Effect of c-peptide on cognitive dysfunction in type 1 diabetic rat

Diabetes mellitus is a common metabolic disorder that associates with structural and functional changes in central and peripheral nervous system and progressive decline in cognitive abilities. Recent experimental and clinical data suggested that C-peptide replacement during type 1 diabetes exerts beneficial effects on diabetic rats. Determine the effect of intraperitoneal [IP] injection of c-peptide on cognitive dysfunction in type 1 diabetic rats. 24 male Sprague dawly rats [230-300 gr] used for this project divided into 3 groups: 1. control group, 2. type 1 diabetic group and 3. Diabetic group that receive C-peptide [25 nmol/kg/daily for 28 day/IP]. Diabetes induced with IV injection of Streptozotocin [60mg/kg]. Twenty one days after onset of diabet, behavioral tests conducted for seven days. In reference memory assessment, the latency of finding platform during four days decline significantly in all groups [P<0.05]. Mean escape time in diabetic group was significantly longer in comparison to other groups [P<0.05] but in comparison to diabetic group with C-peptide group, memory impairement decline significantly [P< 0.05]. During three days of working memory test, the latency required for finding platform decreased significantly [P<0.05] but this time was longer in diabetic group [P<0.05]. C-peptide could improve memory in diabetic group. C-peptide had significant role in control and inhibition of memory disorder progression

[ effect of reversible inactivation of locus coeruleus on long-term potentiation in the dentate gyrus of rat hippocampus]

Introduction: The nucleus locus coeruleus [LC] is located next to the fourth ventricle of the brain. Behavioral and electrophysiological studies have revealed the importance of LC noradrenergic projections in processes such as attention, learning and memory. Long-term potentiation [LTP] in hippocampal neurons is believed to be neural basis of learning and memory. The effects of LC on hippocampal electrophysiology have been investigated since many years ago, but have had different and conflicted results

Objective: In this study the effect of reversible inactivation of LC on induction and maintenance of LTP in hippocampal dentate gyrus [DG] of male anesthetized rats was investigated

Materials and Methods: This is an expelimental study. Inactivation of LC was conducted through bilateral injection of 0.5microl lidocaine [4%]. For producing LTP, two high frequency stimulations [HFS], 5 minutes apart were given to perforant pathway [PP] neurons. The amplitude of population spikes [PS] and the slope of population excitatory post synaptic potentials [PEPSP] were recorded before and 5, 10, 20, 40, 60 and 120 minutes after tetanic stimulations in DG

Results: The findings of this study showed that inactivation of LC had no effect on DG granule cells baseline activity. Also, LC inactivation 5 minutes before HFS had no effect on LTP induction. However, PS amplitude was decreased significantly [P<0.05, P<0.01 respectively] in comparison with control group, 60 and 120 minutes after tetanization. Lidocaine injection after HFS had no effect on induced LTP

Conclusion: According to results, we can conclude that, LC inactivation has no effect on LTP production in DG area, but probably LC neurons regulate part of events that occurs during tetanic stimulations in granular cells and are necessary for maintenance of LTP in PS amplitude