Rat Tail-flick Test Research Articles

Morphine-receptor dissociation constant and the stimulus-effect relation for inhibition of gastrointestinal transit in the rat

The dissociation constant (K A) of morphine for its receptor was determined by the method of partial irreversible blockade of the receptor population using inhibition of gastrointestinal transit of a forced charcoal meal as the pharmacological endpoint. The anti-motility effects of morphine was antagonized when rats were pretreated with buprenorphine (0.3 mg/kg s.c.), a narcotic antagonist analgesic, 30 min before morphine and the extent of gastrointestinal transit was estimated a further 45 min later. With this schedule of drug administration, the agonist action of buprenorphine is minimal and its antagonist action predominates. The value of K A was (1.1±0.2)×10 −5 mol/kg, a value close to that previously reported (2.9×10 −5 mol/kg) by us with these compounds in the rat tail flick test. The value of [A 50] found here was 2.15×10 −6 mol/kg, approximately 1 5 of that of K A. Also, the stimulus-effect relation of the tissue, defined in Stephenson's theory, was plotted and found to be nonlinear. This result, when coupled with the inequality of K A and [A 50], argues against the application of classical drug-receptor theory to this system. The apparent agreement between K A values for anticiception and inhibition of gastrointestinal transit is interesting, but does not necessarily prove equivalent receptors mediating the two different effects.

The involvement of opiate and monoaminergic neuronal systems in the analgesic effects of ketamine

The anesthetic agent, ketamine, has the potential to recruit spinopetal noradrenergic and serotonergic neuronal pathways for its antinociceptive effect. Neurochemically, ketamine has been shown to interact with opiate receptors and thus may increase neuronal activity in the spinopetal monoaminergic (norepinephrine and serotonin) systems in a manner similar to morphine. In addition, ketamine should facilitate the antinociceptive effect of the monoamines at the level of the spinal cord by an action of the drug to prevent the neuronal reuptake of the monoamines. In this study, the analgesic action of both ketamine and morphine, as measured by the tail-flick test in rats, was inhibited by norepinephrine, serotonin and opiate receptor antagonists. Monoaminergic receptor inhibitors were more potent as antagonists of ketamine's analgesia while the opiate receptor antagonist naloxone was more effective against morphine analgesia. The greater sensitivity of the antinociceptive effect of ketamine to monoaminergic antagonist may reflect the importance of the inhibition of norepinephrine and serotonin reuptake in the analgesic action of the drug. Transecting the spinal cord of rats at T4-6 revealed distinct differences between the analgesic mechanisms of ketamine and morphine. For example, the potency of ketamine was increased nearly 9-fold in spinal rats whereas morphine's potency was decreased. This observation suggests that ketamine may activate both analgesic and antanalgesic systems supraspinally, and that its antinociceptive effect in intact animals is a summation of these opposing actions. Partial evidence that supraspinal noradrenergic neurons might be involved in the antanalgesic component of ketamine's action was provided by experiments demonstrating enhanced analgesia in intact animals after depletion of norepinephrine with FLA-63. In spinal animals a significant difference was also observed in the neuronal processes mediating the residual analgesic effects of morphine and ketamine. The analgesic effect of morphine remained primarily sensitive to naloxone but seemed to use a local serotonergic process (sensitive to the serotonergic antagonist methysergide) at higher doses of the opiate. Ketamine's analgesia, on the other hand, was only inhibited by methysergide. In conclusion, although it appears that morphine and ketamine may both activate spinopetal monoaminergic processes through an opiate mechanism, the two drugs differ significantly with regard to some of the components of their antinociceptive actions. The differences may be related to ketamine's ability to alter the metabolism of monoaminergic neurotransmitters involved in pain processing.

Opiate-like analgesic activity in general anaesthetics.

1 The interaction of naloxone with various anaesthetics was studied both in vivo and in vitro.2 Naloxone (10 mg/kg) did not significantly alter the anaesthetic duration of halothane, diethylether, ketamine, pentobarbitone or Althesin.3 Naloxone (10 mg/kg) reduced the analgesic activity of nitrous oxide, ketamine and morphine in the rat tail-flick test. With the exception of pentobarbitone and Althesin, the other anaesthetic agents also induced analgesia but were not antagonized by naloxone.4 Specific [(3)H]-dihydromorphine binding was displaced by the opiates naloxone (IC(50) = 7.6 nm), methionine-enkephalin (Met-enkephalin, IC(50) = 40 nm) and morphine (IC(50) = 54 nm). Similarly, displacement was observed with xylazine (IC(50) = 9 mum), ketamine (IC(50) = 130 mum) and Althesin (IC(50) = 150 mum); other anaesthetics agents tested were inactive in mm concentrations.5 Ketamine (IC(50) = 200 mum) and xylazine (IC(50) = 9.5 mum) were also capable of displacing specific [(3)H]-D-Ala(2)-enkephalin (D-Leu) binding, as were morphine (IC(50) = 95 nm) and Met-enkephalin (IC(50) = 40 nm).6 On the stimulated guinea-pig ileum, Met-enkephalin and morphine inhibited the contractions, the IC(50) values were 30 nm and 50 nm respectively. The anaesthetics ketamine (IC(50) = 10 mum) and Althesin (IC(50) = 8 mum) were active. Xylazine (IC(50) = 12 nm) exhibited considerable potency in inhibiting the contractions on this preparation. Naloxone 0.5 mum produced a 1000 fold shift in the opiate dose-response curve but the anaesthetic responses showed only slight sensitivity to antagonism by naloxone.7 The activity of Althesin was found to be due to the vehicle in which this anaesthetic is solubilised.8 Whilst several anaesthetic agents showed analgesic activity, specific dihydromorphine binding displacement or guinea pig ileum inhibiting activity, these effects showed variable sensitivity to naloxone.

Design for an inexoensive unit for measuring tail flick latencies

A reflex action timer for use in rat tail flick tests is described. This timer utilizes a photoelectric sensor to detect reaction times accurately. It was designed to avoid the sensing groove required in some other such units, can be used as a chronometer/controller in a number of other experimental paradigms, and can be built at low cost.

Enkephalin-like character and analgesia

The opioid activities of enkephalin analogues bearing D- or L-aminopentane-sulfonic/phosphonic acid at position 5 were studied in vitro, in electrically stimulated longitudinal muscle strip of guinea-pig ileum and mouse vas deferens preparations and in vivo in the rat tail-flick test. Using their in vitro effects Met-enkephalin-like, β-endorphin-like, (nor)morphine-like and derivatives of intermediate character could be differentiated. Correlating the in vitro activities with the analgesic activity in vivo it is concluded that the enkephalin-like character in a pentapetide may hinder the expression of analgesic activity, when the compounds are given into the cerebroventicular system.

Tetrapeptide-amide analogues of enkephalin: The role of C-terminus in determining the character of opioid activity

The opioid activities of tetrapeptide-amide analogues of enkephalin /H-Tyr-D-Met-Gly-Phe-NH 2; H-Tyr-D-Nle-Gly-Phe-NH 2/ were studied in isolated, electrically stimulated longitudinal muscle strip of guinea-pig ileum and mouse vas deferens preparations in vitro and in vivo in the rat tail-flick test. Their effects were compared to those of the parent L-Pro 5-NH 2 containing analogues, and to other enkephalin derivatives substituted with D-Met in position 2 and L-amino/imino acids of different character in position 5. It was found that whilst the opioid receptor in mouse vas deferens preferred aliphatic residues of acidic character at the C-terminus of pentapeptides and was highly sensitive to the removal of C-terminal amino acid, the other systems were either much less responsive to these changes, or the effects were opposite to those found in mouse vas deferens.

Analgesic activity of substance P following intracerebral administration in rats

Substance P was found to be a potent, long-lasting analgesic in the tail flick test in rats following intracerebral administration, via chronically indwelling cannulae, into the midbrain periaqueductal gray. Substance P was approximately five times as potent as morphine sulfate on a weight basis; however, it was 25 times more potent than morphine on a molar basis. The analgesic activity produced by Substance P was significantly antagonized by pretreatment with naloxone, a narcotic antagonist. The analgesic activity of Substance P exhibited a rapid onset (1 min.), peaked by 3 minutes post infusion and its duration of activity was between 30 and 60 minutes. Thus, Substance P may be yet another endogenous analgesic peptide.

AGONIST AND ANTAGONIST PROPERTIES OF BUPRENORPHINE, A NEW ANTINOCICEPTIVE AGENT

1. Buprenorphine is a highly lipophilic derivative of oripavine. In rodent antinociceptive assays (writhing, tail pressure), buprenorphine had an action which was rapid in onset and of long duration; it was 25-40 times more potent than morphine after parenteral injection and 7-10 times more potent after oral administration. 2. The log dose-response relationship for buprenorphine was curvilinear in mouse and rat tail flick tests with the antinociceptive effect decreasing at higher, non-toxic doses. 3. Tolerance developed to the antinociceptive activity of buprenorphine in mice. 4. No signs of abstinence were observed on naloxone challenge or after abrupt withdrawal in monkeys receiving buprenorphine chronically for one month. 5. Buprenorphine antagonized the antinociceptive actions of morphine in mouse and rat tail flick tests but was an ineffective antagonist in the rat tail pressure test. 6. Buprenorphine precipitated signs of abstinence in morphine-dependent mice and monkeys but not in morphine-dependent rats. 7. Buprenorphine produced Straub tails in mice. This effect was not antagonized when the animals were pretreated with naloxone. However, in the rat tail pressure test high doses of diprenorphine antagonized established antinociceptive effects of buprenorphine. 8. It is concluded that buprenorphine represents a definite advance in the search for a narcotic antagonist analgesic of low physical dependence potential.

Analgesic activity of enkephalins following intracerebral administration in the rat

Methionine- and leucine-enkephalin were found to be potent, short-acting analgesics in the tail flick test in rats following intracerebral administration, via chronically indwelling cannulae, into the midbrain periaqueductal gray. Morphine sulfate was approximately 4 times as potent as the enkephalins when infused into this same brain site. The analgesia produced by the enkephalins and by morphine was inhibited by pretreatment with naloxone.

Human β-endorphin: Development of tolerance and behavioral activity in rats

Human β-endorphin produced a potent antinociceptive response as estimated by the tail-flick test in rats after intraventricular injection. On a molar basis, the peptide was 21 times more potent than morphine and in addition, the peptide produced morphine-like catatonia and hypothermia. These responses were blocked by naloxone. Repeated injections of the peptide induced tolerance to analgesic response, catatonia and hypothermia. Cross tolerance to morphine was also observed.

Effects of opiates and opiate antagonists on the Straub tail reaction in mice.

1. Subcutaneous injections of opiates produced the Straub tail reaction in mice. The potencies of the opiates in mice were consistent with previous estimates of the analgesic potencies in animals and in man.2. The potencies of sixteen antagonists in counteracting the reaction were consistent with those previously obtained with the rat tail-flick test.3. The (-) isomers of four benzomorphan derivatives were much more potent in counteracting the reaction than their (+) isomers and about twice as potent as their racemates. The activity of the isomers seemed to follow Pfeiffer's rule: the lower the effective dose of a drug, the greater the difference in the pharmacological effects of the optical isomers. One of the trans isomers acted like an opiate, while its cis isomer acted like an antagonist.4. Naloxone and nalorphine fulfilled conventional criteria for competitive antagonism, whereas atropine and the (-) and the (+) isomers of pentazocine and of cyclazocine did not do so.5. The Straub tail test seems to be useful for studying structure-activity relations among opiates and opiate antagonists.

Pharmacological properties related to the mechanism of action of potent analgesic drugs.

Abstract

Analgesic and Anti-Inflammatory Evaluation of Thymotic Acid and Certain Homologs

Ortho-thymotic acid and nine homologs were submitted for general, analgesic, and antistress evaluations in the rat. While all appeared to be nonspecific central nervous system depressants, only 2-methyl-5- tert -butylsalicylic acid appeared to have significant analgesic ability in the rat tail flick test. 2-Hydroxy-4-methyl-5-isopropylbenzoic acid, 2-hydroxy-4-isopropyl-6-methylbenzoic acid, and 2-hydroxy-3-methyl-6-isopropylbenzoic aicd were superior to sodium salicylate and inferior to morphine sulfate in providing significant protection from stress induced by unilateral hind leg tourniquets. The latter two compounds were active in suppressing the acute inflammatory process produced by pedal injection of carrageenin, but were ineffective against chronic inflammation induced by the Mycobacterium butyricum adjuvant.