title: Cholinergic and GABAergic receptor functional deficit in the hippocampus of insulin-induced hypoglycemic and streptozotocin-induced diabetic rats.
abstract: Neurotransmitter receptor functional regulation plays an important role in controlling the excitability and responsiveness of hippocampal neurons. Deregulation of its function is associated with seizure generation, motor deficits, and memory impairment. In the present study we investigated the changes in hippocampal cholinergic and GABA receptor binding and gene expression in insulin-induced hypoglycemic and streptozotocin-induced diabetic rats. Expression of cholinergic enzymes; acetylcholine esterase (AChE) and choline acetyltransferase (ChAT) upregulated and downregulated, respectively, in diabetic group, which was further exacerbated by hypoglycemia. Total muscarinic receptor, muscarinic M1, and GABA maximal binding (B(max)) significantly decreased in hypoglycemic and diabetic rats. In hypoglycemic group, the B(max) showed further decline compared with diabetes. Muscarinic M3 receptor B(max) and gene expression upregulated in hypoglycemic and diabetic group. Alpha7 nicotinic acetylcholine receptor (α7 nAChR) expression significantly downregulated in hypoglycemic and diabetic rats. Gene expression of glutamate decarboxylase (GAD), GABAAα1, and GABAB in hypoglycemic and diabetic rats downregulated, with more significant decrease in hypoglycemic group. Present findings show altered cholinergic, muscarinic, nicotinic receptor expression and thereby function. Decreased GABA receptor expression is associated with decline in GABAergic neurotransmission. Thus cholinergic receptor dysfunction and decreased GABAergic neuroprotective inhibitory function in the hippocampus of hypoglycemic and diabetic rats account for the increased vulnerability of hippocampus predisposing to neuronal damage, which is suggested to contribute to cognitive impairment and memory deficit reported in hypoglycemia and diabetes. Also, recurrent hypoglycemia in diabetes exacerbates the hippocampal dysfunction induced by diabetes, which has clinical significance in diabetes therapy.
authors.affiliation: Molecular Neurobiology and Cell Biology Unit, Centre for Neuroscience, Department of Biotechnology, Cochin University of Science and Technology, Cochin 682 022, Kerala, India.
authors.forename: A
authors.initials: A
authors.lastname: Sherin
authors.forename: J
authors.initials: J
authors.lastname: Anu
authors.forename: K T
authors.initials: KT
authors.lastname: Peeyush
authors.forename: S
authors.initials: S
authors.lastname: Smijin
authors.forename: M
authors.initials: M
authors.lastname: Anitha
authors.forename: B T
authors.initials: BT
authors.lastname: Roshni
authors.forename: C S
authors.initials: CS
authors.lastname: Paulose
mesh_terms: D000110:Acetylcholinesterase / Q000096:biosynthesis; D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D002795:Choline O-Acetyltransferase / Q000096:biosynthesis; D003921:Diabetes Mellitus, Experimental / Q000378:metabolism*; D006624:Hippocampus / Q000378:metabolism / Q000502:physiology*; D007003:Hypoglycemia / Q000139:chemically induced / Q000378:metabolism*; D007004:Hypoglycemic Agents; D007328:Insulin; D008297:Male; D009419:Nerve Tissue Proteins / Q000378:metabolism; D019275:Radiopharmaceuticals; D051381:Rats; D017208:Rats, Wistar; D060888:Real-Time Polymerase Chain Reaction; D043643:Receptor, Muscarinic M1 / Q000096:biosynthesis; D043587:Receptor, Muscarinic M3 / Q000096:biosynthesis; D011950:Receptors, Cholinergic / Q000096:biosynthesis / Q000502:physiology*; D018079:Receptors, GABA / Q000096:biosynthesis / Q000502:physiology*; D011963:Receptors, GABA-A / Q000096:biosynthesis; D018080:Receptors, GABA-B / Q000096:biosynthesis; D011978:Receptors, Nicotinic / Q000096:biosynthesis; D064569:alpha7 Nicotinic Acetylcholine Receptor
chemical_list: D001786:Blood Glucose; C579165:Chrna7 protein, rat; D007004:Hypoglycemic Agents; D007328:Insulin; D009419:Nerve Tissue Proteins; D019275:Radiopharmaceuticals; D043643:Receptor, Muscarinic M1; D043587:Receptor, Muscarinic M3; D011950:Receptors, Cholinergic; D018079:Receptors, GABA; D011963:Receptors, GABA-A; D018080:Receptors, GABA-B; D011978:Receptors, Nicotinic; D064569:alpha7 Nicotinic Acetylcholine Receptor; D002795:Choline O-Acetyltransferase; D000110:Acetylcholinesterase