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A ketogenic diet (KD) is a high-fat, low-carbohydrate metabolic regimen; its effectiveness in the treatment of refractory epilepsy suggests that the mechanisms underlying its anticonvulsive effects differ from those targeted [...]

Heart rate (HR), body temperature (Temp), locomotor activity (LA), and oxygen consumption ([O.sub.2]C) were studied in awake mice lacking one or both of the adenosine [A.sub.1] or [A.sub.2A] receptors ([A.sub.1]R or [A.sub.2A]R, respectively) using telemetry and respirometry, before and after caffeine administration. All parameters were lower during day than night and higher in females than males. When compared with wild-type (WT) littermates, HR was higher in male AIR knockout ([A.sub.1]RKO) mice but lower in [A.sub.2A]RKO mice and intermediate in [A.sub.1]-[A.sub.2A]R double KO mice. A single dose of an unselective [beta]-blocker (timolol; 1 mg/kg) abolished the HR differences between these genotypes. Deletion of [A.sub.1]Rs had little effect on Temp, whereas deletion of [A.sub.2A]RS increased it in females and decreased it in males. [A.sub.1]-[A.sub.2A]RKO mice had lower Temp than WT mice. LA was unaltered in [A.sub.1]RKO mice and lower in [A.sub.2]ARKO and [A.sub.1]-[A.sub.2A]RKO mice than in WT mice. Caffeine injection increased LA but only in mice expressing [A.sub.2]AR. Caffeine ingestion also increased LA in an [A.sub.2A]R-dependent manner in male mice. Caffeine ingestion significantly increased [O.sub.2]C in WT mice, but less in the different KO mice. Injection of 30 mg/kg caffeine decreased Temp, especially in KO mice, and hence in a manner unrelated to [A.sub.1]R or [A.sub.2A]R blockade. Selective [A.sub.2B] antagonism had little or no effect. Thus [A.sub.1]R and [A.sub.2A]R influence HR, Temp, LA, and [O.sub.2]C in mice in a sex-dependent manner, indicating effects of endogenous adenosine. The [A.sub.2A]R plays an important role in the modulation of [O.sub.2]C and LA by acute and chronic caffeine administration. There is also evidence for effects of higher doses of caffeine being independent of both [A.sub.1]R and [A.sub.2A]R. diurnal rhythm; metabolic rate; locomotor activity; adenosine; telemetry

We examined how the endogenous anticonvulsant adenosine might influence [gamma]-aminobutyric acid type A ([GABA.sub.A]) receptor stability and which adenosine receptors (ARs) were involved. Upon repetitive activation (GABA 500 [micro]M), [GABA.sub.A] receptors, microtransplanted into Xenopus oocytes from neurosurgically resected epileptic human nervous tissues, exhibited an obvious [GABA.sub.A]-current ([I.sub.GABA]) run-down, which was consistently and significantly reduced by treatment with the nonselective adenosine receptor antagonist CGS15943 (100 nM) or with adenosine deaminase (ADA) (1 units/ ml), that inactivates adenosine. It was also found that selective antagonists of A2B (MRS1706, 10 nM) or A3 (MRS1334, 30 nM) receptors reduced [I.sub.GABA] run-down, whereas treatment with the specific A1 receptor antagonist DPCPX (10 nM) was ineffective. The selective A2A receptor antagonist SCH58261 (10 nM) reduced or potentiated [I.sub.GABA] run-down in [approximately equal to]40% and [approximately equal to]20% of tested oocytes, respectively. The ADA-resistant, AR agonist 2-chloroadenosine (2-CA) (10 [micro]M) potentiated [I.sub.GABA] run-down but only in [approximately equal to]20% of tested oocytes. CGS15943 administration again decreased [I.sub.GABA] run-down in patch-clamped neurons from either human or rat neocortex slices. [I.sub.GABA] run-down in pyramidal neurons was equivalent in A1 receptor-deficient and wt neurons but much larger in neurons from A2A receptor-deficient mice, indicating that, in mouse cortex, [GABA.sub.A]-receptor stability is tonically influenced by A2A but not by A1 receptors. [I.sub.GABA] run-down from wt mice was not affected by 2-CA, suggesting maximal ARs activity by endogenous adenosine. Our findings strongly suggest that cortical A2-A3 receptors alter the stability of [GABA.sub.A] receptors, which could offer therapeutic opportunities. A2A receptor | A3 receptor | microtransplantation into Xenopus oocyte | temporal lobe epilepsy

The present study was performed to investigate the role of adenosine [A.sub.1] receptors in regulating blood pressure in conscious mice. Adenosine [A.sub.1]-receptor knockout ([A.sub.1]R-/-) mice and their wild-type ([A.sub.1]R+/+) littermates were placed on standardized normal-salt (NS), high-salt (HS), or salt-deficient (SD) diets for a minimum of 10 days before telemetric blood pressure and urinary excretion measurements in metabolic cages. On the NS diet, daytime and nighttime mean arterial blood pressure (MAP) was 7-10 mmHg higher in [A.sub.1]R-/- than in [A.sub.1]R+/+ mice. HS diet did not affect the MAP in [A.sub.1]R-/- mice, but the daytime and nighttime MAP of the [A.sub.1]R+/+ mice increased by ~10 mmHg, to the same level as that in the [A.sub.1]R-/-. On the SD diet, day-and nighttime MAP decreased by ~6 mmHg in both [A.sub.1]R-/- and [A.sub.1]R+/+ mice, although the MAP remained higher in [A.sub.1]R-/- than in [A.sub.1]R+/+ mice. Although plasma renin levels decreased with increased salt intake in both genotypes, the [A.sub.1]R-/- mice had an approximately twofold higher plasma renin concentration on all diets compared with [A.sub.1]R+/+ mice. Sodium excretion was elevated in the [A.sub.1]R-/- compared with the [A.sub.1]R+/+ mice on the NS diet. There was no difference in sodium excretion between the two genotypes on the HS diet. Even on the SD diet, [A.sub.1]R-/- mice had an increased sodium excretion compared with [A.sub.1]R+/+ mice. An abolished tubuloglomerular feedback response and reduced tubular reabsorption can account for the elevated salt excretion found in [A.sub.1]R-/- animals. The elevated plasma renin concentrations found in the [A.sub.1]R-/- mice could also result in increased blood pressure. Our results confirm that adenosine, acting through the adenosine [A.sub.1] receptor, plays an important role in regulating blood pressure, renin release, and sodium excretion. tubuloglomerular feedback; renal function; telemetry; salt diet

Activation of [A.sub.1] adenosine receptors ([A.sub.1]ARs) may be a crucial step in protection against myocardial ischemia-reperfusion (I/R) injury; however, the use of pharmacological [A.sub.1]AR antagonists to inhibit myocardial protection has yielded inconclusive results. In the current study, we have used mice with genetically modified [A.sub.1]AR expression to define the role of [A.sub.1]AR in intrinsic protection and ischemic preconditioning (IPC) against I/R injury. Normal wild-type (WT) mice, knockout mice with deleted ([A.sub.1]K[O.sup.-/-]) or single-copy ([A.sub.1]K[O.sup.+/-]) [A.sub.1]AR, and transgenic mice ([A.sub.1]TG) with increased cardiac [A.sub.1]AR expression underwent 45 min of left anterior descending coronary artery occlusion, followed by 60 min of reperfusion. Subsets of each group were preconditioned with short durations of ischemia (3 cycles of 5 min of occlusion and 5 min of reperfusion) before index ischemia. Infarct size (IF) in WT, [A.sub.1]K[O.sup.+/-], and [A.sub.1]K[O.sup.-/-] mice was (in % of risk region) 58 [+ or -] 3, 60 [+ or -] 4, and 61 [+ or -] 2, respectively, and was less in [A.sub.1]TG mice (39 [+ or -] 4, P < 0.05). A strong correlation was observed between [A.sub.1]AR expression level and response to IPC. IF was significantly reduced by IPC in WT mice (35 [+ or -] 3, P < 0.05 vs. WT), [A.sub.1]K[O.sup.-/-] + IPC(48 [+ or -] 4, P < 0.05 vs. [A.sub.1]K[O.sup.+/-]), and [A.sub.1]TG + IPC mice (24 [+ or -] 2, P < 0.05 vs. [A.sub.1]TG). However, IPC did not decrease IF in [A.sub.1]K[O.sup.-/-] + IPC mice (63 [+ or -] 2). In addition, [A.sub.1]K[O.sup.-/-] hearts subjected to global I/R injury demonstrated diminished recovery of developed pressure and diastolic function compared with WT controls. These findings demonstrate that [A.sub.1]ARs are critical for protection from myocardial I/R injury and that cardioprotection with IPC is relative to the level of [A.sub.1]AR gene expression. myocardial ischemia-reperfusion injury; functional genomics; genetically altered mice

It has been suggested that the developing brain is less vulnerable to the adverse effects of hypoglycemia than the mature brain; however, this issue remains controversial. We also do not know the magnitude or duration of hypoglycemia needed to trigger hypoglycemic brain injury during development. To address this issue a series of in vivo and in vitro studies were performed. First, we established an acute model of insulin-induced hypoglycemia in mice by administering 3 U/kg of neutral-protamine Hagadorn insulin subcutaneously. When we examined degenerating neurons in hippocampus and striatum by TUNEL labeling, injury was observed after 4 h of hypoglycemia in postnatal day (P)7 mice, and we observed more cell injury in animals rendered hypoglycemic at P7 than at P21. Studies of hippocampal slice cultures revealed that reduction in glucose concentration induced more neuronal injury in slices prepared from P3 and P7 than from P14 and P21 mice. Treatment of slices with an adenosine [A.sub.1] receptor ([A.sub.1]AR) antagonist reduced the hypoglycemic damage, whereas agonists increased damage, particularly in slices prepared from very young pups. This suggests a critically important role for [A.sub.1]ARs, which was further demonstrated by the reduction of hypoglycemic damage in hippocampal slices prepared from [A.sub.1]A[R.sup.-/-] mice. Furthermore, insulin-induced hypoglycemia in P7 [A.sub.1]A[R.sup.-/-] mice did not increase TUNEL-positive cells, but a major increase was seen in [A.sub.1]A[R.sup.+/-] mice. These observations show that the developing nervous system is indeed sensitive to acute hypoglycemic injury and that [A.sub.1]AR activation contributes to damage induced by hypoglycemia, particularly in immature mouse brain.

Adenosine is known to stimulate chloride secretion by mouse jejunum. Whereas the receptor on the basolateral side is believed to be [A.sub.2B], the receptor involved in the luminal effect of adenosine has not been identified. We found that jejuna expressed mRNA for all adenosine receptor subtypes. In this study, we investigated the stimulation of chloride secretion by adenosine in jejuna derived from mice lacking the adenosine receptors of [A.sub.1] ([A.sub.1]R) and [A.sub.2A] ([A.sub.2A]R) or control littermates. The jejunal epithelium was mounted in a Ussing chamber, and a new method on the basis of impedance analysis was used to calculate the short-circuit current ([I.sub.sc]) values. Chloride secretion was assessed by the [I.sub.sc] after inhibition of the sodium-glucose cotransporter by adding phloridzin to the apical bathing solution. The effect of apical adenosine on chloride secretion was lost in jejuna from mice lacking the [A.sub.1]R. There was no difference in the response to basolaterally applied adenosine or to apical forskolin. Furthermore, in jejuna from control mice, the effect of apical adenosine was also abolished in the presence of 8-cyclopentyl-1,3-dipropylxanthine, a specific [A.sub.1]R antagonist. Responses to adenosine were identical in jejuna from control and [A.sub.2A]R knockout mice. This study demonstrates that [A.sub.1]R (and not [A.sub.2A]R) mediates the enhancement of chloride secretion induced by luminal adenosine in mice jejunum. intestinal secretion; diarrhea; chloride channels

Periventricular leukomalacia is characterized by a reduction in brain matter and secondary ventriculomegaly and is a major cause of developmental delay and cerebral palsy in prematurely born infants. Currently, our understanding of the pathogenesis of this condition is limited. In animal models, features of periventricular leukomalacia can be induced by hypoxia and activation of [A.sub.1] adenosine receptors ([A.sub.1]ARs). Using mice that are deficient in the [A.sub.1]AR gene ([A.sub.1]AR-/-), we show that [A.sub.1]ARs play a prominent role in the development of hypoxia-induced ventriculomegaly in neonates. Supporting a role for adenosine in the pathogenesis of developmental brain injury, ventriculomegaly was also observed in mice lacking the enzyme adenosine deaminase, which degrades adenosine. Thus, adenosine acting on [A.sub.1]ARs appears to mediate hypoxia-induced brain injury ventriculomegaly during early postnatal development. brain | premature | infant | periventricular leukomalacia