Autoradiographic localization of 5HT₁ binding sites in the medulla oblongata of the rat

Abstract

Serotonin (5HT) binding sites in the medulla oblongata of the rat were localized using autoradiographic techniques with radioactive ligands that express high affinity for the 5HT1 (3H-5HT), 5HT1A (3H-80H-DPAT), or 5HT1B (125I-CYP with isoproterenol) receptor subtypes. 5HT1A sites were concentrated primarily in certain sensory regions of the medulla and in regions that contain serotonergic neurons. 5HT1B sites were diffusely distributed throughout the reticular formation and motor regions as well as being localized to certain sensory regions. A surprising finding was an association of 5HT1B binding sites with the corticospinal tract. 3H-5HT binding generally reflected the combined pattern of 5HT1A and 5HT1B sites but was also extremely dense in the choroid plexus, which exhibited virtually no 5HT1A or 5HT1B ligand binding. Presumably this binding, which was blocked by ketanserin, corresponds to 5HT1C sites. Administration of the serotonergic neurotoxin 5,7-dihydroxytryptamine reduced 5HT1A binding sites in regions of the medulla that contain serotonergic neuronal cell bodies. 5HT1B binding was not significantly altered in any area of the medulla. These studies indicate an important role for 5HT1A ligands in the processing of visceral and somatic sensory information, in regulation of certain cerebellar afferent projections, and in the regulation of serotonergic neuronal activity. 5HT1B ligands would be expected to regulate visceral and somatic efferent activity, as well as sensory information and reticular efferent activity, and might presynaptically regulate cortical inputs to the brain stem and spinal cord.

CP-94,253: a selective serotonin 1B (5-HT 1B ) agonist that promotes satiety

“…Previous results using RU 24969 as a 5-HT 1B probe suggested that the hypophagic e¤ect of 1B stimulation came from postsynaptic e¤ects (Kennett and Curzon 1988). It is relevant that 5-HT 1B receptors in the hindbrain and medial hypothalamus regions presumably involved in modulating ingestion survive 5-HT terminal degeneration produced by 5,7-dihydroxytryptamine (Thor et al 1992;Frankfurt et al 1993). Thus, previous pharmacological and anatomical evidence is consistent with our working hypothesis that CP-94,253 acts postsynaptically in the brain to decrease food intake.…”

Infusion of the serotonin 1B (5-HT 1B ) agonist CP-93,129 into the parabrachial nucleus potently and selectively reduces food intake in rats

“…It is possible that 5-HT 1B receptors code a serotonergic circuit under control of the dorsal raphe that is partly responsible for satiation. In the medulla, 5-HT 1B sites are found postsynaptically (Thor et al 1992), although their localization within the PBN remains to be established. Evidence that 5-HT 2 , possibly 2C, receptors in the lPBN regulate salt intake (Menani et al 1996) prompts further investigations of the anatomical and pharmacological speciÞcity of hindbrain 5-HT receptors in ingestion.…”

Rapid-Onset Obesity With Hypothalamic Dysfunction, Hypoventilation, and Autonomic Dysregulation: Analysis of Hypothalamic and Autonomic Candidate Genes

“…The 5-hydroxytryptamine (serotonin) receptor 1A (HTR 1A ) shows hypothalamic expression and has a known role in appetite control and energy regulation (13). Furthermore, this gene is densely distributed in medullary regions important for cardiorespiratory regulation and has a key role in the autonomic response to homeostatic stress (14,15). Like HTR 1A , the orthopedia (OTP) gene shows hypothalamic expression, with an important role in hypothalamic cell specification in the developing hypothalamus (16).…”