J Vet Sci.  2018 Jul;19(4):483-491. 10.4142/jvs.2018.19.4.483.

Comparison of electrophysiological properties of two types of pre-sympathetic neurons intermingled in the hypothalamic paraventricular nucleus

• Shen Y
• Han SK
• Ryu PD

• KMID: 2417562
• DOI: http://doi.org/10.4142/jvs.2018.19.4.483

Abstract

The hypothalamic paraventricular nucleus (PVN) contains two types of neurons projecting to either the rostral ventrolateral medulla (PVN(RVLM)) or the intermediolateral horn (IML) of the spinal cord (PVN(IML)). These two neuron groups are intermingled in the same subdivisions of the PVN and differentially regulate sympathetic outflow. However, electrophysiological evidence supporting such functional differences is largely lacking. Herein, we compared the electrophysiological properties of these neurons by using patch-clamp and retrograde-tracing techniques. Most neurons (>70%) in both groups spontaneously fired in the cell-attached mode. When compared to the PVN(IML) neurons, the PVN(RVLM) neurons had a lower firing rate and a more irregular firing pattern (p < 0.05). The PVN(RVLM) neurons showed smaller resting membrane potential, slower rise and decay times, and greater duration of spontaneous action potentials (p < 0.05). The PVN(RVLM) neurons received greater inhibitory synaptic inputs (frequency, p < 0.05) with a shorter rise time (p < 0.05). Taken together, the results indicate that the two pre-sympathetic neurons differ in their intrinsic and extrinsic electrophysiological properties, which may explain the lower firing activity of the PVN(RVLM) neurons. The greater inhibitory synaptic inputs to the PVN(RVLM) neurons also imply that these neurons have more integrative roles in regulation of sympathetic activity.

Keyword

action potential; inhibitory postsynaptic current; patch-clamp techniques; rostral ventrolateral medulla; spinal cord lateral horn

MeSH Terms

Action Potentials
Animals
Fires
Horns
Inhibitory Postsynaptic Potentials
Membrane Potentials
Neurons*
Paraventricular Hypothalamic Nucleus*
Patch-Clamp Techniques
Spinal Cord
Spinal Cord Lateral Horn

Figure

• 

  Fig. 1 The firing activity in PVNRVLM and PVNIML neurons. (A) Representative traces showing spontaneous firing activities of a PVNRVLM neuron and a PVNIML neuron. (B and C) Cumulative bar graphs showing the mean frequency of spontaneous spikes (B) and the coefficient of variance (CV) of the interspike interval (ISI) in PVNRVLM and PVNIML neurons (C). (D) Plot of firing rate vs. the CV of the ISI. The curves were drawn by fitting the data with the equation y = a + b × cx. The CV values in the PVNIML neurons tended to be smaller than those in the PVNRVLM neurons at the same firing rate. The values in the bars (B and C) represent the total number of neurons tested. Values represent mean ± SEM. Asterisks indicate p < 0.05 obtained by the unpaired Student's t-test. PVN, paraventricular nucleus; RVLM, rostral ventrolateral medulla; IML, intermediolateral horn of the spinal cord.

• 

  Fig. 2 The parameters of spontaneous action potentials in PVNRVLM and PVNIML neurons. (A) Representative action potentials from a PVNRVLM neuron (solid line; RMP, −56.07 mV; threshold, −43.09 mV; rise time, 0.95 msec; decay time, 1.05 msec; half-APD, 2.15 msec) and a PVNIML neuron (dotted line; RMP, −60.53 mV; threshold, −39.93 mV; rise time, 0.6 msec; decay time, 0.75 msec; half-APD, 1.65 msec) were overlapped at threshold. Cumulative bar graphs showing the 10% to 90% rise time (B), 37% to 90% decay time (C) and half-APD (D) in PVNRVLM and PVNIML neurons. The values in the bars (B–D) represent the total number of neurons tested. Values represent mean ± SEM. Asterisks indicate p < 0.05 by the unpaired Student's t-test. PVN, paraventricular nucleus; RVLM, rostral ventrolateral medulla; IML, intermediolateral horn of the spinal cord; half-APD, duration of action potential at half amplitude.

• 

  Fig. 3 Miniature inhibitory postsynaptic current (mIPSC) in PVNRVLM and PVNIML neurons. Representative current traces of mIPSCs in a PVNRVLM neuron (A) and a PVNIML neuron (B) (Vh = −70 mV). Cumulative bar graphs showing the mean frequency (C) and mean amplitude (D) of the mIPSCs. The values in the bars (C and D) represent the total numbers of neurons tested. Values are mean ± SEM. Asterisk indicates p < 0.05 by the unpaired Student's t-test. PVN, paraventricular nucleus; RVLM, rostral ventrolateral medulla; IML, intermediolateral horn of the spinal cord.

• 

  Fig. 4 The miniature inhibitory postsynaptic current (mIPSC) kinetics in the PVNRVLM and the PVNIML neurons. (A) Representative traces of mIPSCs in a PVNRVLM neuron (black) and a PVNIML neuron (gray) (left). Illustration of the 10% to 90% rise time and the decay time at an expanded time scale (middle and right). (B) Summary bar graphs showing the mean 10% to 90% rise time in the PVNRVLM and PVNIML neurons. (C) Summary bar graphs displaying the weighted decay time constant under a well-fitted second exponential. The values in the bars (B and C) represent the total numbers of neurons tested. Values are mean ± SEM. Double asterisk indicates p < 0.05 by the unpaired Student's t-test. PVN, paraventricular nucleus; RVLM, rostral ventrolateral medulla; IML, intermediolateral horn of the spinal cord.

Reference

1. Abbott LF, Fusi S, Miller KD. Theoretical approaches to neuroscience: examples from single neurons to networks. In : Kandel ER, Schwartz JH, Jessell TM, Siegelbaum SA, Hudspeth AJ, Mack S, editors. Principles of Neural Science. 5th ed. New York: McGraw-Hill Professional Publishing;2012. p. 1601–1617.

2. Badoer E. Hypothalamic paraventricular nucleus and cardiovascular regulation. Clin Exp Pharmacol Physiol. 2001; 28:95–99.

3. Berkefeld H, Fakler B. Repolarizing responses of BK_Ca-Cav complexes are distinctly shaped by their Cav subunits. J Neurosci. 2008; 28:8238–8245.

4. Brown CH, Bains JS, Ludwig M, Stern JE. Physiological regulation of magnocellular neurosecretory cell activity: integration of intrinsic, local and afferent mechanisms. J Neuroendocrinol. 2013; 25:678–710.

5. Carrive P, Gorissen M. Premotor sympathetic neurons of conditioned fear in the rat. Eur J Neurosci. 2008; 28:428–446.

6. Cechetto DF, Saper CB. Neurochemical organization of the hypothalamic projection to the spinal cord in the rat. J Comp Neurol. 1988; 272:579–604.

7. Cham JL, Badoer E. Exposure to a hot environment can activate rostral ventrolateral medulla-projecting neurones in the hypothalamic paraventricular nucleus in conscious rats. Exp Physiol. 2008; 93:64–74.

8. Cham JL, Klein R, Owens NC, Mathai M, McKinley M, Badoer E. Activation of spinally projecting and nitrergic neurons in the PVN following heat exposure. Am J Physiol Regul Integr Comp Physiol. 2006; 291:R91–R101.

9. Chen QH, Toney GM. Identification and characterization of two functionally distinct groups of spinal cord-projecting paraventricular nucleus neurons with sympathetic-related activity. Neuroscience. 2003; 118:797–807.

10. Coote JH. A role for the paraventricular nucleus of the hypothalamus in the autonomic control of heart and kidney. Exp Physiol. 2005; 90:169–173.

11. Cullinan WE, Ziegler DR, Herman JP. Functional role of local GABAergic influences on the HPA axis. Brain Struct Funct. 2008; 213:63–72.

12. Engelmann M, Landgraf R, Wotjak CT. The hypothalamic-neurohypophysial system regulates the hypothalamic-pituitary-adrenal axis under stress: an old concept revisited. Front Neuroendocrinol. 2004; 25:132–149.

13. Erisir A, Lau D, Rudy B, Leonard CS. Function of specific K⁺ channels in sustained high-frequency firing of fast-spiking neocortical interneurons. J Neurophysiol. 1999; 82:2476–2489.

14. Farrant M, Nusser Z. Variations on an inhibitory theme: phasic and tonic activation of GABA_A receptors. Nat Rev Neurosci. 2005; 6:215–229.

15. Hallbeck M, Larhammar D, Blomqvist A. Neuropeptide expression in rat paraventricular hypothalamic neurons that project to the spinal cord. J Comp Neurol. 2001; 433:222–238.

16. Hammond C. The voltage-gated channels of Na⁺ action potentials: generalization. In : Hammond C, editor. Cellular and Molecular Neurophysiology. 3rd ed. San Diego: Academic Press;2008. p. 45–82.

17. Han SK, Chong W, Li LH, Lee IS, Murase K, Ryu PD. Noradrenaline excites and inhibits GABAergic transmission in parvocellular neurons of rat hypothalamic paraventricular nucleus. J Neurophysiol. 2002; 87:2287–2296.

18. Han TH, Lee K, Park JB, Ahn D, Park JH, Kim DY, Stern JE, Lee SY, Ryu PD. Reduction in synaptic GABA release contributes to target-selective elevation of PVN neuronal activity in rats with myocardial infarction. Am J Physiol Regul Integr Comp Physiol. 2010; 299:R129–R139.

19. Hodgkin AL, Huxley AF. A quantitative description of membrane current and its application to conduction and excitation in nerve. J Physiol. 1952; 117:500–544.

20. Jansen AS, Wessendorf MW, Loewy AD. Transneuronal labeling of CNS neuropeptide and monoamine neurons after pseudorabies virus injections into the stellate ganglion. Brain Res. 1995; 683:1–24.

21. Kole MH, Ilschner SU, Kampa BM, Williams SR, Ruben PC, Stuart GJ. Action potential generation requires a high sodium channel density in the axon initial segment. Nat Neurosci. 2008; 11:178–186.

22. Luther JA, Tasker JG. Voltage-gated currents distinguish parvocellular from magnocellular neurones in the rat hypothalamic paraventricular nucleus. J Physiol. 2000; 523:193–209.

23. Palkovits M. Interconnections between the neuroendocrine hypothalamus and the central autonomic system: Geoffrey Harris Memorial Lecture, Kitakyushu, Japan, October 1998. Front Neuroendocrinol. 1999; 20:270–295.

24. Pandit S, Jo JY, Lee SU, Lee YJ, Lee SY, Ryu PD, Lee JU, Kim HW, Jeon BH, Park JB. Enhanced astroglial GABA uptake attenuates tonic GABA_A inhibition of the presympathetic hypothalamic paraventricular nucleus neurons in heart failure. J Neurophysiol. 2015; 114:914–926.

25. Paxinos G, Watson C. The Rat Brain in Stereotaxic Coordinates. 2nd ed. San Diego: Academic Press;1986.

26. Pyner S, Coote JH. Identification of branching paraventricular neurons of the hypothalamus that project to the rostroventrolateral medulla and spinal cord. Neuroscience. 2000; 100:549–556.

27. Rehak R, Bartoletti TM, Engbers JD, Berecki G, Turner RW, Zamponi GW. Low voltage activation of KCa1.1 current by Cav3-KCa1.1 complexes. PLoS One. 2013; 8:e61844.

28. Renaud LP, Bourque CW. Neurophysiology and neuropharmacology of hypothalamic magnocellular neurons secreting vasopressin and oxytocin. Prog Neurobiol. 1991; 36:131–169.

29. Salin PA, Prince DA. Spontaneous GABA_A receptor-mediated inhibitory currents in adult rat somatosensory cortex. J Neurophysiol. 1996; 75:1573–1588.

30. Saper CB. Central autonomic system. In : Paxinos G, editor. The Rat Nervous System. 3rd ed. San Diego: Elsevier;2004. p. 761–796.

31. Sawchenko PE, Brown ER, Chan RK, Ericsson A, Li HY, Roland BL, Kovács KJ. The paraventricular nucleus of the hypothalamus and the functional neuroanatomy of visceromotor responses to stress. Prog Brain Res. 1996; 107:201–222.

32. Sawchenko PE, Li HY, Ericsson A. Circuits and mechanisms governing hypothalamic responses to stress: a tale of two paradigms. Prog Brain Res. 2000; 122:61–78.

33. Schofield PR, Darlison MG, Fujita N, Burt DR, Stephenson FA, Rodriguez H, Rhee LM, Ramachandran J, Reale V, Glencorse TA, Seeburg PH, Barnard EA. Sequence and functional expression of the GABA_A receptor shows a ligand-gated receptor super-family. Nature. 1987; 328:221–227.

34. Stern JE. Electrophysiological and morphological properties of pre-autonomic neurones in the rat hypothalamic paraventricular nucleus. J Physiol. 2001; 537:161–177.

35. Swanson LW, Sawchenko PE. Hypothalamic integration: organization of the paraventricular and supraoptic nuclei. Annu Rev Neurosci. 1983; 6:269–324.

36. Swanson LW, Sawchenko PE. Paraventricular nucleus: a site for the integration of neuroendocrine and autonomic mechanisms. Neuroendocrinology. 1980; 31:410–417.

37. Wu X, Wu Z, Ning G, Guo Y, Ali R, Macdonald RL, De Blas AL, Luscher B, Chen G. γ-Aminobutyric acid type A (GABAA) receptor α subunits play a direct role in synaptic versus extrasynaptic targeting. J Biol Chem. 2012; 287:27417–27430.

38. Xu B, Zheng H, Patel KP. Enhanced activation of RVLM-projecting PVN neurons in rats with chronic heart failure. Am J Physiol Heart Circ Physiol. 2012; 302:H1700–H1711.

39. Zhou FW, Roper SN. Altered firing rates and patterns in interneurons in experimental cortical dysplasia. Cereb Cortex. 2011; 21:1645–1658.