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Comparative Study
. 2007 Jul 1;582(Pt 1):421-33.
doi: 10.1113/jphysiol.2007.131292. Epub 2007 Apr 12.

Independent vasomotor control of rat tail and proximal hairy skin

Mutsumi Tanaka  1 , Youichirou Ootsuka, Michael J McKinley, Robin M McAllen
Affiliations
Comparative Study

Independent vasomotor control of rat tail and proximal hairy skin

Mutsumi Tanaka et al. J Physiol. .

Abstract

Quantitative differences are known to exist between the vasomotor control of hairy and hairless skin, but it is unknown whether they are regulated by common central mechanisms. We made simultaneous recordings from sympathetic cutaneous vasoconstrictor (CVC-type) fibres supplying back skin (hairy) and tail (hairless) in urethane-anaesthetized, artificially ventilated rats. The animal's trunk was shaved and encased in a water-perfused jacket. Both tail and back skin CVC-type fibres were activated by cooling the trunk skin, and independently by the resultant fall in core (rectal) temperature, but their thresholds for activation differed (skin temperatures 38.8 +/- 0.4 degrees C versus 36.8 +/- 0.4 degrees C, core temperatures 38.1 +/- 0.2 degrees C versus 36.8 +/- 0.2 degrees C, respectively; P < 0.01). Back skin CVC-type fibres were more responsive to skin than to core cooling, while the reverse applied to tail fibres. Back skin CVC-type fibres were less responsive than tail fibres to prostaglandin E2 (PGE2) microinjected into the preoptic area. Spectral analysis showed no significant coherence between tail and back skin CVC-type fibre activities during cooling. After preoptic PGE2 injection, a coherent peak at 1 Hz appeared in some animals; this disappeared after partialization with respect to ventilatory pressure, indicating that it was attributable to common ventilatory modulation. Neuronal inhibition in the rostral medullary raphé by microinjected muscimol (2 mM, 60-120 nl) suppressed both tail and back skin CVC-type fibre activities, and prevented their responses to subsequent skin cooling. These results indicate that thermoregulatory responses of hairless and hairy skin vessels are controlled by independent neural pathways, although both depend on synaptic relays in the medullary raphé.

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Figures

Figure 1
Figure 1. Properties of sympathetic nerve discharge to back skin
A, chart record from a representative experiment showing (from top) blood pressure, skin temperature and sympathetic activity recorded from the central end of a nerve supplying back skin (back skin SNA). Shown below the chart record are 3 expanded records of back skin SNA, taken from times denoted on the lower trace: (a) before skin cooling, (b) during skin cooling and (c) after ganglion blockade with hexamethonium (indicated above upper trace). B and C show arterial pulse-triggered histograms of the ongoing back skin SNA (counted events above threshold) during warm baseline conditions (B) and during skin cooling (C) (10 ms bins; 6378 and 9912 events, respectively). Bottom traces show the corresponding mean arterial pressure waveforms.
Figure 2
Figure 2. Firing patterns of back skin MVC-type and CVC-type fibres
A, traces from top show: skin temperature; few-fibre activity in a filament split from the nerve to back skin; identified single unit spikes extracted from the neurogram (1 CVC-type and 2 MVC-type fibres, denoted a and b). Their individual waveforms (superimposed spikes on expanded timescale) are shown below. B, chart record showing skin temperature (top trace), blood pressure (bottom trace) and the responses of the same three single units (as indicated) to four successive episodes of skin cooling. C, arterial pulse-triggered histograms of the ongoing activity (during cooling) of the same three single units (10 ms bins, from top 350, 96 and 185 counted spikes), shown above the corresponding arterial pressure waveform.
Figure 3
Figure 3. Simultaneous recording of tail sympathetic activity and back skin CVC-type fibre activity
A, chart record showing (from top): sympathetic unit activity recorded from a filament in the lateral collector nerve of the tail (tail SNA), sympathetic activity in a filament split from the nerve to back skin (back skin SNA), respiratory pressure and blood pressure. Filled dots and asterisks in the second trace (back skin SNA) indicate two discriminated single CVC-type units. Superimposed spike shapes of each discriminated single unit are shown at the end of their respective traces. B and C show arterial pulse-triggered (B) and respiratory pressure-triggered (C) histograms of tail SNA and back skin CVC-type fibre activity during cooling (bin size 10 ms in B and 100 ms in C; 949 tail SNA spikes and 1237 back skin CVC-type spikes counted in both B and C).
Figure 4
Figure 4. Responses of tail and back skin CVC-type fibres to skin cooling
A, representative chart record showing responses to repeated skin cooling while core temperature was allowed to fall. Traces from top show blood pressure, core (rectal) temperature, skin temperature and few-fibre activities (10 s counts) recorded from back skin CVC-type and tail fibres. Note that when the expected threshold (horizontal dashed line) was crossed during the second and third skin cooling periods, there was no activation of back skin CVC-type fibres. Data from A are replotted in B and C to show back skin CVC-type fibre activity versus skin temperature (B) and versus core temperature (C). D and E show corresponding plots of tail SNA versus skin and core temperatures. Linear regression lines (thick lines) were calculated from appropriate sections of the record to estimate threshold skin temperature and Kskin (B and D), and threshold core temperature and Kcore (C and E) for each nerve (see Methods). Arrows indicate the time sequence of plotted points.
Figure 5
Figure 5. Responses of tail and back skin CVC-type fibres to prostaglandin E2 (PGE2) injection into the preoptic area
Traces from top show blood pressure, core (rectal) temperature, skin temperature and few-fibre activity (10 s counts) of back skin CVC-type and tail fibres. After recovery from a standard cooling sequence (left of trace), PGE2 (30 ng in 120 nl) was injected into the preoptic area (POA) at the time indicated.
Figure 6
Figure 6. Effect of neuronal inhibition in the medullary raphé on tail and back skin CVC-type fibre responses to skin cooling
A, traces from top show blood pressure, core (rectal) temperature, skin temperature and few-unit activity (10 s spike counts) recorded from back skin CVC-type and tail fibres. Vehicle (aCSF 120 nl, middle) and muscimol (120 pmol in 60 nl, right) were injected, as indicated by arrowheads and dashed lines, at times when tail and back skin CVC-type fibres were activated by cooling. B, muscimol and vehicle injection sites plotted onto a standard section, drawn with reference to the atlas of Paxinos & Watson (1998) at the level indicated. Grey circles indicate sites where either muscimol or vehicle was injected alone. Black circles indicate sites where both muscimol and vehicle were injected in the same animal. Abbreviations: GiA, gigantocellular reticular nucleus pars alpha; FN, facial nucleus; py, pyramidal tract; RMg, raphé magnus nucleus; ROb, raphé obscurus nucleus; RPa, raphé pallidus nucleus.
Figure 7
Figure 7. Spectral analysis of tail SNA and back skin CVC-type fibre activity during skin cooling
Examples for illustration are taken from a single representative experiment. Panels A–D show autospectra (% of total power between 0 and 15 Hz) of tail SNA (few-fibres, A), back skin CVC-type fibre activity (few-fibres, B), blood pressure (C) and respiratory pressure (D). Panels E–H show coherence spectra of tail SNA with respect to blood pressure (E) and respiratory pressure (F), and coherence spectra of back skin CVC-type fibre activity with respect to blood pressure (G) and respiratory pressure (H). The coherence spectrum between tail SNA and back skin CVC-type fibre activity is shown in I: note the absence of any clear peak.
Figure 8
Figure 8. Spectral analysis of tail SNA and back skin CVC-type fibre activity after PGE2 injection into the preoptic area
Examples for illustration are taken from the same experiment as in Fig. 7. Panels A–D show autospectra (% of total power between 0 and 15 Hz) of tail SNA (few-fibres, A), back skin CVC-type fibre activity (few-fibres, B), blood pressure (C) and respiratory pressure (D). Panels E–H show coherence spectra of tail SNA with respect to blood pressure (E) and respiratory pressure (F), and coherence spectra of back skin CVC-type fibre activity with respect to blood pressure (G) and respiratory pressure (H). Panels I and J show coherence spectra between tail SNA and back skin CVC-type fibre activity: note the clear peak around 1 Hz in panel I, which disappeared after partialization to remove the common influence on the two signals related to respiratory pressure (panel J).
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