title: Chemical neuroanatomical and psychopharmacological evidence that κ receptor-mediated endogenous opioid peptide neurotransmission in the dorsal and ventral mesencephalon modulates panic-like behaviour.
abstract: The chemical neuroanatomy and the effects of central administration of opioid antagonists on the innate fear-induced responses elicited by electrical (at escape behaviour threshold) stimulation of the midbrain tectum were determined. The aim of the present work was to investigate the interaction between the tecto-nigral endogenous opioid peptide-mediated disinhibitory pathways and nigro-tectal inhibitory links in the control of panic-like behaviour and their organisation in the continuum comprised by the deep layers of the superior colliculus (dlSC) and the dorsolateral columns of the periaqueductal grey matter (dlPAG). Beta-endorphin-labelled neurons and fibres were found in the dorsal midbrain and also in the substantia nigra. Opioid varicose fibres and terminal buttons were widely distributed in PAG columns and in all substantia nigra subdivisions. Microinjections of naltrexone (a non-selective opioid receptor antagonist; 5.0 μg/0.2 μl) or nor-binaltorphimine (a selective κ-opioid receptor antagonist; 5.0 μg/0.2 μl) in the dlSC/dlPAG continuum, in independent groups of animals, induced significant increases in the escape thresholds for midbrain tectum electrical stimulation. The microinjection of naltrexone or nor-binaltorphimine into the SNpr also increased the escape behaviour threshold for electrical stimulation of dlSC/dlPAG. These morphological and neuropharmacological findings support previous evidence from our team for the role played by the interaction between opioidergic and GABAergic mechanisms in the modulation of innate fear-induced responses. The present data offer a neuroanatomical basis for both intratectal axo-axonic/pre-synaptic and tecto-nigral axo-somatic opioid inhibition of GABAergic nigro-tectal neurons that modulate the dorsal midbrain neurons related to the organisation of fear-related emotional responses.
authors: Laboratório de Neuroanatomia & Neuropsicobiologia, Departamento de Farmacologia, Faculdade de Medicina de Ribeirão Preto da Universidade de São Paulo, Av dos Bandeirantes, 3900 Ribeirão Preto, São Paulo 14049-900, Brazil.
authors: Juliana Almeida
authors: JA
authors: da Silva
authors: Renato Leonardo
authors: RL
authors: de Freitas
authors: Gustavo Cavalcanti Dutra
authors: GC
authors: Eichenberger
authors: Cláudia Maria
authors: CM
authors: Padovan
authors: Norberto Cysne
authors: NC
authors: Coimbra
mesh_terms: D000818:Animals; D004558:Electric Stimulation; D007323:Instinct; D008297:Male; D008636:Mesencephalon / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism* / Q000502:physiology; D009271:Naltrexone / Q000031:analogs & derivatives / Q000494:pharmacology; D009445:Neuroanatomy; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D018847:Opioid Peptides / Q000378:metabolism*; D010200:Panic / Q000187:drug effects*; D011600:Psychopharmacology; D051381:Rats; D017208:Rats, Wistar; D017473:Receptors, Opioid, kappa / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013378:Substantia Nigra / Q000166:cytology / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D009435:Synaptic Transmission / Q000187:drug effects*; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
chemical_list: D018847:Opioid Peptides; D017473:Receptors, Opioid, kappa; C051844:norbinaltorphimine; D005680:gamma-Aminobutyric Acid; D009271:Naltrexone