BIOLOGY
OF
REPRODUCTION
Effect
21,
393-399
(1979)
of 6-Hydroxydopamine and Enzyme Activity B.
D.
on Pineal Norepinephrine in the Cyclic Female Rat’ J.
SIIIVERS,2
Department
of
A.
FIX3
and
J.
and
Cell
Physiology
University
of
Lawrence,
M.
Content
YOCHIM4
Biology,
Kansas,
Kansas
66045
ABSTRACT The response of two hydroxyindole-0-methyltransferase rine
(NE)
content
pineal
produced
enzymes, serotonin (HIOMT; E.C.2.1 by
systemic
N-acetyltransferase .1.4) to the
injections
of
(SNAT; of
reduction
6-hydroxydopamine
E.C.2,3.1.5) and pineal norepineph-
(6-OHDA)
was
exam-
ined in the present study twice daily, at 1200 and 2400 h, in the cyclic female rat. In rats sacrificed 3 days postinjection during the dark period (2400 h), injections of 6-OHDA that produced maximal inhibition of SNAT activity (58% of control values) also caused significant decreases in NE content in pineal, hypothalamic and cardiac tissues (48, 75 and 12% of control values, respectively). In rats sacrificed 17 days postinjection at 2400 h, SNAT activity and pineal NE content had returned to control levels, while hypothalamic and cardiac NE content remained significantly depressed (70 and 22% of control levels, respectively). These results confirm the role of NE in the induction of SNAT activity and reveal that 6-OHDA is more effective in decreasing cardiac than pineal NE content.
In
a second
throughout the estrous cycle in both NE content by 6-Ol-IDA did not block ovulation or disrupt the estrous cycle, although the initial cycle was prolonged by 1 day in some animals. Although average l-IIOMT activity during the estrous cycle in 6-OHDA treated animals did not differ from control levels, the amplitude of the circadian alteration in HIOMT activity as well as the relationship of this pineal enzyme to the estrous cycle was altered in animals receiving the drug. These findings suggest that the nocturnal rise in l-IIOMT activity and the relationship of this pineal enzyme to the estrous cycle are regulated, in part, by a NE sensitive component in either the pineal gland, hypothalamus or both.
treated
and
HIOMT
experiment,
control
animals.
activity
Reduction
was
INTRODUCTION It
has
and
been
the
pineal
the
and
Klein,
et 1974).
sympathetic
nephrine
serotonin
Klein
nervous
(NE)
in
the
the
al,,
1971; However,
regulation
role
of
to
Received
May 4, 1979. December 22, 1979. by a Biomedical Research of Kansas. of the Wm. King Candlin
l-IIOMT
alter
ments
is due
which,
unlike
(Jackson because
‘Supported Grant from the University 2 Recipient Award in Physiology, University of Kansas, 1978. Present address: Rockefeller University, New York, NY 10021. 3Present address: Dept. of Pediatrics, Ralph L. Smith Mental Retardation Research Center, University of Kansas Medical Center, Kansas City, KS 66103. Reprint requests.
small
to
1978),
to
In
shown
has
in to 1979),
to
relationship,
in
only
slightly
of NE
these
acute rate of
experi-
l-IIOMT slow
In
HIOMT
addition, activity
(Klein,
to
is 1974,
assess
whether
regulation. SNAT
activity
appeared
(Shivers
activity
relation
Yochim, it
culture
activity
inability
SNAT
HIOMT
vary and
in
of
addition
the
1971).
difficult its
the
is extremely
rise
been
contrast
(Wallen
SNAT,
that
In
SNAT
turnover
of
Lovenberg,
is involved
Yochim,
in
nocturnal
the
it
the
in
1971).
organ
increases
Perhaps
that
and
in in
activity
relative
NE
393
activity
HIOMT
that
glands
1970).
for
activity
Rapport,
rise
sym-
responsible
show
pineal
clearly the
of HIOMT and
marked
et al.,
(Klein
Accepted
rat a
whereas
mela-
levels
however,
to
that
is
(Moore
studies,
NE
stimulates
norepithe
gland
is not
suggest
system
average
pineal
of
studies
nervous
vitro
1974;
and of
the
hydroxyindole-O-methylE.C.2.1.1.4)
vivo
maintaining and
the
system
In
pathetic
N-acetyltransKlein,
enzyme (HIOMT;
defined,
activity
(Volkman
forming
transferase
central
influence
altering
E.C.2.3.1.5)
1971;
the
systems by
enzyme
(SNAT;
Moore
that
nervous
production
ferase Heller,
tonin
documented
sympathetic
melatonin
of
well
measured
of hypothalamic
to
the
1974). that
been
estrous
Because an
and
has
in
cycle of
vivo
this
experi-
SHIVERS
394
could
ment
be
tive
role
of
the
regulation
designed
the
of
estrous
cycle.
aspects
of
neurotoxin
Accordingly,
we
regulation innervation
activity, cycle
a still
in
the
during examined
three
following
the
loss
produced
by
the
(6-OIIDA): rhythmicity and
circadian related
assay
presumpsystem
activity
6-hydroxydopamine
average estrous
test
nervous
HIOMT
l-IIOMT
sympathetic
of
to
sympathetic
alterations
in
I-IIOMT
activity.
MATERIALS
Ani
AND
METHODS
na1s
of Assay
Norepinephrine content, SNAT activity and l-IIOMT activity determinations were made in separate groups of animals sacrificed at 1200 or 2400 h. Previous studies have shown that the activities of both SNAT and I-IIOMT are at their lowest point and peak, respectively, at these times (Shivers and Yochim, 1979). Unlike HIOMT, SNAT activity does not vary throughout the estrous cycle (Shivers and Yochim, 1979). Therefore, SNAT activity was measured in both treated and control animals sacrificed without regard to stage of the reproductive cycle, whereas HIOMT activity was measured in animals sacrificed at designated times throughout the estrous cycle. As with SNAT activity, determinations of pineal, hypothalamic and cardiac NE content were made in animals sacrificed without regard to the stage of the estrous cycle.
SNAT
Assay
Serotonin N-acetyltransferase mined in individual pineal the sacrifice of each animal
glands using
activity was deterimmediately after the radioenzymatic
of
previously
SNAT pmoles
Deguchi
and
(Shivers
and
Axelrod
(1972)
Yochim,
activity are reported N-acetyltryptamine
1979).
described Results
in the present formed/pineal/lO
for
study
as mm
incubation.
tHOM
T Assay
Ilydroxyindole-0-metholtransferase activity was determined in individual pineal glands immediately after the sacrifice of each animal using the radioenzymatic assay of Axelrod et al. (1965) described previously (Wallen and Yochim, 1974). Results for HIOMT activity are reported in the present study as pmoles of melatonin formed/pineal/h incubation.
NE
Mature, virgin Sprague-Dawley (Sasco Co.) rats (200-300 g) were caged individually in air conditioned animal facilities (24 ± 2#{176}C). Animals were housed under artificial illumination provided by banks of cool-white General Electric 40-W fluorescent bulbs. The illumination ranged from 929 lux at the upper cage levels to 486 lux at the lower cage levels. The environmental lighting schedule employed in this study was 14L1OD (lights on 0500-1900 h). Animals were allowed free access to Purina rat chow and water and estrous cycles were staged by recording vaginal smears daily for at least 2 cycles prior to use. Animals were sacrificed using light ether anesthesia followed by cervical dislocation. Animals sacrificed during the dark period were anesthetized with ether in the dark prior to sacrifice and dissection of pineals, hearts and hypothalami in the light. Pineal glands were removed within 30 seconds after decapitation. The hypothalamus was removed from the rest of the brain by making cuts rostral to the optic chiasm and the pons as well as a horizontal cut at the level of the anterior commissure. For determination of norepinephrine content, tissues were frozen with dry ice and stored at -70#{176}C until time of assay.
Time
ET AL.
Content
Determinations
Catecholamine content was measured in individual pineal, hypothalamic and cardiac tissues using the procedure of Keller et al. (1976). Each tissue was homogenized in a minimal volume of 0.1 N HCIO4 containing 0.4 mM NaHSO3 and a known amount of n-methyldopamine serving as an internal standard. An aliquot of the soluble fraction was added to 20 mg acid-washed alumina (ICN Pharmaceuticals, Inc.) (Anton and Sayre, 1962) and 1 ml 0.5 M Tris HCI buffer
(pH
8.4).
Following
a
15
mm
mixing
period,
the alumina was washed 3 times with 1 ml dilute buffer (1 mM NaHSO3, 5 mM Tris HC1, pH 8.4) and the catecholamines were extracted with 150 j.zl 0.1 N HCIO4 containing 0.4 mM Na2 SO3. Catecholamines were separated by high performance liquid chromatography on a Corasil CX column (Waters Associates, Inc.) and assayed electrochemically. External standard solutions of norepinephrine (NE), dopamine (DA) and a-methyldopamine were injected periodically for determinations of absolute amounts of catecholamines present in each tissue. (NE and DA were purchased from Sigma and n-methyldopamine was a gift from R. T. Borchardt.) The amounts of NE present in each tissue were calculated by comparing the ratio of unknown and known NE peaks to cs-methyldopamine peaks in samples and external standards, Results of the NE content determinations in the pineal gland were reported as ng of NE/pineal gland, whereas the determinations in hypothalamic and cardiac tissues were reported as ng of NE/g of tissue.
Effect
of
6-OHDA
on Estrous Cyclicity and Ovulation To determine whether systemic injections of 6-OHDA altered reproductive function, vaginal cyclicity in treated animals was carefully monitored. The initial estrous cycle was prolonged by I day in approximately half of the animals, regardless of the stage of the cycle during which the initial injection was made. Subsequent vaginal cycles were, however, normal, In 4 treated animals sacrificed on metestrus, the oviducts were flushed and examined for the presence of eggs. The results showed that all 4 animals ovulated and the number of eggs was similar to that observed in control animals sacrificed on metestrus. These findings show that systemic injections of 6-OHDA did not block ovulation or chronically disrupt the estrous cycle.
PINEAL
Treatment
NE
CONTENT
AND
ENZYME
on Day 8, rose above
Schedule
The
ACTIVITY
neurotoxin,
6-hydroxydopamine
(6-OHDA),
in producing a selective and prolonged destruction of sympathetic nerve terminals (Thoenen and Tranzer, 1968) is not thought to cross the blood-brain barrier in adult rats (Jack et al., 1972). However, since the pineal gland is believed to lie outside the blood-brain barrier (Wurtman et al., 1968), 6-OHDA should be readily accessible to the gland. To determine the proper dose of 6-Ol-IDA that would maximally deplete the pineal of NE and provide the best model for determining the effect of NE loss on HIOMT activity, SNAT activity was used as an index of the effectiveness of 6-OHDA. Because SNAT activity shows supersensitivity to NE soon after chemical or surgical sympathectomy (Deguchi and Axelrod, 1973), SNAT activity would provide a measure of both NE loss and the development of supersensitivity of the pmneal gland to NE deprivation. Therefore, in the present studies, several treatment schedules were used to determine the dose of 6-OHDA and the time of sacrifice that would produce the greatest inhibition of the nocturnal rise in SNAT activity and presumably produce the maximal depletion of pineal NE content. Immediately prior to injection, 6-hydroxydopamine (6-OHDA; Sigma) was dissolved in a nitrogenated saline-ascorbic acid solution (0.9% NaCI and 0.1% ascorbic acid). Intraperitoneal dosages ranging between 25-45 mg 6-OHDA/ 0.3 ml/300 g BW appeared to be equally effective in decreasing the nocturnal rise in SNAT activity (data not shown). However, the time of sacrifice after 6-OHDA treatment was found to be critical (Fig. 1). In treated rats sacrificed at 2400 h on Day 2, 4 or 6 of the experiment, SNAT activity decreased to 55, 58 and 68% of control levels, respectively (100% = 318 ± 75 pmoles/gland/10 mm) (Fig. 1). The decrease in SNAT activity at 2400 h on Day 4 of the experiment was significant (P
OF
REPRODUCTION
Effect
21,
393-399
(1979)
of 6-Hydroxydopamine and Enzyme Activity B.
D.
on Pineal Norepinephrine in the Cyclic Female Rat’ J.
SIIIVERS,2
Department
of
A.
FIX3
and
J.
and
Cell
Physiology
University
of
Lawrence,
M.
Content
YOCHIM4
Biology,
Kansas,
Kansas
66045
ABSTRACT The response of two hydroxyindole-0-methyltransferase rine
(NE)
content
pineal
produced
enzymes, serotonin (HIOMT; E.C.2.1 by
systemic
N-acetyltransferase .1.4) to the
injections
of
(SNAT; of
reduction
6-hydroxydopamine
E.C.2,3.1.5) and pineal norepineph-
(6-OHDA)
was
exam-
ined in the present study twice daily, at 1200 and 2400 h, in the cyclic female rat. In rats sacrificed 3 days postinjection during the dark period (2400 h), injections of 6-OHDA that produced maximal inhibition of SNAT activity (58% of control values) also caused significant decreases in NE content in pineal, hypothalamic and cardiac tissues (48, 75 and 12% of control values, respectively). In rats sacrificed 17 days postinjection at 2400 h, SNAT activity and pineal NE content had returned to control levels, while hypothalamic and cardiac NE content remained significantly depressed (70 and 22% of control levels, respectively). These results confirm the role of NE in the induction of SNAT activity and reveal that 6-OHDA is more effective in decreasing cardiac than pineal NE content.
In
a second
throughout the estrous cycle in both NE content by 6-Ol-IDA did not block ovulation or disrupt the estrous cycle, although the initial cycle was prolonged by 1 day in some animals. Although average l-IIOMT activity during the estrous cycle in 6-OHDA treated animals did not differ from control levels, the amplitude of the circadian alteration in HIOMT activity as well as the relationship of this pineal enzyme to the estrous cycle was altered in animals receiving the drug. These findings suggest that the nocturnal rise in l-IIOMT activity and the relationship of this pineal enzyme to the estrous cycle are regulated, in part, by a NE sensitive component in either the pineal gland, hypothalamus or both.
treated
and
HIOMT
experiment,
control
animals.
activity
Reduction
was
INTRODUCTION It
has
and
been
the
pineal
the
and
Klein,
et 1974).
sympathetic
nephrine
serotonin
Klein
nervous
(NE)
in
the
the
al,,
1971; However,
regulation
role
of
to
Received
May 4, 1979. December 22, 1979. by a Biomedical Research of Kansas. of the Wm. King Candlin
l-IIOMT
alter
ments
is due
which,
unlike
(Jackson because
‘Supported Grant from the University 2 Recipient Award in Physiology, University of Kansas, 1978. Present address: Rockefeller University, New York, NY 10021. 3Present address: Dept. of Pediatrics, Ralph L. Smith Mental Retardation Research Center, University of Kansas Medical Center, Kansas City, KS 66103. Reprint requests.
small
to
1978),
to
In
shown
has
in to 1979),
to
relationship,
in
only
slightly
of NE
these
acute rate of
experi-
l-IIOMT slow
In
HIOMT
addition, activity
(Klein,
to
is 1974,
assess
whether
regulation. SNAT
activity
appeared
(Shivers
activity
relation
Yochim, it
culture
activity
inability
SNAT
HIOMT
vary and
in
of
addition
the
1971).
difficult its
the
is extremely
rise
been
contrast
(Wallen
SNAT,
that
In
SNAT
turnover
of
Lovenberg,
is involved
Yochim,
in
nocturnal
the
it
the
in
1971).
organ
increases
Perhaps
that
and
in in
activity
relative
NE
393
activity
HIOMT
that
glands
1970).
for
activity
Rapport,
rise
sym-
responsible
show
pineal
clearly the
of HIOMT and
marked
et al.,
(Klein
Accepted
rat a
whereas
mela-
levels
however,
to
that
is
(Moore
studies,
NE
stimulates
norepithe
gland
is not
suggest
system
average
pineal
of
studies
nervous
vitro
1974;
and of
the
hydroxyindole-O-methylE.C.2.1.1.4)
vivo
maintaining and
the
system
In
pathetic
N-acetyltransKlein,
enzyme (HIOMT;
defined,
activity
(Volkman
forming
transferase
central
influence
altering
E.C.2.3.1.5)
1971;
the
systems by
enzyme
(SNAT;
Moore
that
nervous
production
ferase Heller,
tonin
documented
sympathetic
melatonin
of
well
measured
of hypothalamic
to
the
1974). that
been
estrous
Because an
and
has
in
cycle of
vivo
this
experi-
SHIVERS
394
could
ment
be
tive
role
of
the
regulation
designed
the
of
estrous
cycle.
aspects
of
neurotoxin
Accordingly,
we
regulation innervation
activity, cycle
a still
in
the
during examined
three
following
the
loss
produced
by
the
(6-OIIDA): rhythmicity and
circadian related
assay
presumpsystem
activity
6-hydroxydopamine
average estrous
test
nervous
HIOMT
l-IIOMT
sympathetic
of
to
sympathetic
alterations
in
I-IIOMT
activity.
MATERIALS
Ani
AND
METHODS
na1s
of Assay
Norepinephrine content, SNAT activity and l-IIOMT activity determinations were made in separate groups of animals sacrificed at 1200 or 2400 h. Previous studies have shown that the activities of both SNAT and I-IIOMT are at their lowest point and peak, respectively, at these times (Shivers and Yochim, 1979). Unlike HIOMT, SNAT activity does not vary throughout the estrous cycle (Shivers and Yochim, 1979). Therefore, SNAT activity was measured in both treated and control animals sacrificed without regard to stage of the reproductive cycle, whereas HIOMT activity was measured in animals sacrificed at designated times throughout the estrous cycle. As with SNAT activity, determinations of pineal, hypothalamic and cardiac NE content were made in animals sacrificed without regard to the stage of the estrous cycle.
SNAT
Assay
Serotonin N-acetyltransferase mined in individual pineal the sacrifice of each animal
glands using
activity was deterimmediately after the radioenzymatic
of
previously
SNAT pmoles
Deguchi
and
(Shivers
and
Axelrod
(1972)
Yochim,
activity are reported N-acetyltryptamine
1979).
described Results
in the present formed/pineal/lO
for
study
as mm
incubation.
tHOM
T Assay
Ilydroxyindole-0-metholtransferase activity was determined in individual pineal glands immediately after the sacrifice of each animal using the radioenzymatic assay of Axelrod et al. (1965) described previously (Wallen and Yochim, 1974). Results for HIOMT activity are reported in the present study as pmoles of melatonin formed/pineal/h incubation.
NE
Mature, virgin Sprague-Dawley (Sasco Co.) rats (200-300 g) were caged individually in air conditioned animal facilities (24 ± 2#{176}C). Animals were housed under artificial illumination provided by banks of cool-white General Electric 40-W fluorescent bulbs. The illumination ranged from 929 lux at the upper cage levels to 486 lux at the lower cage levels. The environmental lighting schedule employed in this study was 14L1OD (lights on 0500-1900 h). Animals were allowed free access to Purina rat chow and water and estrous cycles were staged by recording vaginal smears daily for at least 2 cycles prior to use. Animals were sacrificed using light ether anesthesia followed by cervical dislocation. Animals sacrificed during the dark period were anesthetized with ether in the dark prior to sacrifice and dissection of pineals, hearts and hypothalami in the light. Pineal glands were removed within 30 seconds after decapitation. The hypothalamus was removed from the rest of the brain by making cuts rostral to the optic chiasm and the pons as well as a horizontal cut at the level of the anterior commissure. For determination of norepinephrine content, tissues were frozen with dry ice and stored at -70#{176}C until time of assay.
Time
ET AL.
Content
Determinations
Catecholamine content was measured in individual pineal, hypothalamic and cardiac tissues using the procedure of Keller et al. (1976). Each tissue was homogenized in a minimal volume of 0.1 N HCIO4 containing 0.4 mM NaHSO3 and a known amount of n-methyldopamine serving as an internal standard. An aliquot of the soluble fraction was added to 20 mg acid-washed alumina (ICN Pharmaceuticals, Inc.) (Anton and Sayre, 1962) and 1 ml 0.5 M Tris HCI buffer
(pH
8.4).
Following
a
15
mm
mixing
period,
the alumina was washed 3 times with 1 ml dilute buffer (1 mM NaHSO3, 5 mM Tris HC1, pH 8.4) and the catecholamines were extracted with 150 j.zl 0.1 N HCIO4 containing 0.4 mM Na2 SO3. Catecholamines were separated by high performance liquid chromatography on a Corasil CX column (Waters Associates, Inc.) and assayed electrochemically. External standard solutions of norepinephrine (NE), dopamine (DA) and a-methyldopamine were injected periodically for determinations of absolute amounts of catecholamines present in each tissue. (NE and DA were purchased from Sigma and n-methyldopamine was a gift from R. T. Borchardt.) The amounts of NE present in each tissue were calculated by comparing the ratio of unknown and known NE peaks to cs-methyldopamine peaks in samples and external standards, Results of the NE content determinations in the pineal gland were reported as ng of NE/pineal gland, whereas the determinations in hypothalamic and cardiac tissues were reported as ng of NE/g of tissue.
Effect
of
6-OHDA
on Estrous Cyclicity and Ovulation To determine whether systemic injections of 6-OHDA altered reproductive function, vaginal cyclicity in treated animals was carefully monitored. The initial estrous cycle was prolonged by I day in approximately half of the animals, regardless of the stage of the cycle during which the initial injection was made. Subsequent vaginal cycles were, however, normal, In 4 treated animals sacrificed on metestrus, the oviducts were flushed and examined for the presence of eggs. The results showed that all 4 animals ovulated and the number of eggs was similar to that observed in control animals sacrificed on metestrus. These findings show that systemic injections of 6-OHDA did not block ovulation or chronically disrupt the estrous cycle.
PINEAL
Treatment
NE
CONTENT
AND
ENZYME
on Day 8, rose above
Schedule
The
ACTIVITY
neurotoxin,
6-hydroxydopamine
(6-OHDA),
in producing a selective and prolonged destruction of sympathetic nerve terminals (Thoenen and Tranzer, 1968) is not thought to cross the blood-brain barrier in adult rats (Jack et al., 1972). However, since the pineal gland is believed to lie outside the blood-brain barrier (Wurtman et al., 1968), 6-OHDA should be readily accessible to the gland. To determine the proper dose of 6-Ol-IDA that would maximally deplete the pineal of NE and provide the best model for determining the effect of NE loss on HIOMT activity, SNAT activity was used as an index of the effectiveness of 6-OHDA. Because SNAT activity shows supersensitivity to NE soon after chemical or surgical sympathectomy (Deguchi and Axelrod, 1973), SNAT activity would provide a measure of both NE loss and the development of supersensitivity of the pmneal gland to NE deprivation. Therefore, in the present studies, several treatment schedules were used to determine the dose of 6-OHDA and the time of sacrifice that would produce the greatest inhibition of the nocturnal rise in SNAT activity and presumably produce the maximal depletion of pineal NE content. Immediately prior to injection, 6-hydroxydopamine (6-OHDA; Sigma) was dissolved in a nitrogenated saline-ascorbic acid solution (0.9% NaCI and 0.1% ascorbic acid). Intraperitoneal dosages ranging between 25-45 mg 6-OHDA/ 0.3 ml/300 g BW appeared to be equally effective in decreasing the nocturnal rise in SNAT activity (data not shown). However, the time of sacrifice after 6-OHDA treatment was found to be critical (Fig. 1). In treated rats sacrificed at 2400 h on Day 2, 4 or 6 of the experiment, SNAT activity decreased to 55, 58 and 68% of control levels, respectively (100% = 318 ± 75 pmoles/gland/10 mm) (Fig. 1). The decrease in SNAT activity at 2400 h on Day 4 of the experiment was significant (P
