title: Orienting and defensive behaviors elicited by superior colliculus stimulation in rats: effects of 5-HT depletion, uptake inhibition, and direct midbrain or frontal cortex application.
abstract: Electrical or chemical stimulation of the superior colliculus (SC) in rats produces orienting and defensive responses. Defensive behaviors are modulated by serotonin (5-hydroxytryptamine, 5-HT), and serotonergic fibers provide a dense innervation of the SC. Here, we examined the role of 5-HT in modulating the behavioral responses of rats elicited by electrical SC stimulation. Low-intensity (107+/-12 microA) stimulation of the SC elicited orienting head movements, while higher intensities (204+/-20 microA) produced running and jumping responses. Treatment with the 5-HT depletor p-chlorophenylalanine (300 mg/kg/day x 3, i.p.) lowered current thresholds to elicit orienting and running by 40 and 21%, respectively. Conversely, concurrent administration of the 5-HT uptake inhibitor fluoxetine (10 mg/kg, i.p.) and the 5-HT(1A) receptor antagonist WAY 100635 (0.5 mg/kg, s.c.) increased threshold currents to produce head and running movements by 41 and 18%, respectively. We investigated the anatomical substrate of this inhibitory effect of 5-HT with intracerebral 5-HT application by means of reverse microdialysis. Application of 5-HT (1-50 mM) into the midbrain immediately adjacent to the SC stimulation electrode resulted in a pronounced (approximately four-fold for 50 mM 5-HT) dose- and time-dependent increase in stimulation thresholds to elicit head movements. Application of 5-HT into the frontal cortex (up to 100 mM) had no significant effect on SC-evoked behavioral responses. These results show that 5-HT exerts an inhibitory influence over orienting and defensive behaviors initiated in the mammalian SC. It appears that this inhibitory effect is mediated, to a large extent, by a direct action of 5-HT at the level of the midbrain.
authors.affiliation: Department of Psychology, Centre for Neuroscience Studies, Queen's University, Kingston, Ont., Canada K7L 3N6. dringenb@psyc.queensu.ca
authors.forename: Hans C
authors.initials: HC
authors.lastname: Dringenberg
authors.forename: Kristopher E B
authors.initials: KE
authors.lastname: Dennis
authors.forename: Summer
authors.initials: S
authors.lastname: Tomaszek
authors.forename: Jody
authors.initials: J
authors.lastname: Martin
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D004558:Electric Stimulation; D010134:Fenclonine / Q000008:administration & dosage; D005473:Fluoxetine / Q000008:administration & dosage; D005625:Frontal Lobe / Q000187:drug effects* / Q000502:physiology; D019416:Head Movements; D008297:Male; D008636:Mesencephalon / Q000187:drug effects* / Q000502:physiology; D017551:Microdialysis / Q000379:methods; D009433:Neural Inhibition; D010879:Piperazines / Q000008:administration & dosage; D011725:Pyridines / Q000008:administration & dosage; D051381:Rats; D020318:Rats, Long-Evans; D012420:Running / Q000502:physiology; D012701:Serotonin / Q000172:deficiency / Q000378:metabolism*; D012702:Serotonin Antagonists / Q000008:administration & dosage; D017367:Selective Serotonin Reuptake Inhibitors / Q000494:pharmacology*; D013268:Stimulation, Chemical; D013477:Superior Colliculi / Q000033:anatomy & histology / Q000187:drug effects* / Q000378:metabolism; D013997:Time Factors
chemical_list: D010134:Fenclonine; D005473:Fluoxetine; D010879:Piperazines; D011725:Pyridines; D012701:Serotonin; D012702:Serotonin Antagonists; D017367:Selective Serotonin Reuptake Inhibitors; C090413:N-(2-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl)-N-(2-pyridinyl)cyclohexanecarboxamide