Distribution of serotonin 5-HT1A-binding sites in the brainstem and the hypothalamus, and their roles in 5-HT-induced sleep and ingestive behaviors in rock pigeons (Columba livia)

• Published in: Behavioural brain research Vol. 295; pp. 45 - 63
• Main Authors: dos Santos, Tiago Souza, Krüger, Jéssica, Melleu, Fernando Falkenburger, Herold, Christina, Zilles, Karl, Poli, Anicleto, Güntürkün, Onur, Marino-Neto, José
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 15-12-2015
• Subjects: 5,7-Dihydroxytryptamine - pharmacology; 5-HT-1A receptor; 8-Hydroxy-2-(di-n-propylamino)tetralin - pharmacology; Animals; Binding Sites; Brain Stem - drug effects; Brain Stem - metabolism; Cerebrospinal fluid; Columba livia; Columbidae - metabolism; Drinking; Feeding; Feeding Behavior - drug effects; Female; Hypothalamus - metabolism; Male; Raphe Nuclei - metabolism; Receptor, Serotonin, 5-HT1A - metabolism; Receptors, Serotonin; Serotonin; Serotonin - metabolism; Serotonin Receptor Agonists - pharmacology; Sleep; Sleep - drug effects; Sleep - physiology; Sleep Aids, Pharmaceutical; PVO; Cerebrospinal fluid; DSD; A6; QF; A8; BNSTl; GCt; ZpFLM; IF; ML; n.IV; MM; POA; IN; 5-HT-1A receptor; DSV; Drinking; AL; AM; POM; TSM; Anl; PVNm; BC; FDB; FLM; PPM; PLH; PVNp; RPO; R; ScD; n.V; SL; SFO; CA; OM; Rt; DMN; Serotonin; ScV; SOE; PMH; CO; CP; Feeding; CS; PMM; Sleep; PD; SCE; VMN; LC; SCI; LHy
• ISSN: 0166-4328; 1872-7549
• DOI: 10.1016/j.bbr.2015.03.059

•5-HT1AR was found in brainstem 5-HT areas and in the hypothalamus of pigeons.•ICV 5-HT or DPAT evokes drinking, sleep, and c-Fos expression in these areas.•5-HT1AR heteroreceptor antagonist blocks 5-HT- and DPAT-evoked drinking and sleep.•5-HT-specific neurotoxin 5,7-DHT does not alter 5-HT activity but does increase sleep.•5-HT1ARs play crucial but complex roles in ingestive and postprandial behavior.
Serotonin 1A receptors (5-HT1ARs), which are widely distributed in the mammalian brain, participate in cognitive and emotional functions. In birds, 5-HT1ARs are expressed in prosencephalic areas involved in visual and cognitive functions. Diverse evidence supports 5-HT1AR-mediated 5-HT-induced ingestive and sleep behaviors in birds. Here, we describe the distribution of 5-HT1ARs in the hypothalamus and brainstem of birds, analyze their potential roles in sleep and ingestive behaviors, and attempt to determine the involvement of auto-/hetero-5-HT1ARs in these behaviors. In 6 pigeons, the anatomical distribution of [3H]8-OH-DPAT binding in the rostral brainstem and hypothalamus was examined. Ingestive/sleep behaviors were recorded (1h) in 16 pigeons pretreated with MM77 (a heterosynaptic 5-HT1AR antagonist; 23 or 69nmol) for 20min, followed by intracerebroventricular ICV injection of 5-HT (N:8; 150nmol), 8-OH-DPAT (DPAT, a 5-HT1A,7R agonist, 30nmol N:8) or vehicle. 5-HT- and DPAT-induced sleep and ingestive behaviors, brainstem 5-HT neuronal density and brain 5-HT content were examined in 12 pigeons, pretreated by ICV with the 5-HT neurotoxin 5,7-dihydroxytryptamine (5,7-DHT) or vehicle (N:6/group). The distribution of brainstem and diencephalic c-Fos immunoreactivity after ICV injection of 5-HT, DPAT or vehicle (N:5/group) into birds provided with or denied access to water is also described. 5-HT1ARs are concentrated in the brainstem 5-HTergic areas and throughout the periventricular hypothalamus, preoptic nuclei and circumventricular organs. 5-HT and DPAT produced a complex c-Fos expression pattern in the 5-HT1AR-enriched preoptic hypothalamus and the circumventricular organs, which are related to drinking and sleep regulation, but modestly affected c-Fos expression in 5-HTergic neurons. The 5-HT-induced ingestivebehaviors and the 5-HT- and DPAT-induced sleep behaviors were reduced by MM77 pretreatment. 5,7-DHT increased sleep per se, decreased tryptophan hydroxylase expression in the raphe nuclei and decreased prosencephalic 5-HT release but failed to affect 5-HT- or DPAT-induced drinking or sleep behavior. 5-HT- and DPAT-induced ingestive and sleep behaviors in pigeons appear to be mediated by heterosynaptic and/or non-somatodendritic presynaptic 5-HT1ARs localized to periventricular diencephalic circuits.