Variations in plasma levels of substance P and effects of a specific substance P antagonist of the NK(1) receptor on preovulatory LH and FSH surges and progesterone secretion in the cycling cynomolgus monkey.

These studies investigated the role of substance P (SP) in the regulation of the hypothalamic-pituitary-ovarian axis in cynomolgus monkeys with normal menstrual cycles. Plasma concentrations of SP were determined in blood samples taken every morning in normally menstruating cynomolgus monkeys throughout the menstrual cycle. There was a significant decreasing linear trend of SP during the follicular phase (cycle day -13 to day 0) and a significant inverse relationship between SP plasma values and plasma 17beta-estradiol (E(2)) values from day -13 to day 0 of the adjusted cycle. Correspondingly, SP area under the curve was significantly greater during the follicular phase than the luteal phase. In a second experiment, plasma concentrations of E(2), luteinizing hormone (LH), follicle-stimulating hormone (FSH) and progesterone and length of cycles were measured after five daily intragastric administrations (10 mg/kg) of an NK(1) receptor (SP receptor) antagonist (RPR 100893; 10 mg/kg) initiated after serum E(2) concentrations had exceeded 125 pg/ml. There was a statistically significant reduction in the amplitude (41% of control) and the area under the curve (37% of control) of the preovulatory LH surge. In addition, there was a reduction of the duration of the LH surge (3 +/- 0.1 days in controls vs. 2.1 +/- 0.2 days in treated animals). The present results show for the first time that there are significant variations in plasma levels of SP, with a strong negative correlation with serum levels of E(2) during the follicular phase of the cynomolgus monkey, and that endogenous SP has a potentiating role in the interactive hypothalamo-anterior-pituitary mechanisms which lead to the preovulatory LH and FSH surges during the menstrual cycle in the monkey.

Stimulatory effect of a specific substance P antagonist (RPR 100893) of the human NK1 receptor on the estradiol-induced LH and FSH surges in the ovariectomized cynomolgus monkey.

Utilizing a human NK1 receptor antagonist (RPR 100893), the present in vivo study was designed to test the hypothesis that endogenous substance P (SP) modulates the action of 17beta-estradiol in inducing luteinizing hormone (LH) and follicle stimulating hormone (FSH) surges in ovariectomized cynomolgus monkey. Plasma concentrations of LH and FSH as well as NK1 receptor antagonist and SP were measured during the development of the negative and positive feedback phases which follow a single administration of estradiol benzoate (50 microg/kg) to long-term ovariectomized monkeys. Daily administration by gastric intubation of 1 mg/kg or 10 mg/kg of the NK1 receptor antagonist (RPR 100893) leads to detectable levels of the antagonist in the blood of treated animals for at least 6 hr after its administration. These levels are in agreement with the experimentally determined IC50 value of the antagonist. The most striking finding of this study is that LH and FSH releases are enhanced during the descending arm of the estradiol benzoate-induced LH and FSH surges, which suggests that endogenous SP normally has an inhibitory role during this time. The enhancement of LH release is approximately 50%, regardless of the amount of the NK1 antagonist used. However, the enhanced FSH release is more important. Furthermore, blockade of the NK1 receptor with the smaller dose of the antagonist leads to a small, but significant, increase in plasma levels of SP, indicating that blockade of SP receptors leads to an increased release of SP. Collectively, these results further substantiate the link which exists between the ovarian steroid 17beta-estradiol and SP systems. Also, for the first time, these results demonstrate an inhibitory involvement of the human NK1 receptor in the 17beta-estradiol-induced pseudo-ovulatory gonadotropin surges in the ovariectomized monkey.

Electrographic studies of the effects of RP 60180, a novel kappa agonist, on the photosensitive baboon Papio papio.

1. The authors describe here the effects of intravenous administration of RP 60180, a novel kappa agonist, on conscious baboons of the species Papio papio, which spontaneously present photically induced epileptic responses. 2. Animals (n = 2) were chronically implanted with epidural recording electrodes and tested whilst seated in a primate chair. The electrocorticogram (ECoG) and electrocardiogram (ECG) were recorded during a control period of at least 30 minutes before the injection of RP 60180 (1 to 4.5 mg/kg i.v.) and immediately afterwards. 3. Qualitatively, up to the dose of 4.5 mg/kg i.v., RP 60180 did not modify ECoG background in term of paroxysmal activity in comparison with that observed during the control period. It did not cause any manifest focal or generalized seizure discharges, nor did it consistently enhance or reduce photically induced myoclonic responses. 4. From the dose of 1 mg/kg i.v., RP 60180 slowed ECG frequency. This effect, which lasted for about 30 minutes post-injection, was most often seen at the higher doses. 5. In another set of experiments, one baboon received the kappa agonist U-50488 (a benzacetamide derivative of spiradoline) at 1 and 3 mg/kg i.v. U-50488, at 3 and to a lesser degree at 1 mg/kg i.v., induced paroxysmal bursts of slow wave ECoG activity and a slowing of the ECG. These effects lasted about 1 hour post-drug administration. During this period, we observed spontaneous vocalization, as if the animal were complaining, as well as shaking.

In vitro and in vivo evidence for a tachykinin NK1 receptor antagonist effect of vapreotide, an analgesic cyclic analog of somatostatin.

Vapreotide, a long-acting somatostatin analog, possesses an analgesic effect. The purpose of this work was to determine a tachykinergic involvement. Vapreotide reduced substance P-induced biting and scratching in mice. This inhibitory effect of substance P action was confirmed by experiments performed on the bronchial apparatus of guinea-pigs known to possess tachykinin NK1 and NK2 receptors. (i) Vapreotide reduced the substance P-induced plasmatic exudation. (ii) It inhibited selectively the tachykinin-dependent second contractile phase induced by electrical field stimulation of isolated bronchi. (iii) It shifted to the right the concentration-effect curve of substance P-induced contraction of isolated main bronchi. The peptide displaced [3H]substance P (IC50 = 3.3 +/- 1.8 x 10(-7) M) from guinea-pig bronchial tachykinin NK1 sites. The displacement of [125I]neurokinin A, a specific tachykinin NK2 receptor ligand, needed higher concentrations (IC50 = 4.5 +/- 0.6 x 10(-6) M). It is concluded that vapreotide possesses an antagonist activity on guinea-pig tachykinin NK1 receptors; the involvement in its analgesic action is discussed.

Molecular determinants of the species selectivity of neurokinin type 1 receptor antagonists.

Most nonpeptide neurokinin (NK)1 antagonists display a marked difference in affinity for rat versus human NK1 receptors. The molecular basis for the species selectivity of RP67580 and CP96,345 has been previously addressed [J. Biol. Chem. 267:25668-25671 (1992); J. Biol. Chem. 268:2319-2323 (1993)]. We are extending these previous results to additional NK1 antagonists, which are members of different chemical families. Included is a new perhydroisoindolol, RPR100893, which unlike its parent compound (RP67580) is human receptor selective. Chimeric rat/human NK1 receptors, as well as rat and human mutant NK1 receptors, were constructed and expressed in COS-1 cells, and affinities for substance P and the various antagonists were determined in binding studies. With human receptor-selective antagonists, the rat R290(S-->I) mutation was the most effective in increasing antagonist affinity (from 7- to 23-fold). Combination with the R116(L-->V) mutation led to an additional increase in affinity for trans-4-hydroxy-1-(1H-indol-3-ylcarbonyl)-L-prolyl-N- methyl-N-(phenylmethyl)-L-tyrosineamide (a derivative of FK888) and to nearly full human receptor affinity for RPR100893 and (+/-)-CP99,994. Based on the gains in affinities, these results confirm and extend the role of residues 116 and 290 of the NK1 receptor in the species selectivity of these three new human receptor-selective NK1 antagonists. In comparison, the affinity of RP67580, the least selective molecule, was most affected by changes at position 116, and combination with mutations at either position 97 (V-->E) or position 290 led to the human receptor phenotype. For the heterosteroid KAN610857, modifications of the rat receptor at positions 97 and 290, and to a lesser degree position 116, were the most effective in reducing affinity. Two double-mutants [R(97,290) and R(116,290)], although different from those identified for RP67580, also displayed human receptor-like affinity. Therefore, the molecular determinants of the species selectivity appear to be different, in part, between rat and human receptor-selective compounds, even between closely related chemical families.

Differential ability of tachykinin NK-1 and NK-2 agonists to produce scratching and grooming behaviours in mice.

Potent and selective NK-1 and NK-2 agonists as well as compounds with lower selectivity and affinity for NK-1 binding sites were compared in their ability to produce scratching and grooming behaviours when injected intracerebroventricularly in mice. Septide, an agonist with a low affinity for NK-1 binding sites, [Sar9, Met(O2)11]SP and to a lesser extent [Pro9]SP, two potent and selective NK-1 agonists were the most effective drugs in stimulating these behaviours. Only high doses of [Apa9,10]SP and [Lys5, Tyr7, Pro8]NKA(4-10), two agonists with low affinity for NK-1 binding sites, produced scratching and grooming responses. Similarly, only high doses of [Lys5, MeLeu9, NLe10]NKA(4-10), a potent NK-2 agonist, produced grooming behaviour. When coinjected with the endopeptidase enzyme inhibitor phosphoramidon, the effects of [Apa9,10]SP, [Lys5, Tyr7, Pro8]NKA(4-10) and [Pro9]SP were markedly enhanced. Analyses of the potency of the different agents to displace 3H-SP binding in mouse subcortical structures revealed that the affinities of the agonists for NK-1 receptors are similar to those previously reported in rat brain. The efficacy of the agonists at producing behavioural responses was not equivalent to their potency to bind to central NK-1 receptors. These findings therefore suggest that a stimulation of NK-1 but also non classical NK-1 receptors are involved in the induction of scratching and grooming behaviours.

Characterization of NK1 and NK2 tachykinin receptors in guinea-pig and rat bronchopulmonary and vascular systems.

1. NK1 and NK2 tachykinin receptors were characterized in guinea-pig and rat bronchopulmonary systems and in the vasculature of the rat by use of radioligand binding and/or functional studies. 2. The radioligands for NK1 and NK2 receptors ([3H]-SP and [3H]-pNKA, respectively) did not label tachykinin receptors in homogenates of rat lungs or bronchi. In contrast, in the guinea-pig, [3H]-SP bound with high affinity to these tissues (KD = 0.23 +/- 0.08 nM and 0.34 +/- 0.05 nM, for lungs and bronchi, respectively). The total number of binding sites was 4.6 fold greater in bronchus (Bmax = 135 +/- 27 fmol mg-1 protein) than in lung homogenates (Bmax = 29.3 +/- 0.1 fmol mg-1 protein). Furthermore, this binding was markedly displaced by CP-96,345 (pKi = 9.5 +/- 0.1) and RP 67580 (pKi = 7.6 +/- 0.1), antagonists of NK1 receptors, slightly displaced by SR 48968 (pKi = 6.6 +/- 0.1), but not affected by actinomycin D or L-659,877, antagonists of NK2 receptors. Specific binding of [3H]-pNKA, detected in guinea-pig bronchi (KD = 5.2 +/- 0.1 nM, and Bmax = 203 +/- 19 fmol mg-1 protein) but not in lungs, was similarly (40 to 53%) displaced by RP 67580 (1 microM), CP-96,345 (10 and 100 nM) or SR 48968 (10 and 100 nM). The displacement approximately doubled (87 to 91%) when SR 48968 (10 nM) was combined with either RP 67580 (1 microM) or CP-96,345 (10 nM), but not when RP 67580 was combined with CP-96,345. 3. In urethane-anaesthetized guinea-pigs, i.v. injections of the NK1 receptor agonists SP, [Pro9]-SP, [Sar9,Met(O2)11]-SP and septide, as well as the NK2 receptor agonists NKA and [Lys5,MeLeu9,NLeu10]-NKA(4-10) (0.1-10 micrograms kg-1, i.v.), dose-dependently increased lung inflation pressure. The most potent of these peptides were septide and [Lys5, MeLeu9,NLeu10]-NKA(4-10) (EC50 = 0.38 +/- 0.07 and 0.07 +/- 0.02 microgram kg-1, respectively). Interestingly, septide was 130 fold less potent than SP in displacing [3H]-SP from its binding sites in the guinea-pig lung, whereas it was 14 fold more potent than SP as a bronchoconstrictor. RP 67580 (0.3-5 mg kg-1, i.v.) and CP-96,345 (0.01-3 mg kg-1, i.v.) dose-dependently reduced the bronchoconstriction produced by the NK1 receptor agonists. Conversely, the NK2 receptor antagonists actinomycin D (1-10 mg kg-1, i.v.) and SR 48968 (0.03-0.3 mg kg-1, i.v.) inhibited specifically the responses induced by NK2 receptor agonists.4. In pentobarbitone-anaesthetized rats, the NK1 and NK2 receptor agonists (0.01-4 microg kg-1, i.v.)produced dose-dependent hypotensive responses. The order of potency was SP = [Sar9, Met(0211]-SP = [Pro9]-SP > septide = NKA >[Lys5, MeLeu9, NLeu 10-NKA.(4-10). RP 67580 (0.13-0.5 mg kg-1,i.v.) and CP-96,345 (0.5-2 mg kg-1, i.v.) antagonized in a dose-related manner (20 to 64%) the vascular effects of both NK, and NK2 receptor agonists, whereas actinomycin D (3 mg kg-1, i.v.) and SR 48968(2 mg kg-1, i.v.) did not. RP 67580 was approximately 4 times more potent than CP-96,345.5. These studies indicate that NK1 and NK2 receptors are both present in the guinea-pig bronchopulmonary system whereas only NK1 receptors are detectable in the rat vasculature under our experimental conditions. Furthermore, NK1 receptors in the guinea-pig bronchopulmonary system are pharmacologically distinct from those present in the rat vascular system, since both agonist potencies and antagonist affinities differ between the two species.

Septide: an agonist for the NK1 receptor acting at a site distinct from substance P.

The hexapeptide [pGlu6,Pro9]substance P (SP)6-11, septide, has been shown to be an agonist as potent as SP in eliciting smooth muscle contraction in several in vitro preparations, while being a poor competitor of labeled SP binding. These results, as well as other pharmacological data, have suggested the existence of either a specific septide receptor or a septide site on the neurokinin (NK)1 receptor distinct from that for SP. We have used rat recombinant NK1 receptor expressed in COS-1 cells to address this issue. Both functional (agonist-induced inositol phosphate accumulation) and radioligand binding studies were conducted on transiently transfected cells. SP and septide elicited similar maximal increases (4-6-fold) in inositol phosphate levels in transfected cells, with EC50 values of 0.05 +/- 0.02 nM for SP and 5 +/- 2 nM for septide. No additivity of the maximal responses to the two agonists was observed, and neither agonist evoked any response in sham-transfected cells. RP 67580 was a competitive inhibitor of SP responses, with an inhibition constant (KB) of 13 +/- 2 nM, in agreement with displacement studies of [3H]SP binding to membranes and intact transfected cells (Ki values of 10 +/- 4 nM, and 1.16 +/- 0.06 nM, respectively). In comparison, septide responses were inhibited by RP 67580 in an uncompetitive fashion, with an apparent KB* value of 1.5 +/- 0.2 nM. Septide was a weak competitor of [3H]SP binding, with dissociation constants (Ki) of 2.9 +/- 0.6 microM and 3.7 +/- 0.9 microM for membranes and intact transfected cells, respectively. Similarly, septide at concentrations up to 10 microM did not affect [3H]RP 67580 binding. In conclusion, we have demonstrated that septide is a potent functional agonist of the NK1 receptor but it seems to act at a specific subsite different from that for SP. Although not ruling out the existence of selective septide receptors in some tissues, these results could explain some of the discrepancies with regard to the pharmacological properties of septide. Furthermore, a specific septide site on the NK1 receptor could represent an original pharmacological target.

NK-1 tachykinin receptor in rat and guinea pig brains: pharmacological and autoradiographical evidence for a species difference.

The affinities of a large variety of peptide or nonpeptide tachykinin analogues were determined on membranes from rat and guinea pig brains using the selective NK-1 radioligand 3H-[Pro9]SP. Nonpeptide antagonists clearly revealed a species difference; (+/-)CP-96,345 was more potent in the guinea pig, while RP 67580 was found to be a better competitor of 3H-[Pro9]SP binding to rat brain membranes. This was confirmed on brain slices by autoradiography. Numerous brain structures were analyzed by optical densitometry. From these data, a heterogeneity of NK-1 binding sites among different structures can be excluded in both rat and guinea pig brains.

Characterization of a human NK1 tachykinin receptor in the astrocytoma cell line U 373 MG.

The human NK1 tachykinin receptor in the astrocytoma cell line U 373 MG was characterized using selective agonists and antagonists described for this receptor in the rat. Specific [3H]substance P binding sites were present on cell homogenates, whereas [3H]neurokinin A or [3H]-senktide binding sites were absent. The binding was saturable and reversible. The binding of [3H]substance P was inhibited by very low concentrations of [L-Pro9]substance P and [Sar9,Met(O2)11]substance P; septide was approximately 1,000-fold less potent. The most potent peptide antagonist was trans-4-hydroxy-1-(1H-indol-3-ylcarbonyl)-L-prolyl-N-methyl-N-(phe nylmethyl)-L- tyrosineamide. The rank order of potency for the nonpeptide antagonists was (S,S)-CP 96,345 > (+/-)-CP 96,345 > (+/-)-2-chlorobenzylquinuclidinone > (R,R)-CP 96,345 > RP 67580 > RP 68651. In [3H]-inositol-labeled cells, substance P stimulated phosphatidylinositol turnover. A good correlation was found when the abilities of NK1 receptor agonists for stimulating inositol phosphate production and for inhibiting [3H]substance P binding were compared. Similarly, the binding and functional assays were well correlated for the antagonists. As a result of its high sensitivity and selectivity, the U 373 MG cell line thus appears an excellent tool for investigating the pharmacology of the human NK1 receptor.

Interaction of the substance P receptor antagonist RP 67580 with the rat brain NK1 receptor expressed in transfected CHO cells.

In the present study, we describe the effects of RP 67580, a substance P non-peptide antagonist, in binding and second messenger experiments performed using transfected Chinese hamster ovary cells expressing the rat NK1 receptor. The cDNA sequence encoding the rat brain substance P receptor was transfected in Chinese hamster ovary cells, and cellular clones which stably express the corresponding protein were isolated. [3H]Substance P binding was performed in homogenates of these transfected cells and revealed the presence of NK1 receptors in displacement experiments, using peptide analogs of three mammalian tachykinins (substance P, neurokinin A, neurokinin B). Scatchard analysis indicated a KD value of 0.33 +/- 0.13 nM and a Bmax value of 5.83 +/- 1.16 pmol/mg of protein. RP 67580, a selective NK1-receptor antagonist was found to displace the specific binding of [3H]substance P. When [3H]RP 67580 was used as a ligand, it displayed a high affinity (KD value: 1.22 +/- 0.27 nM) in transfected cell homogenates and only competed with NK1 receptor ligands. Substance P stimulated the hydrolysis of phosphoinositide in a time- and concentration-dependent manner and this effect was mimicked by selective agonists of the NK1 receptor ([Pro9]SP and septide). RP 67580 did not induce any accumulation of inositol phosphates, but was found to inhibit the inositol phosphate increase mediated by substance P, without affecting the maximal response. From these results, one may conclude that the receptor expressed by the transfected Chinese hamster ovary cells revealed similar binding characteristics as the NK1 receptor present in the rat brain and also confirmed the high affinity and the antagonist properties of RP 67580.

[RP 67580, a potent and selective substance P non-peptide antagonist]. / RP 67580, un antagoniste, non peptidique, puissant et sélectif de la substance P.

The pharmacological properties of 7,7-Diphenyl-2 [1-imino-2 (2-methoxy-phenyl)-ethyl] perhydroisoindol-4-one (3 aR, 7 aR) or RP67580 are described. This compound, derived from a novel chemical family, is a potent and selective substance P (SP) antagonist, in vitro and in vivo. In vitro, it inhibited in a competitive manner (IC50 = 10 nM) 3H-SP binding in rat brain (NK1 receptors). It did not interact with the two other tachykinin receptor sites (NK2 and NK3) nor the other receptor sites tested. Moreover, RP67580 competitively antagonized the contractile activity of SP on guinea-pig ileum (pA2 = 7.16); in contrast, it was inactive in rabbit pulmonary artery and in rat portal vein tissues which contain NK2 and NK3 receptors, respectively. In vivo, in the rat, RP67580 inhibited the plasmatic extravasation induced by administration of SP (ED50 = 0.04 mg/kg i.v.) as well as that induced by antidromic stimulation of a peripheral sensory nerve (ED50 = 0.15 mg/kg i.v.). In mice and rats, RP67580, like morphine, potently blocked the nociceptive effects of phenylbenzoquinone and formalin; its antinociceptive effect does not involve opiate receptors since it was not reversed by naloxone. These results indicate that RP67580 is a particularly valuable tool for investigating the physiological and pathological role of SP.

Pharmacological properties of a potent and selective nonpeptide substance P antagonist.

We describe here the pharmacological properties of RP 67580 [(3aR,7aR)-7,7-diphenyl-2-[1-imino-2-(2-methoxyphenyl)ethyl] perhydroisoindol-4-one], a nonpeptide antagonist of substance P (SP). In vitro, the compound was found to inhibit in a competitive manner (Ki = 4.16 +/- 0.59 nM) [3H]SP binding to neurokinin receptors type 1 (NK1 receptors) in rat brain membranes. Contractions induced by SP and septide (a selective NK1 agonist) in guinea pig ileum were competitively inhibited by RP 67580 (pA2 = 7.16 and 7.59, respectively). Moreover, RP 67580 displayed the profile of a specific antagonist of NK1 receptors: it was not active on NK2 and NK3 receptors as seen in binding assays and in isolated preparations of rabbit pulmonary artery and rat portal vein. In the rat, low intravenous doses of RP 67580 totally inhibited the plasma extravasation induced by SP in the urinary bladder (ED50 = 0.04 mg/kg i.v.) and by antidromic electrical stimulation of the saphenous nerve in the hind paw skin (ED50 = 0.15 mg/kg i.v.). This compound was also active in two classical analgesic tests in mice: phenylbenzoquinone-induced writhing (ED50 = 0.07 mg/kg s.c.) and the formalin test (ED50 = 3.7 mg/kg s.c.). Its potency was of the same order as that of morphine. Thus we conclude that RP 67580, a SP antagonist, belongs to a class of drugs that may be useful in the management of various clinical pathologies where pain and neurogenic inflammation are involved.

Species differences between [3H] substance P binding in rat and guinea-pig shown by the use of peptide agonists and antagonists.

The affinities of various substance P agonists and antagonists for NK1 receptors in rat and guinea-pig tissues were compared. Striking species differences were observed. Both septide and [D-Pro4,D-Trp7,9]SP-(4-11) possessed much higher affinity for sites in the guinea-pig (brain and ileum) than for sites in the rat brain. These results could be explained by differences in the structure of the NK1 receptor according to the species, although the existence of various subtypes of NK1 binding sites in the two species cannot be excluded.

Localization and characterization of substance P binding sites in rat and rabbit eyes.

Specific and high-affinity binding sites for Substance P (SP) were found in eyes from albino rabbits and rats using an in vitro autoradiographic method with 125I-Bolton Hunter SP (BHSP). autoradiograms were generated by apposing 10-20 microns-thick cryostat eye sections to 3H-Hyperfilm or liquid emulsion and quantified by means of image-analysis procedures. Kinetic studies showed that equilibrium was reached after a 75-min incubation at room temperature. In rat retina, specific binding corresponding to approximately 90% of total binding, was reversible, of high affinity (dissociation constant [Kd], 0.13 +/- 0.02 nM). Half-time for dissociation of 125I-BHSP was about 15 min. Unlabeled SP and the two neurokinins (NK) A and B competed in a concentration-dependent manner for retinal sites labeled by 125I-BHSP with the following order of potencies: SP greater than NKA greater than NKB, in agreement with a pharmacologic profile of a SP receptor site. In both species, specific binding was found in the iris sphincter muscle, choroid, and retina. In rats, detectable amounts of SP-binding sites were also expressed in the corneal epithelium and iridial stroma. Quantitative analysis of the autoradiograms revealed that the highest densities of 125I-BHSP binding sites were localized in the iris sphincter muscle in rabbits and the inner retina in rats.

A reinvestigation of the analgesic effects induced by stimulation of the periaqueductal gray matter in the rat. II. Differential characteristics of the analgesia induced by ventral and dorsal PAG stimulation.

This study consists of a detailed analysis of the analgesic effects induced by stimulation of the various parts of the periaqueductal gray matter (PAG) in the freely moving rat. In order to characterize the analgesia, two criteria are considered: (1) the evaluation of the degree of analgesia and behavioral side effects evoked during central stimulation; and (2) the presence of post-effects. Central stimulation (50 Hz sine waves) was delivered via bipolar concentric electrodes and analgesia was quantified by the change in the vocalization threshold induced by electrical stimulation of the tail. Within the ventral PAG, the vocalization threshold increased gradually with the intensity of the central stimulation, the degree of analgesia generally being powerful. There was no relationship between the strength of the analgesic effects and the motor disturbances also produced by stimulation of this region. Antinociceptive effects generally disappeared when the stimulation ceased. Only when the intensity of the stimulation was strong enough to induce very powerful analgesic effects were post-stimulation analgesic effects noticed. Within the dorsal and dorsolateral PAG as well as in the ventral region just surrounding the aqueduct, analgesia appeared suddenly, was generally less pronounced and was always concomitant with strong aversive reactions. In contrast with the analgesia from the ventral PAG, marked post-effects were observed. These latter characteristics were also obtained from stimulation of regions located outside the PAG (colliculi, intercollicular commissure and tectum adjacent to the dorsolateral PAG) although these zones were not extensively studied. By consideration of various data in the literature, it is concluded from this study, which clearly distinguishes stimulation-produced-analgesia (SPA) from ventral PAG versus dorsal PAG, that analgesia induced from this midbrain area involves at least two different neuronal substrates. Whilst the ventral PAG seems to be more preferentially involved in pain modulation, the authenticity of 'analgesia' triggered by stimulation of aversive regions (which are widely spread over the PAG) is questioned and proposals to explain the simultaneous appearance of analgesic effects and aversion are considered.

A reinvestigation of the analgesic effects induced by stimulation of the periaqueductal gray matter in the rat. I. The production of behavioral side effects together with analgesia.

It has been shown that stimulation-produced-analgesia (SPA) in the cat elicited from the periaqueductal gray matter (PAG) is obtained from sites located in the ventral part, particularly the dorsal raphé nucleus (DRN). These data contrast with the numerous studies performed in the rat in which efficient sites seem widely distributed throughout the PAG. These discrepancies led us to reinvestigate SPA from PAG and adjacent structures in the rat. Central stimulation was delivered through bipolar concentric electrodes (one for each animal). Analgesia was evaluated (before and during central stimulation) by measuring the modification in the vocalization threshold induced by electrical tail shocks or by considering the reaction of the animal to pinch. In contrast with the majority of previous studies, these experiments were performed on the totally freely-moving rat. The most striking result was that, in order to obtain analgesia from all regions of the PAG, it was necessary to apply intensities of central stimulation which also triggered other strong behavioral reactions. With intensities of PAG stimulation which did not induce such side effects, very few effective analgesic sites were found (21/129 sites of which 14/83 were strictly located in the PAG). However, it was possible to define two 'pure analgesic regions', both located in the ventral PAG: one centered on the dorsomedial part of the DRN and the other one situated in the ventrolateral PAG. No modification of nociceptive thresholds was observed when stimulating the dorsal and dorsolateral parts of the PAG as well as structures adjacent to these regions; in some rats, an increase in pain reactivity was even noted. When the intensity of central stimulation (applied to the various parts of the PAG) was increased, some stereotyped 'behavioral responses' occurred depending on the location of the stimulation site: motor effects (gnawing, rotation or tremor) in the ventral PAG and aversive effects (flight, jumping and on occasions, distress vocalizations) in the dorsal, dorsolateral PAG and in the ventral region just surrounding the cerebral aqueduct. Under these conditions, analgesia was obtained from practically the entire PAG, the vocalization threshold being increased dramatically on occasions. It must be emphasized that antinociceptive effects associated with other obvious behavioral manifestations (aversive ones) were also obtained from sites located outside the PAG (colliculi and tectum adjacent to the dorsal and dorsolateral PAG).(ABSTRACT TRUNCATED AT 400 WORDS)

Projections from the periaqueductal gray matter to the B3 cellular area (nucleus raphe magnus and nucleus reticularis paragigantocellularis) as revealed by the retrograde transport of horseradish peroxidase in the rat.

Afferent projections from the periaqueductal gray matter (PAG) to the B3 region (nucleus raphe magnus, NRM; and nucleus reticularis paragigantocellularis, NPG) were examined by means of the horseradish peroxidase (HRP) method revealed by using the tetramethylbenzidine (TMB) procedure. Following iontophoretic injection of HRP into the B3 cellular area, numerous labeled neurons were found between the third oculomotor complex and the rostral part of the tegmental nucleus dorsalis of Gudden. The most densely labeled regions were the lateral parts of the dorsal raphe nucleus (wings of the DRN) and Hamilton's nucleus dorsalis of the PAG. Very few neurons were found within the medial part of the DRN. In contrast, results with control injections performed outside the B3 area gave a different distribution of labeled neurons. The functional significance of these connections, particularly those emanating from the wings of the DRN which represent new information, is briefly discussed with regard to mechanisms operative in the control of pain. Although the major PAG-B3 direct projections could underlie a role for the B3 area in PAG-induced analgesia, the comparison of our anatomical and behavioral results points out some problems. Indeed, there is no strict correlation between the location of stimulation sites which induce analgesia in the freely moving rats and the distribution within the PAG of B3 projections. These observations lead us to question the role of direct PAG-B3 connections in the antinociception induced by PAG stimulation and alternative hypotheses are proposed.