Related Experiment Video
Updated: Aug 16, 2026
Disrupting Reconsolidation of Fear Memory in Humans by a Noradrenergic β-Blocker
Published on: December 18, 2014
Biphasic effects of clonidine on conflict behavior: involvement of different alpha-adrenoceptors
1Department of Pharmacology, University of Göteborg, Sweden.
Abstract:
The effect of the alpha-2-adrenoceptor agonist clonidine on anxiety-related behavior was investigated using two different rat anxiety models: a modified Vogel's drinking conflict model and Montgomery's elevated plus-maze. In both models biphasic dose-response curves were obtained; in a narrow low-dose range (6.25-10.0 micrograms/kg) the drug produced anxiolytic-like effects, while anxiogenic-like properties were found after higher doses (12.5-80.0 micrograms/kg). Attempts to block the effects obtained were made in Montgomery's elevated plus-maze. The specific alpha-2-adrenoceptor antagonist idazoxan blocked the anxiolytic-like effect but did not influence the anxiogenic-like activity. Conversely, the specific alpha-1-adrenoceptor antagonist prazosin blocked the anxiogenic-like effect but did not alter the anxiolytic-like activity. These findings may suggest that alpha-1- and alpha-2-adrenergic receptor mechanisms are reciprocally involved in anxiety-related behavior.
More Related Videos
07:02A Computerized Test Battery to Study Pharmacodynamic Effects on the Central Nervous System of Cholinergic Drugs in Early Phase Drug Development
Published on: February 11, 2019
13:20Online Repetitive Transcranial Magnetic Stimulation of Dorsomedial and Dorsolateral Prefrontal Cortex in Cognition Decision Making, and Cognitive Dissonance
Published on: December 5, 2025
Related Concept Videos
01:31Adrenergic Receptors: ɑ Subtype
Adrenaline ≥ Noradrenaline >> Isoprenaline
α-adrenoceptors are further divided into α1 and α2-adrenoceptors.
α1-Adrenoceptors: These receptors are located postsynaptically on the effector organs and cause constriction of smooth muscle mediated by activation of phospholipase C—inositol-1,4,5-trisphosphate...
01:26Adrenergic Receptors: β Subtype
Isoprenaline > Adrenaline > Noradrenaline
Neurotransmitter binding to these receptors causes activation of adenylyl cyclase resulting in increased concentrations of cAMP and modulation of calcium ion channels within the cell. They are further classified into β1, β2, and β3 subtypes.
β1-adrenoceptors: β1-adrenoceptors have equal affinities for...
01:16Adrenergic Agonists: Chemistry and Structure-Activity Relationship
Aromatic ring substitutions: Substituting the aromatic ring with –OH groups at positions 3 and 4 yields catecholamines (e.g., epinephrine), which have a high affinity for adrenoceptors. Hydrogen bonding between –OH groups and receptors enhances adrenergic activity.
Separation of the aromatic...
01:30Adrenergic Agonists: Therapeutic Uses
Emergency and Intensive Care Unit (ICU) applications: Pressor agents increase blood pressure, heart rate, and contractility in shock and organ failure situations. Dopamine can induce vasodilation and stimulate adrenoceptors. Endogenous catecholamines are effective in treating cardiogenic shock. α2-agonists like clonidine can reverse anesthesia-induced hypertension.
Allergies and anaphylaxis:...
01:17Adrenergic Antagonists: Chemistry and Classification of ɑ-Receptor Blockers
Nonselective α-blockers: Nonselective α-blockers contain haloalkylamine or imidazoline moieties. Phenoxybenzamine, with a haloalkylamine...
01:22Adrenergic Antagonists: Pharmacological Actions of ɑ-Receptor Blockers
α1-blockers: These drugs inhibit α1-adrenoceptors on smooth muscle cells, resulting in vasodilation. This vasodilation lowers blood pressure, making α1-blockers valuable in treating hypertension. Additionally, α1-blockers effectively address urinary obstruction...