Hippocampal cellular loss after brief hypotension

Cardiovascular Autonomic Dysfunction in Spinal Cord Injury: Epidemiology, Diagnosis, and Management

Spinal cord injury (SCI) disrupts autonomic circuits and impairs synchronistic functioning of the autonomic nervous system, leading to inadequate cardiovascular regulation. Individuals with SCI, particularly at or above the sixth thoracic vertebral level (T6), often have impaired regulation of sympathetic vasoconstriction of the peripheral vasculature and the splanchnic circulation, and diminished control of heart rate and cardiac output. In addition, impaired descending sympathetic control results in changes in circulating levels of plasma catecholamines, which can have a profound effect on cardiovascular function. Although individuals with lesions below T6 often have normal resting blood pressures, there is evidence of increases in resting heart rate and inadequate cardiovascular response to autonomic provocations such as the head-up tilt and cold face tests. This manuscript reviews the prevalence of cardiovascular disorders given the level, duration and severity of SCI, the clinical presentation, diagnostic workup, short- and long-term consequences, and empirical evidence supporting management strategies to treat cardiovascular dysfunction following a SCI.

Neuroprotection with the P53-Inhibitor Pifithrin-μ after Cardiac Arrest in a Rodent Model

BACKGROUND

The small molecule pifithrin-μ reversibility inhibits the mitochondrial pathway of apoptosis. The neuronal effects of pifithrin-μ applied after cardiac arrest are unknown. We hypothesized that pifithrin-μ reduces neuronal damage in the most vulnerable brain region, the hippocampus, after cardiac arrest.

METHODS

In two randomized controlled series we administered pifithrin-μ or control in 109 rats resuscitated after 8 or 10 min of cardiac arrest. Neuronal damage was blindly assessed with histology (Fluoro Jade B: FJB, cresyl violet: CV) in the most vulnerable brain region (CA1 segment of hippocampus) and with a series of neurobehavioral tests (Open Field Task, Tape-Removal Test, Morris Water Maze test). Mixed ANOVA was used to combine both series, simple comparisons were done with t tests or Mann-Whitney U test.

RESULTS

Pifithrin-μ reduced the number of degenerating, FJB-positive neurons by 25% (mixed ANOVA p group = 0.014). This was more prominent after 8 min cardiac arrest (8 min arrest pifithrin-μ 94 ± 47 vs control 128 ± 37; n = 11 each; 10 min arrest pifithrin-μ 78 ± 44, n = 15 vs control 101 ± 31, n = 18; p group* arrest length interaction = 0.622). The reduction of ischemic CV-positive neurons in pifithrin-μ animals was not significant (ANOVA p group = 0.063). No significant group differences were found in neurobehavioral testing.

CONCLUSION

Temporarily inhibition of apoptosis with pifithrin-μ after cardiac arrest decreases the number of injured neurons in the CA1 segment of hippocampus in a cardiac arrest rat model, without clinical correlate. Further studies should elucidate the role of this neuroprotective agent in different settings and with longer cardiac arrest.

Hypotension and a positive fluid balance are associated with delirium in patients with shock

The pathogenesis of delirium in critically ill patients is multifactorial. How hypotension and hypoxemia affect brain function and whether they can promote delirium remains unclear. A high cumulative positive fluid balance may also have a negative effect on brain function and promote delirium. We hypothesized that delirium would be more likely to develop in patients with low systemic arterial pressure, hypoxemia and a higher positive fluid balance, and investigated these associations in a prospective observational cohort study in patients with shock. After initial resuscitation, episodes of hypotension, defined as a mean arterial pressure (MAP) <65 mmHg or diastolic pressure <60 mmHg, and hypoxemia, defined as peripheral oxygen saturation (SpO2) <90% for more than one minute or any arterial oxygen concentration (PaO2) <90 mmHg, were recorded during the first 5 days of the ICU stay. Fluid balance was evaluated daily and the 5-day cumulative fluid balance recorded. Delirium was assessed using the Confusion Assessment Method for the ICU. A total of 252 patients were admitted with shock during the study period; 185 (73%) developed delirium. Patients who developed delirium also had more episodes of hypotension with a low MAP (p = 0.013) or diastolic pressure (p = 0.018) during the first five days of the ICU stay than those who did not. Patients with a higher cumulative fluid balance during the same period were also more likely to develop delirium (p = 0.01); there was no significant difference in the occurrence of hypoxemia between groups. Joint modeling, combining a linear-mixed model and an adjusted Cox survival model showed that low diastolic pressure (alpha effect = -0.058±0.0013, p = 0.043) and a positive cumulative fluid balance (alpha effect = 0.04±0.003, p = 0.021) were independently associated with delirium. In conclusion, low diastolic pressure and a cumulative positive fluid balance but not hypoxemia were independently associated with development of delirium in patients with shock.

Reviving pragmatic theory of theory of mind

Theory of Mind (ToM) refers to the ability to attribute mental states to self and others. It has been debated whether or not language capacity precedes ToM in development. Evidence from both neurological and developmental studies suggested that while linguistic capacity is important for ToM understanding, pragmatic component, which is a non-structural part of language, is more important for ToM. Moreover, given that pragmatic component of language is subserved by the right hemisphere of the brain, the evidence also indicates a significant overlap between the neural basis of ToM and that of pragmatic comprehension. The pragmatic theory of ToM, which I aim to revive in this review, firmly links pragmatics to ToM. It regards pragmatic aspects of language and ToM as extensively overlapping functions. I argue that research results from both developmental and neurological studies of ToM are beginning to converge to support this theory. Furthermore, I maintain that the pragmatic theory of ToM provides the best explanation for the seemingly incongruent results from recent child and infant studies on the developmental trajectory of ToM. Lastly, I will discuss whether this theory is in agreement with the domain-specific, the nativist framework, or neither.

Restoration of Rostral Ventrolateral Medulla Cystathionine-γ Lyase Activity Underlies Moxonidine-Evoked Neuroprotection and Sympathoinhibition in Diabetic Rats

We recently demonstrated a fundamental role for cystathionine-γ lyase (CSE)-derived hydrogen sulfide (H₂S) in the cardioprotective effect of the centrally acting drug moxonidine in diabetic rats. Whether a downregulated CSE/H₂S system in the rostral ventrolateral medulla (RVLM) underlies neuronal oxidative stress and sympathoexcitation in diabetes has not been investigated. Along with addressing this question, we tested the hypothesis that moxonidine prevents the diabetes-evoked neurochemical effects by restoring CSE/H₂S function within its major site of action, the RVLM. Ex vivo studies were performed on RVLM tissues of streptozotocin (55 mg/kg, i.p.) diabetic rats treated daily for 3 weeks with moxonidine (2 or 6 mg/kg; gavage), H₂S donor sodium hydrosulfide (NaHS) (3.4 mg/kg, i.p.), CSE inhibitor DL-propargylglycine (DLP) (37.5 mg/kg, i.p.), a combination of DLP with moxonidine, or their vehicle. Moxonidine alleviated RVLM oxidative stress, neuronal injury, and increased tyrosine hydroxylase immunoreactivity (sympathoexcitation) by restoring CSE expression/activity as well as heme oxygenase-1 (HO-1) expression. A pivotal role for H₂S in moxonidine-evoked neuroprotection is supported by the following: 1) NaHS replicated the moxonidine-evoked neuroprotection, and the restoration of RVLM HO-1 expression in diabetic rats; and 2) DLP abolished moxonidine-evoked neuroprotection in diabetic rats, and caused RVLM neurotoxicity, reminiscent of a diabetes-evoked neuronal phenotype, in healthy rats. These findings suggest a novel role for RVLM CSE/H₂S/HO-1 in moxonidine-evoked neuroprotection and sympathoinhibition, and as a therapeutic target for developing new drugs for alleviating diabetes-evoked RVLM neurotoxicity and cardiovascular anomalies.

Long-lasting suppression of acoustic startle response after mild traumatic brain injury

Acoustic startle response (ASR) is a defensive reflex that is largely ignored unless greatly exaggerated. ASR is suppressed after moderate and severe traumatic brain injury (TBI), but the effect of mild TBI (mTBI) on ASR has not been investigated. Because the neural circuitry for ASR resides in the pons in all mammals, ASR may be a good measure of brainstem function after mTBI. The present study assessed ASR in Sprague-Dawley rats after mTBI using lateral fluid percussion and compared these effects to those on spatial working memory. mTBI caused a profound, long-lasting suppression of ASR. Both probability of emitting a startle and startle amplitude were diminished. ASR suppression was observed as soon as 1 day after injury and remained suppressed for the duration of the study (21 days after injury). No indication of recovery was observed. mTBI also impaired spatial working memory. In contrast to the suppression of ASR, working memory impairment was transient; memory was impaired 1 and 7 days after injury, but recovered by 21 days. The long-lasting suppression of ASR suggests long-term dysfunction of brainstem neural circuits at a time when forebrain neural circuits responsible for spatial working memory have recovered. These results have important implications for return-to-activity decisions because recovery of cognitive impairments plays an important role in these decisions.

Isoflurane prevents learning deficiencies caused by brief hypoxia and hypotension in adult Sprague Dawley rats

CONTEXT

Hypotension causes histologic changes in the hippocampal CA1 area, while behavior remains unchanged. We believe that an even stronger insult may also cause behavioral changes.

OBJECTIVE

We used a rat hemorrhagic shock model plus temporary hypoxia to assess functional outcome at different time points post-injury. Our hypothesis is that the damage can be attenuated by the use of isoflurane.

MATERIALS AND METHODS

Rats were subjected to brief hypotension. Animals were evaluated at different time points after receiving hypoxia and hypotension, with and without isoflurane treatment.

RESULTS

The administration of isoflurane after the insult protected the animals from memory alterations. No histopatologic changes were found in any of the groups.

DISCUSSION AND CONCLUSIONS

This observation suggests that in this model of hypotension plus hypoxia there is mild cerebral damage that is reflected by memory changes. Exposure to isoflurane after the insult can prevent the onset of memory deficits.