Cholinergic and GABAergic receptor functional deficit in the hippocampus of insulin-induced hypoglycemic and streptozotocin-induced diabetic rats

• Published in: Neuroscience 2012-01, Vol.202, p.69-76
• Main Authors: Sherin, A, Anu, J, Peeyush, K.T, Smijin, S, Anitha, M, Roshni, B.T, Paulose, C.S
• Format: Article
• Language: English
• Subjects: Acetylcholinesterase - biosynthesis; alpha7 Nicotinic Acetylcholine Receptor; Animals; Biological and medical sciences; Blood Glucose - metabolism; Choline O-Acetyltransferase - biosynthesis; cholinergic receptor; diabetes; Diabetes Mellitus, Experimental - metabolism; Diabetes. Impaired glucose tolerance; Endocrine pancreas. Apud cells (diseases); Endocrinopathies; Etiopathogenesis. Screening. Investigations. Target tissue resistance; Fundamental and applied biological sciences. Psychology; GABA; hippocampus; Hippocampus - metabolism; Hippocampus - physiology; hypoglycemia; Hypoglycemia - chemically induced; Hypoglycemia - metabolism; Hypoglycemic Agents; Insulin; Male; Medical sciences; Nerve Tissue Proteins - metabolism; Neurology; Radiopharmaceuticals; Rats; Rats, Wistar; Real-Time Polymerase Chain Reaction; Receptor, Muscarinic M1 - biosynthesis; Receptor, Muscarinic M3 - biosynthesis; Receptors, Cholinergic - biosynthesis; Receptors, Cholinergic - physiology; Receptors, GABA - biosynthesis; Receptors, GABA - physiology; Receptors, GABA-A - biosynthesis; Receptors, GABA-B - biosynthesis; Receptors, Nicotinic - biosynthesis; Vertebrates: nervous system and sense organs
• ISSN: 0306-4522; 1873-7544
• DOI: 10.1016/j.neuroscience.2011.11.058

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 ( Bmax ) significantly decreased in hypoglycemic and diabetic rats. In hypoglycemic group, the Bmax showed further decline compared with diabetes. Muscarinic M3 receptor Bmax 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.