Nerve growth factor-induced hyperexcitability of rat sensory neuron in culture

Abstract

Abnormal spontaneous firing of primary sensory neurons is considered to be a cause of neuropathic pain. However, pathogenic mechanisms of hyperexcitable sensory neurons in neuropathic model animals are unclear. We examined effects of chronic treatment of nerve growth factor (NGF), one of candidate mediators for the pathogenesis, on excitability of sensory neurons by voltage-clamped recording in a cell-attached configuration. From rat dorsal root ganglion (DRG) neurons cultured without NGF, only stable holding currents without spontaneous firing activity were recorded. On the other hand, more than 20% neurons cultured in the presence of NGF for more than 3 days showed spontaneous current spikes at frequencies between 0.1 and 5 Hz. Each spikes had an initial inward phase followed by the outward phase, resulted from spontaneous transient depolarization followed by transient hyperpolarization. These spontaneous spikes were abolished by tetrodotoxin, lidocaine and reduction of extracellular concentration of Na + from 154 mM to 100 mM, in all-or-none fashion, suggesting that spontaneous current spikes reflected spontaneous action potentials. From these results, it became evident that DRG neurons of adult rats had a nature to respond to NGF and obtained the abnormal hyperexcitability to fire spontaneously.Peripheral nerve injury frequently results in severe chronic pain, neuropathic pain that is poorly responsive to general analgesic therapy, and remains as an unsolved problem in health. Experimental injury of the peripheral nerve in experimental animals induces hyperalgesia and allodynia (2,5,13,22,31,32). Although primary sensory neurons of healthy animals are "silent" in electrophysiology without excitatory inputs from other neurons or sensational inputs, abnormal spontaneous firing was observed in sensory neurons of animals with nerve injury (6,11,12,18). Such abnormal firing is considered to be a cause of neuropathic pain. Such spontaneous firing was observed at the local injured site and also at the soma of the dorsal root ganglion (DRG) neurons (30). Subthreshold membrane potential oscillation and the spontaneously generated action potentials were recorded in DRG neurons freshly isolated from nerveinjured rats by the intracellular microelectrode method (1,17,26) and the whole-cell patch clamp method in the current clamp mode (20,27). Nevertheless, the pathogenic mechanisms of the abnormal hyperexcitability of the primary sensory neurons are unclear. Concentration of nerve growth factor (NGF) in DRG was reported to increase after the artificial nerve injury (9), and injection of exogenous NGF into healthy rats induced hyperalgesia (16). These reports suggest that NGF correlates with the pathogenesis of neuropathic pain. Small DRG neurons, which respond to noxious sensation, express TrkA

Chronic Treatment with NGF Induces Spontaneous Fluctuations of Intracellular Ca2+ in Icilin-Sensitive Dorsal Root Ganglion Neurons of the Rat

“…Cell isolation and culture: DRG neurons were isolated from adult male Sprague-Dawley rats (7-12 weeks old), using procedures reported previously [21,23,30]. Rats were killed by cervical dislocation under diethyl ether inhalation anesthesia.…”

“…Such action of NGF is not restricted to the peripheral tissues, but is also seen in the CNS [16,25]. Recently, we reported that rat DRG neurons cultured in the presence of NGF showed spontaneous action potentials [21] and spontaneous rises and falls in the intracellular Ca Among DRG neurons, A-and C-neurons are generally considered to be involved in nociception. It is widely accepted that NGF plays roles in cell survival, apoptosis, differentiation, the growth of axons/dendrites and the expression of various proteins through two types of receptors.…”

“…Such action of NGF is not restricted to the peripheral tissues, but is also seen in the CNS [16,25]. Recently, we reported that rat DRG neurons cultured in the presence of NGF showed spontaneous action potentials [21] and spontaneous rises and falls in the intracellular Ca ] i fluctuations [30]. Among DRG neurons, A-and C-neurons are generally considered to be involved in nociception.…”

, NGF - Induced Changes in Adrenergic Modulation of Calcium Channels of Trigeminal Ganglion Neurons

“…Він через внутрішньоклітинні шляхи підсилює відповіді нейронів спінальних гангліїв на капсаїцин [16,17]. Культивуван-ня нейронів з надлишковою концентрацією ФРНТ (50 -100 нг/мл) спричинює зміни у електрофізіологічних параметрах нейронів, що формують С-та Аδ-волокна [18,19]. По-казано, що цей пептид підвищує збудливість і має вплив на адренергічну модуляцію імпульсної активності нейронів спінальних гангліїв [20].…”

Excitability Properties of Trigeminal Ganglion Neurons

“…Ця модель корисна для визначення повільних змін у клітинних та міжклітинних механізмах, вивчення впливу нейротропних факторів, які виконують нейротрофічну та нейропротекторну функції і, навпаки, відіграють ключову роль при невропатичних порушеннях [13,14]. Однак для з'ясування впливу згаданих агентів потрібно дослідити електрофізіологічні по-каз ники цих нейронів у первинній культу рі.…”