Neuroprotective effects of hibernation-regulating substances against low-temperature-induced cell death in cultured hamster hippocampal neurons

Bat-derived cells use glucose as a cryoprotectant

Evolution of heterothermy in environments with variable temperatures has allowed bats to survive food scarcity during seasonal climatic extremes by using torpor as a hibernation strategy. The controlled reduction of body temperature and metabolism through complex behavioural and physiological adaptations at organismal, organ, cellular and molecular levels includes the ability of tissues and cells to adapt to temperature alterations. Based on the prediction that cells of different tissues cultured in vitro would differ in their ability to withstand freezing and thawing of the medium, we determined the survival rate of bat-derived cells following exposure to -20 °C for 24 h in media with no cryoprotective agents or medium supplemented by glucose in concentration range 0-3333 mM. Cell survival rates were determined in relation to availability of glucose in the medium, organ origin, cell concentration and bat species. In general, increased glucose helped cells survive at sub-zero temperatures, though concentrations up to 80-fold higher than those found in chiropterans were needed. However, cells in glucose-free phosphate buffered saline also survived, suggesting that other mechanisms may be contributing to cell survival at low temperatures. Highest in vitro viability was observed in nervus olfactorius-derived cell cultures, with high survival rates and rapid re-growth under optimal conditions after exposure to -20 °C. Kidney cells from different bat species showed comparable overall survival rate patterns, though smaller chiropteran species appeared to utilise lower glucose levels as a cryoprotectant than larger species. Our in vitro data provide evidence that cells of heterothermic bats can survive sub-zero temperatures and that higher glucose levels in important tissues significantly improve hibernation survival at extremely low temperatures.

Performance of bat-derived macrophages at different temperatures

Heterothermy, as a temperature-dependent physiological continuum, may affect host-pathogen interactions through modulation of immune responses. Here, we evaluated proliferation and functional performance of a macrophage cell line established from the greater mouse-eared (Myotis myotis) bat at 8, 17.5, and 37°C to simulate body temperatures during hibernation, daily torpor and euthermia. Macrophages were also frozen to -20°C and then examined for their ability to proliferate in the immediate post-thaw period. We show that bat macrophages can proliferate at lower temperatures, though their growth rate is significantly slower than at 37°C. The cells differed in their shape, size and ability to attach to the plate surface at both lower temperatures, being spheroidal and free in suspension at 8°C and epithelial-like, spindle-shaped and/or spheroidal at 17.5°C. While phagocytosis at temperatures of 8 and 17.5°C amounted to 85.8 and 83.1% of the activity observed at 37°C, respectively, full phagocytic activity was restored within minutes of translocation into a higher temperature. Bat-derived macrophages were also able to withstand temperatures of -20°C in a cryoprotectant-free cultivation medium and, in the immediate post-thaw period, became viable and were able to proliferate. Our in vitro data enhance understanding of macrophage biology.

The opioid peptide biphalin modulates human corneal epithelial wound healing in vitro

PURPOSE

Analgesic drugs, including nonselective opioids and non-steroidal anti-inflammatory drugs, should be used with great precautions to relieve pain after trauma to the corneal epithelium because of their unfavorable effects on wound healing. Biphalin is a synthetic opioid peptide that has been demonstrated to possess a strong analgesic effect on rodents. The purpose of this study is to investigate the effects of biphalin on human corneal epithelial wound healing.

METHODS

An immortalized human corneal epithelial cell (HCEC) culture was used to analyze the effects of biphalin on wound healing. The toxicity of biphalin at various concentrations was measured by the MTT assay. The effects of 1μM and 10μM biphalin on wound closure, cell migration and proliferation were tested in an in vitro scratch assay of HCECs. Naloxone, a non-selective competitive opioid receptor antagonist, was also used to inhibit the effects of biphalin in all experiments.

RESULTS

Biphalin did not cause any toxic effect on HCECs at concentrations lower than 100μM at various incubation time points. Biphalin significantly increased wound healing at 1μM concentration in an in vitro scratch assay of HCECs (P<0.05). It also significantly increased migration of HCECs (P<0.01). There was no significant difference between the biphalin and control groups of HCECs in the Ki67 proliferation assay.

CONCLUSION

Biphalin, which is a synthetic opioid peptide, promotes corneal epithelial wound healing by increasing cell migration. This role should be evaluated in further in vivo and clinical studies.

Delta Opioids: Neuroprotective Roles in Preclinical Studies

Since ancient times, opioids have been used clinically and abused recreationally. In the early stages (about 1,000 AD) of opium history, an Arab physician, Avicenna, administered opioids to control diarrhea and eye diseases. ¹ Opioids have very strong pain relieving properties and they also regulate numerous cellular responses. Opioid receptors are expressed throughout the body, including the nervous system, heart, lungs, liver, gastrointestinal tract, and retina. ^2-6 Delta opioid receptors (DORs) are a very attractive target from the perspective of both receptor function and their therapeutic potential. Due to a rapid progress in mouse mutagenesis and development of small molecules as DOR agonist, novel functions and roles of DORs have emerged in recent years. This review article focuses on the recent advances in the neuroprotective roles of DOR agonists in general and retina neuroprotection in particular. Rather than being exhaustive, this review highlights the selected studies of DOR function in neuroprotection. We also highlight our preclinical studies using rodent models to demonstrate the potentials of DOR agonists for retinal neuroprotection. Based on existing literature and our recently published data on the eye, DOR agonists possess therapeutic abilities that protect the retina and optic nerve injury against glaucoma and perhaps other retinopathies as well. This review also highlights the signaling events associated with DOR for neuroprotection in the eye. There is a need for translational research on DORs to recognize their potential for clinical application such as in glaucoma.

The Mechanism Enabling Hibernation in Mammals

Some rodents including squirrels and hamsters undergo hibernation. During hibernation, body temperature drops to only a few degrees above ambient temperature. The suppression of whole-body energy expenditure is associated with regulated, but not passive, reduction of cellular metabolism. The heart retains the ability to beat constantly, although body temperature drops to less than 10 °C during hibernation. Cardiac myocytes of hibernating mammals are characterized by reduced Ca²⁺ entry into the cell membrane and a concomitant enhancement of Ca²⁺ release from and reuptake by the sarcoplasmic reticulum. These adaptive changes would help in preventing excessive Ca²⁺ entry and its overload and in maintaining the resting levels of intracellular Ca²⁺. Adaptive changes in gene expression in the heart prior to hibernation may be indispensable for acquiring cold resistance. In addition, protective effects of cold-shock proteins are thought to have an important role. We recently reported the unique expression pattern of cold-inducible RNA-binding protein (CIRP) in the hearts of hibernating hamsters. The CIRP mRNA is constitutively expressed in the heart of a nonhibernating euthermic hamster with several different forms probably due to alternative splicing. The short product contained the complete open reading frame for full-length CIRP, while the long product had inserted sequences containing a stop codon, suggesting production of a C-terminal deletion isoform of CIRP. In contrast to nonhibernating hamsters, only the short product was found in hibernating animals. Thus, these results indicate that CIRP expression in the hamster heart is regulated at the level of alternative splicing, which would permit a rapid increment of functional CIRP when entering hibernation. We will summarize the current understanding of the cold-resistant property of the heart in hibernating animals.

Delta Opioid Receptors and Cardioprotection

The opioid receptor family, with associated endogenous ligands, has numerous roles throughout the body. Moreover, the delta opioid receptor (DORs) has various integrated roles within the physiological systems, including the cardiovascular system. While DORs are important modulators of cardiovascular autonomic balance, they are well-established contributors to cardioprotective mechanisms. Both endogenous and exogenous opioids acting upon DORs have roles in myocardial hibernation and protection against ischaemia-reperfusion (I-R) injury. Downstream signalling mechanisms governing protective responses alternate, depending on the timing and duration of DOR activation. The following review describes models and mechanisms of DOR-mediated cardioprotection, the impact of co-morbidities and challenges for clinical translation.

Stereological study of the effects of morphine consumption and abstinence on the number of the neurons and oligodendrocytes in medial prefrontal cortex of rats

Quantitative studies to date on the effects of opioid consumption and abstinence on the nervous system using modern stereological methods have not received enough attention. In addition, they have yielded controversial results. The present study was conducted to investigate the effects of morphine, with or without abstinence, on the neurons and oligodendrocytes of the medial prefrontal cortex (MPFC) in rats using quantitative stereological methods. The male rats were divided into four groups: the first (saline [SAL]) and second (morphine [MOR]) groups were treated with saline and an escalating dose of morphine (5-20 mg/kg) for 30 days, respectively; the third (SAL+abstinence [ABS]) and fourth (MOR+ABS) groups were treated in the same manner as the previous groups plus they had a 30-day abstinence period. The results showed that the volume of the MPFC and its subdivisions decreased by approximately 15% in the MOR group compared with that in the SAL group (P<0.05). In addition, the volume decreased by approximately 24% in the MOR+ABS group compared with that in the SAL+ABS group (P<0.05). The number of neurons in the MOR and MOR+ABS groups decreased by approximately 44% and 35%, respectively, compared with that in their corresponding control groups. Moreover, the number of the oligodendrocytes in the MOR and MOR+ABS groups decreased by approximately 41% and 37%, respectively. No significant difference was noted in the number of cells in the MOR and MOR+ABS groups. In conclusion, morphine consumption leads to a permanent reduction in the number of neurons and oligodendrocytes, and no additional neuron and oligodendrocyte loss occurs after abstinence.

Tau Phosphorylation by GSK3 in Different Conditions

Almost a 20% of the residues of tau protein are phosphorylatable amino acids: serine, threonine, and tyrosine. In this paper we comment on the consequences for tau of being a phosphoprotein. We will focus on serine/threonine phosphorylation. It will be discussed that, depending on the modified residue in tau molecule, phosphorylation could be protective, in processes like hibernation, or toxic like in development of those diseases known as tauopathies, which are characterized by an hyperphosphorylation and aggregation of tau.

Adenosine and Opioid Receptors Do Not Trigger the Cardioprotective Effect of Mild Hypothermia

Mild hypothermia (32°C-34°C) exerts a potent cardioprotection in animal models of myocardial infarction. Recently, it has been proposed that this beneficial effect is related to survival signaling. We, therefore, hypothesized that the well-known cardioprotective pathways dependent on adenosine and/or opioid receptors could be the trigger of hypothermia-induced salvage. Open-chest rabbits were accordingly exposed to 30 minutes of coronary artery occlusion (CAO) under normothermic (NT) or hypothermic ([HT] 32°C) conditions. In the latter, hypothermia was induced by total liquid ventilation with temperature-controlled perfluorocarbons in order to effect ultrafast cooling and to accurately control cardiac temperature. After 4 hours of reperfusion, infarct and no-reflow zone sizes were assessed and quantified as a percentage of the risk zone. In animals experiencing HT ischemia, the infarct size was dramatically reduced as compared to NT animals (9% ± 3% vs 55% ± 2% of the risk zone, respectively). Importantly, administration of opioid and adenosine receptor antagonists (naloxone [6 mg/kg iv] and 8-( p-sulfophenyl) theophylline [20 mg/kg iv], respectively) did not alter the infarct size or affect the cardioprotective effect of hypothermia. Doses of these 2 antagonists were appropriately chosen since they blunted infarct size reduction induced by selective opioid or adenosine receptor stimulation with morphine (0.3 mg/kg iv) or N6-cyclopentyladenosine ([CPA] 100 μg/kg iv), respectively. Therefore, the cardioprotective effect of mild hypothermia is not triggered by either opioid or adenosine receptor activation, suggesting the involvement of other cardioprotective pathways.

Induced hypothermia for infants with hypoxic- ischemic encephalopathy using a servo-controlled fan: an exploratory pilot study

OBJECTIVE

Several trials suggest that hypothermia is beneficial in selected infants with hypoxic-ischemic encephalopathy. However, the cooling methods used required repeated interventions and were either expensive or reported significant temperature variation. The objective of this pilot study was to describe the use, efficacy, and physiologic impact of an inexpensive servo-controlled cooling fan blowing room-temperature air.

PATIENTS AND METHODS

A servo-controlled fan was manufactured and used to cool 10 infants with hypoxic-ischemic encephalopathy to a rectal temperature of 33 degrees C to 34 degrees C. The infants were sedated with phenobarbital, but clonidine was administered to some infants if shivering or discomfort occurred. A servo-controlled radiant warmer was used simultaneously with the fan to prevent overcooling. The settings used on the fan and radiant warmer differed slightly between some infants as the technique evolved.

RESULTS

A rectal temperature of 34 degrees C was achieved in a median time of 58 minutes. Overcooling did not occur, and the mean temperature during cooling was 33.6 degrees C +/- 0.2 degrees C. Inspired oxygen requirements increased in 6 infants, and 5 infants required inotropic support during cooling, but this was progressively reduced after 1 to 2 days. Dehydration did not occur. Five infants shivered when faster fan speeds were used, but 4 of the 5 infants had hypomagnesemia. Shivering was controlled with clonidine in 4 infants, but 1 infant required morphine.

CONCLUSIONS

Servo-controlled fan cooling with room-temperature air, combined with servo-controlled radiant warming, was an effective, simple, and safe method of inducing and maintaining rectal temperatures of 33 degrees C to 34 degrees C in sedated infants with hypoxic-ischemic encephalopathy. After induction of hypothermia, a low fan speed facilitated accurate temperature control, and warmer-controlled rewarming at 0.2 degrees C increments every 30 minutes resulted in more appropriate rewarming than when 0.5 degrees C increments every hour were used.

Histamine in the nervous system

Histamine is a transmitter in the nervous system and a signaling molecule in the gut, the skin, and the immune system. Histaminergic neurons in mammalian brain are located exclusively in the tuberomamillary nucleus of the posterior hypothalamus and send their axons all over the central nervous system. Active solely during waking, they maintain wakefulness and attention. Three of the four known histamine receptors and binding to glutamate NMDA receptors serve multiple functions in the brain, particularly control of excitability and plasticity. H1 and H2 receptor-mediated actions are mostly excitatory; H3 receptors act as inhibitory auto- and heteroreceptors. Mutual interactions with other transmitter systems form a network that links basic homeostatic and higher brain functions, including sleep-wake regulation, circadian and feeding rhythms, immunity, learning, and memory in health and disease.

Endogenous opiates and behavior: 2006

This paper is the 29th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning 30 years of research. It summarizes papers published during 2006 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurological disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

Reversible reduction in dendritic spines in CA1 of rat and ground squirrel subjected to hypothermia-normothermia in vivo: A three-dimensional electron microscope study

A study was made at electron microscope level of changes in the three-dimensional (3-D) morphology of dendritic spines and postsynaptic densities (PSDs) in CA1 of the hippocampus in ground squirrels, taken either at low temperature during hibernation (brain temperature 2-4 degrees C), or after warming and recovery to the normothermic state (34 degrees C). In addition, the morphology of PSDs and spines was measured in a non-hibernating mammal, rat, subjected to cooling at 2 degrees C at which time core rectal temperature was 15 degrees C, and then after warming to normothermic conditions. Significant differences were found in the proportion of thin and stubby spines, and shaft synapses in CA1 for rats and ground squirrels for normothermia compared with cooling or hibernation. Hypothermia induced a decrease in the proportion of thin spines, and an increase in stubby and shaft spines, but no change in the proportion of mushroom spines. The changes in redistribution of these three categories of spines in ground squirrel are more prominent than in rat. There were no significant differences in synapse density determined for ground squirrels or rats at normal compared with low temperature. Measurement of spine and PSD volume (for mushroom and thin spines) also showed no significant differences between the two functional states in either rats or ground squirrels, nor were there any differences in distances between neighboring synapses. Spinules on dendritic shafts were notable qualitatively during hibernation, but absent in normothermia. These data show that hypothermia results in morphological changes which are essentially similar in both a hibernating and a non-hibernating animal.