ميزان فعاليت نورون هاي هسته ميخي شكل موش صحرايي نر در پاسخ به فرمالين

The firing rate of neurons in the nucleus cuneiformis in response to formalin in male rats

Introduction: Although formalin-induced activity in primary afferent fibers and spinal dorsal horn is well described, the midbrain neural basis underlying each phase of behavior in the formalin test has not been yet clarified. The present study was designed to investigate the nucleus cuneiformis (CnF) neuronal responses during two phases after subcutaneous injection of formalin into the hind paw of rat. Methods: In this study, 76 male NMRI adult rats, weighing 230-320 g were used. Control group (n = 24) was merely tested for determining spontaneous firing rate of CnF neurons. In the formalin group, formalin-induced neural activity of 37 cells were simultaneously recorded from the CnF during first phase (0-5 min) and second phase (15-60 min) of formalin test at 5-min intervals, using an extracellular single unit recording technique. Saline group (n = 15) received 50jlt saline s.c. instead of formalin into the plantar surface of hind paw 15 min after baseline recording. Results: The baseline firing rate of neurons in the CnF varied between 1.2 and 39.2 spikes/sec and the average frequency of spontaneous activity over 1 h was 11.8 ± 1.1 spikes/sec. There were three neural clusters after formalin injection. Neurons in cluster 1 (46%) exhibited severe, transient excitatory response in the first (acute) phase, while neurons in cluster 2 (35%) exhibited tonic but long-lasting excitatory response in the second (chronic) phase. Cluster 3, a small portion of neurons (about one fifth), failed to show any evident responses to formalin test. Conclusion: Our findings suggest that alteration of neural activity and pattern in the spontaneous background of CnF neurons can mediate a role in the transmission of nociceptive information induced by the peripheral injection of formalin and can be discussed in light of the role of these neurons in nociceptive information processing following peripheral stimuli.