334
Brain Research 171 (1979) 334--338 © Elsevier/North-Holland Biomedical Press
Medullary reticular formation lesions and lordosis reflex in female rats
DOAN MODIANOS and DONALD PFAFF The Rockefeller University, New York, N.Y. 10021 (U.S.A.)
(Accepted April 5th, 1979)
The lateral vestibular nucleus (LVN) and nucleus reticularis gigantoceUularis (NGc) have been implicated in the control of the lordosis reflex of female rats ~'-4, an estrogen dependent behavior 1A1 necessary for reproduction. This reflex, precisely characterized by film analysis s, consists of a dorsiflexion of the vertebral column: elevation of the rump and head and depression of the thorax. Lesions of LVN and N G c produce significant decrements in the ability of female rats to display lordosisZ. In rats given lesions of both LVN and NGc, results suggested that the contribution of each was not dependent upon the integrity of the other. Further, the magnitude of lordosis deficit was correlated with amount of giant cell loss in N G c and Deiters' cell loss in LVN. Finally, lordosis is facilitated by electrical stimulation of LVN 4. In the lesion experiments, effects of NGc damage on lordosis were not as great as effects of LVN damage 3. Since the NGc lesions were small relative to the size of the structure and since postoperative recovery periods before testing were long, possible NGc effects on lordosis may have been reduced due to subtotal lesions and subsequent recovery of function. If so, then larger NGc lesions in an experiment with behavioral testing sooner after surgery might reveal a greater role of NGc in the control of lordosis. The present experiment tested this possibility. The experiment used 40 ovariectomized Sprague-Dawley female rats, weighing 245-295 g, housed with a reversed light-dark cycle. Each rat received daily intramuscular injections of 10 /~g estradiol benzoate dissolved in sesame oil. These injections led to a high pre-operative level of lordosis reflex performance in all rats. Animals were divided into 4 equal groups, each of which received bilateral lesions. One group (n = 10) received lesions in LVN; a second group (n = 10) received lesions in NGc; and as controls for surgical procedure and for brain damage independent of location, a third group (n = 10) received lesions in cerebellar cortex (CC); and the final group (n = 10) received lesions in the spinal nucleus of the trigeminal nerve (SpV). Lesions were made by passing DC anodal current through a stainless steel dental broach (tip diameter ----- 100 #m) insulated except at the tip. Address correspondence to: Dept. of Psychology, Fordham University, Bronx, N.Y. 10458, U.S.A. attention of Dr. Modianos.
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Fig. 1. Mean lordosis quotients for all rats during pre-operative tests and for each lesion group during postoperative tests.
On the day of surgery, each rat was tested for lordosis in response to manual stimulation of the flanks, rump, and perineum 10. Lordosis was evaluated using a 0-3 scale (3 = maximum lordosis reflex strength), and the following measures were calculated for each animal: lordosis quotient (percentage of non-zero responses) and mean lordosis reflex strength (average of the non-zero responses). Each rat was manually stimulated 20 times, stimulations being given in 4 blocks of 5 stimuli each. The time between blocks of manual stimulations was approximately 10 min. Immediately after pre-operative testing surgery was conducted. Preliminary experiments had shown that after control surgical procedures under light halothane anesthesia, lordosis performance would return to normal well before 4 h. Therefore, 4 h after surgery postoperative testing was conducted using the same procedures employed pre-operatively. Non-parametric statistics were used for the evaluation of behavioral results. Immediately after post-operative testing each animal was anesthetized with chloral hydrate and transcardially perfused with 0 . 9 ~ saline followed by 10~o formalin, and the brain was extracted and placed in formalin. Frozen sections (50 #m) were stained with Luxol fast blue and cresyl violet, and examined for lesion placement. For each animal and each group, lesion volume (in cu. ram) was calculated. NGc lesions (mean volume = 1.52 cu. ram) were centered just anterior to the inferior olive, and extended from the ventral border of the medial longitudinal fasciculus dorsally, to the upper border of the inferior olive ventrally. These lesions seldom fused in the midline, nor did they extend beyond the medial 1]3 of the facial nerve nucleus laterally. NGc lesions had pronounced effects upon lordosis quotient (Fig. 1): post-operatively, 6 of 10 NGc lesion rats never displayed lordosis (post-op vs pre-op, P < 0.005). The NGc group post-operative performance was significantly worse than both the spinal trigeminal nucleus group and the cerebellar cortex lesion group (each
336 100
~
LVN ( + ) : r = - 0 . 8 0 ,
p< 0.01
NGc ( o ) : r = - 0 . 6 8 ,
p
Brain Research 171 (1979) 334--338 © Elsevier/North-Holland Biomedical Press
Medullary reticular formation lesions and lordosis reflex in female rats
DOAN MODIANOS and DONALD PFAFF The Rockefeller University, New York, N.Y. 10021 (U.S.A.)
(Accepted April 5th, 1979)
The lateral vestibular nucleus (LVN) and nucleus reticularis gigantoceUularis (NGc) have been implicated in the control of the lordosis reflex of female rats ~'-4, an estrogen dependent behavior 1A1 necessary for reproduction. This reflex, precisely characterized by film analysis s, consists of a dorsiflexion of the vertebral column: elevation of the rump and head and depression of the thorax. Lesions of LVN and N G c produce significant decrements in the ability of female rats to display lordosisZ. In rats given lesions of both LVN and NGc, results suggested that the contribution of each was not dependent upon the integrity of the other. Further, the magnitude of lordosis deficit was correlated with amount of giant cell loss in N G c and Deiters' cell loss in LVN. Finally, lordosis is facilitated by electrical stimulation of LVN 4. In the lesion experiments, effects of NGc damage on lordosis were not as great as effects of LVN damage 3. Since the NGc lesions were small relative to the size of the structure and since postoperative recovery periods before testing were long, possible NGc effects on lordosis may have been reduced due to subtotal lesions and subsequent recovery of function. If so, then larger NGc lesions in an experiment with behavioral testing sooner after surgery might reveal a greater role of NGc in the control of lordosis. The present experiment tested this possibility. The experiment used 40 ovariectomized Sprague-Dawley female rats, weighing 245-295 g, housed with a reversed light-dark cycle. Each rat received daily intramuscular injections of 10 /~g estradiol benzoate dissolved in sesame oil. These injections led to a high pre-operative level of lordosis reflex performance in all rats. Animals were divided into 4 equal groups, each of which received bilateral lesions. One group (n = 10) received lesions in LVN; a second group (n = 10) received lesions in NGc; and as controls for surgical procedure and for brain damage independent of location, a third group (n = 10) received lesions in cerebellar cortex (CC); and the final group (n = 10) received lesions in the spinal nucleus of the trigeminal nerve (SpV). Lesions were made by passing DC anodal current through a stainless steel dental broach (tip diameter ----- 100 #m) insulated except at the tip. Address correspondence to: Dept. of Psychology, Fordham University, Bronx, N.Y. 10458, U.S.A. attention of Dr. Modianos.
335 lO0 //L / / / / / /
//',6,
8o
"5 o- 60 o3 0 ~-
0
40
20
Pre-o
/// - - -
/ i s
/ / /
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i l l I I I i i i
/// I I / I I I
iii iii
ffJ
III iii
//J
CerebeE Spin.
C~x.
LVN
NGc
Nucl.~
Lesion Iocotion
Fig. 1. Mean lordosis quotients for all rats during pre-operative tests and for each lesion group during postoperative tests.
On the day of surgery, each rat was tested for lordosis in response to manual stimulation of the flanks, rump, and perineum 10. Lordosis was evaluated using a 0-3 scale (3 = maximum lordosis reflex strength), and the following measures were calculated for each animal: lordosis quotient (percentage of non-zero responses) and mean lordosis reflex strength (average of the non-zero responses). Each rat was manually stimulated 20 times, stimulations being given in 4 blocks of 5 stimuli each. The time between blocks of manual stimulations was approximately 10 min. Immediately after pre-operative testing surgery was conducted. Preliminary experiments had shown that after control surgical procedures under light halothane anesthesia, lordosis performance would return to normal well before 4 h. Therefore, 4 h after surgery postoperative testing was conducted using the same procedures employed pre-operatively. Non-parametric statistics were used for the evaluation of behavioral results. Immediately after post-operative testing each animal was anesthetized with chloral hydrate and transcardially perfused with 0 . 9 ~ saline followed by 10~o formalin, and the brain was extracted and placed in formalin. Frozen sections (50 #m) were stained with Luxol fast blue and cresyl violet, and examined for lesion placement. For each animal and each group, lesion volume (in cu. ram) was calculated. NGc lesions (mean volume = 1.52 cu. ram) were centered just anterior to the inferior olive, and extended from the ventral border of the medial longitudinal fasciculus dorsally, to the upper border of the inferior olive ventrally. These lesions seldom fused in the midline, nor did they extend beyond the medial 1]3 of the facial nerve nucleus laterally. NGc lesions had pronounced effects upon lordosis quotient (Fig. 1): post-operatively, 6 of 10 NGc lesion rats never displayed lordosis (post-op vs pre-op, P < 0.005). The NGc group post-operative performance was significantly worse than both the spinal trigeminal nucleus group and the cerebellar cortex lesion group (each
336 100
~
LVN ( + ) : r = - 0 . 8 0 ,
p< 0.01
NGc ( o ) : r = - 0 . 6 8 ,
p
