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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

A subpopulation of interneurons from Layer III increased their firing frequency after the application of CRF. In (A) we show an example of ALF interneuron that converted to AHF firing pattern after the application of CRF. The graphs in (B) show the average of firing frequency against interspike interval number from 14 ALF at one times threshold and two times threshold (It and I2t respectively). (C) Shows an example of a wALF (weakly adapting low frequency) interneuron that converted to AHF type after the application of CRF. A plot of the average of firing frequency against interspike interval number from the five ALF interneurons that converted to AHF after the application of CRF is shown in (D).
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Figure 11: A subpopulation of interneurons from Layer III increased their firing frequency after the application of CRF. In (A) we show an example of ALF interneuron that converted to AHF firing pattern after the application of CRF. The graphs in (B) show the average of firing frequency against interspike interval number from 14 ALF at one times threshold and two times threshold (It and I2t respectively). (C) Shows an example of a wALF (weakly adapting low frequency) interneuron that converted to AHF type after the application of CRF. A plot of the average of firing frequency against interspike interval number from the five ALF interneurons that converted to AHF after the application of CRF is shown in (D).

Mentions: Corticotropin-releasing factor had variable and highly complex effects on the excitability of cells located in Layer III which are almost exclusively GABAergic interneurons. In contrast to pyramidal cells DOI had no effect on any recordings done in this cell layer. We have previously shown that interneurons in Layer III fire with five well-defined and differing spike patterns (Gavrilovici et al., 2012). The naming of these firing patterns were adopted from the nomenclature defined in Ascoli et al. (2008). Here we found that CRF altered the spiking patterns of some, but not all these subtypes. There were two types of outcomes on these interneurons. One response converted low frequency firing patterns to high frequency ones. While the second type of response showed a conversion from a high frequency spiking patterns to low. In some recordings there was no apparent effect of CRF. In Figure 11A we show an example of the conversion of an ALF interneuron (<50 Hz average firing frequency at two times threshold (I2t); also see methods for description of classifications) to an AHF phenotype (>50 Hz at I2t). All interneurons having this initial phenotype responded in this manner (Control: 44.0 ± 0.1; CRF: 62.3 ± 0.6 Hz, p < 0.001, n = 14). The graph in Figure 11B shows the averaged interspike frequency versus spike interval relationship for all 14 recordings. One line shows the relationship at the threshold (It) where a train of action potentials is elicited, while the other shows the relation at I2t. It is evident that CRF produced a dramatic change in the input/output responses of these cells. Similarly those cells that had the weakly ALF phenotype (wALF) all converted to an AHF pattern (Figure 11C; Control: 29.1 0 ± 0.6; CRF: 69.1 ± 0.8 Hz, p < 0.001, n = 6). The average change in the input/output for this population is shown in Figure 11D. The second type of responses were more variable. Interneurons that initially fired with an AHF phenotype sometimes converted to ALF pattern (Figures 12A,B; Control: 62.9 ± 0.9; CRF: 43.9 ± 1.0 Hz, p < 0.001, n = 6) but another cohort did not change (n = 7; not shown). NAvHF interneurons (>100 Hz) similarly had variable responses; some did not change (n = 4) while another group converted to the weakly adapting low frequency interneuron phenotype (wALF; Figures 12C,D, Control: 101.3 ± 1.0; CRF: 28.1 ± 0.9 Hz, p < 0.001, n = 5). The fifth pattern that we identified (Gavrilovici et al., 2012), strongly ALF, which occurred in less than 5% of the 205 recordings, was not seen in 38 recordings we did here and so we are unsure as to the effects of CRF on these cells.


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)

A subpopulation of interneurons from Layer III increased their firing frequency after the application of CRF. In (A) we show an example of ALF interneuron that converted to AHF firing pattern after the application of CRF. The graphs in (B) show the average of firing frequency against interspike interval number from 14 ALF at one times threshold and two times threshold (It and I2t respectively). (C) Shows an example of a wALF (weakly adapting low frequency) interneuron that converted to AHF type after the application of CRF. A plot of the average of firing frequency against interspike interval number from the five ALF interneurons that converted to AHF after the application of CRF is shown in (D).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 11: A subpopulation of interneurons from Layer III increased their firing frequency after the application of CRF. In (A) we show an example of ALF interneuron that converted to AHF firing pattern after the application of CRF. The graphs in (B) show the average of firing frequency against interspike interval number from 14 ALF at one times threshold and two times threshold (It and I2t respectively). (C) Shows an example of a wALF (weakly adapting low frequency) interneuron that converted to AHF type after the application of CRF. A plot of the average of firing frequency against interspike interval number from the five ALF interneurons that converted to AHF after the application of CRF is shown in (D).
Mentions: Corticotropin-releasing factor had variable and highly complex effects on the excitability of cells located in Layer III which are almost exclusively GABAergic interneurons. In contrast to pyramidal cells DOI had no effect on any recordings done in this cell layer. We have previously shown that interneurons in Layer III fire with five well-defined and differing spike patterns (Gavrilovici et al., 2012). The naming of these firing patterns were adopted from the nomenclature defined in Ascoli et al. (2008). Here we found that CRF altered the spiking patterns of some, but not all these subtypes. There were two types of outcomes on these interneurons. One response converted low frequency firing patterns to high frequency ones. While the second type of response showed a conversion from a high frequency spiking patterns to low. In some recordings there was no apparent effect of CRF. In Figure 11A we show an example of the conversion of an ALF interneuron (<50 Hz average firing frequency at two times threshold (I2t); also see methods for description of classifications) to an AHF phenotype (>50 Hz at I2t). All interneurons having this initial phenotype responded in this manner (Control: 44.0 ± 0.1; CRF: 62.3 ± 0.6 Hz, p < 0.001, n = 14). The graph in Figure 11B shows the averaged interspike frequency versus spike interval relationship for all 14 recordings. One line shows the relationship at the threshold (It) where a train of action potentials is elicited, while the other shows the relation at I2t. It is evident that CRF produced a dramatic change in the input/output responses of these cells. Similarly those cells that had the weakly ALF phenotype (wALF) all converted to an AHF pattern (Figure 11C; Control: 29.1 0 ± 0.6; CRF: 69.1 ± 0.8 Hz, p < 0.001, n = 6). The average change in the input/output for this population is shown in Figure 11D. The second type of responses were more variable. Interneurons that initially fired with an AHF phenotype sometimes converted to ALF pattern (Figures 12A,B; Control: 62.9 ± 0.9; CRF: 43.9 ± 1.0 Hz, p < 0.001, n = 6) but another cohort did not change (n = 7; not shown). NAvHF interneurons (>100 Hz) similarly had variable responses; some did not change (n = 4) while another group converted to the weakly adapting low frequency interneuron phenotype (wALF; Figures 12C,D, Control: 101.3 ± 1.0; CRF: 28.1 ± 0.9 Hz, p < 0.001, n = 5). The fifth pattern that we identified (Gavrilovici et al., 2012), strongly ALF, which occurred in less than 5% of the 205 recordings, was not seen in 38 recordings we did here and so we are unsure as to the effects of CRF on these cells.

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