Central projections of nociceptive input originating from the low back and limb muscle in rats.

Since clinical features of chronic muscle pain originating from the low back and limbs are different (higher prevalence and broader/duller sensation of low back muscle pain than limb muscle pain), spinal and/or supraspinal projection of nociceptive information could differ between the two muscles. We tested this hypothesis using c-Fos immunohistochemistry combined with retrograde-labeling of dorsal horn (DH) neurons projecting to ventrolateral periaqueductal grey (vlPAG) or ventral posterolateral nucleus of the thalamus (VPL) by fluorogold (FG) injections into the vlPAG or VPL. C-Fos expression in the DH was induced by injecting 5% formalin into the multifidus (MF, low back) or gastrocnemius-soleus (GS, limb) muscle.

Rat dorsal horn neurons primed by stress develop a long-lasting manifest sensitization after a short-lasting nociceptive low back input.

Background: A single injection of nerve growth factor (NGF) into a low back muscle induces a latent sensitization of rat dorsal horn neurons (DHNs) that primes for a manifest sensitization by a subsequent second NGF injection. Repeated restraint stress also causes a latent DHN sensitization.

Objective: In this study, we investigated whether repeated restraint stress followed by a single NGF injection causes a manifest sensitization of DHNs.

Spinal cord fractalkine (CX3CL1) signaling is critical for neuronal sensitization in experimental nonspecific, myofascial low back pain.

Neuroactive substances released by activated microglia contribute to hyperexcitability of spinal dorsal horn neurons in many animal models of chronic pain. An important feedback loop mechanism is via release of fractalkine (CX3CL1) from primary afferent terminals and dorsal horn neurons and binding to CX3CR1 receptors on microglial cells. We studied the involvement of fractalkine signaling in latent and manifest spinal sensitization induced by two injections of nerve growth factor (NGF) into the lumbar multifidus muscle as a model for myofascial low back pain.

Innervation of the thoracolumbar fascia.

The aim of the study was to obtain information on the sensory functions of the thoracolumbar fascia (TLF). The types of nerve fibres present in the TLF were visualized with specific antibodies to neuropeptides and sympathetic fibres. Most data were obtained from the TLF in rats, but some findings from the human fascia are also included.

Action potentials and subthreshold potentials of dorsal horn neurons in a rat model of myositis: a study employing intracellular recordings in vivo.

Intracellular in vivo recordings from rat dorsal horn neurons were made to study the contribution of microglia to the central sensitization of spinal synapses induced by a chronic muscle inflammation. To block microglia activation, minocycline was continuously administered intrathecally during development of the inflammation. The aim was to test whether an inflammation-induced sensitization of dorsal horn neurons is mediated by changes in synaptic strength or other synaptic changes and how activated microglia influence these processes.