Parte II: Análisis de la Situación Turística

PERK was used to label neurons in the dorsal horn receiving nociceptive-specific primary afferent input. As expected PERK showed a strong upregulation in laminae I-II in an area larger than where PH3S10 was expressed but still overlapping. Coexpression of PH3S10 and PERK populations was assessed at 30min, a time point used to obtain the maximum overlap of the two populations given their respective time course of expression following noxious stimulation (Figure 4.10). Indeed, PERK expression peaks 5 minutes post-formalin but is still strongly expressed at 30 minutes. 58% of all PH3S10-expressing cells colabelled with PERK (mean PH3S10 population 26.3 ± 1.2), while 42% of PERK-expressing cells also expressed PH3S10 (mean PERK population 30.7 ± 3.7). For deeper laminae III-V, similar percentages of colocalisation were observed. 53% of PH3S10-expressing cells colabelled PERK (mean PH3S10 population 10.3 ± 0.6) and 40% of PERK- expressing cells also coexpressed PH3S10

Cellular characterisation of PH3S10 in the dorsal horn following noxious stimulation

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difference in percentage overlap values when using 5 sections with maximum response per animal from either the PH3S10 or PERK population.

Figure 4.7 Formalin-induced PH3S10 is partially expressed in PERK labelled neurons in the dorsal horn. A, C) Dorsal horn images of PERK (green) and PH3S10 (red) double labelling

taken in a single focal plane in a formalin-stimulated animal, in laminae I-II (A) and III-V (C). The final image shows a merge of the first two images; colocalisation appears yellow. White line indicates medial border between lamina I and white matter; arrowheads indicate examples of colocalisation. Scale bar 30µm (A), 50µm (C). B, D) Venn diagram depicting overlap of PH3S10/PERK populations in laminae I-II (B) and III-V (D). Percentages indicate percentage of population not double labelled; values in parentheses indicate population size expressed as group mean (immunopositive cells per 40µm section) ± SEM (n=3, 5 sections per animal).

Cellular characterisation of PH3S10 in the dorsal horn following noxious stimulation

4.3.7 PH3S10 colocalises with the immediate early gene products c-Fos and Zif268

c-Fos and Zif268 are IEG markers of neuronal plasticity known to have maximal expression in the ipsilateral dorsal horn 1-2h after noxious stimulation. Robust upregulation of both c-Fos and Zif268 was observed 1h post-formalin. Both populations had a larger and more anatomically widespread distribution compared to the PH3S10 population. 60% of PH3S10 coexpressed c-Fos (mean PH3S10 population 19.3 ± 4.2), while 17% of c-Fos coexpressed PH3S10 (mean c-Fos population 38.5 ± 2.4) (Figure 4.8, Table 4.2). 57% of the PH3S10 population of neurons coexpressed Zif268 (mean PH3S10 population 10.6 ± 1.1), while 12% of the Zif268 population coexpressed PH3S10 (mean Zif268 population 59.5 ± 6.6) (Figure 4.9, Table 4.2). Importantly, there were no differences in percentage overlap values when using 5 sections with maximum response per animal from either the PH3S10 or c-Fos/Zif268 population.

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Figure 4.8 Formalin-induced PH3S10 colocalises with immediate early gene product and marker of nociceptive synaptic plasticity, c-Fos. Dorsal horn images of double labelling for

PH3S10 and c-Fos in formalin-stimulated animals taken in a single focal plane. A) Top row contains low power images and bottom row higher power images of the same region. First column images (green) indicate positive staining for c-Fos. Second column images (red) indicate PH3S10, and third column images are column 1 and 2 images merged; colocalisation appears yellow. White line indicates medial border between lamina I and white matter; arrowhead indicates example of PH3S10 nuclei not double labelled with c-Fos. Scale bar upper, 50µm; lower, 30µm. B) Venn diagram depicting overlap of two populations. Percentages indicate percentage of population not double labelled; values in parentheses indicate population size expressed as mean value (immunopositive cells per 40µm section) ± SEM (n=4, 5 sections per animal).

Cellular characterisation of PH3S10 in the dorsal horn following noxious stimulation

Figure 4.9 Formalin-induced PH3S10 colocalises with immediate early gene product Zif268. Dorsal horn images of double labelling for PH3S10 and Zif268 in formalin-stimulated

animals taken in a single focal plane. A) Top row contains low power images and bottom row higher power images of the same region. First column images (green) indicate positive staining for c-Fos. Second column images (red) indicate PH3S10, and third column images are column 1 and 2 images merged; colocalisation appears yellow. White line indicates medial border between lamina I and white matter; arrowhead indicates example of Zif268 nucleus not double labelled with PH3S10. Scale bar upper, 50µm; lower, 30µm. B) Venn diagram depicting overlap of PH3S10 and Zif268 populations. Percentages indicate percentage of population not double labelled; values in parentheses indicate population size expressed as mean value (immunopositive cells per 40µm section) ± SEM (n=4, 5 sections per animal).

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Table 4.2 Summary of population sizes and overlap of PH3S10 with markers of the pain pathway in the ipsilateral dorsal horn post-formalin. Values are presented as mean ± SEM

per tissue slice, 40µm thickness (n=3/4 animals each colocalisation; 5 tissue sections per animal). Marker Population Size (# cells) PH3S10 population size (# cells) Double labelled (# cells) % PH3S10 expressing Marker % Marker expressing PH3S10 Time point investigated PERK (Lam1-2) PERK (Lam3-5) 30.7 ± 3.7 16.6 ± 5.5 26.3 ± 1.2 10.3 ± 0.6 8.9 ± 4.1 5.1 ± 1.1 58% 53% 42% 40% 30 min NK1 (Lam 1) NK1 (Lam3-5) 6.5 ± 1.5 6.1 ± 1.2 27.1 ± 3.8 18.2 ± 3.6 1.3 ± 0.7 0.8 ± 0.4 5% 4% 17% 17% 1h c-Fos (Lam1-2) 38.5 ± 2.4 19.3 ± 4.2 6.2 ± 1.2 60% 17% 1h Zif268 (Lam1-2) 59.5 ± 6.6 10.6 ± 1.1 6.3 ± 1.2 57% 12% 1h

Cellular characterisation of PH3S10 in the dorsal horn following noxious stimulation

4.4 Discussion

PH3S10 is a histone modification associated with transcriptional activation in neurons and is regulated by ERK/MAPK signalling in various forms of neuronal plasticity. In this chapter it was shown that PH3S10 is upregulated in the dorsal horn of spinal cord neurons immediately and transiently after noxious hindpaw stimulation. It was also shown that PH3S10 occurred within neurons expressing markers of the pain pathway, PERK, NK1, c-Fos, and Zif268.

4.4.1 Intracellular signalling: linking PERK, PH3S10, and IEG events in models