Bivalent opioid peptide analogues with reduced distances between pharmacophores.

To investigate the role of distance between two opioid peptide pharmacophores on in vitro and in vivo activities, three new bivalent opioid analogues have been synthesized in which the dipeptide Tyr-D-Phe was connected with diamine moieties ("bridges"). The analogue with a hydrazine bridge has high receptor affinity to mu, kappa, and delta receptor types, as well as potent and long acting antinociceptive activity after intraperitoneal administration.

Different behavioral responses of rats to kainate injections into the dorsal and median raphe nuclei.

A local injection of kainic acid (KA) into the dorsal raphe nucleus (NRD) increased the motor activity and produced head shakes, hind limb abduction, forepaw treading and sniffing. This syndrome was antagonized partly by cyproheptadine and completely by naloxone. An injection of KA into the median raphe nucleus (NRM) produced sedation, catalepsy and analgesia, which were accompanied by a decrease in the beta-endorphin immunoreactivity in the mesencephalon. Naloxone completely reversed the behavioral inhibition after KA injections into the NRM, while a pretreatment with cyproheptadine augmented the catalepsy. KA injected into the NRD and NRM depressed the forebrain level of serotonin and slightly elevated that of 5-hydroxyindoleacetic acid. The results demonstrate that besides serotonin the opioid system is also involved in various effects induced by activation of the raphe nuclei.

Changes in hippocampal immunoreactive dynorphin and neoendorphin content following intra-amygdalar kainic acid-induced seizures.

Kainic acid (KA) injected focally into the amygdala induced spontaneous recurrent motor seizures. One to 6 hr after the injection of KA, the hippocampal ir-dynorphin (ir-DYN) was significantly lowered whereas 24 hr after the injection it increased. The hippocampal level of ir-alpha-neoendorphin decreased 6 hr after KA injection, and reached the control level 24 hr after the injection. Chlordiazepoxide (5 mg/kg) and phenobarbital (40 mg/kg) blocked convulsions as well as the increase in the ir-DYN content. Cycloheximide (500 micrograms icv) also antagonized the increase in the hippocampal ir-DYN. The above findings suggest that hippocampal dynorphin-related peptides are released during the seizures and that these peptides may play a physiological role in the seizure phenomena and limbic excitability.

The effect of various opiate receptor agonists on the seizure threshold in the rat. Is dynorphin an endogenous anticonvulsant?

The effects of various opiate receptor agonists on the seizure threshold after an intravenous infusion of pentylenetetrazol were investigated in rats. The mu- and epsilon-receptor agonists, morphine (20-40 micrograms) and beta-endorphin (5-10 micrograms) show proconvulsant properties towards clonic and tonic seizures. The delta-receptor agonist (D-Ala2,D-Leu5-enkephalin, DADL 5-40 micrograms) and alpha-neoendorphin (20-40 micrograms) show pro- and anticonvulsant properties towards clonic and tonic seizures, respectively. Anticonvulsant properties of DADL are possibly due to its action on the spinal cord, since after the intrathecal injection this effect is still observed. Similarities between DADL and alpha-neoendorphin suggest that they may act through the same receptor. The kappa-receptor agonist dynorphin A (5-20 micrograms) and its degradation-resistant analogue D-Arg-dynorphin1-13 (10 micrograms) show significant anticonvulsant properties. Our present results suggest that the kappa-receptor agonist dynorphin may act physiologically as an endogenous anticonvulsant, in contrast to other opioid peptides.

Analgesic effects of mu-, delta- and kappa-opiate agonists and, in particular, dynorphin at the spinal level.

To investigate the role of multiple opiate receptors in spinal mechanisms of antinociception the activity of various opiate receptor agonists was determined against different nociceptive stimuli in the mouse and rat. Intrathecal administration of the putative kappa-receptor agonists dynorphin A (DYN), bremazocine, and ethylketocyclazocine, as well as the delta-agonist D-Ala2,D-Leu5-enkephalin and the mu-agonists, Tyr-D-Ala-Gly-MePhe-NH-(CH2)2OH and morphine resulted in a dose-dependent antinociceptive effect. The order of potencies was similar for visceral and thermal pain. Inhibition of writhing in mice was much more strongly antagonized by MR 2266 than by naloxone, and des-Tyr1-DYN1-13 was 50 times less potent than DYN in this test suggesting that DYN acts through the kappa-receptor. It is concluded that mu-, delta- and kappa-opiate receptors are involved in spinally mediated antinociception related to kinds of noxious stimuli.

Comparison of the pharmacological actions of desmethylclomipramine and clomipramine.

This research compares the effects, in mice and rats, of desmethylclomipramine (DCLOM) and clomipramine (CLOM). DCLOM antagonized the hypothermia induced in mice by reserpine or apomorphine to a much greater extent than CLOM. Reserpine ptosis in mice was depressed by DCLOM only. Similarly, only DCLOM was effective in the behavioral despair test in rats. DCLOM increased the 5-hydroxytryptamine (5-HT) pressor effect in pithed rats, but to a lesser extent than CLOM by several factors. Only DCLOM increased the noradrenaline (NA) pressor effect. The depletion of NA induced by 6-hydroxydopamine was depressed by DCLOM only. The 5-HT depletion induced by p-chloromethamphetamine was antagonized only by CLOM. The results obtained show that the noradrenergic mechanism is of prime importance in the action of DCLOM and of much more importance than in the action of CLOM.

The effect of L-DOPA and L-5-hydroxytryptophan on the pentetrazole seizures in rats after lesions of the median raphe nucleus and substantia nigra.

Electrolytic lesions of the median raphe nucleus and substantia nigra markedly increased susceptibility to pentetrazole seizures in rats. L-5-hydroxytryptophan, considerably increasing the serotonin (5-HT) level in the brain, markedly inhibited the seizures and abolished the seizure-enhanced effect of lesion of the substantia nigra. L-DOPA tended to potentiate the seizures-enhancing effect produced by lesions of the median raphe nucleus. The changes in the brain 5-HT level and the intensity of pentetrazole seizures were correlated. The results indicate that the balance between neurotransmitter systems in the brain is of importance to the susceptibility to pentetrazole convulsions.