In vitro evidence and age-related changes for nicotinic but not muscarinic acetylcholine receptors in the central nervous system of Sepia officinalis.
Binding putative muscarinic ([3H]-NMS and [3H]-QNB) or nicotinic ([3H]-cytisine) acetylcholine receptors was quantitatively studied through the use of in vitro binding experiments on either membrane preparations or brain sections of juvenile (3 months), mature (15 months) or senescent (23 months) cuttlefish. No specific binding could be detected with muscarinic receptor ligands under any of the experimental conditions employed (ligand concentrations, buffers, ionic charges, types of tissue, i.e., brain sections or membrane preparations). On the other hand, [3H]-cytisine demonstrated a specific and saturable binding with a single class of high affinity binding sites (Kd of 2.6-34.6 nM; Bmax of 128-1682 fmol/mg tissue equivalent, depending on the central structure). This binding was found to be heterogeneous throughout the central regions (optic lobe>pedal lobe; superior frontal lobe>...precommissural lobe; vertical lobe>...anterior basal lobe; subvertical lobe; inferior frontal lobe; median basal lobe). These results question the existence of muscarinic-like receptors in the cuttlefish brain, or at least of a pharmacological dissimilarity from vertebrate muscarinic receptors. In contrast, nicotinic-like receptors are widely present; interestingly, their density was found to be significantly reduced in most nervous central lobes of senescent cuttlefish when compared with mature animals. The most significant decrease (-71%) was found in the anterior part of the superior frontal lobe, which is involved in visual learning; this might be related to the changes, previously demonstrated, in cholinergic neurons in this lobe in the course of aging.
Bellanger
Cécile
C
Laboratoire de Psychophysiologie du Comportement des Céphalopodes, Université de Caen, Esplanade de la Paix, 14032 Caen Cedex, France. cecile.bellanger@unicaen.fr
Halm
Marie-Pierre
MP
Dauphin
François
F
Chichery
Raymond
R
D000109:Acetylcholine / Q000378:metabolism; D000375:Aging / Q000502:physiology*; D000470:Alkaloids / Q000378:metabolism; D000818:Animals; D001392:Azocines / Q000378:metabolism; D001667:Binding, Competitive / Q000502:physiology; D001921:Brain / Q000033:anatomy & histology / Q000378:metabolism*; D002799:Cholinergic Fibers / Q000378:metabolism; D049832:Decapodiformes / Q000033:anatomy & histology / Q000378:metabolism*; D007858:Learning / Q000502:physiology; D018727:Muscarinic Antagonists / Q000378:metabolism; D019832:N-Methylscopolamine / Q000378:metabolism; D018733:Nicotinic Antagonists / Q000378:metabolism; D017729:Presynaptic Terminals / Q000378:metabolism; D011807:Quinolizines / Q000378:metabolism; D011813:Quinuclidinyl Benzilate / Q000378:metabolism; D011869:Radioligand Assay; D011976:Receptors, Muscarinic / Q000378:metabolism*; D011978:Receptors, Nicotinic / Q000378:metabolism*; D013045:Species Specificity; D009435:Synaptic Transmission / Q000502:physiology*; D000093843:Quinolizidine Alkaloids
D000109:Acetylcholine; D000470:Alkaloids; D001392:Azocines; D018727:Muscarinic Antagonists; D019832:N-Methylscopolamine; D018733:Nicotinic Antagonists; D011807:Quinolizines; D011813:Quinuclidinyl Benzilate; D011976:Receptors, Muscarinic; D011978:Receptors, Nicotinic; C004712:cytisine; D000093843:Quinolizidine Alkaloids