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Suppression of piriform cortex activity in rat by corticotropin-releasing factor 1 and serotonin 2A/C receptors.

Narla C, Dunn HA, Ferguson SS, Poulter MO - Front Cell Neurosci (2015)

Bottom Line: Application of forskolin did not mimic CRFR1 activity but instead blocked it, while a protein kinase A antagonist had no effect.DOI had no effect when applied alone indicating that the prior activation of CRFR1 receptors was critical for DOI to show significant effects similar to CRF.These data show that CRF and 5-HT, acting through both CRFR1 and 5-HT2A/CRs, reduce the activation of the PC.

View Article: PubMed Central - PubMed

Affiliation: Molecular Medicine Research Group, Department of Physiology and Pharmacology, Robarts Research Institute, Faculty of Medicine, Schulich School of Medicine, University of Western Ontario London, ON, Canada.

ABSTRACT
The piriform cortex (PC) is richly innervated by corticotropin-releasing factor (CRF) and serotonin (5-HT) containing axons arising from central amygdala and Raphe nucleus. CRFR1 and 5-HT2A/2CRs have been shown to interact in manner where CRFR activation subsequently potentiates the activity of 5-HT2A/2CRs. The purpose of this study was to determine how the activation of CRFR1 and/or 5-HT2Rs modulates PC activity at both the circuit and cellular level. Voltage sensitive dye imaging showed that CRF acting through CRFR1 dampened activation of the Layer II of PC and interneurons of endopiriform nucleus. Application of the selective 5-HT2A/CR agonist 2,5-dimethoxy-4-iodoamphetamine (DOI) following CRFR1 activation potentiated this effect. Blocking the interaction between CRFR1 and 5-HT2R with a Tat-CRFR1-CT peptide abolished this potentiation. Application of forskolin did not mimic CRFR1 activity but instead blocked it, while a protein kinase A antagonist had no effect. However, activation and antagonism of protein kinase C (PKC) either mimicked or blocked CRF modulation, respectively. DOI had no effect when applied alone indicating that the prior activation of CRFR1 receptors was critical for DOI to show significant effects similar to CRF. Patch clamp recordings showed that both CRF and DOI reduced the synaptic responsiveness of Layer II pyramidal neurons. CRF had highly variable effects on interneurons within Layer III, both increasing and decreasing their excitability, but DOI had no effect on the excitability of this group of neurons. These data show that CRF and 5-HT, acting through both CRFR1 and 5-HT2A/CRs, reduce the activation of the PC. This modulation may be an important blunting mechanism of stressor behaviors mediated through the olfactory cortex.

No MeSH data available.


Related in: MedlinePlus

Activation of CRFR1 before the application of DOI potentiated the CRF effects. Representative images in (A) show control (left), after the application of CRF (middle) and the subsequent application of DOI following CRF (right). The image on right was taken after 15 min of perfusion with CRF. In (B–D) we show quantitation of CRFR1 and 5-HT2A/CR activation over the range of stimulation frequencies used to activate the circuit. *#p < 0.01. *CRF effect is significantly different compared to control. # DOI following CRF effect is significantly different from CRF. DOI was immediately applied after the CRF application was stopped. However, there was at least 15–17 min time lapse between when the DOI application was started and the slice was stimulated for the recording. The perfusion bath emptying rate was maintained at 1 ml per min. When DOI was added in the absence of CRF.
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Figure 5: Activation of CRFR1 before the application of DOI potentiated the CRF effects. Representative images in (A) show control (left), after the application of CRF (middle) and the subsequent application of DOI following CRF (right). The image on right was taken after 15 min of perfusion with CRF. In (B–D) we show quantitation of CRFR1 and 5-HT2A/CR activation over the range of stimulation frequencies used to activate the circuit. *#p < 0.01. *CRF effect is significantly different compared to control. # DOI following CRF effect is significantly different from CRF. DOI was immediately applied after the CRF application was stopped. However, there was at least 15–17 min time lapse between when the DOI application was started and the slice was stimulated for the recording. The perfusion bath emptying rate was maintained at 1 ml per min. When DOI was added in the absence of CRF.

Mentions: It has been previously reported that CRFR1 potentiates 5-HT2R mediated signaling in vitro (Magalhaes et al., 2010). Therefore, we wished to see if these receptors could alter PC activation and perhaps act in similar synergistic manner. We used the relatively selective 5-HT2A/C receptor agonist DOI. Surprisingly, DOI had no effect on the PC circuit activation (n = 5). Figure 4A shows images of the signal distribution (1 s after the end of 1 s 60 Hz stimulus) before and after the application of DOI. The quantification of these results shows that no frequency of stimulation altered circuit activity in all three layers of PC (Figures 4B–D). To test if prior CRFR1 activation could induce a DOI response we first applied CRF and then DOI. Under these conditions DOI produced similar responses to those produced by CRF. In Figure 5 we show images of responses taken before and after the application of these agonists. In Figure 5A the control response is in the left panel while in the middle panel we show the activity of CRF and in the right panel we show the effect of DOI. It is evident that DOI further reduced the effects of the activation of this circuit [F(1,9) = 9.82, p < 0.01, n = 9]. In Figure 5B we show the quantitation of the effects of CRF and DOI after CRF in all three layer of PC. These data show that 5-HT2A/CR activity is dependent on the prior activation of CRFR1. Unlike CRF, the effects of DOI were not reversible within 30 min of “washouts” that were attempted in these experiments.


Suppression of piriform cortex activity in rat by corticotropin-releasing factor 1 and serotonin 2A/C receptors.

Narla C, Dunn HA, Ferguson SS, Poulter MO - Front Cell Neurosci (2015)

Activation of CRFR1 before the application of DOI potentiated the CRF effects. Representative images in (A) show control (left), after the application of CRF (middle) and the subsequent application of DOI following CRF (right). The image on right was taken after 15 min of perfusion with CRF. In (B–D) we show quantitation of CRFR1 and 5-HT2A/CR activation over the range of stimulation frequencies used to activate the circuit. *#p < 0.01. *CRF effect is significantly different compared to control. # DOI following CRF effect is significantly different from CRF. DOI was immediately applied after the CRF application was stopped. However, there was at least 15–17 min time lapse between when the DOI application was started and the slice was stimulated for the recording. The perfusion bath emptying rate was maintained at 1 ml per min. When DOI was added in the absence of CRF.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4446537&req=5

Figure 5: Activation of CRFR1 before the application of DOI potentiated the CRF effects. Representative images in (A) show control (left), after the application of CRF (middle) and the subsequent application of DOI following CRF (right). The image on right was taken after 15 min of perfusion with CRF. In (B–D) we show quantitation of CRFR1 and 5-HT2A/CR activation over the range of stimulation frequencies used to activate the circuit. *#p < 0.01. *CRF effect is significantly different compared to control. # DOI following CRF effect is significantly different from CRF. DOI was immediately applied after the CRF application was stopped. However, there was at least 15–17 min time lapse between when the DOI application was started and the slice was stimulated for the recording. The perfusion bath emptying rate was maintained at 1 ml per min. When DOI was added in the absence of CRF.
Mentions: It has been previously reported that CRFR1 potentiates 5-HT2R mediated signaling in vitro (Magalhaes et al., 2010). Therefore, we wished to see if these receptors could alter PC activation and perhaps act in similar synergistic manner. We used the relatively selective 5-HT2A/C receptor agonist DOI. Surprisingly, DOI had no effect on the PC circuit activation (n = 5). Figure 4A shows images of the signal distribution (1 s after the end of 1 s 60 Hz stimulus) before and after the application of DOI. The quantification of these results shows that no frequency of stimulation altered circuit activity in all three layers of PC (Figures 4B–D). To test if prior CRFR1 activation could induce a DOI response we first applied CRF and then DOI. Under these conditions DOI produced similar responses to those produced by CRF. In Figure 5 we show images of responses taken before and after the application of these agonists. In Figure 5A the control response is in the left panel while in the middle panel we show the activity of CRF and in the right panel we show the effect of DOI. It is evident that DOI further reduced the effects of the activation of this circuit [F(1,9) = 9.82, p < 0.01, n = 9]. In Figure 5B we show the quantitation of the effects of CRF and DOI after CRF in all three layer of PC. These data show that 5-HT2A/CR activity is dependent on the prior activation of CRFR1. Unlike CRF, the effects of DOI were not reversible within 30 min of “washouts” that were attempted in these experiments.

Bottom Line: Application of forskolin did not mimic CRFR1 activity but instead blocked it, while a protein kinase A antagonist had no effect.DOI had no effect when applied alone indicating that the prior activation of CRFR1 receptors was critical for DOI to show significant effects similar to CRF.These data show that CRF and 5-HT, acting through both CRFR1 and 5-HT2A/CRs, reduce the activation of the PC.

View Article: PubMed Central - PubMed

Affiliation: Molecular Medicine Research Group, Department of Physiology and Pharmacology, Robarts Research Institute, Faculty of Medicine, Schulich School of Medicine, University of Western Ontario London, ON, Canada.

ABSTRACT
The piriform cortex (PC) is richly innervated by corticotropin-releasing factor (CRF) and serotonin (5-HT) containing axons arising from central amygdala and Raphe nucleus. CRFR1 and 5-HT2A/2CRs have been shown to interact in manner where CRFR activation subsequently potentiates the activity of 5-HT2A/2CRs. The purpose of this study was to determine how the activation of CRFR1 and/or 5-HT2Rs modulates PC activity at both the circuit and cellular level. Voltage sensitive dye imaging showed that CRF acting through CRFR1 dampened activation of the Layer II of PC and interneurons of endopiriform nucleus. Application of the selective 5-HT2A/CR agonist 2,5-dimethoxy-4-iodoamphetamine (DOI) following CRFR1 activation potentiated this effect. Blocking the interaction between CRFR1 and 5-HT2R with a Tat-CRFR1-CT peptide abolished this potentiation. Application of forskolin did not mimic CRFR1 activity but instead blocked it, while a protein kinase A antagonist had no effect. However, activation and antagonism of protein kinase C (PKC) either mimicked or blocked CRF modulation, respectively. DOI had no effect when applied alone indicating that the prior activation of CRFR1 receptors was critical for DOI to show significant effects similar to CRF. Patch clamp recordings showed that both CRF and DOI reduced the synaptic responsiveness of Layer II pyramidal neurons. CRF had highly variable effects on interneurons within Layer III, both increasing and decreasing their excitability, but DOI had no effect on the excitability of this group of neurons. These data show that CRF and 5-HT, acting through both CRFR1 and 5-HT2A/CRs, reduce the activation of the PC. This modulation may be an important blunting mechanism of stressor behaviors mediated through the olfactory cortex.

No MeSH data available.


Related in: MedlinePlus