tuncay özgünen | Çukurova University (original) (raw)

Papers by tuncay özgünen

The apparent change in the egg membrane potential at fertilization gives rise to fertilization po... more The apparent change in the egg membrane potential at fertilization gives rise to fertilization potential (FP). FP is the initial, transient electrical block to polyspermy as shown in most species especially those exhibiting external fertilization, and it protects the egg from a second sperm entry until the permanent, mechanical block is set up. Polyspermy is lethal in most species, and for a successful fertilization resting membrane potential (RMP) and FP of the egg have to be held in optimum ranges. Shifts in environmental pH may interfere with a successful fertilization by affecting these bioelectrical potentials. In the present study, we investigated how pH alterations affected the RMP and FP parameters of the egg in the frog, Rana cameranoi. Egg membrane potentials were recorded by the conventional microelectrode technique. RMP and FP parameters were evaluated. Ten percent Ringer solution (pH=7.80) was used for the control group. Acidic (Acd) and alkaline (Alk) experimental groups were kept in the Ringer solutions at pH 6.50 and 9.00, respectively.

International Journal of Gynecology & Obstetrics, 1993

in preeclamptic pregnancies.

International Journal of Neuroscience, 2002

The aim of the present study was to investigate the effects of excitotoxic damage of the serotone... more The aim of the present study was to investigate the effects of excitotoxic damage of the serotonergic cell bodies in the median raphe nucleus (MRN) on the scopolamine-induced working memory deficits in a single-trial light/dark inhibitory avoidance task. Rats were given 1 mg/kg of scopolamine hydrobromide (intraperitonal, i.p.) or saline before the inhibitory avoidance training, in which initial preference to the dark compartment (escape latency) was used to measure nonmnemonic behaviors, and response latency to enter the dark compartment immediately after the shock was used to measure working memory. It was found that scopolamine significantly reduced escape latencies in sham-lesioned rats, whereas it had no effect in the rats with MRN lesions. Although MRN lesion per se did not alter response latency, it prevented scopolamine-induced decrease in this parameter. These results suggest that the antagonistic interactive processes between serotonergic projections of the MRN and the muscarinic cholinergic system modulate nonmnemonic attentional component of working memory formation in the inhibitory avoidance.

European Neuropsychopharmacology, 2006

In the present study, the effects of N-methyl-d-aspartate (NMDA) receptor antagonist, d,l-2-amino... more In the present study, the effects of N-methyl-d-aspartate (NMDA) receptor antagonist, d,l-2-amino-5-phosphonopentanoic acid (AP5) bilaterally infused into the dorsal hippocampus (2.0 Al /5 Ag), on the retrieval of fear memory to partial and whole foreground cues were evaluated by using a step-through passive avoidance and Pavlovian fear conditioning. In the both conditioning tasks, following a 30-s preshock exposure period to the shockassociated context, rats received a single shock in a foreground manner for fear memory exhibition by freezing. Rats with AP5 infusion 5 min before the retrieval tests showed profound freezing deficits either immediately or 48 h after the shock in the testing section of the passive avoidance chamber where foreground cues was partially presented. In the Pavlovian conditioning chamber where fear conditioning was tested in the whole of the context that was explicitly paired with the shock, AP5 rats in all infusion schedules exhibited robust freezing responses. These results showed that hypofunction of the hippocampal NMDA receptors impaired the retrieval of fear memory to partial, and not whole, foreground cues. This suggests that NMDA receptors of the hippocampus are involved in the formation of background context representations about foreground events when there is a deficit in perceiving certain sensory properties of the foreground retrieval cues. D

European Journal of Pharmacology, 2001

The aim of the present study was to determine the involvement of the median raphe serotonergic sy... more The aim of the present study was to determine the involvement of the median raphe serotonergic system in the effects of ketamine on anxiety behaviours and related memory. The effects of ketamine pretreatment (3 and 10 mg/kg, i.p.) on three types of fear-motivated behaviours, unconditioned one-way escape, conditioned avoidance and freezing were tested. Experiments were performed with the inhibitory avoidance apparatus in rats with ibotenic acid lesions of the median raphe nucleus. It was found that 10 mg/kg ketamine had an anxiogenic-like effect on one-way escape type of fear and anxiolytic-like effect on conditioned freezing-related fear; these effects were unaffected by median raphe lesions. Both ketamine doses impaired freezing-related fear memory. Ketamine (10 mg/kg) also produced an anxiolytic-like effect on avoidance type of fear and impaired avoidance memory. The median raphe lesions attenuated the anxiolytic action of the drug on the avoidance type of fear and prevented ketamine-induced avoidance memory impairment. These results suggest that the anxiolytic-like effect of ketamine on avoidance-type fear is mediated through the median raphe serotonergic system.

The apparent change in the egg membrane potential at fertilization gives rise to fertilization po... more The apparent change in the egg membrane potential at fertilization gives rise to fertilization potential (FP). FP is the initial, transient electrical block to polyspermy as shown in most species especially those exhibiting external fertilization, and it protects the egg from a second sperm entry until the permanent, mechanical block is set up. Polyspermy is lethal in most species, and for a successful fertilization resting membrane potential (RMP) and FP of the egg have to be held in optimum ranges. Shifts in environmental pH may interfere with a successful fertilization by affecting these bioelectrical potentials. In the present study, we investigated how pH alterations affected the RMP and FP parameters of the egg in the frog, Rana cameranoi. Egg membrane potentials were recorded by the conventional microelectrode technique. RMP and FP parameters were evaluated. Ten percent Ringer solution (pH=7.80) was used for the control group. Acidic (Acd) and alkaline (Alk) experimental groups were kept in the Ringer solutions at pH 6.50 and 9.00, respectively.

International Journal of Gynecology & Obstetrics, 1993

in preeclamptic pregnancies.

International Journal of Neuroscience, 2002

The aim of the present study was to investigate the effects of excitotoxic damage of the serotone... more The aim of the present study was to investigate the effects of excitotoxic damage of the serotonergic cell bodies in the median raphe nucleus (MRN) on the scopolamine-induced working memory deficits in a single-trial light/dark inhibitory avoidance task. Rats were given 1 mg/kg of scopolamine hydrobromide (intraperitonal, i.p.) or saline before the inhibitory avoidance training, in which initial preference to the dark compartment (escape latency) was used to measure nonmnemonic behaviors, and response latency to enter the dark compartment immediately after the shock was used to measure working memory. It was found that scopolamine significantly reduced escape latencies in sham-lesioned rats, whereas it had no effect in the rats with MRN lesions. Although MRN lesion per se did not alter response latency, it prevented scopolamine-induced decrease in this parameter. These results suggest that the antagonistic interactive processes between serotonergic projections of the MRN and the muscarinic cholinergic system modulate nonmnemonic attentional component of working memory formation in the inhibitory avoidance.

European Neuropsychopharmacology, 2006

In the present study, the effects of N-methyl-d-aspartate (NMDA) receptor antagonist, d,l-2-amino... more In the present study, the effects of N-methyl-d-aspartate (NMDA) receptor antagonist, d,l-2-amino-5-phosphonopentanoic acid (AP5) bilaterally infused into the dorsal hippocampus (2.0 Al /5 Ag), on the retrieval of fear memory to partial and whole foreground cues were evaluated by using a step-through passive avoidance and Pavlovian fear conditioning. In the both conditioning tasks, following a 30-s preshock exposure period to the shockassociated context, rats received a single shock in a foreground manner for fear memory exhibition by freezing. Rats with AP5 infusion 5 min before the retrieval tests showed profound freezing deficits either immediately or 48 h after the shock in the testing section of the passive avoidance chamber where foreground cues was partially presented. In the Pavlovian conditioning chamber where fear conditioning was tested in the whole of the context that was explicitly paired with the shock, AP5 rats in all infusion schedules exhibited robust freezing responses. These results showed that hypofunction of the hippocampal NMDA receptors impaired the retrieval of fear memory to partial, and not whole, foreground cues. This suggests that NMDA receptors of the hippocampus are involved in the formation of background context representations about foreground events when there is a deficit in perceiving certain sensory properties of the foreground retrieval cues. D

European Journal of Pharmacology, 2001

The aim of the present study was to determine the involvement of the median raphe serotonergic sy... more The aim of the present study was to determine the involvement of the median raphe serotonergic system in the effects of ketamine on anxiety behaviours and related memory. The effects of ketamine pretreatment (3 and 10 mg/kg, i.p.) on three types of fear-motivated behaviours, unconditioned one-way escape, conditioned avoidance and freezing were tested. Experiments were performed with the inhibitory avoidance apparatus in rats with ibotenic acid lesions of the median raphe nucleus. It was found that 10 mg/kg ketamine had an anxiogenic-like effect on one-way escape type of fear and anxiolytic-like effect on conditioned freezing-related fear; these effects were unaffected by median raphe lesions. Both ketamine doses impaired freezing-related fear memory. Ketamine (10 mg/kg) also produced an anxiolytic-like effect on avoidance type of fear and impaired avoidance memory. The median raphe lesions attenuated the anxiolytic action of the drug on the avoidance type of fear and prevented ketamine-induced avoidance memory impairment. These results suggest that the anxiolytic-like effect of ketamine on avoidance-type fear is mediated through the median raphe serotonergic system.