4α-phorbol 12,13-didecanoate activates cultured mouse dorsal root ganglia neurons independently of TRPV4

Background and Purpose

The Ca²⁺-permeable cation channel TRPV4 is activated by mechanical disturbance of the cell membrane and is implicated in mechanical hyperalgesia. Nerve growth factor (NGF) is increased during inflammation and causes mechanical hyperalgesia. 4α-phorbol 12,13-didecanoate (4αPDD) has been described as a selective TRPV4 agonist. We investigated NGF-induced hyperalgesia in TRPV4 wild-type (+/+) and knockout (–/–) mice, and the increases in [Ca²⁺]_i produced by 4αPDD in cultured mouse dorsal root ganglia neurons following exposure to NGF.

Experimental Approach

Withdrawal thresholds to heat, von Frey hairs and pressure were measured in mice before and after systemic administration of NGF. Changes in intracellular Ca²⁺ concentration were measured by ratiometric imaging with Fura-2 in cultured DRG and trigeminal ganglia (TG) neurons during perfusion of TRPV4 agonists.

Key Results

Administration of NGF caused a significant sensitization to heat and von Frey stimuli in TRPV4 +/+ and –/– mice, but only TRPV4 +/+ mice showed sensitization to noxious pressure. 4αPDD stimulated a dose-dependent increase in [Ca²⁺]_i in neurons from +/+ and –/– mice, with the proportion of responding neurons and magnitude of increase unaffected by the genotype. In contrast, the selective TRPV4 agonist GSK1016790A failed to stimulate an increase in intracellular Ca²⁺ in cultured neurons. Responses to 4αPDD were unaffected by pretreatment with NGF.

Conclusions and Implications

TRPV4 contributes to mechanosensation in vivo, but there is little evidence for functional TRPV4 in cultured DRG and TG neurons. We conclude that 4αPDD activates these neurons independently of TRPV4, so it is not appropriate to refer to 4αPDD as a selective TRPV4 agonist.     

The Ultrasound-guided “Peripheral IJ”: Internal Jugular Vein Catheterization using a Standard Intravenous Catheter

Background

Obtaining vascular access is difficult in certain patients. When routine peripheral venous catheterization is not possible, several alternatives may be considered, each with its own strengths and limitations.

Discussion

We describe a novel technique for establishing vascular access in Emergency Department (ED) patients: the placement of a standard catheter-over-needle device into the internal jugular vein using real-time ultrasound guidance. We present a series of patients for whom this procedure was performed after other attempts at vascular access were unsuccessful. In all cases, the procedure was performed quickly and without complications.

Conclusion

Although further study of this technique is required, we believe this procedure may be a valuable option for ED patients requiring rapid vascular access.     

Accuracy of emergency physicians using ultrasound measurement of crown-rump length to estimate gestational age in pregnant females

Study objective

The objective of this study is to evaluate the accuracy of emergency providers (EPs) of various levels of training in determination of gestational age (GA) in pregnant patients using bedside ultrasound measurement of crown-rump length (CRL).

Methods

We conducted a prospective, cross-sectional, observational study of patients in obstetrical care at an urban county hospital. We enrolled a convenience sample of women at 6 to 14 weeks gestation as estimated by last menstrual period. Emergency providers used ultrasound to measure the CRL. Repeat CRL measurements were performed by either an obstetrical ultrasound technician or senior obstetrician and used as the criterion standard for true GA (TGA).

Results

One hundred five patients were evaluated by 20 providers of various levels of training. The average time required to complete the CRL measurement was 85 seconds. When CRL measurements performed by EPs were compared with the TGAs, the average correlation was 0.935 (0.911-0.959). Using standard accepted variance for CRL measurements at different GAs according to the obstetrics literature (±3 days for 42-70 days and ±5 days for 70-90 days), correlation between EP ultrasound and measured TGA was 0.947 (0.927-0.967).

Conclusions

Emergency providers can quickly and accurately determine GA in first-trimester pregnancies using bedside ultrasound to calculate the CRL. Emergency providers should consider using ultrasound to calculate the CRL in patients with first-trimester bleeding or pain because this estimated GA may serve as a valuable data point for the future care of that pregnancy.