title: Muscimol in the deep layers of the superior colliculus/mesencephalic reticular formation blocks expression but not acquisition of fear-potentiated startle in rats.
abstract: Deposits of the retrograde tracer Fluoro-Gold into the ventrolateral nucleus reticularis pontis caudalis labeled neurons in the deep layers of the superior colliculus/mesencephalic reticular formation (deep SC/Me). To test the involvement of this area in the fear-potentiated startle effect, rats were implanted with cannulas into the deep SC/Me and trained for fear-potentiated startle after infusion of the GABA(A) agonist muscimol (0.1 microg/0.5 microl). Two days later, they were tested for fear-potentiated startle. Rats then received a 2nd training session without any infusions, and 2 days later they were reinfused with muscimol (0.1 microg/0.5 microl) and tested for fear-potentiated startle. Local infusion of muscimol into the deep SC/Me completely blocked the expression but not the acquisition of fear-potentiated startle. These results indicate that a synapse in the midbrain is critical for the expression of fear-potentiated startle.
authors.affiliation: Department of Psychiatry and Behavioral Sciences, Emory University, Atlanta, Georgia 30322, USA. emeloni@emory.edu
authors.forename: E G
authors.initials: EG
authors.lastname: Meloni
authors.forename: M
authors.initials: M
authors.lastname: Davis
mesh_terms: D000818:Animals; D001362:Avoidance Learning / Q000187:drug effects / Q000502:physiology*; D015986:Confounding Factors, Epidemiologic; D005239:Fear / Q000187:drug effects / Q000502:physiology*; D018755:GABA Agonists / Q000008:administration & dosage*; D008297:Male; D008636:Mesencephalon / Q000502:physiology; D008845:Microinjections; D009118:Muscimol / Q000008:administration & dosage*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013216:Reflex, Startle / Q000187:drug effects / Q000502:physiology*; D012154:Reticular Formation / Q000187:drug effects / Q000502:physiology*; D013477:Superior Colliculi / Q000187:drug effects / Q000502:physiology*
chemical_list: D018755:GABA Agonists; D009118:Muscimol