Cold stress alters characteristics of sympathetic  nerve discharge bursts

Frequency-domain analyses were used to determine the effect of cold stress on the relationships between the discharge bursts of sympathetic nerve pairs, sympathetic and aortic depressor nerve pairs, and sympathetic and phrenic nerve pairs in chloralose-anesthetized, baroreceptor-innervated rats. Sympathetic nerve discharge (SND) was recorded from the renal, lumbar, splanchnic, and adrenal nerves during decreases in core body temperature from 38 to 30°C. The following observations were made. 1) Hypothermia produced nonuniform changes in the level of activity in regionally selective sympathetic nerves. Specifically, cold stress increased lumbar and decreased renal SND but did not significantly change the level of activity in splanchnic and adrenal nerves. 2) The cardiac-related pattern of renal, lumbar, and splanchnic SND bursts was transformed to a low-frequency (0–2 Hz) pattern during cooling, despite the presence of pulse-synchronous activity in arterial baroreceptor afferents. 3) Peak coherence values relating the discharges between sympathetic nerve pairs decreased at the cardiac frequency but were unchanged at low frequencies (0–2 Hz), indicating that the sources of low-frequency SND bursts remain prominently coupled during progressive reductions in core body temperature. 4) Coherence of discharge bursts in phrenic and renal sympathetic nerve pairs in the 0- to 2-Hz frequency band increased during mild hypothermia (36°C) but decreased during deep hypothermia (30°C). We conclude that hypothermia profoundly alters the organization of neural circuits involved in regulation of sympathetic nerve outflow to selected regional circulations.

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Regulation of the sympathetic nerve discharge bursting pattern during heat stress

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1998.275.6.r1992 ◽

1998 ◽

Vol 275 (6) ◽

pp. R1992-R2001 ◽

Cited By ~ 24

Author(s):

Michael J. Kenney ◽

Dale E. Claassen ◽

Michelle R. Bishop ◽

Richard J. Fels

Keyword(s):

Heat Stress ◽

Frequency Domain ◽

Phrenic Nerve ◽

Sympathetic Nerve ◽

Core Body Temperature ◽

Low Frequency ◽

Sympathetic Nerves ◽

Frequency Components ◽

Pattern Transformation ◽

Nerve Discharge

Frequency-domain analyses were used to determine the effect of heat stress on the relationships between the discharge bursts of sympathetic nerve pairs and sympathetic and phrenic nerve pairs in chloralose-anesthetized rats. Sympathetic nerve discharge (SND) was recorded from the renal, splanchnic, splenic, and lumbar nerves during increases in core body temperature (Tc) from 38 to 41.4 ± 0.3°C. The following observations were made: 1) hyperthermia transformed the cardiac-related bursting pattern of SND to a pattern that contained low-frequency, non-cardiac-related bursts, 2) the pattern transformation was uniform in regionally selective sympathetic nerves, 3) hyperthermia enhanced the frequency-domain coupling between SND and phrenic nerve bursts, and 4) low-frequency SND bursts recorded during hyperthermia contained significantly more activity than cardiac-related bursts. We conclude that acute heat stress profoundly affects the organization of neural circuits responsible for the frequency components in sympathetic nerve activity and that SND pattern transformation provides an important strategy for increasing the level of activity in sympathetic nerves during increased Tc.

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Sympathetic nerve responses to hyperthermia in the anesthetized rat

Journal of Applied Physiology ◽

10.1152/jappl.1995.78.3.881 ◽

1995 ◽

Vol 78 (3) ◽

pp. 881-889 ◽

Cited By ~ 46

Author(s):

M. J. Kenney ◽

C. C. Barney ◽

T. Hirai ◽

C. V. Gisolfi

Keyword(s):

Heart Rate ◽

Sympathetic Nerve ◽

Neural Circuits ◽

Core Body Temperature ◽

Sympathetic Nerves ◽

Basic Pattern ◽

Sympathetic Nervous ◽

Core Body ◽

Cardiopulmonary Baroreceptors ◽

Nerve Discharge

The aim of the present study was to characterize the sympathetic nerve responses to hyperthermia in chloralose-anesthetized rats. Discharges were recorded from the renal, lumbar, and splanchnic sympathetic nerves. Mean arterial pressure, heart rate, and sympathetic nerve discharge (SND) were recorded continuously during progressive increases in core body temperature (Tc) from 38.0 to 41.0 degrees C. The following observations were made: 1) significant increases in renal, lumbar, and splanchnic SND were observed during hyperthermia; 2) autospectral analysis of renal and lumbar SND revealed that the frequency distribution of SND can be altered during progressive increases in Tc; and 3) increases in splanchnic SND to acute heating were similar in baroreceptor-innervated and -denervated rats. We conclude that 1) hyperthermia is a potent stimulus to the sympathetic nervous system and increases the activity in three sympathetic nerves that innervate different regional arterial beds, 2) acute heating influences the neural circuits involved in generating SND as evidenced by changes in the basic pattern of renal and lumbar SND, and 3) the increase in splanchnic SND during hyperthermia is not opposed by the arterial and cardiopulmonary baroreceptors.

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Paraventricular nucleus bicuculline alters frequency components of sympathetic nerve discharge bursts

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.2001.281.3.h1233 ◽

2001 ◽

Vol 281 (3) ◽

pp. H1233-H1241 ◽

Cited By ~ 31

Author(s):

Michael J. Kenney ◽

Mark L. Weiss ◽

Kaushik P. Patel ◽

Yan Wang ◽

Richard J. Fels

Keyword(s):

Paraventricular Nucleus ◽

Sympathetic Nerve ◽

Cardiac Cycle ◽

Low Frequency ◽

Sympathetic Nerves ◽

Receptor Antagonism ◽

Gaba Agonist ◽

Frequency Components ◽

Induced Changes ◽

Nerve Discharge

Autospectral and coherence analyses were used to determine the effect of paraventricular nucleus (PVN) GABAA receptor antagonism [microinfusion or microinjections of bicuculline methiodide (BMI) 100 pmoles] on sympathetic nerve discharge (SND) frequency components (bursting pattern and relationships between discharges in regionally selective nerves) in α-chloralose-anesthetized rats. SND was recorded from the renal, splenic, and lumbar nerves. The following observations were made. First, PVN BMI microinjections, but not PVN saline or cortical BMI microinjections, transformed the cardiac-related SND bursting pattern in baroreceptor-innervated rats to one characterized by the presence of low-frequency bursts not synchronized to the cardiac cycle or phrenic nerve discharge bursts. Second, SND pattern changes were similar in the renal, splenic, and lumbar nerves, and peak coherence values relating low-frequency bursts in sympathetic nerve pairs (renal-splenic, renal-lumbar, and splenic-lumbar) were significantly increased from preinjection control after PVN BMI microinjection. Third, PVN BMI microinjections significantly increased the coupling between low-frequency SND bursts in baroreceptor-denervated rats. Finally, PVN BMI-induced changes in the SND bursting pattern were not observed after PVN pretreatment with muscimol (GABA agonist, 1 nmole). We conclude that PVN GABAA receptor antagonism profoundly alters the frequency components in sympathetic nerves.

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Altered frequency responses of sympathetic nerve discharge bursts after IL-1β and mild hypothermia

Journal of Applied Physiology ◽

10.1152/japplphysiol.01250.2001 ◽

2002 ◽

Vol 93 (1) ◽

pp. 280-288 ◽

Cited By ~ 3

Author(s):

M. J. Kenney ◽

F. Blecha ◽

R. J. Fels ◽

D. A. Morgan

Keyword(s):

Sympathetic Nerve ◽

Neural Circuits ◽

Mild Hypothermia ◽

Sympathetic Nerves ◽

Interscapular Brown Adipose Tissue ◽

Frequency Responses ◽

Brown Adipose ◽

Complex Relationships ◽

Colonic Temperature ◽

Nerve Discharge

Although interleukin-1β (IL-1β) administration produces nonuniform changes in the level of sympathetic nerve discharge (SND), the effect of IL-1β on the frequency-domain relationships between discharges in different sympathetic nerves is not known. Autospectral and coherence analyses were used to determine the effect of IL-1β and mild hypothermia (60 min after IL-1β, colonic temperature from 38°C to 36°C) on the relationships between renal-interscapular brown adipose tissue (IBAT) and splenic-lumbar sympathetic nerve discharges in chloralose-anesthetized rats. The following observations were made. 1) IL-1β did not alter renal-IBAT coherence values in the 0- to 2-Hz frequency band or at the cardiac frequency (CF). 2) Peak coherence values relating splenic-lumbar discharges at the CF were significantly increased after IL-1β and during hypothermia. 3) Hypothermia after IL-1β significantly reduced the coupling (0–2 Hz and CF) between renal-IBAT but not splenic-lumbar SND bursts. 4) Combining IL-1β and mild hypothermia had a greater effect on renal-IBAT SND coherence values than did mild hypothermia alone. These data demonstrate functional plasticity in sympathetic neural circuits and suggest complex relationships between immune products and SND regulation.

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