Deconstructing endogenous pain modulations

Treatment of Headaches in the ED With Lower Cervical Intramuscular Bupivacaine Injections: A 1-Year Retrospective Review of 417 Patients

OBJECTIVE

The primary objective of this retrospective chart review is to describe 1 year's experience of an academic emergency department (ED) in treating a wide spectrum of headache classifications with intramuscular injections of 0.5% bupivacaine bilateral to the spinous process of the lower cervical vertebrae.

BACKGROUND

Headache is a common reason that patients present to an ED. While there are a number of effective therapeutic interventions available for the management of headache pain, there clearly remains a need for other treatment options. The intramuscular injection of 1.5 mL of 0.5% bupivacaine bilateral to the sixth or seventh cervical vertebrae has been used to treat headache pain in our facility since July 2002. The clinical setting for the study was an academic ED with an annual volume of over 75,000 patients.

METHODS

We performed a retrospective review of over 2805 ED patients with the discharge diagnosis of headache and over 771 patients who were coded as having had an anesthetic injection between June 30, 2003 and July 1, 2004. All adult patients who had undergone paraspinous intramuscular injection with bupivacaine for the treatment of their headache were gleaned from these 2 larger databases and were included in this retrospective chart review. A systematic review of the medical records was accomplished for these patients.

RESULTS

Lower cervical paraspinous intramuscular injections with bupivacaine were performed in 417 patients. Complete headache relief occurred in 271 (65.1%) and partial headache relief in 85 patients (20.4%). No significant relief was reported in 57 patients (13.7%) and headache worsening was described in 4 patients (1%). Overall a therapeutic response was reported in 356 of 417 patients (85.4%). Headache relief was typically rapid with many patients reporting complete headache relief in 5 to 10 minutes. Associated signs and symptoms such as nausea, vomiting, photophobia, phonophobia, and allodynia were also commonly relieved.

CONCLUSION

Our observations suggest that the intramuscular injection of small amounts of 0.5% bupivacaine bilateral to the sixth or seventh cervical spinous process appears to be an effective therapeutic intervention for the treatment of headache pain in the outpatient setting.

Medullary raphe neurons facilitate brown adipose tissue activation

Recent evidence suggests that neurons in the medullary raphe are critical to the activation of brown adipose tissue (BAT), the major source of nonshivering heat production in the rat. Yet it is unclear which medullary raphe cells participate in cold defense and how participating cells contribute to BAT activation. Therefore, we recorded extracellularly from raphe cells during three thermoregulatory challenges that evoked an increase in BAT temperature in anesthetized rats: central cold, ambient cold, or intracerebroventricular prostaglandin E2 (PGE2) injection. Physiologically identified serotonergic (p5HT) cell discharge increased in response to cold or PGE2 administration and was positively correlated with BAT temperature. However, none of the 147 physiologically identified non-serotonergic (non-p5HT) cells recorded responded to thermoregulatory challenges that evoked an increase in BAT temperature. To test for modulation of BAT activation by non-p5HT cells that are either excited (ON cells) or inhibited (OFF cells) by noxious cutaneous stimulation, noxious stimuli were applied during evoked BAT temperature increases. Noxious stimulation suppressed BAT activation, suggesting that cells inhibited by noxious stimulation facilitate spinal circuits controlling BAT. To test whether medullary OFF cells modulate BAT activity, the mu-opiate receptor agonist (d-Ala2, N-Me-Phe4, Gly-ol5)-enkephalin (DAMGO) was microinjected into the raphe magnus, a manipulation that selectively activates OFF cells. DAMGO microinjection blocked noxious stimulation-evoked suppression of PGE2-induced BAT temperature increases. Thus, both p5HT and non-p5HT OFF cells in the medullary raphe facilitate BAT activation in response to cold challenge or pyrogen.

Ventromedial medulla: pain modulation and beyond

The midbrain periaqueductal gray (PAG) and ventromedial medulla (VMM) are generally viewed as the core of an endogenous descending modulatory system. However, available data demonstrate that PAG and VMM do not specifically target nociceptive transmission and that activation of either structure affects numerous homeostatic physiological processes. Pseudorabies virus (PRV) is a useful tracer that is retrogradely and transynaptically transported. PRV injections into homeostatic effector organs invariably label VMM neurons, both serotonergic and nonserotonergic. Studies in anesthetized rats have implicated two types of nonserotonergic VMM neurons in nociceptive modulation: ON cells are thought to facilitate nociception and OFF cells to inhibit nociception. Yet, in the unanesthetized animal, the discharge of VMM neurons changes in response to innocuous stimuli and during situations unrelated to nociception. In particular, VMM cells appear to modulate the timing of micturition, with ON cells promoting the initiation of voiding and OFF cells promoting urine storage. VMM cells also modulate sensory transmission. During both micturition and sleep, OFF cells discharge and sensory responsiveness is depressed. In sum, the VMM is hypothesized to modulate spinal sensory, autonomic, and motor circuits in order to maintain homeostasis.