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Acute hypoxia activates hypothalamic paraventricular nucleus-projecting catecholaminergic neurons in the C1 region
Abstracts / Autonomic Neuroscience: Basic and Clinical 192 (2015) 56–141
P4.11 Acute hypoxia activates hypothalamic paraventricular nucleus-projecting catecholaminergic neurons in the C1 region T.M. Silvaa, A.C. Takakurab, T.S. Moreiraa a Department of Physiology and Biophysics, Institute of Biomedical Science, University of São Paulo, São Paulo, Brazil b Department of Pharmacology, Institute of Biomedical Science, University of São Paulo, São Paulo, Brazil C1 cells reside in the rostral and intermediate portions of the ventrolateral medulla (RVLM) and can be activated by hypoxia. These neurons regulate the hypothalamic pituitary axis via direct projections to the hypothalamic paraventricular nucleus (PVH) and regulate the autonomic nervous system via projections to sympathetic and parasympathetic preganglionic neurons. Based on the various effects attributed to the C1 cells and what is currently known of their synaptic inputs, our hypothesis is that acute hypoxia (AH) activates PVH projecting catecholaminergic neurons in the RVLM. Anterograde tracer, Phaseolus vulgaris leucoagglutinin (PHA-L) was unilaterally injected into the RVLM and a retrograde tracer Cholera toxin B (CTB) was unilaterally injected into the PVH region. After ten days, male Wistar rats that received CTB injection into the PVH were subjected to AH (8% O2, balanced with N2) or normoxia (21% O2) for 3 hours. Acute hypoxia significantly increased Fos immunoreactivity in the C1 region (68.5 ± 2.0), and half of the RVLM cells activated are catecholaminergic (35.5 ± 2.3). We observed that 30 ± 4% of the PVH projecting RVLM cells that were activated by AH were also C1 cells. The presence of varicosities containing PHA-L in PVH region was also observed. The present results suggest that catecholaminergic C1-PVH projection is hypoxia sensitive and the pathway between these two important brain areas can certainly be one more piece in the complex puzzle of neural control of autonomic regulation during hypoxia. Financial support: FAPESP, CNPq and CAPES/ PROEX.
doi:10.1016/j.autneu.2015.07.050
P4.12 Respiratory modulated bursting of sympathetic activity L.J.B. Brianta,b,c, E.L. O’Callaghana, A.R. Champneysc, J.F.R. Patona,b a School of Physiology and Pharmacology, University of Bristol, UK b CRICBristol, University of Bristol, UK c Department of Engineering Mathematics, University of Bristol, UK In the spontaneously hypertensive (SH) rat, sympathetic nerve activity (SNA) exhibits amplified respiratory bursting (Simms et al. 2009). The physiological significance of this rhythm is not understood. We therefore aimed to assess the impact of respiratory modulation of SNA on vascular resistance (VR). We constructed a mathematical model of the sympathetic innervation of an artery; respiratory-modulated bursting in the model produced greater changes in VR than frequencymatched tonic patterns. This was due to an accumulation of NA during bursting. These modelling results were then tested in vivo. Adult male Wistar (WKY; n = 8) and SH (n = 8) rats were anaesthetised (1.2-1.5 g/kg urethane and 60 mg/kg α-chloralose). Blood pressure (BP) was measured from the carotid artery and blood flow (BF) from the femoral using a flow probe. A cuff electrode was placed on the left sympathetic chain between L2 and L3. The nerve was stimulated with respiratory bursting and tonic patterns of the same average firing frequency (2-10Hz). At 8Hz stimulation, VR (=BP/BF; normalised) was greater in response to bursting (57.8 ± 4.0%) than to tonic (44.8 ± 4.9%; p b 0.01; 2-way repeated-measures ANOVA) in WKY rats. In SH
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rats, 8Hz stimulation with bursting (44.6 ± 3.9%) produced a VR that was not different to tonic (37.4 ± 3.5%; p N 0.05). These results were also seen at 10Hz stimulation. In conclusion, respiratory modulation of SNA appears to be important in producing robust changes in VR. The mechanism that generates this pattern-dependency appears to be absent in the SH rat. We shall use the model to explore the biological parameters that may explain these data. doi:10.1016/j.autneu.2015.07.051
P4.13 A slow-fast approach to studying the emergence and amplitude of respiratory bursting in sympathetic preganglionic neurones Linford J.B. Brianta,c, Mathieu Desrochesb, Alan R. Champneysc a School of Physiology and Pharmacology, University of Bristol, UK b INRIA, Paris c Department of Engineering Mathematics, University of Bristol, UK Introduction: Sympathetic nerve activity (SNA) is intrinsically ‘bursty’, exhibiting multiple bursting rhythms. One of these rhythms is entrained to respiration, due to central coupling with respiratory pattern generators. This rhythm is especially relevant in hypertension, as SNA in the spontaneously hypertensive (SH) rat exhibits amplified respiratory bursting (Simms et al. 2009) a component of which originates centrally (Moraes et al. 2014). Recent evidence also suggests that a contribution to this amplified respiratory bursting could come from changes in the excitability of sympathetic preganglionic neurones (SPNs); in particular, a diminishment of their A-type potassium current, IA (Briant et al. 2014). Methods: We present a mathematical reduction of a biophysical SPN model that has been fitted to experiment data from normotensive rats. This reduced model is shown to still be consistent with the data, but crucially allows us to understand how the number of spikes per burst is controlled by key parameters of the model - notably those related to IA. A slow-fast investigation of this reduced model revealed how bursting solutions emerge, and how the spike-adding process is organised upon IA parameter variation. We could tune IA parameters such that the spikeadding resulted in SH-like bursts. Conclusion: These analytical results help us to understand how altering properties of IA can influence the amplitude of respiratory bursts in SPNs, resulting in burst amplitudes recorded in the hypertensive rat. Simms et al. J Physiol. 2009 Feb 1;587(Pt 3):597-610. Moraes et al. Hypertension. 2014 Jun;63(6):1309-18. Briant et al. J Neurophysiol. 2014 Dec 1;112(11):2756-78. doi:10.1016/j.autneu.2015.07.052
P5 Cardiac Control P5.1 Effect of B-type natriuretic peptide and phosphodiesterase 2A is coupled to neurotransmitter release in pro-hypertensive rats K. Liu, C.- Lu, D. Li, D.J. Paterson Department of Physiology, Anatomy and Genetics, University of Oxford, United Kingdom Background: B-type natriuretic peptide (BNP) decreases cardiac sympathetic neurotransmission by attenuating activation of neuronal calcium channels and the intracellular calcium transient via a cGMPprotein kinase G (PKG)-phosphodiesterase 2 (PDE2A) coupled pathway.
P4.11 Acute hypoxia activates hypothalamic paraventricular nucleus-projecting catecholaminergic neurons in the C1 region T.M. Silvaa, A.C. Takakurab, T.S. Moreiraa a Department of Physiology and Biophysics, Institute of Biomedical Science, University of São Paulo, São Paulo, Brazil b Department of Pharmacology, Institute of Biomedical Science, University of São Paulo, São Paulo, Brazil C1 cells reside in the rostral and intermediate portions of the ventrolateral medulla (RVLM) and can be activated by hypoxia. These neurons regulate the hypothalamic pituitary axis via direct projections to the hypothalamic paraventricular nucleus (PVH) and regulate the autonomic nervous system via projections to sympathetic and parasympathetic preganglionic neurons. Based on the various effects attributed to the C1 cells and what is currently known of their synaptic inputs, our hypothesis is that acute hypoxia (AH) activates PVH projecting catecholaminergic neurons in the RVLM. Anterograde tracer, Phaseolus vulgaris leucoagglutinin (PHA-L) was unilaterally injected into the RVLM and a retrograde tracer Cholera toxin B (CTB) was unilaterally injected into the PVH region. After ten days, male Wistar rats that received CTB injection into the PVH were subjected to AH (8% O2, balanced with N2) or normoxia (21% O2) for 3 hours. Acute hypoxia significantly increased Fos immunoreactivity in the C1 region (68.5 ± 2.0), and half of the RVLM cells activated are catecholaminergic (35.5 ± 2.3). We observed that 30 ± 4% of the PVH projecting RVLM cells that were activated by AH were also C1 cells. The presence of varicosities containing PHA-L in PVH region was also observed. The present results suggest that catecholaminergic C1-PVH projection is hypoxia sensitive and the pathway between these two important brain areas can certainly be one more piece in the complex puzzle of neural control of autonomic regulation during hypoxia. Financial support: FAPESP, CNPq and CAPES/ PROEX.
doi:10.1016/j.autneu.2015.07.050
P4.12 Respiratory modulated bursting of sympathetic activity L.J.B. Brianta,b,c, E.L. O’Callaghana, A.R. Champneysc, J.F.R. Patona,b a School of Physiology and Pharmacology, University of Bristol, UK b CRICBristol, University of Bristol, UK c Department of Engineering Mathematics, University of Bristol, UK In the spontaneously hypertensive (SH) rat, sympathetic nerve activity (SNA) exhibits amplified respiratory bursting (Simms et al. 2009). The physiological significance of this rhythm is not understood. We therefore aimed to assess the impact of respiratory modulation of SNA on vascular resistance (VR). We constructed a mathematical model of the sympathetic innervation of an artery; respiratory-modulated bursting in the model produced greater changes in VR than frequencymatched tonic patterns. This was due to an accumulation of NA during bursting. These modelling results were then tested in vivo. Adult male Wistar (WKY; n = 8) and SH (n = 8) rats were anaesthetised (1.2-1.5 g/kg urethane and 60 mg/kg α-chloralose). Blood pressure (BP) was measured from the carotid artery and blood flow (BF) from the femoral using a flow probe. A cuff electrode was placed on the left sympathetic chain between L2 and L3. The nerve was stimulated with respiratory bursting and tonic patterns of the same average firing frequency (2-10Hz). At 8Hz stimulation, VR (=BP/BF; normalised) was greater in response to bursting (57.8 ± 4.0%) than to tonic (44.8 ± 4.9%; p b 0.01; 2-way repeated-measures ANOVA) in WKY rats. In SH
69
rats, 8Hz stimulation with bursting (44.6 ± 3.9%) produced a VR that was not different to tonic (37.4 ± 3.5%; p N 0.05). These results were also seen at 10Hz stimulation. In conclusion, respiratory modulation of SNA appears to be important in producing robust changes in VR. The mechanism that generates this pattern-dependency appears to be absent in the SH rat. We shall use the model to explore the biological parameters that may explain these data. doi:10.1016/j.autneu.2015.07.051
P4.13 A slow-fast approach to studying the emergence and amplitude of respiratory bursting in sympathetic preganglionic neurones Linford J.B. Brianta,c, Mathieu Desrochesb, Alan R. Champneysc a School of Physiology and Pharmacology, University of Bristol, UK b INRIA, Paris c Department of Engineering Mathematics, University of Bristol, UK Introduction: Sympathetic nerve activity (SNA) is intrinsically ‘bursty’, exhibiting multiple bursting rhythms. One of these rhythms is entrained to respiration, due to central coupling with respiratory pattern generators. This rhythm is especially relevant in hypertension, as SNA in the spontaneously hypertensive (SH) rat exhibits amplified respiratory bursting (Simms et al. 2009) a component of which originates centrally (Moraes et al. 2014). Recent evidence also suggests that a contribution to this amplified respiratory bursting could come from changes in the excitability of sympathetic preganglionic neurones (SPNs); in particular, a diminishment of their A-type potassium current, IA (Briant et al. 2014). Methods: We present a mathematical reduction of a biophysical SPN model that has been fitted to experiment data from normotensive rats. This reduced model is shown to still be consistent with the data, but crucially allows us to understand how the number of spikes per burst is controlled by key parameters of the model - notably those related to IA. A slow-fast investigation of this reduced model revealed how bursting solutions emerge, and how the spike-adding process is organised upon IA parameter variation. We could tune IA parameters such that the spikeadding resulted in SH-like bursts. Conclusion: These analytical results help us to understand how altering properties of IA can influence the amplitude of respiratory bursts in SPNs, resulting in burst amplitudes recorded in the hypertensive rat. Simms et al. J Physiol. 2009 Feb 1;587(Pt 3):597-610. Moraes et al. Hypertension. 2014 Jun;63(6):1309-18. Briant et al. J Neurophysiol. 2014 Dec 1;112(11):2756-78. doi:10.1016/j.autneu.2015.07.052
P5 Cardiac Control P5.1 Effect of B-type natriuretic peptide and phosphodiesterase 2A is coupled to neurotransmitter release in pro-hypertensive rats K. Liu, C.- Lu, D. Li, D.J. Paterson Department of Physiology, Anatomy and Genetics, University of Oxford, United Kingdom Background: B-type natriuretic peptide (BNP) decreases cardiac sympathetic neurotransmission by attenuating activation of neuronal calcium channels and the intracellular calcium transient via a cGMPprotein kinase G (PKG)-phosphodiesterase 2 (PDE2A) coupled pathway.