Modulation of inhibitory and excitatory neurotransmissions by Zn2+ on the substantia gelatinosa neurons of the trigeminal subnucleus caudalis in mice.

The substantia gelatinosa of the trigeminal subnucleus caudalis has been considered to be an essential location for the transference of orofacial sensory signals. The co-localization of inhibitory and excitatory neurotransmitters in the same substantia gelatinosa (SG) neurons has demonstrated their essential part in the modification of nociceptive transmission. Zn2+ is particularly numerous in the mammalian central nervous system. There are proofs demonstrating the role of Zn2+ in the modulation of voltage- and ligand-gated ion channels. However, little is known about what roles Zn2+ may play in the modulation of signal transmission in the SG neurons of the trigeminal subnucleus caudalis (Vc). Therefore, in this study, we used the whole-cell patch clamp technique to find out the effect of Zn2+ on the responses of three main neurotransmitters (glycine, GABA, and glutamate) on SG neurons of the Vc in mice. We have proved that Zn2+ induces a big potentiation of glycine receptor-mediated response but attenuates GABA- and glutamate-induced responses at micromolar concentrations, however, enhances glutamate-induced response at nanomolar concentration. Taken together, these data demonstrated that Zn2+ can modulate glycine, GABA and glutamate-mediated actions on the SG neurons of the Vc and support an important mechanism in spinal sensory information signaling.

Intracisternal and intraperitoneal administration of morphine attenuates mechanical allodynia following compression of the trigeminal ganglion in rats.

AIMS: To investigate the effects of morphine on mechanical allodynia following compression of the trigeminal ganglion in the rat. METHODS: Experiments were carried out on male Sprague-Dawley rats weighing between 250 and 260 g. For compression, a 4% agar solution (8 microL) was injected into the trigeminal ganglion. In the control group, rats were sham operated without agar injections. The authors evaluated the effects of intraperitoneal or intracisternal administration of morphine on mechanical allodynia evoked by air-puff stimulation of the vibrissa pad area 14 days following compression of the trigeminal ganglion. RESULTS: Mechanical allodynia was established within 3 days and lasted beyond postoperative day 24. Intraperitoneal administration of morphine (2 or 5 mg/kg) significantly blocked mechanical allodynia ipsilateral to the compression of the trigeminal ganglion. Intraperitoneal administration of morphine also inhibited mechanical allodynia on the contralateral side. Moreover, intracisternal administration of morphine (5 microg) strongly suppressed both ipsilateral and contralateral mechanical allodynia. The antiallodynic effects of morphine were blocked by pretreatment with naloxone, an opioid receptor antagonist. CONCLUSION: These results suggest that the application of a high dose of morphine may be of great benefit in treating trigeminal neuralgia-like nociception.