dizocilpine-maleate and naloxonazine

Dynorphin A-(1-17) has been found to produce spinal antianalgesia and allodynia. Thus, we studied whether dynorphin A-(1-17) modulates substance P release evoked by the C-fiber-selective stimulant capsaicin (1 microM) from trigeminal nucleus caudalis slices. Very low concentrations of dynorphin A-(1-17) (0.01-0.1 nM) strongly facilitated capsaicin-evoked substance P release. This dynorphin A-(1-17) effect was not blocked by the opioid receptor antagonists naloxone (100 nM), beta-funaltrexamine (20 nM), naloxonazine (1 nM), nor-binaltorphimine (3 nM) and ICI 174,864 (N,N-dialyl-Tyr-Aib-Phe-Leu; 0.3 microM). Yet, the effect of dynorphin A-(1-17) was blocked by the NMDA receptor antagonist MK-801 ((+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d] cyclohepten-5-10-imine maleate; 0.3 microM). Neonatal treatment with capsaicin (50 mg/kg s.c.), which destroys substance P-containing primary afferents, abolished the excitatory effect of dynorphin A-(1-17) on K+-evoked substance P release. In conclusion, dynorphin A-(1-17) increases substance P release from C-fibers by the activation of NMDA receptors which supports the involvement of presynaptic mechanisms in dynorphin-induced antianalgesia and allodynia.

Topics: Animals; Animals, Newborn; Capsaicin; Dizocilpine Maleate; Dynorphins; Enkephalin, Leucine; Excitatory Amino Acid Antagonists; In Vitro Techniques; Male; Naloxone; Naltrexone; Narcotic Antagonists; Nerve Fibers; Neurons, Afferent; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Substance P; Trigeminal Nuclei

To characterize how systemic morphine induces Fos protein in dorsomedial striatum and nucleus accumbens (NAc), we examined the role of receptors in striatum, substantia nigra (SN), and ventral tegmental area (VTA). Morphine injected into medial SN or into VTA of awake rats induced Fos in neurons in ipsilateral dorsomedial striatum and NAc. Morphine injected into lateral SN induced Fos in dorsolateral striatum and globus pallidus. The morphine infusions produced contralateral turning that was most prominent after lateral SN injections. Intranigral injections of [D-Ala2, N-Me-Phe4, Gly-ol5]-enkephalin (DAMGO), a mu opioid receptor agonist, and of bicuculline, a GABAA receptor antagonist, induced Fos in ipsilateral striatum. Fos induction in dorsomedial striatum produced by systemic administration of morphine was blocked by (1) SN and VTA injections of the mu1 opioid antagonist naloxonazine and (2) striatal injections of either MK 801, an NMDA glutamate receptor antagonist, or SCH 23390, a D1 dopamine receptor antagonist. Fos induction in dorsomedial striatum and NAc after systemic administration of morphine seems to be mediated by dopamine neurons in medial SN and VTA that project to medial striatum and NAc, respectively. Systemic morphine is proposed to act on mu opioid receptors located on GABAergic interneurons in medial SN and VTA. Inhibition of these GABA interneurons disinhibits medial SN and VTA dopamine neurons, producing dopamine release in medial striatum and NAc. This activates D1 dopamine receptors and coupled with the coactivation of NMDA receptors possibly from cortical glutamate input induces Fos in striatal and NAc neurons. The modulation of target gene expression by Fos could influence addictive behavioral responses to opiates.

Topics: Afferent Pathways; Analgesics, Opioid; Animals; Behavior, Animal; Benzazepines; Bicuculline; Corpus Striatum; Dizocilpine Maleate; Dopamine Antagonists; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalins; Excitatory Amino Acid Antagonists; Female; GABA Antagonists; Gene Expression Regulation; Genes, fos; Genes, Immediate-Early; Injections; Injections, Intraperitoneal; Interneurons; Morphine; Motor Activity; Naloxone; Nerve Tissue Proteins; Nucleus Accumbens; Proto-Oncogene Proteins c-fos; Rats; Rats, Sprague-Dawley; Receptors, Dopamine D1; Receptors, GABA-A; Receptors, N-Methyl-D-Aspartate; Receptors, Opioid, mu; Substantia Nigra; Tegmentum Mesencephali