiovascular-related pain responses can vary with the source of animal. We next evaluated the contribution of ongoing peripheral nerve activity to the expression of the Phase 2 pressor, tachycardia, and flinch responses. After Phase 1 subsided, but before Phase 2 began, we locally anesthetized the ipsilateral or contralateral (control) hindpaw with a hydrophilic lidocaine derivative, QX-314 (2%). Intraplantar QX-314 blocked Phase 2 pressor, tachycardia and behavioral responses only when injected into the paw that received formalin (2.5% or 10.0%). We conclude that persistent ongoing activity in peripheral afferent fibers during Phase 2 is required for the persistent pain evoked by formalin.

Anesthesia↗

PubMed1994

Evidence for presynaptic N-methyl-D-aspartate autoreceptors in the spinal cord dorsal horn.

The N-methyl-D-aspartate (NMDA) receptor has been implicated in a variety of systems that undergo plastic changes in the central nervous system. We used electron microscopic immunocytochemistry with an antibody directed against an alternatively spliced exon near the C terminus of NMDAR1, the essential functional subunit of the NMDA receptor, to study the distribution of the NMDA receptor in the spinal cord and CA1 region of the hippocampus, two regions where NMDA-mediated long-term plasticity has been demonstrated. In CA1, we found that the NMDA receptor is exclusively expressed on postsynaptic structures. By contrast, in the spinal cord we found that in about one-third of labeled synapses, the receptor is located in the presynaptic terminal, immediately adjacent to the vesicle release site at the active zone. Using combined postembedding immunocytochemistry, we also showed that > 70% of the NMDA receptor immunoreactive terminals are glutamate positive, which suggests that the presynaptic NMDA receptor is an autoreceptor. Nerve ligation studies demonstrated that the receptor is transported in dorsal roots and sciatic nerve to the spinal cord and periphery, respectively. These data indicate that an NMDA autoreceptor is located in terminals of primary afferent fibers, where it could facilitate the transmission of inputs to the spinal cord by increasing the release of neurotransmitter from the primary afferent terminal.

Amino Acid Sequence↗

PubMed1994

Synaptic relationship between substance P and the substance P receptor: light and electron microscopic characterization of the mismatch between neuropeptides and their receptors.

Light microscopic studies have demonstrated significant mismatches in the location of neuropeptides and their respective binding sites in the central nervous system. In the present study we used an antiserum raised against a synthetic peptide corresponding to the carboxyl-terminal tail of the substance P (SP) receptor (SPR) to further explore the relationship between a neuropeptide and its receptor. Light microscopy revealed an excellent correlation between the patterns of SPR immunoreactivity and of 125I-labeled SPR-binding sites in the central nervous system. The SPR appeared to be exclusively expressed by neurons; in fact, the SPR decorates the somatic and dendritic surface of neurons, producing Golgi-like images. Electron microscopic analysis in cortex, striatum, and spinal cord revealed that approximately 70% of the surface membrane of immunoreactive neurons is SPR laden. Simultaneous electron microscopic labeling of SP and SPR demonstrated significant mismatch at the synaptic level. Although some SP terminals contacted SPR-immunoreactive membrane, no more than 15% of the SPR-laden membrane apposed synaptic terminals. These results suggest that in contrast to more "classical" central and peripheral nervous system synapses, wherein the receptor immediately apposes the site of neurotransmitter storage and release, much of the surface of SPR-expressing neurons can be targeted by SP that diffuses a considerable distance from its site of release.

Animals↗

PubMed1994

Diffuse noxious inhibitory controls reduce the expression of noxious stimulus-evoked Fos-like immunoreactivity in the superficial and deep laminae of the rat spinal cord.

Behavioral and electrophysiological studies have shown that a noxious stimulus applied to one part of the body can reduce the response to a subsequent noxious stimulus elsewhere on the body. This phenomenon is referred to as diffuse noxious inhibitory controls (DNIC). In the present study we used immunocytochemical labeling for the Fos protein product of the c-fos proto-oncogene to determine the location of lumbar spinal nociresponsive neurons that are inhibited by a spatially remote noxious stimulus. Repetitive hindpaw pinch evoked pronounced Fos-like immunoreactivity in the superficial and deep laminae of the lumbar spinal cord. Placing the tail in 50 degrees C water before each hindpaw pinch significantly reduced Fos-like immunoreactivity in these regions. These data demonstrate that nociresponsive neurons in both the superficial and deep laminae of the spinal cord are sensitive to inhibition by a spatially remote noxious conditioning stimulus.

Animals↗