Hooded seals (Cystophora cristata) rely on large stores of oxygen, either bound to hemoglobin or myoglobin (Mb), to support prolonged diving activity. Pups are born with fully developed hemoglobin stores, but their Mb levels are only 25–30% of adult levels. We measured changes in muscle [Mb] from birth to 1 year of age in two groups of captive hooded seal pups, one being maintained in a seawater pool and one on land during the first 2 months. All pups fasted during the first month, but were fed from then on. The [Mb] of the swimming muscle musculus longissimus dorsi (LD) doubled during the month of fasting in the pool group. These animals had significantly higher levels and a more rapid rise in LD [Mb] than those kept on land. The [Mb] of the shoulder muscle, m. supraspinatus, which is less active in both swimming and hauled-out animals, was consistently lower than in the LD and did not differ between groups. This suggests that a major part of the postnatal rise in LD [Mb] is triggered by (swimming) activity, and this coincides with the previously reported rapid early development of diving capacity in wild hooded seal pups. Liver iron concentration, as determined from another 25 hooded seals of various ages, was almost 10 times higher in young pups (1–34 days) than in yearling animals and adults, and liver iron content of pups dropped during the first month, implying that liver iron stores support the rapid initial rise in [Mb].

There is an urgent need to better understand the mechanisms involved in scar formation in the brain. It is well known that astrocytes are critically engaged in this process. Here, we analyze incipient scar formation one week after a discrete ischemic insult to the cerebral cortex. We show that the infarct border zone is characterized by pronounced changes in the organization and subcellular localization of the major astrocytic protein AQP4. Specifically, there is a loss of AQP4 from astrocytic endfoot membranes that anchor astrocytes to pericapillary basal laminae and a disassembly of the supramolecular AQP4 complexes that normally abound in these membranes. This disassembly may be mechanistically coupled to a downregulation of the newly discovered AQP4 isoform AQP4ex. AQP4 has adhesive properties and is assumed to facilitate astrocyte mobility by permitting rapid volume changes at the leading edges of migrating astrocytes. Thus, the present findings provide new insight in the molecular basis of incipient scar formation.

Stroke is the main cause for acquired disabilities. Pharmaceutical or mechanical removal of the thrombus is the cornerstone of stroke treatment but can only be administered to a subset of patients and within a narrow time window. Novel treatment options are therefore required. Here we induced stroke by permanent occlusion of the distal medial cerebral artery of wild-type mice and knockout mice for the lactate receptor hydroxycarboxylic acid receptor 1 (HCA₁). At 24 h and 48 h after stroke induction, we injected L-lactate intraperitoneal. The resulting atrophy was measured in Nissl-stained brain sections, and capillary density and neurogenesis were measured after immunolabeling and confocal imaging. In wild-type mice, L-lactate treatment resulted in an HCA₁-dependent reduction in the lesion volume accompanied by enhanced angiogenesis. In HCA₁ knockout mice, on the other hand, there was no increase in angiogenesis and no reduction in lesion volume in response to L-lactate treatment. Nevertheless, the lesion volumes in HCA₁ knockout mice—regardless of L-lactate treatment—were smaller than in control mice, indicating a multifactorial role of HCA₁ in stroke. Our findings suggest that L-lactate administered 24 h and 48 h after stroke is protective in stroke. This represents a time window where no effective treatment options are currently available.

The neurogenic potential of the brain decreases during ageing, whereas the risk of neurodegenerative diseases and stroke rises. This creates a mismatch between the rate of neuron loss and the brain's capacity for replacement. Adult neurogenesis primarily occurs in the subgranular zone (SGZ) and the ventricular‐subventricular zone (V‐SVZ). Exercise enhances SGZ neurogenesis, and we previously showed that V‐SVZ neurogenesis is induced by exercise via activation of the lactate receptor HCA₁. Here, we investigated how high‐intensity interval training (HIIT) and medium‐intensity interval training (MIIT) affect neurogenesis in these niches. Wild‐type (WT) and HCA₁ knockout (KO) mice were randomized to sedentary, HIIT or MIIT (n = 5–8 per group) for 3 weeks. In the SGZ, HIIT increased the density of doublecortin (DCX)‐positive cells in WT mice by 85% (5.77±1.76 vs. 3.12±1.54 cells/100 µm, P = 0.013) and KO mice (67% increase; 7.91±2.92 vs. 4.73±1.63 cells/100 µm, P = 0.004). MIIT did not alter the density of DCX‐positive cells in either genotype. HIIT increased the density of Ki‐67‐positive cells only in KO mice (P = 0.038), whereas no differences in nestin‐positive cells were observed. In the V‐SVZ, HIIT increased the density of DCX‐positive cells in WT mice by 155% (117.79±39.72 vs. 46.25±19.96 cells/100 µm, P < 0.001) and MIIT increased the density of DCX‐positive cells by 80% (83.26±39.48 vs. 46.25±19.96 cells/100µm, P = 0.027). No exercise‐induced changes were observed in KO mice. Similar patterns were noted for Ki‐67 positive and DCX/Ki‐67 double‐positive cells in the V‐SVZ. These findings suggest that HIIT enhances neurogenesis more robustly than MIIT in both niches, with HCA₁ playing a crucial role in V‐SVZ neurogenesis. image Key points: The neurogenic potential of the brain decreases with age, whereas the risk of neurodegenerative diseases and stroke increases, highlighting a mismatch between neuronal loss and replacement capacity. Exercise enhances neurogenesis in both the subgranular zone and the ventricular‐subventricular zone. High‐intensity interval exercise is more effective than medium‐intensity interval exercise at promoting neurogenesis in both the subgranular zone and the ventricular‐subventricular zone of wild‐type mice. The enhancement of neurogenesis in the ventricular‐subventricular zone is dependent on the activation of the HCA₁ receptor, as evidenced by the ability of medium‐ and high‐intensity interval exercise to induce neurogenesis in wild‐type mice and the lack of this effect in HCA₁ knockout mice. By contrast, neurogenesis in the subgranular zone is independent on the activation of the HCA₁ receptor, highlighting that neurogenesis in the two major neurogenic niches are regulated differently.

Aquaporin‐4 (AQP4) is the main water channel in brain and is enriched in perivascular astrocyte processes abutting brain microvessels. There is a rich literature on the role of AQP4 in experimental stroke. While its role in oedema formation following middle cerebral artery occlusion (MCAO) has been studied extensively, its specific impact on infarct volume remains unclear. This study investigated the effects of total and partial AQP4 deletion on infarct volume in mice subjected to distal medial cerebral artery (dMCAO) occlusion. Compared to MCAO, this model induces smaller infarcts confined to neocortex, and less oedema. We show that AQP4 deletion significantly reduced infarct volume as assessed 1 week after dMCAO, suggesting that the role of AQP4 in stroke goes beyond its effect on oedema formation and dissolution. The reduction in infarct volume was associated with increased astrocyte reactivity in the peri‐infarct areas. No significant differences were observed in the number of microglia among the genotypes. These findings provide new insights in the role of AQP4 in ischaemic injury indicating that AQP4 affects both infarct volume and astrocyte reactivity in the peri‐infarct zone. image Key points: Aquaporin‐4 (AQP4) is the main water channel in brain and is enriched in perivascular astrocyte processes abutting microvessels. A rich literature exists on the role of AQP4 in oedema formation following middle cerebral artery occlusion (MCAO). We investigated the effects of total and partial AQP4 deletion on infarct volume in mice subjected to distal medial cerebral artery occlusion (dMCAO), a model inducing smaller infarcts confined to neocortex and less oedema compared to MCAO. AQP4 deletion significantly reduced infarct volume 1 week after dMCAO, suggesting a broader role for AQP4 in stroke beyond oedema formation. The reduction in infarct volume was associated with increased astrocyte reactivity in the peri‐infarct areas, while no significant differences were observed in the number of microglia among the genotypes. These findings provide new insights into the role of AQP4 in stroke, indicating that AQP4 affects both infarct volume and astrocyte reactivity in the peri‐infarct zone.