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PubMed1981

Catecholestrogens and induction of sexual behavior in the ovariectomized rat.

The ability of the catecholestrogens, 4-hydroxyestradiol (4-OHE2) and 2-hydroxyestradiol (2-OHE2) to induce lordosis in ovariectomized rats primed with progesterone was assessed following either short- or long-term exposure to the steroids. 4-OHE2 successfully induced lordosis whether administered as two bolus intrajugular injections separated by a 3-hour interval or continuously for 7 days via subcutaneously implanted osmotic minipumps. 2-OHE2, however, was ineffective under both conditions. When administered subcutaneously in conjunction with 3 days of estradiol benzoate (E2B) treatment, neither of the catecholestrogens exhibited any antiestrogenic effect as compared with the lordosis response to E2B alone. Likewise, simultaneous administration of 2-OHE2 did not significantly alter the response to intrajugular injections of estradiol (E2) or 4-OHE2. The results indicate that 4-OHE2 (but not 2-OHE2) mimicks the lordosis-inducing action of E2 and that neither catecholestrogen has any antiestrogenic effect in this behavioral test system.

Animals↗

PubMed1982

Effects of monoamine oxidase inhibition on female sexual behavior, serotonin levels and type A and B monoamine oxidase activity.

Administration of various monoamine oxidase (MAO) inhibitors to ovariectomized-adrenalectomized, estrogen and progesterone-treated female rats was utilized to study possible relationships between the lordosis response and levels of preoptic-hypothalamic MAO and serotonin (5HT). Depending on the drug and dose, behavioral changes ranged from no effect to complete abolition of the lordosis response. Surprisingly, only those treatments which substantially inhibited both the A and B forms of MAO affected lordosis. However, behavioral deficits were related to increases in 5HT levels in a graded manner. In fact, a sigmoid-shaped dose-response curve was generated by plotting either the lordosis quotient or quality score versus the percent increase in preoptic-hypothalamic 5HT. Proceptivity was reduced by some treatments but not abolished, suggesting that different neurotransmitters may mediate receptive and proceptive components of female sexual behavior. In general, these results support the hypothesis that 5HT may exert inhibitory control over hormone dependent female sexual behavior and suggest that previously reported changes in MAO activity and 5HT levels following gonadal steroid treatment could pay a role in hormonal facilitation of female sexual behavior.

Animals↗

PubMed1982

Enhancement by progesterone of 5-hydroxytryptophan inhibition of the copulatory response in the female rat.

A study was made of the influence of different hormonal treatments used to induce copulatory behavior in ovariectomized female rats (lordosis behavior), on the effects of an endogenous increase of 5-HT or catecholamines achieved by DL-5-HTP and L-Dopa. The lordosis response (LR) has been shown to be inhibited by increased serotonergic and catecholaminergic neuronal activity. The 5-HT agonist lysergic acid diethylamide (LSD) has been found to inhibit the LR. This effect was recently shown to be enhanced by increasing doses of progesterone. In the present study it was demonstrated that the inhibitory effect of the 5-HT precursor 5-hydroxytryptophan was also potentiated by increased doses of progesterone. However, the effect of DL-5-HTP on spontaneous behaviors in an exploratory situation was not influenced by progesterone treatment. In contrast to the results with DL-5-HTP, progesterone had no modulating effects on the lordosis-inhibiting action of the catecholamine precursor levo-dopa. This elective effect on the influence of a progesterone-dependent response suggests a direct relationship between 5-HT mechanisms and the progesterone action involved in the LR. Possible mechanisms underlying the observed interactive effect of progesterone and serotonin on lordosis behavior, such as a progesterone-induced alteration of serotonergic transmission, are discussed.

5-Hydroxytryptophan↗

PubMed1991

GABAergic control of receptivity in the female rat.

GABAergic neurotransmission has been implicated in the control of the steroid-dependent behavior, lordosis. GABA has dual effects on lordosis: it facilitates lordosis through actions in the medial hypothalamus (mHYP) and it inhibits lordosis through actions in the preoptic area (POA). In the present study, gonadally intact and ovariectomized female rats were behaviorally tested with a sexually active male. Brains were removed from sexually receptive female either 1 or 24 h after behavioral testing. There was a significant difference in endogenous GABA concentration in HYP and POA between receptive, postreceptive and ovariectomized nonreceptive females. Specifically, GABA levels in postreceptive females were higher in the HYP (20%) and lower in the POA (21%) in comparison to receptive females (p less than 0.05). There was also a significant change in binding parameters of 3H-muscimol in the HYP and POA of receptive females as compared to 24 h postreceptive and ovariectomized rats. Attempts to modulate 3H-GABA release from hypothalamic tissue slices by estrogen or progesterone in ovariectomized rats yielded no effect on this parameter.

Animals↗

PubMedDate not supplied

Cervical spine alignment in the immobilized ice hockey player. A computed tomographic analysis of the effects of helmet removal.

To determine if helmet removal causes a significant increase in lordosis of the cervical spine in ice hockey players, we radiographically assessed the position of the cervical spine in subjects immobilized to a standard spine backboard wearing shoulder pads both with and without a helmet. Ten adult male volunteers (ages, 18 to 28 years) with no previous history of cervical spine injuries were fitted with an appropriately sized ice hockey helmet and shoulder pads and immobilized in a supine position to a standard spine backboard. Computerized tomographic lateral scout scans were obtained of the cervical spine for three conditions: 1) no equipment (control), 2) helmet and shoulder pads, and 3) shoulder pads only (helmet removed). With the helmet removed and the shoulder pads remaining, a significant increase in C2 to C7 lordosis was found when compared with the other two conditions. Individual segmental measurements revealed a significant increase in cervical lordosis at the C6-7 level with the helmet removed compared with the helmet and shoulder pads condition. Our results demonstrate that the removal of an ice hockey helmet from a supine player causes a significant increase in lordosis (extension) of the cervical spine. We recommend that ice hockey helmets not be removed from injured players, with rare exceptions, because doing so results in unnecessary motion of the cervical spine.

Adult↗

PubMed1986

Intracranial sites regulating the biphasic action of progesterone in estrogen-primed golden hamsters.

Diencephalic and mesencephalic neural sites regulating the biphasic effect of progesterone (P) were investigated using the hormone implantation technique in ovariectomized female golden hamsters primed with estrogen. Double barreled cannulae were implanted unilaterally and bilaterally in the medial preoptic area, anterior hypothalamus, ventromedial hypothalamus (VMH), central gray, or interpeduncular nucleus. Testing was conducted using a sequential paradigm; facilitation tests commenced after 44 h of estrogen priming. P-filled cannulae placed in the VMH region facilitated lordosis behavior in 42% and 60% of unilaterally and bilaterally implanted females, respectively. In the anterior hypothalamus, only P implants adjacent to the VMH area effectively promoted receptivity. Lordosis behavior was also observed in 20-36% of females with P implants in the medial preoptic area. P implants in central gray and interpeduncular nucleus regions had no significant facilitating effect on sexual behavior. Tests for inhibition occurred 24 h after facilitation testing and consisted of a pretest, followed by systemic P administration and a behavioral test 4-5 h later. During the pretest for inhibition, females that were receptive in the facilitation test attacked males more rapidly than previously nonreceptive animals and showed decrements in lordosis scores after systemic P delivery. This biphasic effect of P completely inhibited receptivity among several animals in the VMH group. Additional experiments, however, investigating the biphasic effect of P implants in the VMH suggested that the occurrence of copulation in the facilitation test may have been involved in mediating the subsequent increase in aggressive behavior and the suppression of sexual responsiveness in the inhibition test. Nevertheless, a final experiment showed that when P was implanted sequentially in the VMH, facilitation and, more importantly, a later reduction in lordosis behavioral scores occurred even when copulation was eliminated in the facilitation test. P implants in mesencephalic regions exerted no significant inhibitory effect on receptivity. These findings demonstrate that the biphasic action of P in the female hamster is regulated by nerve cells located in the diencephalon, especially in the VMH region.

Animals↗

PubMed1996

In vivo regulation of central nervous system progesterone receptors: cocaine induces steroid-dependent behavior through dopamine transporter modulation of D5 receptors in rats.

To characterize the membrane pathway by which the cocaine-sensitive dopamine transporter (DAT) modulates progesterone receptor activation, steroid-dependent behavior lordosis was used in estrogen-primed ovariectomized Sprague-Dawley rats with stereotaxic implanted third ventricle cannulas. Lordosis in response to solicitous males was observed in females after intercerebral ventricular administration of DAT antagonists WIN35,428 (80 ng) and cocaine (0.016-1.6 micrograms). Significantly, antisense oligonucleotides (AS) to DAT mRNA also induced reproductive behavior. In contrast, the D1-D2 receptor membrane-repopulation inhibitor N-ethoxycarbonyl-2 ethoxy-1,2-dihydroquinoline and the D1-like antagonist SCH23390 blocked cocaine-inducible behavior. Further, facilitation of behavior by AS to the DAT was suppressed by N-ethoxycarbonyl-2 ethoxy-1,2-dihydroquinoline. Behavior was not dependent on D2 receptors, since animals pretreated with the D2 antagonist sulpride displayed lordosis after cocaine challenge. Antisense oligonucleotides to D5 but not D1 dopamine receptor mRNA suppressed reproductive behavior associated with cocaine. Microinjections of cocaine to the ventromedial nucleus (VMN) but not arcuate nucleus or preoptic area potentiated lordosis, suggesting the functional presence of DAT in the VMN. Finally, cocaine facilitation of behavior was blocked by both antiprogestin RU486 and progesterone receptor AS microinjected into either the third ventricle or the VMN. Collectively, the data provide strong evidence for cocaine modulation of reproductive behavior through presynaptic cocaine-sensitive dopamine transporters and postsynaptic D5 dopamine receptor mediation of progesterone receptor-dependent behavior in rat central nervous system.

Animals↗

PubMed2000

Decrease of sexual receptivity by prolylendopeptidase inhibitor in female rats.

The effects of a prolylendopeptidase inhibitor, 1-[3-(2-indanylanylacetyl)-L-thioprolyl]pyrrolidine (Z-321), on lordosis behavior were investigated in estrogen and progesterone-treated ovariectomized rats. Females were orally administered 100, 200 or 300 mg/kg Z-321 or the vehicle (control). The mean lordosis quotient in the rats given 300 mg/kg Z-321 was lower than that in control group, but that in rats given 100 or 200 mg/kg Z-321 was not lower. Thus, Z-321 suppressed lordosis in estrogen and progesterone-treated ovariectomized rats. Peptide neurotransmitters, especially those containing proline, are thought to be involved in the inhibitory mechanisms for lordosis behavior.

Animals↗

PubMed1989

Brain aromatase activity and behavioral consequences in the male rat treated in utero with 4-hydroxy-androstenedione.

Pregnant female rats were given daily injections of a potent aromatase inhibitor, 4-hydroxy-delta 4-androstenedione (4OHA), throughout the latter half of the pregnancy (days 11 to 22; the day of insemination was designated as Day O) and male fetuses and pups were obtained. Control animals were male offspring of mothers treated with oil vehicle. When measured by the tritium-water method, significant reductions in the aromatase activity were detected in the hypothalamic and preoptic continuum (HPOA) of the male fetuses and pups, over a period from day 16 of the pregnancy until a day after birth. All parturitions in the experimental as well as control animals occurred on day 22 of the pregnancy. Behavioral and anatomical consequences of the prenatal treatment were examined in adulthood. When mounted by stud male rats, the male litters of the 4OHA-treated mother showed lordosis at a significantly higher frequency both in terms of the number of positive test sessions (each consisted of a 20-min period in which the subject showed lordosis at least once) and the lordosis quotient (percent lordosis occurrence per 10 mounts). When placed with receptive female rats, the experimental animals were no less active in mounting or ejaculating than the control. No significant difference existed between the experimental and control animals in the weight of the testes or the accessorial genitalia, or the serum testosterone levels. Partial but significant intervention of behavioral defeminization of the brain was associated with decreased HPOA aromatase activity during the prenatal period.

Androstenedione↗

PubMed1992

Metabolism of dihydrotestosterone to 3 alpha-androstanediol in brain and plasma: effect on behavioural activity in female rats.

Six experiments were carried out to determine whether dihydrotestosterone (5 alpha-androstan-17 beta-ol-3-one; DHT) acts to inhibit oestradiol (OE2)-induced lordosis behaviour after its metabolic conversion to 5 alpha-androstane-3 alpha,17 beta-diol (3 alpha-androstanediol, 3 alpha-Adiol). In experiments 1 and 2, ovariectomized rats were treated with several doses of DHT or 3 alpha-Adiol, injected with OE2 and progesterone, and tested for lordosis responsiveness. Significant inhibition of lordosis occurred after a dose of 3 alpha-Adiol which was approximately threefold less than the effective DHT dose. In experiments 3 and 4, plasma concentrations of DHT and 3 alpha-Adiol were measured after the injection of these steroids to ovariectomized rats at doses shown to be both sufficient or insufficient to inhibit lordosis. Behaviourally effective dosages of DHT and 3 alpha-Adiol produced circulating concentrations of 3 alpha-Adiol greater than those produced by behaviourally ineffective doses of DHT or 3 alpha-Adiol. At 30 min after injection of DHT (experiment 3), 78.8% of plasma androgens were in the form of 3 alpha-Adiol, while after injection of 3 alpha-Adiol, only 7.4% were DHT. When plasma DHT and 3 alpha-Adiol were measured at 3, 6, 9 and 12 h after steroid injection (experiment 4), plasma levels of 3 alpha-Adiol produced by the behaviourally subthreshold dose of DHT were significantly lower than levels produced by behaviourally sufficient dosages of DHT or 3 alpha-Adiol. In experiments 5 and 6, concentrations of DHT and 3 alpha-Adiol were measured in five brain regions 1 and 6 h after injection of behaviourally sufficient doses of these steroids to ovariectomized females. At 1 h after injection, similar levels of DHT and 3 alpha-Adiol were measured in DHT- and 3 alpha-Adiol-injected females, and DHT concentrations in the preoptic area were significantly higher in both groups than in any other brain area. At 6 h, animals injected with DHT had significantly higher levels of DHT in all brain areas combined than did 3 alpha-Adiol- or vehicle-injected animals. Brain concentrations of 3 alpha-Adiol were not different between groups injected with DHT, 3 alpha-Adiol or vehicle at this time. In brain, 34.6% of DHT had been converted to 3 alpha-Adiol after 1 h and 53.0% of 3 alpha-Adiol had been converted to DHT.(ABSTRACT TRUNCATED AT 400 WORDS)

Androstenediol↗

PubMed2003

Ventral correction of postsurgical cervical kyphosis.

OBJECT: Cervical kyphotic deformation may develop after surgery involving either the ventral or dorsal approach. Regardless of the cause, the development of a cervical kyphotic deformity should be avoided, if possible, and corrected if present, when appropriate. The authors describe their experience with a technique for the ventral correction of iatrogenic (postoperative) cervical kyphosis. METHODS: A retrospective review of cases involving correction of postoperative iatrogenic cervical kyphosis via an ventral approach was performed. The authors conducted an ventral approach to kyphosis correction. The procedure required specific head positioning (in extension), convergent distraction pins, and an ventrally placed implant (axially dynamic when appropriate) with multiple points of fixation including at least one point of intermediate fixation. The pre- and postoperative sagittal angle and clinical status were evaluated. During a nearly 14-month period, 12 patients met the inclusion criteria. Ten patients underwent a minimum of 6 months of follow up. They comprised the study population. Most patients presented with mechanical neck pain as part of their symptom profile. The mean magnitude of deformity correction (pre- to postoperative) was 20 degrees of lordosis. The mean postoperative sagittal angle was 6 degrees of lordosis. The mean change in the sagittal angle during the follow-up period was 2.2 degrees of lordosis. CONCLUSIONS: The ventral approach to correction of cervical deformity led to the achievement of lordosis in all but one patient. This posture was effectively maintained during the follow-up period. All patients exhibited improvement postoperatively; three experienced complete resolution of their preoperative symptoms. When symptoms are related to postsurgical kyphosis, deformity correction should be considered. Such a procedure may be performed effectively via an ventral approach in most circumstances.

Adolescent↗

PubMed2004

Anterior correction of cervical kyphotic deformity: effects on myelopathy, neck pain, and sagittal alignment.

OBJECT: Cervical myelopathy may develop as a result of spinal cord compression with or without deformity. The effect of persistent kyphotic deformity on the ability of the cervical cord to recover following decompressive surgery is not known. METHODS: Between 1997 and 2000, a total of 28 patients with progressive myelopathy and kyphotic deformity underwent anterior decompression, deformity correction (0-4 degrees of lordosis), and fusion with anterior plating. Patients received clinical and radiological follow-up care, with independent analysis. Variables assessed included patient characteristics, severity of preoperative myelopathy, neck pain, and cervical sagittal alignment. Twenty-six patients (93%) underwent follow-up review for a minimum of 18 months. Two patients died: one died in the perioperative period and was excluded from further analysis, and in the other only 3 months of follow-up data could be obtained. Local deformity was corrected to neutral or lordosis in 24 cases (89%), and the overall cervical curve was corrected to neutral or lordosis in 20 cases (74%). There was a significant improvement in myelopathy scores in those patients in whom the target (0 to 4 degrees of lordosis) local angle was achieved (p = 0.04). There was a variable change in overall cervical sagittal alignment following local correction. Improvement in myelopathy was unrelated to patient age, previous surgery, or number of segments fused. Improvement in pain score was not related to correction of kyphotic angle. CONCLUSIONS: The correction of sagittal alignment may promote recovery in spinal cord function in patients with kyphotic deformity.

Activities of Daily Living↗

PubMed2001

Spinal deformities in Noonan syndrome: a clinical review of sixty cases.

BACKGROUND: Skeletal abnormalities, including spinal deformities, in Noonan syndrome have been described, but no detailed and systematic study of such spinal deformities has been presented in the literature. METHODS: The cases of sixty patients with Noonan syndrome were reviewed retrospectively, and the general appearance, growth disturbance, and mental status of the patients were documented. Spinal deformities were evaluated radiographically, and the frequency, pattern, and severity of the curves were documented. RESULTS: Spinal deformity was present in eighteen (30%) of the sixty patients. Two patients had congenital spinal deformity. Of the remaining sixteen patients with scoliosis, nine had a single thoracic curve, four had a single thoracolumbar curve, and three had a double major curve. Thoracic lordosis was also present in three of these sixteen patients. No patient had only increased kyphosis or lordosis. The mean age when the spinal deformities were detected was nine years; seven deformities were detected before the age of seven years. Overall, surgery was recommended to eleven of the eighteen patients; it was recommended for the treatment of scoliosis (mean, 68.5 degrees; range, 45 degrees to 125 degrees ) in eight patients and for the treatment of an associated thoracic lordosis (8 degrees, 15 degrees, and 18 degrees ) in three. Seven of the eleven patients underwent spinal arthrodesis. The operation was deferred in one patient because malignant hyperthermia developed during the induction of anesthesia. CONCLUSIONS: Scoliosis with an associated thoracic lordosis occurs more frequently in Noonan syndrome than has been reported previously. Since the deformities tend to develop early and are relatively severe, a clinical and, if necessary, radiographic assessment of the spine with careful follow-up should be performed for early detection and treatment of spinal deformity. Although malignant hyperthermia is rare, all patients with Noonan syndrome should be considered to be at risk for the development of this complication before operative treatment.

Adolescent↗

PubMed1991

[Anatomical restoration of thoracolumbar spine with burst fracture].

A burst fracture was created in the L1 vertebra of six fresh human cadaver spines and reduction was performed using AO fixator intern, reduction fixation (RF) device, and Steffee plate instrumentation systems to determine the reduction force (distraction vs distraction plus lordosis) contributing to the anatomical restoration of thoracolumbar spine. These three pedicular screw devices were applied to the specimens following the use of standard clinical technique for each device. The AO fixator intern and the RF device provided independent control of distraction and lordosis correction. The Steffee device maintained a set distraction and lordosis. The RF device provided pre-set fixed incremental lordosis, while the AO provided variable angular correction. Plain X-rays and CT scans were taken of the specimens before and after creation of the fracture and following application of each device. Results demonstrated that the symmetric lordotic distraction of the disc space and vertebral body provided by the RF device achieved the best possible reduction of the intracanal fragment and sagittal alignment.

Adult↗

PubMed1990

Polysegmental lumbar osteotomies and transpedicled fixation for correction of long-curved kyphotic deformities in ankylosing spondylitis. Report on 177 cases.

Despite conservative therapy in ankylosing spondylitis, kyphotic deformities are common. Mono-segmental lumbar osteotomy had a high complication rate. Therefore, a poly-segmental lordosis osteotomy of the lumbar spine was introduced in four to six segments using trans-pedicled screws and threaded rods in eight to ten segments (isolated correction is possible for each segment). Instead of dangerous short kinking, a poly-segmental lordosis osteotomy results in harmonious lordosis with a correction per segment of about 10 degrees, and complications are decreased. Of 177 patients undergoing the operation, there was a 2.3% mortality rate with cardiopulmonary problems, 2.3% with irreversible complications, and 18.1% with reversible complications, mostly small root lesions, of which 7% were reoperated. The 173 surviving patients had a correction of 43%, and improvement in body height of 9 cm, and improvement of flexion by 57%. Fifty-three patients have been followed for more tha 18 months. the visual axis in all cases was horizontal. No pseudoarthrosis occurred. After correction, the frequent spondylodiscitis healed. Ninety-two percent were pain free compared with 15% before the operation. Loss of correction of body height was 20%, of flexion 4%, and of the lordosis 7%, which was 18% in 37 patients after three years.

Adult↗

PubMed1990

Decreased inhibitory influences from forebrain on proceptivity and receptivity in old female rats.

Female rats of Long-Evans strain were divided into a young group (3 to 4 months of age, mo) and an aged group (over 19 mo). Rats were ovariectomized and implanted subcutaneously with 14%, 20% or 33% estradiol benzoate (E2)-cholesterol mixture-filled Silastic capsules. Proceptivity and receptivity were compared between young rats and aged rats. There was no age difference in the lordosis quotient (LQ) or in the incidence of lordosis, but the incidence of solicitation was lower in aged rats than in young rats. Proceptivity and receptivity were examined again after anterior roof deafferentation (ARD) of the brain. ARD enhanced LQ in young rats and old prolonged vaginal cornification (PVC) rats but not in old anestrous (ANE) rats. ARD also increased the incidence of solicitation in both young and aged rats. However, the extent of enhancement of these two behaviors was smaller in the aged rats than in the young rats. These results demonstrate that there is decreased inhibitory influence from the forebrain on solicitation and lordosis following induction by exogenous estradiol in advancing age and that the disinhibition of lordosis is more prominent in ANE rats than in PVC rats.

Aging↗

PubMed1993

Progesterone facilitates thrust in female hamsters implanted with estradiol at the medial preoptic area.

Progesterone (P) facilitates male-like sexual behavior in female hamsters primed with estrogen. Since estrogen plus P activates lordosis in female hamsters and the site of the hormonal action is at the ventromedial hypothalamus (VMH), it is possible that the same hormones act at the same site to induce male-like sexual behavior. However, VMH lesion abolishes lordosis, but not thrust, in ovariectomized female hamsters treated with estrogen plus P. Therefore, we tried another brain site--the medial preoptic area (mPOA). We implanted cannula, 27 gauge and filled with estradiol at the tip, at the mPOA or the VMH bilaterally in ovariectomized female hamsters. The hamsters received subcutaneous injections of P (0.5 mg in 0.05 ml sesame oil) at noon every fourth day. Behavior tests were conducted the same night of the injection day and the day before. The procedure was repeated five times. During a test night, each experimental female hamster was paired with a male hamster first and then with another estrous female. Recorded behavioral events were duration of lordosis and frequency of thrust. Both mPOA and VMH groups displayed lordosis only on the day of P injection, without any significant group difference. As to the male-like sexual behavior, 9 out of 54 mPOA females displayed thrust at least once but none of 27 VMH females ever did. Furthermore, 7 of the 9 females displayed thrust only on the day of the P injection. We conclude that the mPOA was also the site for the activation of male sex behavior in female hamsters. However, the hormones acting at the mPOA to induce thrusts were estrogen plus P.

Animals↗

PubMed1997

Estrogen induces axonal outgrowth in the nucleus retroambiguus-lumbosacral motoneuronal pathway in the adult female cat.

In 1995, we discovered a new pathway in the cat, which originates from the nucleus retroambiguus (NRA) and terminates in a distinct set of lumbosacral hindlimb, axial, and pelvic floor motoneuronal cell groups [VanderHorst VGJM, Holstege G (1995) Caudal medullary pathways to lumbosacral motoneuronal cell groups in the cat: evidence for direct projections possibly representing the final common pathway for lordosis. J Comp Neurol 359:457-475]. The NRA is a compact group of interneurons located laterally in the caudal medulla oblongata. Its projection to lumbosacral motoneurons is thought to represent the final common pathway for male mounting and for female receptive or lordosis behavior. However, females only display lordosis behavior. However, females only display lordosis behavior when they are in estrus, which suggests that the NRA-lumbosacral pathway is only active during estrus. This raised the question of whether estrogen affects this pathway. The effect of estrogen on the NRA-lumbosacral projection was studied light microscopically, using wheat-germ agglutinin horseradish peroxidase (WGA-HRP) as a tracer. The rubrospinal pathway served as control. The density of labeled NRA fibers in their target hindlimb motoneuronal cell groups appeared abundant in estrous and very weak in nonestrous cats. Such differences were not found in the rubrospinal pathway. For electron microscopical study, the NRA projection to the semi-membranosus motoneuronal cell group was selected. In this cell group, an almost ninefold increase of labeled profiles was found in estrous versus nonestrous cats. Moreover, the semimembranous motoneuronal cell group contained labeled growth cones in estrous, but not in nonestrous, cats. The present study is the first to show that estrogen induces axonal outgrowth of a precisely identified pathway in the adult mammalian central nervous system. The possible mechanisms underlying this outgrowth are discussed.

Animals↗