Plasticity of &mgr; and delta Opioid Receptors in the Superficial Dorsal Horn of the Adult Rat Spinal Cord Following Dorsal Rhizotomies: A Quantitative Autoradiographic Study.

The aim was to study the regulation of &mgr; and delta opioid binding sites in the superficial layers (laminae I - II) of the dorsal horn of the adult rat spinal cord 1, 2, 4 and 12 weeks after unilateral dorsal rhizotomies of various extents. Using quantitative autoradiography and highly selective tritiated opioid ligands, we have shown that the decrease in [3H]Tyr*-d-Ala-Gly-NMe-Phe-Gly-ol ([3H]DAMGO) (&mgr; sites) and [3H]Tyr*-d-Thr-Gly-Phe-Leu-Thr ([3H]DTLET) (delta sites) binding in the side ipsilateral to the lesion as compared to the intact side is related to the number of dorsal roots cut. In the segment central to the lesion, 1 week after the lesion, ipsilateral/contralateral side binding ratios for [3H]DAMGO were 0.70, 0.49, 0.36 and 0.25 when 1, 3, 5 and 7 roots respectively were sectioned. For [3H]DTLET, the ratios were 0.71, 0.54, 0.42 and 0.39. The time-related analysis of binding ratios showed that, in partially deafferented spinal segments after long-term deafferentation (12 weeks postlesion) there were greater numbers of &mgr; and delta binding sites than in cases of short-term deafferentation (1 - 2 weeks). By contrast, in spinal segments considered as completely deafferented, there was no difference in the remaining &mgr; and delta binding sites at 12 weeks as compared to 1 week postlesion. Consequently, it is deduced that the partial recovery of &mgr; and delta binding observed after long-term partial deafferentation could be associated with neuronal plasticity (probably collateral sprouting) of fine diameter primary afferent fibres arising from intact dorsal roots.

The Distribution of &mgr; and delta Opioid Binding Sites Belonging to a Single Cervical Dorsal Root in the Superficial Dorsal Horn of the Rat Spinal Cord: A Quantitative Autoradiographic Study.

Numerous studies have demonstrated a dense concentration of opioid receptors in the superficial layers (laminae I - II) of the spinal cord. These receptors are located both pre- and postsynaptically at this level. The purpose of this study was to assess the distribution of opioid receptors belonging to a single (C7) dorsal root. Thus, quantitative autoradiography of &mgr; ([3H]Tyr-d-Ala-Gly-NMe-Phe-Gly-ol; [3H]DAMGO) and delta ([3H]Tyr-d-Thr-Gly-Phe-Leu-Thr; [3H]DTLET) opioid binding sites was performed for several experimental groups: control rats with intact dorsal roots and lesioned rats with a unilateral dorsal rhizotomy of (a) the C7 root alone, (b) the three successive roots rostral and caudal to the spared C7 root, and (c) the seven roots C4 - Th2. By subtracting results of the 'C7 cut' group from the 'intact' group or by subtracting results of the C4 - Th2 cut group from the C7 spaced group, it was possible to measure the distribution of &mgr; and delta opioid binding sites belonging to the C7 root. The combination of these two methods of calculation allowed us to demonstrate a significant distribution over two segments rostral and one segment caudal to the segment of entry. For [3H]DAMGO, the distribution was 10% (P < 0.05) in the C5, 27%, (P < 0.001) in the C6, 38% (P < 0.001) in the C7 and 14% (P < 0.05) in the C8 segment. For [3H]DTLET, the distribution was 11% (P=0.05) in the C5, 27%, (P < 0.01) in the C6, 37% (P < 0.001) in the C7 and 18% (P < 0.05) in the C8 segment. It is also noted that rostral distributions spread more densely and further than the caudal ones.

Regulation of opioid binding sites in the superficial dorsal horn of the rat spinal cord following loose ligation of the sciatic nerve: comparison with sciatic nerve section and lumbar dorsal rhizotomy.

The aim of the present study was to quantify time-related modifications in mu and delta opioid binding sites in the superficial layers (laminae I and II) of the L4 lumbar segment in a rat model of mononeuropathy induced by loose ligation of the sciatic nerve. We have shown a 28% (P < 0.01) and 24% (P < 0.01) decrease in ipsi/contralateral side binding ratios for tritiated (Tyr*-D-Ala-Gly-NMe-Phe-Gly-ol) ([3H]DAMGO) and tritiated (Tyr*-D-Thr-Gly-Phe-Leu-Thr) ([3H]DTLET) respectively, at two weeks postlesion which correspond to the delay of maximal hyperalgesia and of maximal alteration of fine diameter primary afferent fibers. In contrast, no change in [3H]U.69593 specific binding could be detected at this postlesion delay. For longer survival delays (four, eight and 15 weeks postlesion), mu and delta binding ratios return towards control values (approximately equal to 1), probably reflecting the occurrence of a long-term neuroplasticity (i.e. a new equilibrium in the metabolism of primary neurons, or collateral sprouting from intact primary afferents) following loose nerve ligation. In addition, a comparison of the results obtained in this model with those measured after sciatic nerve section and lumbar dorsal rhizotomy was performed in order to compare the degree of loss in opioid binding sites in these three types of lesion. The section of the sciatic nerve induced at eight days postlesion an 18% (P < 0.01) and 28% (P < 0.01) decrease in binding ratio for [3H]DAMGO and [3H]DTLET, respectively. At two weeks postlesion the loss was 24% (P < 0.01) for the two ligands, and at longer delays (four and 12 weeks), a progressive recovery in binding ratio was observed. Thus, it appears that both sciatic nerve lesions we have studied result in mu and delta binding modifications which have similar intensity and similar time course from two to 12-15 weeks postlesion. In contrast, the unilateral rhizotomy of nine consecutive dorsal roots (T13-S2), which is known to induce a massive degeneration of fine diameter primary afferent fibers, is followed by a dramatic decrease in binding ratios for [3H]DAMGO (53%, P < 0.001) and [3H]DTLET (45%, P < 0.001) at two weeks postlesion. These data suggest that the more deprived the dorsal horn is of fine diameter primary afferent fibers, the more dramatic is the opioid binding loss in the ipsilateral side as compared to the contralateral side.(ABSTRACT TRUNCATED AT 400 WORDS)

Autoradiographic distribution of mu, delta and kappa opioid binding sites in the superficial dorsal horn, over the rostrocaudal axis of the rat spinal cord.

The purpose of this study was to use [3H]DAMGO, [3H]DTLET and [3H]EKC in the presence of 100 nM DAMGO and 100 nM DTLET, combined with a quantitative autoradiography to analyse the different proportions and the rostrocaudal distribution of mu, delta and kappa opioid binding sites in the superficial layers (laminae I and II) of the cervical (C6-C8), thoracic (T5-T7), lumbar (L3-L5) and sacral (S2-S3) dorsal horn of the rat. The proportions of the three main types of opioid binding sites, assessed by autoradiography in laminae I and II, were found homogeneous at each segmental level considered: 70.4-74.3%, 18.4-20.3% and 7.3-9.5% for mu, delta, kappa sites, respectively. The physiological relevance of these data is discussed.

Time-related decreases in mu and delta opioid receptors in the superficial dorsal horn of the rat spinal cord following a large unilateral dorsal rhizotomy.

The aim of the present study was to measure the time-related modifications of mu and delta opioid binding sites in the superficial layers of the dorsal horn of the rat spinal cord after a C4-T2 unilateral dorsal rhizotomy. Using specific ligands, namely [3H]DAMGO for mu sites and [3H]DTLET for delta sites, and a quantitative autoradiographic analysis, we have observed: (a) a decrease in binding on the ipsilateral side to the lesion as early as the first day postrhizotomy, the maximal loss being attained at 8 days postlesion, (b) after 8 days postlesion, the residual binding remains stable over the period of analysis (90 days), (c) the loss of mu receptors (71-74%) is significantly more pronounced than the loss of delta receptors (57-62%) and (d) affinities of postsynaptic mu and delta receptors are similar to those of the total receptor population in the superficial layers of the dorsal horn. Comparison of these results with the degeneration of primary afferent fibers reported in literature favors the localization of the majority of mu and delta opioid binding sites on fine diameter primary afferent fibers.

Pre- and postsynaptic distribution of mu, delta and kappa opioid receptors in the superficial layers of the cervical dorsal horn of the rat spinal cord.

Highly selective tritiated ligands and quantitative autoradiography have been used to study mu, delta and kappa binding sites in the dorsal horn of the rat spinal cord. We have measured the proportions of the 3 main types of opioid binding sites in the superficial layers of the cervical dorsal horn (laminae I and II). The proportions of mu, delta and kappa sites were 70 +/- 4%, 23 +/- 2% and 7 +/- 1%, respectively, over the whole C4-T2 extent. Similar percentages were encountered at the level of each individual segment from C4 to T2. Eight days after a unilateral dorsal rhizotomy C4-T2, dramatic decreases were seen on the ipsilateral side to the lesion by comparison to the intact side. In the C7 segment, these decreases were 76 +/- 1%, 61 +/- 1% and 53 +/- 3% for mu, delta and kappa binding sites, respectively. The C7 segment can be considered as completely deafferented, so we attribute the residual values to postsynaptic binding whereas the decrease can be attributed to a loss of the presynaptic sites. These results are discussed with respect to the contribution of pre- and postsynaptic depressive effects of opiates on the transmission of noxious messages at the level of the dorsal horn.

Monoarthritis induces complex changes in mu-, delta- and kappa-opioid binding sites in the superficial dorsal horn of the rat spinal cord.

Recently, an experimental model of monoarthritis was described in the rat induced by injection with Freund's adjuvant of the tibio-tarsal joint of one hindlimb. After injection, the clinical and behavioural signs of arthritis are stable from weeks 2 to 6 post-injection. Our purpose was to study the regulation of mu-, delta- and kappa-opioid binding sites in the superficial layers (laminae I-II) of the lumbar and cervical enlargements of the spinal cord 2, 4 and 6 weeks post-injection. Using quantitative receptor autoradiography and highly selective opioid ligands, we found complex changes consisting of a bilateral increase in specific [3H]DAMGO (Tyr*-D-Ala-Gly-NMe-Phe-Gly-ol) and [3H]pCl-DPDPE (Tyr*-D-Pen-Gly-Cl-Phe-D-Pen) binding at 2 weeks post-injection and a bilateral decrease in [3H]U-69593 ((5 alpha,7 alpha,8 beta)-(-)-N-methyl-N-[7-(1-pyrrolidinyl)-1- oxaspiro(4,5)dec-8-yl]) specific binding at 4 weeks post-injection. These changes were restricted to the lumbar level. At 6 weeks post-injection, there was a bilateral increase in [3H]pCl-DPDPE specific binding at both lumbar and cervical levels. Altogether, these results suggest that, after probable local changes in endogenous opioid peptides, the three types of opioid binding sites are differentially involved in the development of the pathological process. These results contrast with the lack of significant modification in mu-, delta- and kappa-opioid binding classically reported at various levels of the spinal cord in polyarthritic rats at 3 weeks post-injection and verified for 2, 4 and 6 weeks post-injection in the present study.

Up-regulation of [3H]DAMGO and [3H]DTLET opioid binding sites in laminae I-II of the spinal cord in intact and deafferented morphine-tolerant rats.

Using quantitative autoradiography and selective opioid ligands, we have measured the effects of morphine-induced tolerance on [3H]DAMGO and [3H]DTLET binding sites in the superficial spinal dorsal horn (laminae I-II) of intact and deafferented rats (unilateral C4-T2 dorsal rhizotomy). In intact rats, the treatment induced an up-regulation of 26% and 39% for [3H]DAMGO and [3H]DTLET binding sites, respectively, without modification of receptor affinity. In deafferented rats, the treatment similarly induced an up-regulation of 31% and 29% for [3H]DAMGO and [3H]DTLET binding sites, respectively, on the contralateral side, and of 21% and 25%, respectively, on the ipsilateral side. These data demonstrate that the up-regulation induced by morphine tolerance is of similar magnitude for both presynaptic (on primary afferent fibers) and postsynaptic (on spinal neurons) opioid binding sites in the rat dorsal horn.

Application of nitric oxide synthase inhibitor, N omega-nitro-L-arginine methyl ester, on injured nerve attenuates neuropathy-induced thermal hyperalgesia in rats.

This study tested the ability of a nitric oxide synthase inhibitor, N omega-nitro-L-arginine methyl ester (L-NAME), to attenuate behavioral hyperalgesia in a rat model of neuropathic pain [Bennett, G.J. and Xie, Y.-K., Pain, 33 (1988) 87-107]. A mononeuropathy was produced by chronic constriction injury (CCI) of the sciatic nerve. Thermal hyperalgesia was assessed by a reduction of paw withdrawal latency to a noxious heat source. Following CCI, there was significant hyperalgesia in groups of rats treated with D-NAME (n = 7), an inactive isomer of L-NAME, saline (n = 7) or systemic L-NAME (n = 10). In contrast, when L-NAME was applied directly and continuously to the site of CCI (5.0 micrograms/microliter per h for up to 2 weeks) via an osmotic pump implanted at the time of the injury, no significant thermal hyperalgesia was observed (n = 8). The results suggest the involvement of nitric oxide in the development and maintenance of thermal hyperalgesia in a rat model of neuropathy. The blockade of nitric oxide production at the site of injury may provide a new approach for treatment of neuropathic pain.

Effects of acetaminophen on monoaminergic systems in the rat central nervous system.

Although acetaminophen is a well established analgesic, its mechanism of action is still unknown. We investigated whether this drug could affect central monoaminergic neurotransmission in rats. Significant increases in serotonin (5-HT) levels were found in the posterior cortex, hypothalamus, striatum, hippocampus and brain stem, but not spinal cord, 45 min after per os administration of 200-400 mg/kg of acetaminophen. However, this treatment altered neither the levels of 5-hydroxyindoleacetic acid nor the accumulation of 5-hydroxytryptophan after blockade of aromatic L-amino acid decarboxylase. On the other hand, a decrease in both the levels of the dopamine (DA) metabolite, dihydroxyphenylacetic acid, and the accumulation of dihydroxyphenylalanine were noted in the striatum of acetaminophen-treated rats. Finally, acetaminophen administration significantly increased noradrenaline (NA) levels in the posterior cortex. In vitro studies showed that acetaminophen (1 mM) enhanced K+-evoked overflow of [3H]5-HT, but not [3H]DA and [3H]NA, previously taken up in brain slices, and exerted no direct effect on monoamine oxidase A, tyrosine hydroxylase and catechol-O-methyl-transferase activities. These results indicate that acetaminophen affects central monoaminergic neurotransmission, thereby suggesting that monoamines (especially 5-HT) might participate in its analgesic action.

Acetaminophen distribution in the rat central nervous system.

Based on the evidence that the antinociceptive effects of acetaminophen could be mediated centrally, tissue distribution of the drug after systemic administration was determined in rat anterior and posterior cortex, striatum, hippocampus, hypothalamus, brain stem, ventral and dorsal spinal cord. In a first study, rats were treated with acetaminophen at 100, 200 or 400 mg/kg per os (p.o.), and drug levels were determined at 15, 45, 120, 240 min by high performance liquid chromatography (HPLC) coupled with electrochemical detection (ED). In a second study, 45 min after i.v. administration of [3H]acetaminophen (43 microCi/rat; 0.65 microg/kg), radioactivity was counted in the same structures, plus the septum, the anterior raphe area and the cerebellum. Both methods showed a homogeneous distribution of acetaminophen in all structures studied. Using the HPLC-ED method, maximal distribution appeared at 45 min. Tissue concentrations of acetaminophen then decreased rapidly except at the dose of 400 mg/kg where levels were still high 240 min after administration, probably because of the saturation of clearance mechanisms. Tissue levels increased with the dose up to 200 mg/kg and then leveled off up to 400 mg/kg. Using the radioactive method, it was found that the tissue/blood ratio was remarkably constant throughout the CNS, ranking from 0.39 in the dorsal spinal cord to 0.46 in the cerebellum. These results, indicative of a massive impregnation of all brain regions, are consistent with a central antinociceptive action of acetaminophen.

A controlled one-year trial of dextromethorphan in amyotrophic lateral sclerosis.

In a one-year parallel group double-blind placebo-controlled study of dextromethorphan (1.5 mg/kg) in amyotrophic lateral sclerosis, no significant differences were observed in the rate of progression (Norris scale) in comparing 24 patients randomly assigned to the dextromethorphan group and 25 patients randomly assigned to the placebo group. Of the 24 patients in the dextromethorphan group, 17 had limb onset and 7 had bulbar onset disease; average duration of disease was 12.5 +/- 6 months and sex ratio (M:F) was 1.4:1. Of the 25 patients in the placebo group, 18 had limb onset and 7 had bulbar onset disease; average duration of disease was 9.9 +/- 6 months and sex ratio (M:F) was 1.55:1. Dextromethorphan is a weak noncompetitive N-methyl-D-aspartate (NMDA) antagonist and higher doses or other potent NMDA receptor antagonists should be tested.

Very high frequency pulsed Doppler apparatus.

A study of a method for exploration of microvessels is presented. Theoretical considerations taking into account the backscattering of ultrasound wave from a red cell and the attenuation versus frequency (up to 180 MHz) show that a frequency in the range of 80 to 120 MHz is most favorable for small depths of exploration (300 microns). The characteristics of the 113 MHz Doppler system which was built are described. The minimum detectable signal is 3 microV, the lateral resolution around 20 microns and the minimum length of the Doppler sample volume about 80 microns. The Doppler data are displayed in the form of a frequency spectrum. The first encouraging tests carried out using 20 microns rectangular glass capillary tubes and 50 to 150 microns microvessels of the mesentery of rat have demonstrated the resolution and the sensitivity of the system. A discussion illustrates the difficult problem of motion artefacts and the improvements which have to be made. From a technical point of view the authors think that it is possible to work with such a high frequency but there are two main difficulties: the processing of a very low frequency Doppler spectrum and the optimization of the probe (dimensions and shape).