Activation of histaminergic H3 receptors in the rat basolateral amygdala improves expression of fear memory and enhances acetylcholine release.
The basolateral amygdala (BLA) is involved in learning that certain environmental cues predict threatening events. Several studies have shown that manipulation of neurotransmission within the BLA affects the expression of memory after fear conditioning. We previously demonstrated that blockade of histaminergic H3 receptors decreased spontaneous release of acetylcholine (ACh) from the BLA of freely moving rats, and impaired retention of fear memory. In the present study, we examined the effect of activating H3 receptors within the BLA on both ACh release and expression of fear memory. Using the microdialysis technique in freely moving rats, we found that the histaminergic H3 agonists R-alpha-methylhistamine (RAMH) and immepip, directly administered into the BLA, augmented spontaneous release of ACh in a similar manner. Levels of ACh returned to baseline on perfusion with control medium. Rats receiving intra-BLA, bilateral injections of the H3 agonists at doses similar to those enhancing ACh spontaneous release, immediately after contextual fear conditioning, showed stronger memory for the context-footshock association, as demonstrated by longer freezing assessed at retention testing performed 72 h later. Post-training, bilateral injections of 15 ng oxotremorine also had a similar effect on memory retention, supporting the involvement of the cholinergic system. Thus, our results further support a physiological role for synaptically released histamine, that in addition to affecting cholinergic transmission in the amygdala, modulates consolidation of fear memories
Dipartimento di Farmacologia Preclinica e Clinica, V.le G. Pieraccini 6, Universitá di Firenze, 50139 Firenze, Italy.
Iacopo
I
Cangioli
Elisabetta
E
Baldi
Pier Francesco
PF
Mannaioni
Corrado
C
Bucherelli
Patrizio
P
Blandina
M Beatrice
MB
Passani
D000109:Acetylcholine / Q000378:metabolism*; D000679:Amygdala / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D002800:Cholinesterase Inhibitors / Q000494:pharmacology; D003213:Conditioning, Psychological / Q000187:drug effects / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D005239:Fear / Q000187:drug effects / Q000502:physiology*; D006632:Histamine / Q000378:metabolism*; D017442:Histamine Agonists / Q000494:pharmacology; D007093:Imidazoles / Q000494:pharmacology; D008297:Male; D008568:Memory / Q000187:drug effects / Q000502:physiology*; D008761:Methylhistamines / Q000494:pharmacology; D018721:Muscarinic Agonists / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D010095:Oxotremorine / Q000031:analogs & derivatives* / Q000494:pharmacology; D010880:Piperidines / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D018100:Receptors, Histamine H3 / Q000187:drug effects / Q000378:metabolism*; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology
D002800:Cholinesterase Inhibitors; D017442:Histamine Agonists; D007093:Imidazoles; D008761:Methylhistamines; D018721:Muscarinic Agonists; D010880:Piperidines; D018100:Receptors, Histamine H3; C085755:4-(1H-imidazol-4-ylmethyl)piperidine; D010095:Oxotremorine; C042743:oxotremorine M; C069357:alpha-methylhistamine; D006632:Histamine; D000109:Acetylcholine