An impairment of cortical GABAergic neurons is involved in alkalosis-induced brain dysfunctions

Hypocapnia attenuates local skin thermal perception to innocuous warm and cool stimuli in normothermic resting humans

When one is exposed to a stressful situation in their daily life, a common response is hyperventilation. Although the physiological significance of stress-induced hyperventilation remains uncertain, this response may blunt perception of the stress-inducing stimulus. This study examined the effects of voluntary hyperventilation and resultant hypocapnia on the local skin thermal detection threshold in normothermic resting humans. Local skin thermal detection thresholds were measured in 15 young adults (three females) under three breathing conditions: 1) spontaneous breathing (Control trial), 2) voluntary hypocapnic hyperventilation (HH trial), and 3) voluntary normocapnic hyperventilation (NH trial). Local skin thermal detection thresholds were measured using thermostimulators containing a Peltier element that were attached to the forearm and forehead. The temperature of the probe was initially equilibrated to the skin temperature, then gradually increased or decreased at a constant rate (±0.1 °C/s) until the participants felt warmth or coolness. The difference between the initial skin temperature and the local skin temperature at which the participant noticed warmth/coolness was assessed as an index of the local skin warm/cool detection threshold. Local detection of warm and cool stimuli did not differ between the Control and NH trials, but it was blunted in the HH trial as compared with the Control and NH trials, except for detection of warm stimuli on the forearm. These findings suggest that hyperventilation-induced hypocapnia, not hyperventilation per se, attenuates local skin thermal perception, though changes in responses to warm stimuli may not be clearly perceived at some skin areas (e.g., forearm).

CO2 combining power and outcomes in patients with acute ischaemic stroke or transient ischaemic attack

Background and purpose

The clinical significance of carbon dioxide combining power (CO₂CP) in ischaemic cerebrovascular disease is not well established, and the role of CO₂CP in the prognosis of acute ischaemic stroke (AIS) or transient ischaemic attack (TIA) has not been reported. The objective of the study was to investigate the associations between CO₂CP and clinical outcomes in patients with AIS or TIA.

Methods

Data were derived from the China National Stroke Registry III. Patients were classified into five groups by quintiles of CO₂CP levels and three groups according to the normal range of CO₂CP (23–29 mmol/L). Multivariable Cox and logistic regressions were adopted to explore the associations of CO₂CP levels with all-cause death and poor functional outcomes (modified Rankin Scale (mRS) 3–6/2–6) at 3 months and 1 year.

Results

Among 9531 patients included in the study, the median (IQR) CO₂CP was 24.9 (23.0–27.0) mmol/L. After adjustment for potential confounders, patients in the first CO₂CP quintile (21.1–23.3 mmol/L) had higher risk of all-cause death and poor functional outcomes (mRS score of 3–6/2–6) (HR or OR with 95% CI 2.37 (1.32 to 4.25), 1.49 (1.20 to 1.83) and 1.21 (1.03 to 1.42), respectively) compared with those in the fourth quintile. Similar results were found for outcomes at 1 year. Furthermore, all associations were also significant when CO₂CP was <23 mmol/L compared with CO₂CP of 23–29 mmol/L.

Conclusions

Decreased CO₂CP was associated with high risk of all-cause death and poor functional outcomes in patients with AIS or TIA.

Seizure initiation in infantile spasms vs. focal seizures: proposed common cellular mechanisms

Infantile spasms (IS) and seizures with focal onset have different clinical expressions, even when electroencephalography (EEG) associated with IS has some degree of focality. Oddly, identical pathology (with, however, age-dependent expression) can lead to IS in one patient vs. focal seizures in another or even in the same, albeit older, patient. We therefore investigated whether the cellular mechanisms underlying seizure initiation are similar in the two instances: spasms vs. focal. We noted that in-common EEG features can include (i) a background of waves at alpha to delta frequencies; (ii) a period of flattening, lasting about a second or more - the electrodecrement (ED); and (iii) often an interval of very fast oscillations (VFO; ~70 Hz or faster) preceding, or at the beginning of, the ED. With IS, VFO temporally coincides with the motor spasm. What is different between the two conditions is this: with IS, the ED reverts to recurring slow waves, as occurring before the ED, whereas with focal seizures the ED instead evolves into an electrographic seizure, containing high-amplitude synchronized bursts, having superimposed VFO. We used in vitro data to help understand these patterns, as such data suggest cellular mechanisms for delta waves, for VFO, for seizure-related burst complexes containing VFO, and, more recently, for the ED. We propose a unifying mechanistic hypothesis - emphasizing the importance of brain pH - to explain the commonalities and differences of EEG signals in IS versus focal seizures.

[Effect of acupuncture pretreatment on action potential of cerebellar Purkenje cells in ex vivo ischemic rat brain slices]

OBJECTIVE

To investigate the effect of acupuncture pretreatment at specific acupoints on action potential of cerebellar Purkenje cells in rats early after cerebral ischemia.

METHODS

Forty male SD rats were randomized into control group, ischemia group, acupuncture pretreatment group and acupuncture pretreatment plus ischemia group. The rats in acupuncture groups received acupuncture pretreatment at Baihui and bilateral Zusanli twice daily for 7 consecutive days, after which brain slices were prepared and perfused at a lowered rate to simulate in vivo ischemic stroke. Microelectrode and whole cell current clamp technique were used for recording the action potentials of cerebellar Purkenje cells to detect changes in spike encoding of the cells.

RESULTS

Compared with those in the control group, the rat brain slices early after simulated ischemia showed significantly shortened inter-spike intervals, increased standard deviation of spike timing and decreased voltage of threshold potentials (P<0.01), suggesting overexcitation of the Purkinje cells. Acupuncture pretreatment at Baihui and bilateral Zusanli obviously suppressed overexcitation of the Purkinje cells in response to ischemia.

CONCLUSION

Acupuncture pretreatment at Baihui and bilateral Zusanli can improve ischemic stroke by suppressing overexcitation of Purkenje cells in rats.

Serum Bicarbonate Concentration and Cognitive Function in Hypertensive Adults

BACKGROUND AND OBJECTIVES

Cognitive function worsens as kidney function declines, but mechanisms contributing to this association are not completely understood. Metabolic acidosis, a common complication of CKD, leads to neural networks overexcitation and is involved in cerebral autoregulation. We aimed to evaluate the association between serum bicarbonate concentration as a measure of metabolic acidosis, and cognitive function in hypertensive adults with and without CKD.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Five cognitive summary scores were measured (global cognitive function, executive function, memory, attention/concentration, and language) in 2853 participants in the Systolic BP Intervention Trial (SPRINT). Multivariable linear regression models adjusted for demographics, comorbidities, systolic BP, medications, eGFR and albuminuria evaluated the cross-sectional association between bicarbonate and cognition at SPRINT baseline. In a subset (n=681) who underwent brain magnetic resonance imaging, the models were adjusted for white matter hyperintensity volume, vascular reactivity, and cerebral blood flow.

RESULTS

The mean age (SD) was 68 (8.5) years. Global cognitive and executive functions were positively associated with serum bicarbonate (estimate [SEM]: 0.014 [0.006]; P=0.01, and 0.018 [0.006]; P=0.003, respectively). Each 1 mEq/L lower bicarbonate level had a similar association with global cognitive and executive function as being 4.3 and 5.4 months older, respectively. The association with global cognition persisted after magnetic resonance imaging findings adjustment (estimate [SEM]: 0.03 [0.01]; P=0.01). There was no association between serum bicarbonate level and memory, attention/concentration, and language.

CONCLUSIONS

In a large cohort of hypertensive adults, higher serum bicarbonate levels were independently associated with better global cognitive and executive performance. (ClinicalTrials.gov: NCT01206062).