The gigantocellular depressor area revisited

Autonomic dysreflexia: a cardiovascular disorder following spinal cord injury

Autonomic dysreflexia (AD) is a serious cardiovascular disorder in patients with spinal cord injury (SCI). The primary underlying cause of AD is loss of supraspinal control over sympathetic preganglionic neurons (SPNs) caudal to the injury, which renders the SPNs hyper-responsive to stimulation. Central maladaptive plasticity, including C-fiber sprouting and propriospinal fiber proliferation exaggerates noxious afferent transmission to the SPNs, causing them to release massive sympathetic discharges that result in severe hypertensive episodes. In parallel, upregulated peripheral vascular sensitivity following SCI exacerbates the hypertensive response by augmenting gastric and pelvic vasoconstriction. Currently, the majority of clinically employed treatments for AD involve anti-hypertensive medications and Botox injections to the bladder. Although these approaches mitigate the severity of AD, they only yield transient effects and target the effector organs, rather than addressing the primary issue of central sympathetic dysregulation. As such, strategies that aim to restore supraspinal reinnervation of SPNs to improve cardiovascular sympathetic regulation are likely more effective for AD. Recent pre-clinical investigations show that cell transplantation therapy is efficacious in reestablishing spinal sympathetic connections and improving hemodynamic performance, which holds promise as a potential therapeutic approach.

Hypertension before and after posterior circulation infarction: analysis of data from the South London Stroke Register

BACKGROUND

Postmortem data have shown that blood pressure before death correlates more closely with a narrowing of the vertebral arteries than any other vessel studied. This study explores a possible association between hypertension, both before and after posterior circulation infarction (POCI) compared to anterior circulation infarction (ACI).

METHODS

Patients with a first-ever stroke enrolled in the South London Stroke Register between 2000 and 2006 were included. Chi-square tests and multivariable logistic regression were used to compare risk factors including hypertension, sex, smoking history, diabetes, and hypercholesterolemia in patients with POCI compared to ACI. Chi-square testing was used to compare the incidence of newly diagnosed hypertension after POCI and ACI. Absolute blood pressure readings recorded before stroke and 7 days after stroke were also compared between groups.

RESULTS

On multivariable analysis, POCI was significantly associated with male sex (odds ratio [OR] 2.24; 95% confidence interval [CI] 1.55-3.22; P < .001) and hypertension (OR 1.69; 95% CI 1.15-2.50; P = .008). After stroke, patients with POCI were more likely to be newly diagnosed with hypertension during a 1-year follow-up period (OR 2.15; 95% CI 1.20-3.86; P = .009) and as an inpatient (OR 3.27; 95% CI 1.49-7.13; P = .002). Systolic blood pressure was significantly higher in the POCI group before stroke (152 v 146 mm Hg; P = .027). Diastolic blood pressure was significantly higher 7 days poststroke (81 v 74 mm Hg; P = .01) in patients not previously diagnosed with hypertension.

CONCLUSIONS

This study has shown a significant association between hypertension before and after POCI compared to ACI. We believe further investigation with brainstem imaging and recordings of sympathetic nervous system activity after stroke is warranted.

Medial vestibular connections with the hypocretin (orexin) system

The mammalian medial vestibular nucleus (MVe) receives input from all vestibular endorgans and provides extensive projections to the central nervous system. Recent studies have demonstrated projections from the MVe to the circadian rhythm system. In addition, there are known projections from the MVe to regions considered to be involved in sleep and arousal. In this study, afferent and efferent subcortical connectivity of the medial vestibular nucleus of the golden hamster (Mesocricetus auratus) was evaluated using cholera toxin subunit-B (retrograde), Phaseolus vulgaris leucoagglutinin (anterograde), and pseudorabies virus (transneuronal retrograde) tract-tracing techniques. The results demonstrate MVe connections with regions mediating visuomotor and postural control, as previously observed in other mammals. The data also identify extensive projections from the MVe to regions mediating arousal and sleep-related functions, most of which receive immunohistochemically identified projections from the lateral hypothalamic hypocretin (orexin) neurons. These include the locus coeruleus, dorsal and pedunculopontine tegmental nuclei, dorsal raphe, and lateral preoptic area. The MVe itself receives a projection from hypocretin cells. CTB tracing demonstrated reciprocal connections between the MVe and most brain areas receiving MVe efferents. Virus tracing confirmed and extended the MVe afferent connections identified with CTB and additionally demonstrated transneuronal connectivity with the suprachiasmatic nucleus and the medial habenular nucleus. These anatomical data indicate that the vestibular system has access to a broad array of neural functions not typically associated with visuomotor, balance, or equilibrium, and that the MVe is likely to receive information from many of the same regions to which it projects.