Simultaneous activation of N-methyl-D-aspartate and neurokinin-1 receptors modulates c-Fos and Zif/268 expression in the rat trigeminal nucleus caudalis

Neurokinin-1 Receptor-Immunopositive Neurons in the Medullary Dorsal Horn Provide Collateral Axons to both the Thalamus and Parabrachial Nucleus in Rats

It has been suggested that the trigemino-thalamic and trigemino-parabrachial projection neurons in the medullary dorsal horn (MDH) are highly implicated in the sensory-discriminative and emotional/affective aspects of orofacial pain, respectively. In previous studies, some neurons were reported to send projections to both the thalamus and parabrachial nucleus by way of collaterals in the MDH. However, little is known about the chemoarchitecture of this group of neurons. Thus, in the present study, we determined whether the neurokinin-1 (NK-1) receptor, which is crucial for primary orofacial pain signaling, was expressed in MDH neurons co-innervating the thalamus and parabrachial nucleus. Vesicular glutamate transporter 2 (VGLUT2) mRNA, a biomarker for the subgroup of glutamatergic neurons closely related to pain sensation, was assessed in trigemino-parabrachial projection neurons in the MDH. After stereotactic injection of fluorogold (FG) and cholera toxin subunit B (CTB) into the ventral posteromedial thalamic nucleus (VPM) and parabrachial nucleus (PBN), respectively, triple labeling with fluorescence dyes for FG, CTB and NK-1 receptor (NK-1R) revealed that approximately 76 % of the total FG/CTB dually labeled neurons were detected as NK-1R-immunopositive, and more than 94 % of the triple-labeled neurons were distributed in lamina I. In addition, by FG retrograde tract-tracing combined with fluorescence in situ hybridization (FISH) for VGLUT2 mRNA, 54, 48 and 70 % of FG-labeled neurons in laminae I, II and III, respectively, of the MDH co-expressed FG and VGLUT2 mRNA. Thus, most of the MDH neurons co-innervating the thalamus and PBN were glutamatergic. Most MDH neurons providing the collateral axons to both the thalamus and parabrachial nucleus in rats were NK-1R-immunopositive and expressed VGLUT2 mRNA. NK-1R and VGLUT2 in MDH neurons may be involved in both sensory-discriminative and emotional/affective aspects of orofacial pain processing.

Peripheral purinergic receptor modulation influences the trigeminal ganglia nitroxidergic system in an experimental murine model of inflammatory orofacial pain

ATP plays an important role as an endogenous pain mediator generating and/or modulating pain signaling from the periphery to the central nervous system. The aim of this study was to analyze the role of peripheral purinergic receptors in modulation of the nitroxidergic system at a trigeminal ganglia level by monitoring changes in nitric oxide synthase isoforms. We also evaluated Fos-positive neurons in brainstem (spinal trigeminal nucleus) and pain-related behavior. We found that local administration of the P2 purinergic receptor antagonist pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS) decreased face-rubbing activity, nitric oxide synthase isoform expression in trigeminal ganglia, and Fos expression in spinal trigeminal nucleus after subcutaneous injection of formalin. These results suggest a role for peripheral P2 purinergic receptors in orofacial pain transmission through modulation of the nitroxidergic system. .

Fos expression induced by activation of NMDA and neurokinin-1 receptors in the trigeminal subnucleus caudalis in vitro: role of protein kinases

Activity-induced neuronal plasticity is partly facilitated by the expression of the immediate-early gene c-fos and the resulting transcription factor Fos. Expression of Fos is associated with nociceptive afferent activation, but a detailed stimulation-transcription pathway for Fos expression has not yet been determined in the trigeminal system. This study utilized a novel in vitro model to determine whether Fos expression can be induced in trigeminal subnucleus caudalis by NMDA or neurokinin-1 receptor activation, and whether inhibition of intracellular kinases has any effect on Fos expression induced by activation of these receptors. Brainstems of male Wistar rats were excised and maintained in artificial cerebrospinal fluid at 37°C. NMDA or the specific neurokinin-1 receptor agonist [Sar(9),Met(O(2))(11)]-SP was applied. These agonists were subsequently tested in the presence of the protein kinase A inhibitor Rp-cAMP or protein kinase C inhibitor chelerythrine chloride. In all experiments the sodium channel blocker tetrodotoxin was used to prevent indirect neuronal activation. Brainstems were processed immunocytochemically for Fos expression, and positive cells were counted in the trigeminal subnucleus caudalis. NMDA and [Sar(9),Met(O(2))(11)]-SP significantly increased Fos expression, but these increases could be prevented by chelerythrine chloride. Rp-cAMP had no effect on Fos induced by NMDA but caused a significant reduction in Fos induced by [Sar(9),Met(O(2))(11)]-SP. These data demonstrate that in trigeminal subnucleus caudalis activation of either NK1 or NMDA receptors alone induces Fos expression; protein kinases A and C are involved in NK1R-induced Fos while protein kinase A is not required for NMDA receptor-induced Fos.

Expression of FOS, EGR-1, and ARC in the amygdala and hippocampus of female rats during formation of the intromission mnemonic of pseudopregnancy

Pseudopregnancy (PSP) in the female rat is a neuroendocrine condition that is induced by repeated and intermittent vaginocervical stimulation received during mating and involves the expression of bicircadian prolactin surges and cessation of normal estrous cyclicity for 10-12 days postmating. The temporal patterning and number of intromissions received by the female are critical for PSP initiation, and thus, short-term encoding of VCS occurs during transduction of intromissions into PSP. In this experiment, we characterized and compared the mating-induced neural activation patterns within amygdalar and hippocampal regions using expression of the immediate early genes FOS, EGR-1, and ARC. Cycling female rats mated on proestrus received 15 or 5 intromissions under paced or nonpaced mating conditions. High numbers of intromissions during nonpaced mating or low numbers received during paced mating are sufficient to induce PSP, while five nonpaced intromissions and mounts without intromission are insufficient. Here we demonstrate that the CA1 region of the hippocampus was selectively sensitive to PSP-sufficient but not PSP-insufficient mating stimulation by showing significant effects of paced mating for all three IEGs. Paced mating also stimulated the expression of ARC within the basolateral, cortical, and central nuclei of the amygdala. The posterodorsal medial amygdala also showed selective EGR-1 responses to PSP-sufficient mating stimulation. There was no effect of hemisphere on IEG expression. The postmating expression profiles of these IEGs provide evidence that limbic areas involved in encoding and consolidation of memory are involved in initiating the neuroendocrine memory of PSP.

Involvement of NMDA receptors in Zif/268 expression in the trigeminal nucleus caudalis following formalin injection into the rat whisker pad

We investigated the involvement of N-methyl-D-aspartate (NMDA) glutamate receptor in the expression of the proteins Zif/268 and c-Fos elicited by painful stimuli. To this purpose, the effect of the administration of MK-801, an NMDA receptor antagonist, on Zif/268 and c-Fos expression following a noxious stimulus, represented by formalin injection into the whisker pad of rats, was examined in neurons of the trigeminal nucleus caudalis. Furthermore, the co-localization of formalin injection-evoked Zif/268 and c-Fos expression and subunit 1 of the NMDA receptor (NR1) was studied in this nucleus. Zif/268 or c-Fos immunoreactivity elicited by formalin injection was significantly reduced by pretreatment with MK-801 in the superficial layer of the trigeminal nucleus caudalis; more than 40% of the neurons expressing Zif/268 and c-Fos in this layer were also immunolabeled by NR1. On the other hand, there was little effect of MK-801 administration on Zif/268 and c-Fos immunoreactivity in the nucleus proprius and deep lamina V of the trigeminal nucleus caudalis, while most neurons expressing Zif/268 or c-Fos in these two regions were labeled by NR1. These results point out differences between the superficial and deeper layers of the trigeminal nucleus caudalis in the involvement of NMDA receptor in the mechanisms underlying the expression of protein products of immediate early genes induced by painful stimuli.

Modulation of primary afferent-mediated neurotransmission and Fos expression by glutamate uptake inhibition in rat spinal neurones in vitro

The effect of altered endogenous levels of synaptic glutamate on neurotransmission and synaptic dorsal horn Fos expression was determined in rat spinal cord in vitro. The uptake inhibitor L-trans-pyrrolidine-2,4-dicarboxylate (L-PDC, 1mM) was tested against dorsal root-ventral root potentials (DR-VRP), afferent-mediated slow dorsal horn excitatory postsynaptic potentials (DR-EPSP) and nociceptive afferent-induced synaptic currents (EPSCs) of substantia gelatinosa neurones. L-PDC reduced DR-VRP fast and slow peak amplitude and duration (P<0.05), slow DR-EPSP amplitude and duration (P<0.005) and EPSC amplitude (P<0.05). The Group II/III mGluR antagonist (RS)-alpha-cyclopropyl-4-phosphonophenylglycine (CPPG, 100 microM) reduced L-PDC inhibition of synaptic potentials. The Group II antagonist (2S)-2-amino-2-(1S,2S-2-carboxycycloprop-1-yl)-3-(xanth-9-yl)propanoic acid (LY341495, 300 nM) and the Group III antagonist (RS)-alpha-methylserine-O-phosphate (MSOP, 10 microM) partially reversed EPSC inhibition by L-PDC. The Group III agonist L(+)-2-amino-4-phosphonobutyric acid (L-AP4, 30 microM) mimicked CPPG-sensitive inhibitory effects of L-PDC on DR-VRP (P<0.001) and the slow DR-EPSP (P<0.005). L-PDC (1mM) or L-AP4 (30 microM) reduced afferent-evoked dorsal horn Fos expression, this effect was reversed by CPPG. These data suggest that increased synaptic glutamate levels may activate inhibitory Group II/III mGluR receptors and impact significantly on nociceptive neurotransmission and transcriptional adaptive responses of target neurones.