Tuncay Özgünen

Effects of ketamine on different types of anxiety/fear and related memory in rats with lesions of the median raphe nucleus

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.

Effect of gonadotrophin dose on oocyte retrieval in superovulated BALB/c mice

Mice are commonly used animal models in reproductive and developmental research. In order to get satisfying results from such experiments, large numbers of ova must be available and this can be achieved by using various ovulation induction protocols. To obtain an optimal response from these stimulation protocols, parameters such as breeding-housing conditions of the animal strains, the best age for superovulation, and type and dose of gonadotrophins must be optimized. The aim of this study was to investigate the impact of exogenous stimulation with increasing amounts of gonadotrophins on the number and quality of oocytes/pre-embryos recovered from outbred BALB/c mice. A dose-response analysis was performed by stimulating prepubescent (21- to 25-day-old) and sexually mature (6 to 8 weeks old) female mice with hMG, which contains equal amounts of follicle-stimulating hormone (FSH) and luteinizing hormone (LH). The stimulation dose contained 5, 10, 15, 20, 25 or 30 IU of FSH/LH. The effect of increasing stimulation was assessed by monitoring the number and maturity of ova recovered from the tubes. The data were analyzed by using a one-way Anova test and student t-test. Increasing stimulation doses in the prepubescent females resulted in an increased number of ova. A maximum of 55 ova per mouse was reached when stimulating with 20 IU of FSH/LH; higher stimulation doses showed no further increase in oocyte recovery. In the prepubescent group, a maximal number of recovered mature ova was reached with 15 IU of FSH/LH. In the sexually mature female group, 20 IU of FSH/LH gave the best quantitative and qualitative results. Positive effects of copulation on the number and maturity of oocytes in all induction doses were more evident in the prepubescent females and these parameters were significantly more improved (P < 0.05) in this group when compared to the pubertal females. Our findings led to the conclusion that ovulation induction of prepubescent outbred BALB/c mice with 15 IU FSH/LH and sexually mature ones with 20 IU FSH/LH give the best results in terms of oocyte number and maturity.

Median raphe nucleus mediates forming long-term but not short-term contextual fear conditioning in rats

The brain serotonin is involved in mediation of emotional behaviour including anxiety and related fear conditioning. It is known that the median raphe nucleus (MRN) is the origin of a serotonergic pathway and mainly innervates septo-hippocampal formation which plays an important role in emotional cognition. However, its regulatory role in different types of fear conditioning is still unclear. In the present study, the animals underwent ibotenic acid or sham lesions of the median raphe nucleus and the effects of MRN lesions on immediate and delayed fear conditioning to multiple contextual cues were studied. Freezing behaviour served as a measure of contextual fear. Sham-lesioned animals showed reliable conditional freezing when observed immediately following foot-shock (1.0 mA) for 3-min test and 48 h after the shock for 12-min test. Rats with MRN lesions displayed robust freezing behaviour immediately after the shock, even though they showed a marked deficit in freezing 48 h following the shock. These findings indicate that the MRN-serotonergic septo-hippocampal pathway is involved in the regulation of anxiety related to fear conditioning triggered by contextual cues, suggesting that short-term contextual fear is independent on the MRN while long-term contextual fear depends on the MRN.

Hypofunction of the dorsal hippocampal NMDA receptors impairs retrieval of memory to partially presented foreground context in a single-trial fear conditioning in rats

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 microl /5 microg), 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 shock-associated 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.

DIFFERENTIAL CONTRIBUTIONS OF RIGHT AND LEFT BRAINS TO PAW SKILL IN RIGHT- AND LEFT-PAWED FEMALE RATS

Paw preference and paw frequency was studied in female rats. Paw preference was assessed using a modified version of food reaching task in quadrupedal position. Of 68 rats, 56 (82.4%) were right-handed, 7 (10.3%) were left-handed, and 5 (7.4%) were mixed-handed. There were significantly more right-handers than left-handers. The distribution of right minus left (L) paw reach (R + L = 50) was not U-shaped, it was J-shaped like in humans. Estrus cycle was a significant factor influencing the right-paw entry scores: most of left-handers were in estrus and proestrus, most of left-handers were in estrus, and most of mixed-handers were in postestrus. In right- and non-right-handers, the frequency of right-paw usage (right-hand skill) increased linearly with testing days, but the frequency of left-hand usage (left-hand skill) did not show significant changes with the successive testing days. Controlling for body weight and estrus only accentuated these results. It was concluded that distribution of hand preference in rats is J-shaped and there is a right-sided population bias in handedness in rats like in humans. The results suggested that motor learning in paw skill is mainly involved the left brain in right- and mixed-handed rats, not the right brain: only the left brain has the inbuilt capacity for motor learning in female rats. Such an asymmetric cognitive control in an animal model may have a major impact in many aspects of biology in respect to normal functioning, superior talents, and disease (see Geschwind, 1985).

Effects of excitotoxic median raphe lesion on working memory deficits produced by the dorsal hippocampal muscarinic receptor blockade in the inhibitory avoidance in rats.

The experiments investigated the interactions between median raphe nucleus (MRN) serotonergic and septo-hippocampal muscarinic cholinergic systems in the modulation of forming and storing performances of working memory. Rats with ibotenic acid-induced MRN-lesion bilaterally received scopolamine (2-4 microg/each side) infusion into the dentate gyrus of the dorsal hippocampus and were tested in a single trial step-through inhibitory avoidance. Initial preference to the dark compartment (escape latency) was taken as the measure of non-mnemonic behaviours and response latency to enter the dark compartment immediately after the foot-shock was used to measure working memory. The high-dose scopolamine infusion 10 min before the training decreased escape latencies in the sham-lesioned rats, whereas had no effect in the MRN-lesioned rats. Although MRN lesion per se did not alter response latency, it alleviated pre-training scopolamine-induced decrease, but aggravated post-training scopolamine-induced reduction in this parameter. These results suggest that the antagonistic interactive processes between MRN-serotonergic and hippocampal cholinergic systems modulate non-mnemonic component of working memory formation, whereas the storing performance of working memory is modulated by the synergistic interactions between these systems in the hippocampus, mainly in the dentate gyrus.

EFFECTS OF EXCITOTOXIC MEDIAN RAPHE LESIONS ON SCOPOLAMINE-INDUCED WORKING MEMORY DEFICITS IN INHIBITORY AVOIDANCE

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, IP) 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.

A Rare Skin Lesion During Pregnancy: Localized Cutaneous Leishmaniasis

Leishmaniasis is an infectious disease that is spread by phlebotomine sand flies. These flies cause infections called cutaneous and/or visceral leishmaniasis in humans. In this paper, we present a pregnant patient who was diagnosed with localized cutaneous leishmaniasis, a localized form of the disease, and the treatment we applied to the patient. The patient was given systemic amphotericin-B treatment, however the immunosuppressive state of pregnancy and the diabetes of the patient complicated the treatment. Although the size of the lesion regressed during pregnancy, we could not completely cure the disease.

The Effects of Chronic Hyperoxia (80%) on the Behavior of Rat Litters

In our previous reports it was shown that oxygen at 40% and 80% inhibited pregnancy and birth rate of rats (4, 5). In this study, pregnant female rats in the third trimester were exposed to hyperoxia and the births were performed in a hyperoxic cabin. The action of hyperoxia is known to be stressful for living organisms. Brain and lungs are two organs which are most sensitive to hyperoxia, and have been intensively investigated (3, 7, 8, 11). Extensive literature exists regarding the acute effects and toxicity of normobaric hyperoxia (3, 12). Few reports have appeared to examine behavioral changes in rats that were exposed chronically to hyperoxia (8–10). On the other hand, the cerebral circulation is sensitive to changes in blood oxygen. Also, hyperoxia reduced cerebral blood flow (3). Low blood flow will especially influence the brain stem, a region that is vulnerable, and develop specific necrosis during hyperoxic oxygen exposure (1). There is also evidence that the central nervous system (CNS) is particularly sensitive to the toxic effects of hyperoxia, even three hours exposure with 95% oxygen produced neural necrosis in the rat (2). The study has been carried out to obtain chronic hyperoxic rat litters and to investigate the effects of hyperoxic conditions on the changes of behavioral patterns of the rat litters (6). This is the reason, we chose these parameters to get a suitable method for testing ontogeny of open field behavior to determine hyperoxic-caused modifications of locomotor activity.