Effects of carnosine on long-term plasticity of medial perforant pathway/dentate gyrus synapses in urethane-anesthetized rats: an in vivo model

Carnosine as an effective neuroprotector in brain pathology and potential neuromodulator in normal conditions

Carnosine (b-alanyl-L-histidine) is an endogenous dipeptide widely distributed in excitable tissues, such as muscle and neural tissues-though in minor concentrations in the latter. Multiple benefits have been attributed to carnosine: direct and indirect antioxidant effect, antiglycating, metal-chelating, chaperone and pH-buffering activity. Thus, carnosine turns out to be a multipotent protector against oxidative damage. However, the role of carnosine in the brain remains unclear. The key aspects concerning carnosine in the brain reviewed are as follows: its concentration and bioavailability, mechanisms of action in neuronal and glial cells, beneficial effects in human studies. Recent literature data and the results of our own research are summarized here. This review covers studies of carnosine effects on both in vitro and in vivo models of cerebral damage, such as neurodegenerative disorders and ischemic injuries and the data on its physiological actions on neuronal signaling and cerebral functions. Besides its antioxidant and homeostatic properties, new potential roles of carnosine in the brain are discussed.

Neonatal vaccination with bacillus Calmette-Guérin and hepatitis B vaccines modulates hippocampal synaptic plasticity in rats

Immune activation can exert multiple effects on synaptic transmission. Our study demonstrates the influence of neonatal vaccination on hippocampal synaptic plasticity in rats under normal physiological conditions. The results revealed that neonatal BCG vaccination enhanced synaptic plasticity. In contrast, HBV hampered it. Furthermore, we found that the cytokine balance shifted in favour of the T helper type 1/T helper type 2 immune response in BCG/HBV-vaccinated rats in the periphery. The peripheral IFN-γ:IL-4 ratio was positively correlated with BDNF and IGF-1 in the hippocampus. BCG raised IFN-γ, IL-4, BDNF and IGF-1 and reduced IL-1β, IL-6, and TNF-α in the hippocampus, whereas, HBV triggered the opposite effects.

Effects of cold exposure on behavioral and electrophysiological parameters related with hippocampal function in rats

Aim: Behavioral and mental changes may occur in people exposed to cold stress by decreasing their work efficiency and their mental capacity while increasing the number of accidents on the job site. The goal of this study was to explore the effect of cold stress in spatial learning performance excitability and LTP.

Materials and Methods: Three to four month old rats were randomly divided into four groups to form a control group and a cold stress group for each sex. The groups of cold stressed animals were placed in a cold room ambient temperature of 4°C for 2 h day. Adrenal glands and body weight (g) were recorded in control and stressed rats during the cold exposure. Spatial learning (acquisition phase) and memory (probe trial) were tested in the Morris water maze (MWM) immediately after daily exposure. Latency to locate the hidden platform, distance moved (DM), mean distance to platform, swim speed (SS) and time spent in the platform quadrant were compared between genders and treatments. Field potential recordings were made, under urethane anesthesia, from the dentate gyrus (DG) granule-cell layer, with stimulation of the medial perforant pathway 2 h after the probe trial. This study examined spatial memory as measured by MWM performance and hippocampal long-term potentiation (LTP) in the DG after exposure to cold in a repeated stress condition for 2 h/day for 5 days.

Results: The cold-exposed female rats needed less time to find the hidden platform on day 1 (43.0 ± 13.9 s vs. 63.2 ± 13.2 s), day 2 (18.2 ± 8.4 s vs. 40.9 ± 12.2 s) and on day 4 (8.0 ± 2.1 s vs. 17.2 ± 7.0 s) while cold-exposed male rats showed a decreased escape latency (EL) on day 1 only (37.3 ± 12.5 s vs. 75.4 ± 13.1 s). Cold-exposed male rats spent less time in the target quadrant (30.08 ± 6.11%) than the control male rats (37.33 ± 8.89%). Two hour cold exposure decreased population spike (PS) potentiation during both induction (218.3 ± 21.6 vs. 304.5 ± 18.8%) and maintenance intervals (193.9 ± 24.5 vs. 276.6 ± 25.4%) in male rats. Meanwhile cold exposure did not affect the body weight (C: 221 ± 2.5 vs. S: 222 ± 1.7) but it impacts the adrenal gland relative weight (S: 27.1 ± 1.8 mg vs. C: 26.2 ± 1.4 mg).

Conclusion: Overall, the results show that repeated cold exposure can selectively improve spatial learning in adult female rats, but impaired retention memory for platform location in male rats. It is possible that impaired LTP underlies some of the impaired retention memory caused by cold exposure in the male rats.

Postsynaptic density protein (PSD)-95 expression is markedly decreased in the hippocampal CA1 region after experimental ischemia-reperfusion injury

Synaptic plasticity is important for functional recovery after cerebral ischemic injury. In the present study, we investigated chronological change in the immunoreactivity of PSD-95, a kind of postsynaptic density protein, in the hippocampus proper (CA1-3 regions) after 5 min of transient cerebral ischemia in gerbils. PSD-95 immunoreactivity was observed in MAP-2-immunoreactive dendrites in the CA1-3 regions of the sham group. The PSD-95 immunoreactivity was shown as beaded structure in the MAP-2-immunoreactive dendrites. However, PSD-95 immunoreactivity began to be dramatically decreased in MAP-2-immunoreactive dendrites in the CA1 region, not CA2-3 region, at early time after ischemia-reperfusion. At 5 days after ischemia-reperfusion, MAP-2 immunoreactivity almost disappeared in the ischemic CA1 region, and PSD-95 immunoreactivity was much lower than that in the sham group. In brief, PSD-95 immunoreactivity in the CA1 dendrites was markedly decreased at early time after ischemia-reperfusion. We suggest that decreased PSD-95 immunoreactivity in the ischemic CA1 region may lead to a deficit of postsynaptic plasticity in the brain.

Acute effects of electro-acupuncture (EA) on hippocampal long term potentiation (LTP) of perforant path-dentate gyrus granule cells synapse related to memory

Acupuncture, a traditional Chinese therapeutic method, has been widely used in clinical practice to treat diseases such as stroke, Bell's palsy, Alzheimer disease, Parkinson diseases, dysmenorrhea and chronic pain. Mounting lab data had suggested that electro-acupuncture could alleviate dementia and restore long term potentiation of hippocampus in rat. Clinical data also indicated that electro-acupuncture could improve electrical activity of brain in vascular dementia patients. However, its biological basis and acute effects on hippocampal long term potentiation (LTP) remain not well understood. Therefore, we sought to investigate whether acute electro-acupuncture (acupoints: ST36 and SP6; continuous wave, 2 mV, 2Hz; lasted 20 min) could enhance LTP of perforant path-dentate gyrus granule cells in anesthetized rat and explore its underlying mechanisms. We found that electro-acupuncture could significantly increase PS2/PS 1 in pair pulse test (P <0.05, inter-pulse interval: 20ms and 90ms). When compared to control group, electro-acupuncture could significantly enhance LTP to about 234% which was about 143% of that in control group (P <0.05). It suggested that electro-acupuncture could modulate the function of interneurons in hippocampus hence increase LTP.

Electrophysiological evidence of biphasic action of carnosine on long-term potentiation in urethane-anesthetized rats

Carnosine is a dipeptide synthesized by the carnosine synthetase from β-alanine and l-histidine. The well-known effects of carnosine may be related with mechanisms producing long-term potentiation which is one of the electrophysiological signs of memory. In the present study we aimed to investigate the effect of four different doses of carnosine on long-term potentiation in urethane-anesthetized rat. A bipolar stimulating electrode was placed in the medial perforant path and a double-barrel glass micropipette was placed in the dentate gyrus as the recording electrode. Artificial cerebrospinal fluid (in the control group) or carnosine (0.1, 1, 10, and 100μg/μL) was infused into the dentate gyrus. Our results showed that the I/O curve of the excitatory postsynaptic potential slope or population spike amplitude was not significantly shifted by carnosine. We found that population spike amplitude increased to 244% and 287% at the dose of 100μg/μL in the post-tetanic and induction phases, respectively, but decreased to 163% and 186% at the dose of 0.1μg/μL and to 145% and 162% at the dose of 1μg/μL when compared with 203% and 232% of the control values. However, there were no significant differences for the slope of excitatory postsynaptic potential. Carnosine had no effect on the EPSP slope or PS amplitude recorded from the dentate gyrus in response to test stimuli when high-frequency stimulation was not delivered. In the present study, we speculated that the effects of carnosine in lower or higher doses could be explained by its effect on different processes, such as soluble guanylyl cyclase inhibition or the conversion of carnosine into histamine.