AMERICAN
Vol.
JOURNAL
OP
~‘HYSIOLOGY
228, No. 2, February
1975.
Prded
in U.S.A.
Hypothalamic cooling
heating
and
in monoamine-depleted
C. J. WOOLF, Depardment
HELEN
of Physiology,
P. LABURN, Uuiersity
of the
rabbits
G. H. WILLIES,
WOOLF, C. J-, HELEN P. LABURN, G. H. WILLIES, AND C. ROSEN DOR F F. Hypothalamic heating and cooling in monoamine-depleted rabbits. -4m. J. Physiol. 228(Z): 569-574. 1975.-The role of monoamines in the thermoregulatory responses induced by hypothalamic heating and cooling was investigated in conscious rabbits. Depletion of hypothalamic catecholamines by pretreatment with 6-hydroxydopamine (6-OHDA) greatly attenuated the rectal temperature and vasomotor responses to hypothalamic heating and cooling. Pretreatment with p-chlorophenylalanine (PCP,4) depleted the animals of 5-hydroxytryptamine (5-HT). The results obtained are consistent with 5-HT having an inhibitory role in the rabbit’s vasomotor response to heat stress and activating heat conservation during cold stress. Reserpinized rabbits were depleted of both norepinephrine (NE) and 5-HT and were found to be unresponsive to h,vpothalamic temperature changes. We conclude that the integrity of the monoaminergic system is vital for the correct functioning of the hypothalamus in maintaining a constant body temperature. temperature
AND
C. ROSENDORFF
WitwntersrnndMedicnZSchool,Johanneho-g
regulation
THE EXISTENCE of adrenergic, serotinergic, dopaminergic, and cholinergic fiber systems and terminations in the hypothalamus has led to the idea that these different fiber systems may be related in a specific fashion to the functional activity of the hypothalamus (1, 2 1, 25). Ablation studies, single-unit work, electrical, chemical, and thermal stimulations have all conilirmed that the hypothalamus is the major site of temperature regulation in the homeotherm (10). Control of body core temperature is thought to be exerted by three functional pathways: heat loss, heat conservation, and a mutual cross-inhibition between the two major pathways (4) The neuronal substra te for the hypothalamic temperature controller remains obscure, with the role of the monoamines uncertain. Feldberg and Myers (17) in 1964 demonstrated that microinjections of the monoamines 5-hydroxytryptamine (5-HT) and norepinephrine (NE) into the cerebral ventricle or directly into the hypothalamus ( 18) of the cat elicited specific thermoregulatory responses, hypothermia for NE and hyperthermia for 5-HT, indicating that the monoamines might specifically activate either the heat-loss or heat-conservati on pathways. A considerable amount of work has now been performed in an attempt to elucidate the role of 5-HT and NE in thermoregulation. A variety of species has been tested, via different injection routes, at different doses and at
2001,
South
Africa
different ambient temperatures (2, 5, 20, 27, 29, 33). Feldberg (16) has classified the responses of different species to microinjections of 5-HT and NE into four groups, but even this complex classification is not compatible with some of the intraspecific responses found. In the rabbit alone, hyper- and hypothermic responses to microinjections of 5-HT have been found (5, 37), Moreover, the results of microinjection studies of 5-HT and NE in the rabbit do not always agree with the pharmacological manipulation of these monoamines. The amount of injected monoamines in these studies is large compared to the concentrations of endogenous monoamines in the hypothalamus, whose levels are less than 1 pg/g (1). However, studies using agents such as monoamine 0xiaTase (MAO) inhibitors (14), reserpine (12), and desmethylimipramine (13), which alter the concentration of endogenous monoamines, have produced results consistent with some role for these amines in temperature regulation. Since these studies were reported, new techniques for producing amine depletion have become available. 6-Hydroxydopamine (6-OHDA), when injected into brain tissue, causes an irreversible destruction of catecholaminergic nerves in that region (8, 39). @-Chlorophenylalanine (PCPA) when administered intraperitoneally selectively depletes the brain of 5-HT (30). Both 5-HT and NE can be depleted by reserpine ( 12, 23). The present investigation has studied the responses of rabbits to hypothalamic heating and cooling after depletion of 5-HT, NE, and both 5-HT and NE. This has been performed to determine whether the central activation of the heat-loss or heat-conservation pathways requires the integrity of the hypothalamic monoaminergic systems. MATERIALS
ASD
METHODS
Experiments were performed on 30 adult New Zealand white rabbits, weighing between 2.5 and 3.0 kg. The local temperature of the hypothalamus of these rabbits was altered by means of two thermodes (24) (OD = 0.6 mm) through which hot or cold water was circulated by means of a Haake thermostatically controlled water pump. The hypothalamic temperature was monitored by means of a fine thermistor probe (OD = 0.4 mm). Six days before the experiments were performed, headplates were screwed to the skull in a modification of the Bonnier and Gangloff method (34), under paraldehyde anesthesia. The headplates were aligned stereotaxically and the tips of the two 569
Downloaded from www.physiology.org/journal/ajplegacy by ${individualUser.givenNames} ${individualUser.surname} (192.236.036.029) on August 15, 2018. Copyright © 1975 American Physiological Society. All rights reserved.
570 thermodes, when int reduced through the guide holes of the headplates, were positioned on either side of the anterior hypothalamus. The tip of the thermistor probe was in the midline and 2 mm from each of the thermode tips. The position of these probes after insertion was checkkd by means of lateral and anterior cranial X rays. For the entire duration of the experiment, the animals were conscious and lightly restrained in conventional stocks. All experiments were conducted in a temperature-controlled room at Zl-23°C. Skin temperature was measured by means ofa thermistor probe which was taped to the shaved ear in the region between the central ear artery and the marginal ear vein. Rectal temperature means of another was monitored bY thermistor mounted on the end of a polyethylene tube, introduced 10 cm into the rectum. The thermistors were connected to bridge circuits, whose outputs were recorded continuously on a Beckman Dynograph. Control rectal and skin temperature responses to induced hypothalamic temperature increases and decreases of 3°C were first recorded in 10 rabbits. Experimental animals were depleted of monoamines. The hypothalamus was depleted of NE by pretreatment on two occasions 2 days apart of 200 pg of 6-OHDA dissolved in 20 ~1 of normal saline injected into both sides of the hypothalamus of three rabbits through a stereotaxically placed (coordinates aI3 - 16 mm) (34) steel cannula (OD = 0.4 mm). In three other animals the whole brain was depleted of NE by an intracisternal injection of 600 pg of 6-OHDA dissolved in 60 ~1 of normal saline. In both groups the experiments were performed 5 days after the 6-OHDA injections, this interval being optimal for NE depletion (8). Control animals in these cases were given intrahypothalamic injections of 20 ~1 of normal saline. Five rabbits were depleted of 5-HT by intraperitoneal injections of p-chlorophenylalanine (PCPA), 150 mg/kg suspended in 4 ml of sterile corn oil. Injections were given every day for 3 days and the animal was used 2 days later. Control animals in these cases were given intraperitoneal injections of 4 ml of sterile corn oil. In five control animals saline was substituted for 6-OHDA, and corn oil was substituted for PCPA; these rabbits responded to hypothalamic heating and cooling in the same way as the untreated rabbits. Four rabbits were also depleted of both 5-HT and NE by intramuscular injection of reserpine 1 mg/kg for two consecutive days; the experiment was performed the following day. The extent of depletion of the monoamines in each case was determined from brain extracts using a spec trophotofluorometric technique (32). RESULTS
Typical responses to hypothalamic heating and cooling in control, 6-OHDA treated, PCPA-treated, and reserpinized rabbits are shown in Figs. 1 and 2. The mean responses are shown in Fig. 3. Each series of experiments consisted of 10 results for heating and 10 results for cooling. On average the control rabbits were heated and cooled twice each, and the 6-OHDA-treated rabbits, the PCPA-
WOOLF,
LABURN,
WILLIES,
AND
ROSENDORFF
OC TS
Tr Thy
temp.
Hypothaiomic
A: cow01
+lO.O +2.0+5.
rabb
Rectal temp Skin temp.
+5.0 +l.Ot 25
+10.0+2.0+5.0
B: 6 - #-IDA
rabbit
treated
1
t5.0
*1.0+25-
-5.0
- 1.0 - 2.5
t
t
+JQO+~O+~OJ” PCA, treated rabbit / .” +5.0
-.-*.-.-.a- -,-*.- -.*-.-4-r -‘-‘a,
‘\
+ 1.0 + 2.5.
0
, -e---4---4--,* -5,0 ml,. w25 -
t
---*---*--
,e-- ,s----• t
tlO.0 +2.0+5+O-” Reserpinetreated rabb’t
+5.0 + 1.0 t2.5.
0
0
0 I
- 5.0 - 1.0 -2.5 J ? 0
1I
I+ tine
5
I 10
(minutes) 15
1
20
25
I
30
FIG 1. Typical temperature responses for hypothalamic heating redrawn from original data. Effects on rectal and skin temperature are shown for control (A), 6-OHDA-treated (B), PCPA-treated (C), and reserpinized rabbits (D). Hypothalamic temperature was raised by approximately 3°C for 15 min (arrows). Zero levels for skin and rectal and hypothalamic temperatures were taken from preheating levels. Heating in all cases was only commenced once all temperatures had stabilized fcr at least 45 min. Note different temperature scales for hypothalamic, T hs, skin, Tsk, and rectal, TTe, temperatures.
treated, and the reserpinized rabbits cooled 3 times each. Efects of hypothalamic heating and cat&g Hypothalamic heating (Figs. 1A and 3) era1 vasodilatation as evidenced by a
were
heated
and
on untreated rabbits. resulted in periphxnean rise in ear
Downloaded from www.physiology.org/journal/ajplegacy by ${individualUser.givenNames} ${individualUser.surname} (192.236.036.029) on August 15, 2018. Copyright © 1975 American Physiological Society. All rights reserved.
MONOAMINES
AND
TEMPERATURE
571
REGULATION
skin temperature of 4.9 & 0.8 @EM) “C. Vasodilatation commenced within a few rninutes of onset of heating and was usually followed by initiation of vigorous panting. Rectal temperature fell by 0.33 =t: 0.05”C. When heating was terminated, body and skin temperatures returned to preheating levels. The time between the onset of hypothalamic temperature changes and the maximum rectal and skin temperature changes, as well as the initial rate of change of these temperatures, are shown in Tables 1 and 2. Cooling the hypothalamus (Figs. 2A and 3) resulted in peripheral vasoconstriction causing a mean fall in ear skin temperature of 4.5 =t 0.5”C. Rectal temperature rose by a mean value of 0.58 & 0.08”C. Shivering is not easily detectable in rabbits and was not obvious in the control experiments. Effects of hypothahnic heating and cooling on rabbits treated with 6-OHDA. Hypothalamic heating in the 6-OHDAtreated animals resulted in significant attenuation of both skin and rectal responses (Figs. 1B and 3). Figure 3 shows that the mean rise in skin temperature was 1.1 & 0.5”C, and the mean fall in rectal temperature was as little as 0.06 & 0.01 “C. Panting was absent in all animals during heating. Hypothalamic cooling in the 6-OHDA-treated rabbits resulted in a similar marked attenuation, or absence, of response in both skin and rectal temperatures, as seen in Figs. 2B and 3. Ear skin temperature fell by 0.7 =I= 0.3”C, and rectal temperature increased by 0.07 & 0.03”C. The
“C Tr
A: cord +1.0+2.5
-5.0
-1.0
rob&
1
- 10.0 - 2.0 * 5.0 +5.0
e e---e
Thy
Ts +5.0
*-.-.a
J t B: 6 -0HDA
+l.O +2.
rabbit
treated
- 10.0 - 2.0 -5.0-I f5.0
C: PCA
+1.0+2.5
treated
rabbit
1
0
0
-*
I _
A---
-,-•----.----n--“4
--
Control t re,
min
t&, min dT./dt 1 t-0, *C/min dT,/dr [ t=~, *C/min
24.4 zt4.1 14.2 zt2.2 0.02-40.01 0.92*0.31
6-OHDA
14.9 h2.3 18.5 zt2.2 0.004~0.01 0.17 *0.11*
PCPA
- no- 2.0 - 5.0’
10.6 ztl .Ot 6.6 zt0.9t 0.40~0.07~ 3.60+0.57$
+ 5.0 +l,o +2+5-
Values are means & SE. Effect of PCPA and 6-OHDA pretreatment on the time (in min) between onset of hypothalamic temperature changes and peak rectal (tre) and skin (t& temperature changes and on the initial rate of rectal and skin temperature changes dT,/dt, and dT S/di, in *C/min, following a 3°C rise in hypothalamic temperature for 15 min. Statistical differences between control and experimental results were calculated from the * P < 0.05. Student t test. t P < 0.01. $ P < O*OOl.
2. Efects of hypothalamic coo&g GOHDA-treated rabbits
TABLE
Control
t rel min t&, min dT./dt 1 t-0, ‘C/min dT s/dt ] 1-0, ‘C/min
29.0 h4.5 16,4 ztl.8 0.03*0.01 0.44ztO.04
on p@Y 6-OHDA
13.9 *1.1* 20.1 zk0.9 0.02*0.01 0.05h0.03t
I
and
PCPA
23.7 zt2.0 22.7 M.85: 0.02&0.003$ 0.46&O. 10
Values are means II= SE. Effect of PCPA and 6-OHDA pretreatment on the time (in min) between onset of hypothalamic temperature changes and peak rectal (tre) and skin (t& temperature changes; and on the initial rate of rectal and skin temperature changes dT,/dt, and dT,/df, in “C/min, following a 3 “C fall in hypothalamic temperature for 15 min. Statistical differences between control and experimental results were calculated from the Student t test. * P < 0.01. t P < O*OUl. $ P < 0.05.
-. 4, -‘-*.-.-
t L=J’--4 0: Reserpine
~-l-a”----c
--*
-5
- 5.0 - 1.0 -2.5
heating on PCPA and
temp.
t
’ *.
1. Efect of hypothalamic 6-UHDA-treated rabbits ~-------
TABLE
Hypothalamic Redo1 temp. Skin temp.
treated
*- -
.-.-. a- - *
- -.I
t
rabbit
- 5.0 - 1.0-25.
t I
- 10.0 -2.0~so-
time I 10
(minutes) I 15
t r
r
1
-20 25 30 FIG. 2. Typical temperature responses for hypothalamic cooling redrawn from original data. Effects on rectal and skin temperatures are shown for control (A), 6-OHDA-treated (I?), PCPA-treated (C), and reserpinized rabbits (D). Hypothalamic temperature was lowered by approximately 3*C for 15 min (arrows). Zero levels for skin, rectal and hypothalamic temperatures were taken from precooling levels. Cooling in all cases was only commenced once all temperatures had stabilized for at least 45 min. Note different temperature scales for hypothalamic, T h Y, skin, Tsk, and rectal, T,,, temperatures, 0
5
resting rectal temperatures of these rabbits below that of the control animals. Effects of hy@alamic heating and cooling z&h PCPA. Resting rectal temperatures treated rabbits did not differ from those rabbits. Heating the hypothalamus in this and 3, and Table 1) caused a cutaneous with the ear skin temperature increasing
were
0.6-l.O”C
on rabbits treated of the PCPAof the control series (Figs. 1C vasodilatation, more rapidly
Downloaded from www.physiology.org/journal/ajplegacy by ${individualUser.givenNames} ${individualUser.surname} (192.236.036.029) on August 15, 2018. Copyright © 1975 American Physiological Society. All rights reserved.
572
WOOLF, l.07 HY POTbiAiAbfli HEATING
'-"~HYPOTHALAMIC COOLING
LMURN,
WILLIES,
AND
ROSENDORFF
those of the control animals. The PCPA-treated animals showed a 25-35 % depletion of 5-HT. In those experiments in which 6-OHDA kvas injected into the hypothalamus only, there was an inadequate amount of brain tissue for this assay method. However, the depleting effects of 6-OHDA on NE content of a localized area of the rabbit brain have previously been verified by fluorescence histochemistry in this laboratory. In rabbits treated intracisternally with GOHDA, a whole-brain depletion of NE by 35-50 % of control values was found. 5-HT levels in these rabbits were 80-90 % of control values. Dopamine levels were not measured, but both reserpine and 6-OHDA are well knolvn to cause dopamine depletion (8, 23). DISCUSSION
Cont. PCA Rectal :p
45
Skimp
Vol.
JOURNAL
OP
~‘HYSIOLOGY
228, No. 2, February
1975.
Prded
in U.S.A.
Hypothalamic cooling
heating
and
in monoamine-depleted
C. J. WOOLF, Depardment
HELEN
of Physiology,
P. LABURN, Uuiersity
of the
rabbits
G. H. WILLIES,
WOOLF, C. J-, HELEN P. LABURN, G. H. WILLIES, AND C. ROSEN DOR F F. Hypothalamic heating and cooling in monoamine-depleted rabbits. -4m. J. Physiol. 228(Z): 569-574. 1975.-The role of monoamines in the thermoregulatory responses induced by hypothalamic heating and cooling was investigated in conscious rabbits. Depletion of hypothalamic catecholamines by pretreatment with 6-hydroxydopamine (6-OHDA) greatly attenuated the rectal temperature and vasomotor responses to hypothalamic heating and cooling. Pretreatment with p-chlorophenylalanine (PCP,4) depleted the animals of 5-hydroxytryptamine (5-HT). The results obtained are consistent with 5-HT having an inhibitory role in the rabbit’s vasomotor response to heat stress and activating heat conservation during cold stress. Reserpinized rabbits were depleted of both norepinephrine (NE) and 5-HT and were found to be unresponsive to h,vpothalamic temperature changes. We conclude that the integrity of the monoaminergic system is vital for the correct functioning of the hypothalamus in maintaining a constant body temperature. temperature
AND
C. ROSENDORFF
WitwntersrnndMedicnZSchool,Johanneho-g
regulation
THE EXISTENCE of adrenergic, serotinergic, dopaminergic, and cholinergic fiber systems and terminations in the hypothalamus has led to the idea that these different fiber systems may be related in a specific fashion to the functional activity of the hypothalamus (1, 2 1, 25). Ablation studies, single-unit work, electrical, chemical, and thermal stimulations have all conilirmed that the hypothalamus is the major site of temperature regulation in the homeotherm (10). Control of body core temperature is thought to be exerted by three functional pathways: heat loss, heat conservation, and a mutual cross-inhibition between the two major pathways (4) The neuronal substra te for the hypothalamic temperature controller remains obscure, with the role of the monoamines uncertain. Feldberg and Myers (17) in 1964 demonstrated that microinjections of the monoamines 5-hydroxytryptamine (5-HT) and norepinephrine (NE) into the cerebral ventricle or directly into the hypothalamus ( 18) of the cat elicited specific thermoregulatory responses, hypothermia for NE and hyperthermia for 5-HT, indicating that the monoamines might specifically activate either the heat-loss or heat-conservati on pathways. A considerable amount of work has now been performed in an attempt to elucidate the role of 5-HT and NE in thermoregulation. A variety of species has been tested, via different injection routes, at different doses and at
2001,
South
Africa
different ambient temperatures (2, 5, 20, 27, 29, 33). Feldberg (16) has classified the responses of different species to microinjections of 5-HT and NE into four groups, but even this complex classification is not compatible with some of the intraspecific responses found. In the rabbit alone, hyper- and hypothermic responses to microinjections of 5-HT have been found (5, 37), Moreover, the results of microinjection studies of 5-HT and NE in the rabbit do not always agree with the pharmacological manipulation of these monoamines. The amount of injected monoamines in these studies is large compared to the concentrations of endogenous monoamines in the hypothalamus, whose levels are less than 1 pg/g (1). However, studies using agents such as monoamine 0xiaTase (MAO) inhibitors (14), reserpine (12), and desmethylimipramine (13), which alter the concentration of endogenous monoamines, have produced results consistent with some role for these amines in temperature regulation. Since these studies were reported, new techniques for producing amine depletion have become available. 6-Hydroxydopamine (6-OHDA), when injected into brain tissue, causes an irreversible destruction of catecholaminergic nerves in that region (8, 39). @-Chlorophenylalanine (PCPA) when administered intraperitoneally selectively depletes the brain of 5-HT (30). Both 5-HT and NE can be depleted by reserpine ( 12, 23). The present investigation has studied the responses of rabbits to hypothalamic heating and cooling after depletion of 5-HT, NE, and both 5-HT and NE. This has been performed to determine whether the central activation of the heat-loss or heat-conservation pathways requires the integrity of the hypothalamic monoaminergic systems. MATERIALS
ASD
METHODS
Experiments were performed on 30 adult New Zealand white rabbits, weighing between 2.5 and 3.0 kg. The local temperature of the hypothalamus of these rabbits was altered by means of two thermodes (24) (OD = 0.6 mm) through which hot or cold water was circulated by means of a Haake thermostatically controlled water pump. The hypothalamic temperature was monitored by means of a fine thermistor probe (OD = 0.4 mm). Six days before the experiments were performed, headplates were screwed to the skull in a modification of the Bonnier and Gangloff method (34), under paraldehyde anesthesia. The headplates were aligned stereotaxically and the tips of the two 569
Downloaded from www.physiology.org/journal/ajplegacy by ${individualUser.givenNames} ${individualUser.surname} (192.236.036.029) on August 15, 2018. Copyright © 1975 American Physiological Society. All rights reserved.
570 thermodes, when int reduced through the guide holes of the headplates, were positioned on either side of the anterior hypothalamus. The tip of the thermistor probe was in the midline and 2 mm from each of the thermode tips. The position of these probes after insertion was checkkd by means of lateral and anterior cranial X rays. For the entire duration of the experiment, the animals were conscious and lightly restrained in conventional stocks. All experiments were conducted in a temperature-controlled room at Zl-23°C. Skin temperature was measured by means ofa thermistor probe which was taped to the shaved ear in the region between the central ear artery and the marginal ear vein. Rectal temperature means of another was monitored bY thermistor mounted on the end of a polyethylene tube, introduced 10 cm into the rectum. The thermistors were connected to bridge circuits, whose outputs were recorded continuously on a Beckman Dynograph. Control rectal and skin temperature responses to induced hypothalamic temperature increases and decreases of 3°C were first recorded in 10 rabbits. Experimental animals were depleted of monoamines. The hypothalamus was depleted of NE by pretreatment on two occasions 2 days apart of 200 pg of 6-OHDA dissolved in 20 ~1 of normal saline injected into both sides of the hypothalamus of three rabbits through a stereotaxically placed (coordinates aI3 - 16 mm) (34) steel cannula (OD = 0.4 mm). In three other animals the whole brain was depleted of NE by an intracisternal injection of 600 pg of 6-OHDA dissolved in 60 ~1 of normal saline. In both groups the experiments were performed 5 days after the 6-OHDA injections, this interval being optimal for NE depletion (8). Control animals in these cases were given intrahypothalamic injections of 20 ~1 of normal saline. Five rabbits were depleted of 5-HT by intraperitoneal injections of p-chlorophenylalanine (PCPA), 150 mg/kg suspended in 4 ml of sterile corn oil. Injections were given every day for 3 days and the animal was used 2 days later. Control animals in these cases were given intraperitoneal injections of 4 ml of sterile corn oil. In five control animals saline was substituted for 6-OHDA, and corn oil was substituted for PCPA; these rabbits responded to hypothalamic heating and cooling in the same way as the untreated rabbits. Four rabbits were also depleted of both 5-HT and NE by intramuscular injection of reserpine 1 mg/kg for two consecutive days; the experiment was performed the following day. The extent of depletion of the monoamines in each case was determined from brain extracts using a spec trophotofluorometric technique (32). RESULTS
Typical responses to hypothalamic heating and cooling in control, 6-OHDA treated, PCPA-treated, and reserpinized rabbits are shown in Figs. 1 and 2. The mean responses are shown in Fig. 3. Each series of experiments consisted of 10 results for heating and 10 results for cooling. On average the control rabbits were heated and cooled twice each, and the 6-OHDA-treated rabbits, the PCPA-
WOOLF,
LABURN,
WILLIES,
AND
ROSENDORFF
OC TS
Tr Thy
temp.
Hypothaiomic
A: cow01
+lO.O +2.0+5.
rabb
Rectal temp Skin temp.
+5.0 +l.Ot 25
+10.0+2.0+5.0
B: 6 - #-IDA
rabbit
treated
1
t5.0
*1.0+25-
-5.0
- 1.0 - 2.5
t
t
+JQO+~O+~OJ” PCA, treated rabbit / .” +5.0
-.-*.-.-.a- -,-*.- -.*-.-4-r -‘-‘a,
‘\
+ 1.0 + 2.5.
0
, -e---4---4--,* -5,0 ml,. w25 -
t
---*---*--
,e-- ,s----• t
tlO.0 +2.0+5+O-” Reserpinetreated rabb’t
+5.0 + 1.0 t2.5.
0
0
0 I
- 5.0 - 1.0 -2.5 J ? 0
1I
I+ tine
5
I 10
(minutes) 15
1
20
25
I
30
FIG 1. Typical temperature responses for hypothalamic heating redrawn from original data. Effects on rectal and skin temperature are shown for control (A), 6-OHDA-treated (B), PCPA-treated (C), and reserpinized rabbits (D). Hypothalamic temperature was raised by approximately 3°C for 15 min (arrows). Zero levels for skin and rectal and hypothalamic temperatures were taken from preheating levels. Heating in all cases was only commenced once all temperatures had stabilized fcr at least 45 min. Note different temperature scales for hypothalamic, T hs, skin, Tsk, and rectal, TTe, temperatures.
treated, and the reserpinized rabbits cooled 3 times each. Efects of hypothalamic heating and cat&g Hypothalamic heating (Figs. 1A and 3) era1 vasodilatation as evidenced by a
were
heated
and
on untreated rabbits. resulted in periphxnean rise in ear
Downloaded from www.physiology.org/journal/ajplegacy by ${individualUser.givenNames} ${individualUser.surname} (192.236.036.029) on August 15, 2018. Copyright © 1975 American Physiological Society. All rights reserved.
MONOAMINES
AND
TEMPERATURE
571
REGULATION
skin temperature of 4.9 & 0.8 @EM) “C. Vasodilatation commenced within a few rninutes of onset of heating and was usually followed by initiation of vigorous panting. Rectal temperature fell by 0.33 =t: 0.05”C. When heating was terminated, body and skin temperatures returned to preheating levels. The time between the onset of hypothalamic temperature changes and the maximum rectal and skin temperature changes, as well as the initial rate of change of these temperatures, are shown in Tables 1 and 2. Cooling the hypothalamus (Figs. 2A and 3) resulted in peripheral vasoconstriction causing a mean fall in ear skin temperature of 4.5 =t 0.5”C. Rectal temperature rose by a mean value of 0.58 & 0.08”C. Shivering is not easily detectable in rabbits and was not obvious in the control experiments. Effects of hypothahnic heating and cooling on rabbits treated with 6-OHDA. Hypothalamic heating in the 6-OHDAtreated animals resulted in significant attenuation of both skin and rectal responses (Figs. 1B and 3). Figure 3 shows that the mean rise in skin temperature was 1.1 & 0.5”C, and the mean fall in rectal temperature was as little as 0.06 & 0.01 “C. Panting was absent in all animals during heating. Hypothalamic cooling in the 6-OHDA-treated rabbits resulted in a similar marked attenuation, or absence, of response in both skin and rectal temperatures, as seen in Figs. 2B and 3. Ear skin temperature fell by 0.7 =I= 0.3”C, and rectal temperature increased by 0.07 & 0.03”C. The
“C Tr
A: cord +1.0+2.5
-5.0
-1.0
rob&
1
- 10.0 - 2.0 * 5.0 +5.0
e e---e
Thy
Ts +5.0
*-.-.a
J t B: 6 -0HDA
+l.O +2.
rabbit
treated
- 10.0 - 2.0 -5.0-I f5.0
C: PCA
+1.0+2.5
treated
rabbit
1
0
0
-*
I _
A---
-,-•----.----n--“4
--
Control t re,
min
t&, min dT./dt 1 t-0, *C/min dT,/dr [ t=~, *C/min
24.4 zt4.1 14.2 zt2.2 0.02-40.01 0.92*0.31
6-OHDA
14.9 h2.3 18.5 zt2.2 0.004~0.01 0.17 *0.11*
PCPA
- no- 2.0 - 5.0’
10.6 ztl .Ot 6.6 zt0.9t 0.40~0.07~ 3.60+0.57$
+ 5.0 +l,o +2+5-
Values are means & SE. Effect of PCPA and 6-OHDA pretreatment on the time (in min) between onset of hypothalamic temperature changes and peak rectal (tre) and skin (t& temperature changes and on the initial rate of rectal and skin temperature changes dT,/dt, and dT S/di, in *C/min, following a 3°C rise in hypothalamic temperature for 15 min. Statistical differences between control and experimental results were calculated from the * P < 0.05. Student t test. t P < 0.01. $ P < O*OOl.
2. Efects of hypothalamic coo&g GOHDA-treated rabbits
TABLE
Control
t rel min t&, min dT./dt 1 t-0, ‘C/min dT s/dt ] 1-0, ‘C/min
29.0 h4.5 16,4 ztl.8 0.03*0.01 0.44ztO.04
on p@Y 6-OHDA
13.9 *1.1* 20.1 zk0.9 0.02*0.01 0.05h0.03t
I
and
PCPA
23.7 zt2.0 22.7 M.85: 0.02&0.003$ 0.46&O. 10
Values are means II= SE. Effect of PCPA and 6-OHDA pretreatment on the time (in min) between onset of hypothalamic temperature changes and peak rectal (tre) and skin (t& temperature changes; and on the initial rate of rectal and skin temperature changes dT,/dt, and dT,/df, in “C/min, following a 3 “C fall in hypothalamic temperature for 15 min. Statistical differences between control and experimental results were calculated from the Student t test. * P < 0.01. t P < O*OUl. $ P < 0.05.
-. 4, -‘-*.-.-
t L=J’--4 0: Reserpine
~-l-a”----c
--*
-5
- 5.0 - 1.0 -2.5
heating on PCPA and
temp.
t
’ *.
1. Efect of hypothalamic 6-UHDA-treated rabbits ~-------
TABLE
Hypothalamic Redo1 temp. Skin temp.
treated
*- -
.-.-. a- - *
- -.I
t
rabbit
- 5.0 - 1.0-25.
t I
- 10.0 -2.0~so-
time I 10
(minutes) I 15
t r
r
1
-20 25 30 FIG. 2. Typical temperature responses for hypothalamic cooling redrawn from original data. Effects on rectal and skin temperatures are shown for control (A), 6-OHDA-treated (I?), PCPA-treated (C), and reserpinized rabbits (D). Hypothalamic temperature was lowered by approximately 3*C for 15 min (arrows). Zero levels for skin, rectal and hypothalamic temperatures were taken from precooling levels. Cooling in all cases was only commenced once all temperatures had stabilized for at least 45 min. Note different temperature scales for hypothalamic, T h Y, skin, Tsk, and rectal, T,,, temperatures, 0
5
resting rectal temperatures of these rabbits below that of the control animals. Effects of hy@alamic heating and cooling z&h PCPA. Resting rectal temperatures treated rabbits did not differ from those rabbits. Heating the hypothalamus in this and 3, and Table 1) caused a cutaneous with the ear skin temperature increasing
were
0.6-l.O”C
on rabbits treated of the PCPAof the control series (Figs. 1C vasodilatation, more rapidly
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572
WOOLF, l.07 HY POTbiAiAbfli HEATING
'-"~HYPOTHALAMIC COOLING
LMURN,
WILLIES,
AND
ROSENDORFF
those of the control animals. The PCPA-treated animals showed a 25-35 % depletion of 5-HT. In those experiments in which 6-OHDA kvas injected into the hypothalamus only, there was an inadequate amount of brain tissue for this assay method. However, the depleting effects of 6-OHDA on NE content of a localized area of the rabbit brain have previously been verified by fluorescence histochemistry in this laboratory. In rabbits treated intracisternally with GOHDA, a whole-brain depletion of NE by 35-50 % of control values was found. 5-HT levels in these rabbits were 80-90 % of control values. Dopamine levels were not measured, but both reserpine and 6-OHDA are well knolvn to cause dopamine depletion (8, 23). DISCUSSION
Cont. PCA Rectal :p
45
Skimp
