Sex steroids modulate motor-correlated increases in cerebellar discharge

Sex disparities of human neuromuscular decline in older humans

Females typically live longer than males but, paradoxically, spend a greater number of later years in poorer health. The neuromuscular system is a critical component of the progression to frailty, and motor unit (MU) characteristics differ by sex in healthy young individuals and may adapt to ageing in a sex-specific manner due to divergent hormonal profiles. The purpose of this study was to investigate sex differences in vastus lateralis (VL) MU structure and function in early to late elderly humans. Intramuscular electromyography signals from 50 healthy older adults (M/F: 26/24) were collected from VL during standardized submaximal contractions and decomposed to quantify MU characteristics. Muscle size and neuromuscular performance were also measured. Females had higher MU firing rate (FR) than males (P = 0.025), with no difference in MU structure or neuromuscular junction transmission (NMJ) instability. All MU characteristics increased from low- to mid-level contractions (P < 0.05) without sex × level interactions. Females had smaller cross-sectional area of VL, lower strength and poorer force steadiness (P < 0.05). From early to late elderly, both sexes showed decreased neuromuscular function (P < 0.05) without sex-specific patterns. Higher VL MUFRs at normalized contraction levels previously observed in young are also apparent in old individuals, with no sex-based difference of estimates of MU structure or NMJ transmission instability. From early to late elderly, the deterioration of neuromuscular function and MU characteristics did not differ between sexes, yet function was consistently greater in males. These parallel trajectories underscore the lower initial level for older females and may offer insights into identifying critical intervention periods. KEY POINTS: Females generally exhibit an extended lifespan when compared to males, yet this is accompanied by a poorer healthspan and higher rates of frailty. In healthy young people, motor unit firing rate (MUFR) at normalized contraction intensities is widely reported to be higher in females than in age-matched males. Here we show in 50 people that older females have higher MUFR than older males with little difference in other MU parameters. The trajectory of decline from early to late elderly does not differ between sexes, yet function is consistently lower in females. These findings highlight distinguishable sex disparities in some MU characteristics and neuromuscular function, and suggest early interventions are needed for females to prevent functional deterioration to reduce the ageing health-sex paradox.

Sex Differences in Neuromuscular Aging: The Role of Sex Hormones

Males and females experience different trajectories of neuromuscular function across the lifespan, with females demonstrating accelerated deconditioning in later life. We hypothesize that the menopause is a critical period in the female lifespan, during which the dramatic reduction in sex hormone concentrations negatively impacts synaptic input to the motoneuron pool, as well as motor unit discharge properties.

Monitoring of sprint and change of direction velocity, vertical jump height, and repeated sprint ability in sub-elite female football players throughout their menstrual cycle

AIMS

The aim of this study was to investigate the associations between the early follicular (EF, i.e., menstruation), late follicular (LF), and middle luteal (ML) phases of the menstrual cycle and different factors that may influence football performance.

METHODS

To this end, 11 eumenorrheic sub-elite female football players underwent field tests to assess sprint speed, lower extremity power, repeated sprint ability, velocity on change of direction, and technical skills at each cycle phase.

RESULTS

Performance during the 15-m change of direction ability test, 15-m ball dribbling test, squat jump height, total sprint time [sum of 7 sprints] and decrement score [(mean sprint time/best sprint time × 100) - 100], maximum and mean heart rate, and perceived exertion did not significantly differ among menstrual cycle phases. Conversely, the linear sprint velocity over 10, 20, 30-m distances was decreased in EF vs LF (10-, 20- and 30-m) and in ML vs LF (10- and 20-m) (p < 0.05). The 40-m sprint velocity did not change in the different menstrual cycle phases.

CONCLUSION

Overall, our study suggests that sex hormone fluctuations during the menstrual cycle are not associated with vertical jump, velocity on change of direction, and repeated sprint ability, but may influence linear sprint velocity over short distances (10, 20, and 30 m).

Menstrual Cycle Associated Alteration of Vastus Lateralis Motor Unit Function

BACKGROUND

Estrogen and progesterone are the primary female sex hormones and have net excitatory and inhibitory effects, respectively, on neuronal function. Fluctuating concentrations across the menstrual cycle has led to several lines of research in relation to neuromuscular function and performance; however evidence from animal and cell culture models has yet to be demonstrated in human motor units coupled with quantification of circulating hormones. Intramuscular electromyography was used to record motor unit potentials and corresponding motor unit potential trains from the vastus lateralis of nine eumenorrheic females during the early follicular, ovulation and mid luteal phases of the menstrual cycle, alongside assessments of neuromuscular performance. Multi-level regression models were applied to explore effects of time and of contraction level. Statistical significance was accepted as p < 0.05.

RESULTS

Knee extensor maximum voluntary contraction, jump power, force steadiness, and balance did not differ across the menstrual phases (all p > 0.4). Firing rate of low threshold motor units (10% maximum voluntary contraction) was lower during the ovulation and mid luteal phases (β = - 0.82 Hz, p < 0.001), with no difference in motor unit potentials analysed from 25% maximum voluntary contraction contractions. Motor unit potentials were more complex during ovulation and mid luteal phase (p < 0.03), with no change in neuromuscular junction transmission instability (p > 0.3).

CONCLUSIONS

Assessments of neuromuscular performance did not differ across the menstrual cycle. The suppression of low threshold motor unit firing rate during periods of increased progesterone may suggest a potential inhibitory effect and an alteration of recruitment strategy; however this had no discernible effect on performance. These findings highlight contraction level-dependent modulation of vastus lateralis motor unit function over the eumenorrheic cycle, occurring independently of measures of performance.

Sex-Specific Reliability of Lower-Limb Corticospinal Excitability and Silent Periods

ABSTRACT

Pagan, JI, Harmon, KK, Girts, RM, MacLennan, RJ, Beausejour, JP, Hernandez-Sarabia, JA, Coker, NA, Carr, JC, Ye, X, DeFreitas, JM, and Stock, MS. Sex-specific reliability of lower-limb corticospinal excitability and silent periods. J Strength Cond Res 37(9): 1882-1887, 2023-Transcranial magnetic stimulation (TMS) is a research tool that has potential to provide new insights into strength training-induced adaptations. However, using TMS to study the lower limbs is challenging, and sex-specific reliability has yet to be reported. We examined the reliability of corticospinal excitability and silent periods for the rectus femoris, vastus lateralis, and biceps femoris in both sexes. Thirteen males and 14 females reported to the laboratory twice. During both trials, a double cone coil was used to deliver 20 pulses to the rectus femoris hotspot with a stimulator output of 130% of active motor threshold. Motor-evoked potential peak-to-peak amplitude, which reflects corticospinal excitability, and silent period duration were quantified. Our results offer 4 novel findings. First, corticospinal excitability and silent period demonstrated higher reliability for the females. Second, regardless of sex and muscle, the silent period was more reliable than corticospinal excitability. Third, reliability was highest for our target muscle (rectus femoris), with lower reliability for the vastus lateralis and biceps femoris, suggesting that these methods cannot be used to study coactivation. Fourth, active motor threshold showed less variability than corticospinal excitability and silent period but increased at trial 2 in females. Many of the intraclass correlation coefficients were excellent (≥0.90), although we attribute this finding to variability between subjects. Reliability of lower-limb TMS measures may be sex, muscle, and variable dependent. Our findings suggest that both males and females should be included in lower-limb TMS research, although combining data between sexes should be approached cautiously.

Effects of the menstrual cycle phase on anterior cruciate ligament neuromuscular and biomechanical injury risk surrogates in eumenorrheic and naturally menstruating women: A systematic review

BACKGROUND

Eumenorrheic women experience cyclic variations in sex hormones attributed to the menstrual cycle (MC) which can impact anterior cruciate ligament (ACL) properties, knee laxity, and neuromuscular function. This systematic review aimed to examine the effects of the MC on ACL neuromuscular and biomechanical injury risk surrogates during dynamic tasks, to establish whether a particular MC phase predisposes women to greater ACL injury risk.

METHODS

PubMed, Medline, SPORTDiscus, and Web of Science were searched (May-July 2021) for studies that investigated the effects of the MC on ACL neuromuscular and biomechanical injury risk surrogates. Inclusion criteria were: 1) injury-free women (18-40 years); 2) verified MC phases via biochemical analysis and/or ovulation kits; 3) examined neuromuscular and/or biomechanical injury risk surrogates during dynamic tasks; 4) compared ≥1 outcome measure across ≥2 defined MC phases.

RESULTS

Seven of 418 articles were included. Four studies reported no significant differences in ACL injury risk surrogates between MC phases. Two studies showed evidence the mid-luteal phase may predispose women to greater risk of non-contact ACL injury. Three studies reported knee laxity fluctuated across the MC; two of which demonstrated MC attributed changes in knee laxity were associated with changes in knee joint loading (KJL). Study quality (Modified Downs and Black Checklist score: 7-9) and quality of evidence were low to very low (Grading of Recommendations Assessment Development and Evaluation: very low).

CONCLUSION

It is inconclusive whether a particular MC phase predisposes women to greater non-contact ACL injury risk based on neuromuscular and biomechanical surrogates. Practitioners should be cautious manipulating their physical preparation, injury mitigation, and screening practises based on current evidence. Although variable (i.e., magnitude and direction), MC attributed changes in knee laxity were associated with changes in potentially hazardous KJLs. Monitoring knee laxity could therefore be a viable strategy to infer possible ACL injury risk.

Muscle Performance during the Menstrual Cycle Correlates with Psychological Well-Being, but Not Fluctuations in Sex Hormones

PURPOSE

We aimed to study variations in strength and power performance during the menstrual cycle (MC) in eumenorrheic young women and during the pill cycle in oral contraceptives (OC) users.

METHODS

Forty healthy, normal-weight women between 18 and 35 yr (n = 30 eumenorrheic women; n = 10 OC users) completed this prospective cohort study. Seven to nine times during the MC/pill-cycle, the participants completed a physical performance test series, a questionnaire about psychological well-being, blood sampling, and determination of body mass. The physical tests included isometric handgrip strength, elbow flexor strength, countermovement jump (CMJ) height, and a 10-s Wingate bike test.

RESULTS

No direct correlation was observed between the variations in sex hormones and physical performance parameters. However, positive correlations were observed between physical performance outcomes and self-reported motivation, perception of own physical performance level, pleasure level, and arousal level. CMJ was 6% lower in the late luteal phase (LL) compared with the midluteal phase (ML) (P = 0.04). Wingate peak power was 3% lower in early follicular (EF) compared with the ML (P = 0.04). Furthermore, Wingate average power was 2%-5% lower in LL compared with all other MC phases. In line with these observations, physical pain was higher in EF and LL, and the pleasure level was lower in EF compared with the other MC phases. In OC users, we observed no variation in performance and self-reported parameters between the placebo-pill phase and the OC-pill phase.

CONCLUSIONS

Impairments in CMJ and Wingate performance were observed at the end and start of MC compared with other MC phases, which were associated with lower psychological well-being, but not the sex hormone fluctuations.

De Novo Synthesized Estradiol: A Role in Modulating the Cerebellar Function

The estrogen estradiol is a potent neuroactive steroid that may regulate brain structure and function. Although the effects of estradiol have been historically associated with gonadal secretion, the discovery that this steroid may be synthesized within the brain has expanded this traditional concept. Indeed, it is accepted that de novo synthesized estradiol in the nervous system (nE2) may modulate several aspects of neuronal physiology, including synaptic transmission and plasticity, thereby influencing a variety of behaviors. These modulations may be on a time scale of minutes via non-classical and often membrane-initiated mechanisms or hours and days by classical actions on gene transcription. Besides the high level, recent investigations in the cerebellum indicate that even a low aromatase expression can be related to the fast nE2 effect on brain functioning. These pieces of evidence point to the importance of an on-demand and localized nE2 synthesis to rapidly contribute to regulating the synaptic transmission. This review is geared at exploring a new scenario for the impact of estradiol on brain processes as it emerges from the nE2 action on cerebellar neurotransmission and cerebellum-dependent learning.

The Influence of the Menstrual Cycle on Muscle Strength and Power Performance

This study aimed to investigate the fluctuations of muscle performance in the Smith machine half-squat exercise during three different phases of the menstrual cycle. Thirteen resistance-trained and eumenorrheic women volunteered to participate in the study (58.6 ± 7.8 kg, 31.1 ± 5.5 years). In a pre-experimental test, the half-squat one-repetition maximum (1RM) was measured. Body mass, tympanic temperature and urine concentration of the luteinizing hormone were estimated daily for ~30 days to determine the early follicular phase (EFP), the late follicular phase (LFP), and the mid-luteal phase (MLP) of the menstrual cycle. On the second day of each phase, performance of the Smith machine half-squats was assessed using 20, 40, 60 and 80% of one repetition maximum (1RM). In each load, force, velocity, and power output were measured during the concentric phase of the exercise by means of a rotatory encoder. The data were analyzed using one-way repeated measures ANOVA coupled with magnitude-based inferences. Overall, force, velocity and power output were very similar in all menstrual cycle phases with unclear differences in most of the pairwise comparisons and effect sizes >0.2. The results of this investigation suggest that eumenorrheic females have similar muscle strength and power performance in the Smith machine half-squat exercise during the EFP, LFP, and MLP phases of the menstrual cycle.

Menstrual cycle-associated modulations in neuromuscular function and fatigability of the knee extensors in eumenorrheic women

Sex hormone concentrations of eumenorrheic women typically fluctuate across the menstrual cycle and can affect neural function such that estrogen has neuroexcitatory effects, and progesterone induces inhibition. However, the effects of these changes on corticospinal and intracortical circuitry and the motor performance of the knee extensors are unknown. The present two-part investigation aimed to 1) determine the measurement error of an exercise task, transcranial magnetic stimulation (TMS)-, and motor nerve stimulation (MNS)-derived responses in women ingesting a monophasic oral contraceptive pill (hormonally-constant) and 2) investigate whether these measures were modulated by menstrual cycle phase (MCP), by examining them before and after an intermittent isometric fatiguing task (60% of maximal voluntary contraction, MVC) with the knee extensors until task failure in eumenorrheic women on days 2, 14, and 21 of the menstrual cycle. The repeatability of neuromuscular measures at baseline and fatigability ranged between moderate and excellent in women taking the oral contraceptive pill. MVC was not affected by MCP ( P = 0.790). Voluntary activation (MNS and TMS) peaked on day 14 ( P = 0.007 and 0.008, respectively). Whereas corticospinal excitability was unchanged, short-interval intracortical inhibition was greatest on day 21 compared with days 14 and 2 ( P < 0.001). Additionally, time to task failure was longer on day 21 than on both days 14 and 2 (24 and 36%, respectively, P = 0.030). The observed changes were larger than the associated measurement errors. These data demonstrate that neuromuscular function and fatigability of the knee extensors vary across the menstrual cycle and may influence exercise performance involving locomotor muscles.

NEW & NOTEWORTHY The present two-part study first demonstrated the repeatability of transcranial magnetic stimulation- and electrical motor nerve stimulation-evoked variables in a hormonally constant female population. Subsequently, it was demonstrated that the eumenorrheic menstrual cycle affects neuromuscular function. Changing concentrations of neuroactive hormones corresponded to greater voluntary activation on day 14, greater intracortical inhibition on day 21, and lowest fatigability on day 21. These alterations of knee extensor neuromuscular function have implications for locomotor activities.

Local Estrogen Synthesis Regulates Parallel Fiber-Purkinje Cell Neurotransmission Within the Cerebellar Cortex

Estrogens affect cerebellar activity and cerebellum-based behaviors. Within the adult rodent cerebellum, the best-characterized action of estradiol is to enhance glutamatergic signaling. However, the mechanisms by which estradiol promotes glutamatergic neurotransmission remain unknown. Within the mouse cerebellum, we found that estrogen receptor activation of metabotropic glutamate receptor type 1a strongly enhances neurotransmission at the parallel fiber-Purkinje cell synapse. The blockade of local estrogen synthesis within the cerebellum results in a diminution of glutamatergic neurotransmission. Correspondingly, decreased estrogen availability via gonadectomy or blockade of aromatase activity negatively affects locomotor performance. These data indicate that locally derived, and not just gonad-derived, estrogens affect cerebellar physiology and function. In addition, estrogens were found to facilitate parallel fiber-Purkinje cell synaptic transmission in both sexes. As such, the actions of estradiol to support cerebellar neurotransmission and cerebellum-based behaviors might be fundamental to understanding the normal processing of activity within the cerebellar cortex.

Endocrine disorders and the cerebellum: from neurodevelopmental injury to late-onset ataxia

Hormonal disorders are a source of cerebellar ataxia in both children and adults. Normal development of the cerebellum is critically dependent on thyroid hormone, which crosses both the blood-brain barrier and the blood-cerebrospinal fluid barrier thanks to specific transporters, including monocarboxylate transporter 8 and the organic anion-transporting polypeptide 1C1. In particular, growth and dendritic arborization of Purkinje neurons, synaptogenesis, and myelination are dependent on thyroid hormone. Disturbances of thyroid hormone may also impact on cerebellar ataxias of other origin, decompensating or aggravating the pre-existing ataxia manifesting with motor ataxia, oculomotor ataxia, and/or Schmahmann syndrome. Parathyroid disorders are associated with a genuine cerebellar syndrome, but symptoms may be subtle. The main conditions combining diabetes and cerebellar ataxia are Friedreich ataxia, ataxia associated with anti-GAD antibodies, autoimmune polyglandular syndromes, aceruloplasminemia, and cerebellar ataxia associated with hypogonadism (especially Holmes ataxia/Boucher-Neuhäuser syndrome). The general workup of cerebellar disorders should include the evaluation of hormonal status, including thyroid-stimulating hormone and free thyroxine levels, and hormonal replacement should be considered depending on the laboratory results. Cerebellar deficits may be reversible in some cases.

A Critical Period in Purkinje Cell Development Is Mediated by Local Estradiol Synthesis, Disrupted by Inflammation, and Has Enduring Consequences Only for Males

Identifying and understanding critical periods in brain development is essential to decoding the long-term impact of widespread, poorly defined, and frequently occurring insults such as inflammation. Using the laboratory rat Rattus norvegicus, we have discovered a narrowly constrained critical period in Purkinje neuron development subject to dysregulation by inflammation. The onset and offset of heightened vulnerability are attributed to a tightly orchestrated gene expression profile present only during the second postnatal week and not the first or third weeks. Genes expressed during this time code for enzymes and receptors which are critical not only for prostaglandin production and activity but also for estradiol production via the aromatase enzyme and estradiol action via the α isoform of the estrogen receptor. The two synthetic pathways are connected by prostaglandin E2 (PGE2) activation of the aromatase enzyme, as we reported previously (Dean et al., 2012b) and confirm here. Dysregulation of the PGE2-estradiol pathway during the second week by treatment with PGE2 or lipopolysaccharides produces enduring consequences as a result of reduced growth of Purkinje dendritic trees and impaired juvenile social play behavior, but only in males. The deleterious consequences of inflammation locally in the cerebellum are prevented by peripheral treatment with the cyclooxygenase inhibitor nimesulide or the aromatase inhibitor formestane. These findings highlight a novel regulatory pathway that creates a critical period in brain development vulnerable to dysregulation by inflammation.

SIGNIFICANCE STATEMENT

The cerebellum is increasingly appreciated for its role in social, emotional, and cognitive behaviors. It is consistently and severely affected in neuropsychiatric disorders originating during development, such as autism spectrum disorder and schizophrenia. We have identified a critical period in rat development during the second week of life that is dysregulated by inflammatory insults. An intrinsic program of gene expression determines the critical period. The enduring consequences of inflammation during the second postnatal week are stunted dendrites of the cerebellum's principal neurons, Purkinje cells, and impairments in later social behavior. These changes are not evident if inflammation occurs during the first or third week, highlighting the importance of fine-grained analyses of developmental processes and the factors that influence them.

Maximal force and tremor changes across the menstrual cycle

PURPOSE

Sex hormones have profound effects on the nervous system in vitro and in vivo. The present study examines the effect of the menstrual cycle on maximal isometric force (MVC) and tremor during an endurance task.

METHODS

Nine eumenorrheic females participated in five study visits across their menstrual cycle. In each menstrual phase, an MVC and an endurance task to failure were performed. Tremor across the endurance task was quantified as the coefficient of variation in force and was assessed in absolute time and relative percent time to task failure.

RESULTS

MVC decreases 23% from ovulation to the mid luteal phase of the menstrual cycle. In absolute time, the mid luteal phase has the highest initial tremor, though the early follicular phase has substantially higher tremor than other phases after 150 s of task performance. In relative time, the mid luteal phase has the highest level of tremor throughout the endurance task.

CONCLUSIONS

Both MVC and tremor during an endurance task are modified by the menstrual cycle. Performance of tasks and sports which require high force and steadiness to exhaustion may be decreased in the mid luteal phase compared to other menstrual phases.

Menstrual cycle mediates vastus medialis and vastus medialis oblique muscle activity

PURPOSE

Sports medicine professionals commonly describe two functionally different units of the vastus medialis (VM), the VM, and the vastus medialis oblique (VMO), but the anatomical support is equivocal. The functional difference of the VMO is principle to rehabilitation programs designed to alleviate anterior knee pain, a pathology that is known to have a greater occurrence in women. The purpose of this study was to determine whether the motor units of the VM and VMO are differentially recruited and if this recruitment pattern has an effect of sex or menstrual cycle phase.

METHODS

Single motor unit recordings from the VM and VMO were obtained for men and women during an isometric ramp knee extension. Eleven men were tested once. Seven women were tested during five different phases of the menstrual cycle, determined by basal body temperature mapping. The recruitment threshold and the initial firing rate at recruitment were determined from 510 motor unit recordings.

RESULTS

The initial firing rate was lower in the VMO than that in the VM in women (P < 0.001) but not in men. There was no difference in recruitment thresholds for the VM and VMO in either sex or across the menstrual cycle. There was a main effect of menstrual phase on initial firing rate, showing increases from the early follicular to late luteal phase (P = 0.003). The initial firing rate in the VMO was lower than that in the VM during ovulatory (P = 0.009) and midluteal (P = 0.009) phases.

CONCLUSION

The relative control of the VM and VMO changes across the menstrual cycle. This could influence patellar pathologies that have a higher incidence in women.

Depo-provera effects on Wistar rat performance in the Y-maze

Medroxyprogesterone acetate is the most commonly used progestin component of hormone therapy. The goal of the present study was to determine whether Medroxyprogesterone affects rat behavior using a Y-maze test. Twenty-four female Wistar rats were randomly selected into three groups; control group, a low dose (13 mg/ml MPA) group and a high dose (33 mg/1 ml MPA) group. Doses of Medroxyprogesterone were delivered by intramuscular injection for a period of 3 weeks. Medroxyprogesterone administration resulted in a decrease in memory and locomotion activity of rats (p < 0.05). Despite Medroxyprogesterone being effective in modulating hormonal interaction to prevent conception in actively reproducing females, cognitive impairment could be one of its adverse effects.

The cerebellum as a target for estrogen action

This review focuses on the effects of estrogens upon the cerebellum, a brain region long ignored as a site of estrogen action. Highlighted are the diverse effects of estradiol within the cerebellum, emphasizing the importance of estradiol signaling in cerebellar development, modulation of synaptic neurotransmission in the adult, and the potential influence of estrogens on various health and disease states. We also provide new data, consistent with previous studies, in which locally synthesized estradiol modulates cerebellar glutamatergic neurotransmission, providing one underlying mechanism by which the actions of estradiol can affect this brain region.

The effects of medroxy progesterone acetate on the pro-inflammatory cytokines, TNF-alpha and IL-1beta in the early phase of the spinal cord injury

OBJECTIVES

Spinal cord injuries (SCIs) have high morbidity and mortality rates and currently the definitive treatment of complete SCIs are still not possible. We investigated the effects of the medroxy progesterone acetate on the pro-inflammatory cytokines, TNF-alpha and IL-1beta in the early phase of the SCI.

METHODS

Forty-eight Wistar albino male rats were divided equally into four groups each consisting of 12 rats. All animals underwent T10-T12 laminectomy. We administered placebo, and 8 mg/kg medroxy progesterone acetate (MPA) intra-peritoneally into control and progesterone group at 30 minutes after the clip-compression trauma in spinal cord. We performed only T10-T12 laminectomy and clip-compression trauma in laminectomy and trauma group, respectively. Half of the rats from each group were killed at 1 hour and the other half were killed at 6 hours after the trauma. Spinal cord segments were then removed and stored at -80 °C in phosphate buffer. TNF-alpha and IL-1beta levels were determined using ELISA kit.

RESULTS

We have found that there was an increase only in the TNF-alpha level at 6 hours after the trauma comparing to control group. MPA appeared to lower the TNF-alpha level significantly in the trauma group.

DISCUSSION

This experimentally proven anti-inflammatory effect of MPA via acting upon TNF-alpha may offer new therapeutic options in human subjects with SCIs.

Classical androgen receptors in non-classical sites in the brain

Androgen receptors are expressed in many different neuronal populations in the central nervous system where they often act as transcription factors in the cell nucleus. However, recent studies have detected androgen receptor immunoreactivity in neuronal and glial processes of the adult rat neocortex, hippocampal formation, and amygdala as well as in the telencephalon of eastern fence and green anole lizards. This review discusses previously published findings on extranuclear androgen receptors, as well as new experimental results that begin to establish a possible functional role for androgen receptors in axons within cortical regions. Electron microscopic studies have revealed that androgen receptor immunoreactive processes in the rat brain correspond to axons, dendrites and glial processes. New results show that lesions of the dorsal CA1 region by local administration of ibotenic acid reduce the density of androgen receptor immunoreactive axons in the cerebral cortex and the amygdala, suggesting that these axons may originate in the hippocampus. Androgen receptor immunoreactivity in axons is also decreased by the intracerebroventricular administration of colchicine, suggesting that androgen receptor protein is transported from the perikaryon to the axons by fast axonal transport. Androgen receptors in axons located in the cerebral cortex and amygdala and originating in the hippocampus may play an important role in the rapid behavioral effects of androgens.

Region-, age-, and sex-specific effects of fetal diazepam exposure on the postnatal development of neurosteroids

Fetal exposure to diazepam (DZ), a positive modulator of GABA(A) receptors and an agonist at mitochondrial benzodiazine receptors, induces long-term neural and behavioral effects. This study evaluated whether the early manipulation influenced the normal development of brain levels of neurosteroids or altered steroid action at GABA(A) receptors. Pregnant dams were injected over gestation days 14 through 20 with DZ (2.5 mg/kg) or the vehicle. Male and female offspring were analyzed at five postnatal ages. The levels of progesterone (P), dihydroprogesterone (DHP), 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha,5alpha-THP), testosterone (T), dihydrotestosterone, and 5alpha-androstan-3alpha,17beta diol were measured in the cerebral cortex and diencephalon. The results indicated that development of brain steroid levels and the impact of fetal DZ exposure were region- and sex-specific. Age-related changes in brain steroids did not mirror associated changes in circulating P and T. Age regulated the levels of all 3 progestins in the cerebral cortex, and fetal DZ exposure interacted with the development of P and DHP. The development of 3alpha,5alpha-THP in the cortex was markedly influenced by sex, with levels in males decreasing over postnatal development whereas they increased over postpubertal development in females. An adolescent surge in T levels was observed in male cortex and fetal DZ exposure prevented that surge. Steroid levels in the diencephalon were altered by age mainly in females, and DZ exposure had little effect in this region. The data support region-specific regulation of brain steroid synthesis. Only in the cerebral cortex are relevant mechanisms readily modifiable by fetal DZ exposure. However, neither sex nor fetal DZ exposure altered the response of GABA(A) receptors in adult cortex to neurosteroid.

Effects of 17β-estradiol on the spontaneous activity of substantia nigra neurons: Evidence for a non-genomic mechanism

Clinical and experimental evidence suggests that female sex hormones (estradiol and progesterone) affect structures in the central nervous system that are involved in the control of movement. Using conventional electrophysiological techniques to record extracellular action potentials in the substantia nigra of urethane-anesthetized rats, it was found that microiontophoretic applications of 17beta-estradiol were able to modify the spontaneous activity of nigral neurons. 17beta-estradiol produced significant changes in the firing frequency (excitation and inhibition) and increased the rhythmicity of the majority of cells studied. These changes appear to be influenced by the sex and the hormonal status of the animal. Effects are of short latency and are not blocked by the administration of tamoxifen. We conclude that estradiol produces changes in the firing rate and discharge pattern of nigral cells in the urethane-anesthetized rat via a non-genomic mechanism.

Glial expression of estrogen and androgen receptors after rat brain injury

Estrogens and androgens can protect neurons from death caused by injury to the central nervous system. Astrocytes and microglia are major players in events triggered by neural lesions. To determine whether glia are direct targets of estrogens or androgens after neural insults, steroid receptor expression in glial cells was assessed in two different lesion models. An excitotoxic injury to the hippocampus or a stab wound to the parietal cortex and hippocampus was performed in male rats, and the resultant expression of steroid receptors in glial cells was assessed using double-label immunohistochemistry. Both lesions induced the expression of estrogen receptors (ERs) and androgen receptors (ARs) in glial cells. ERalpha was expressed in astrocytes immunoreactive (ERalpha-ir) for glial fibrillary acidic protein or vimentin. AR immunoreactivity colocalized with microglial markers, such as Griffonia simplicifolia lectin-1 or OX-6. The time course of ER and AR expression in glia was studied in the stab wound model. ERalpha-ir astrocytes and AR-ir microglia were observed 3 days after lesion. The number of ERalpha-ir and AR-ir glial cells reached a maximum 7 days after lesion and returned to low levels by 28 days postinjury. The studies of ERbeta expression in glia were inconclusive; different results were obtained with different antibodies. In sum, these results suggest that reactive astrocytes and reactive microglia are a direct target for estrogens and androgens, respectively.

Rapid anxiolytic activity of progesterone and pregnanolone in male rats

The effect of different doses of progesterone (1.0, 3.0, 10.0, 30.0, and 100.0 mg/kg) and pregnanolone (1.0, 3.0, 10.0, and 30.0 mg/kg) upon burying defensive and elevated plus-maze (EPM) tests was investigated in adult male rats and compared with the effects of diazepam (0.25. 0.50, 1.0, and 2.0 mg/kg). All drugs were suspended in a 0.2% methylcellulose solution and administered intraperitoneally 30 min prior to testing. Progesterone and pregnanolone were found to produce anxiolytic-like effects similar to those of diazepam. Thus, at certain doses, both drugs significantly increased the latency for burying and decreased the cumulative burying behavior, without modifying the number of shocks, and increased the time spent in the open arms of the maze, without affecting the spontaneous locomotor activity. These data clearly demonstrate that the defensive burying paradigm is useful to detect the anxiolytic-like properties of pregnanolone. An important finding was that progesterone produces significant behavioral effects 30 min after its administration. This finding suggests a rapid bioconversion of progesterone to its active ring-A reduced metabolites; however, the possibility remains that rapid behavioral effects of progesterone are due to a direct interaction with specific steroid receptors located on the plasma membrane, independently from the gamma-aminobutyric acid(A) (GABA(A)) receptor complex modulation.

Endogenous levels of 5 alpha-reduced progestins and androgens in fetal vs. adult rat brains

5 Alpha-reduced metabolites of certain steroids have been shown to have important functions in adult brains and may play a role in brain development. To assess which 5 alpha-reduced steroid metabolites may have an impact during development, endogenous levels of 5 alpha-reduced androgens and progestins and their parent hormones were measured in male and female fetal brains over the last 5 days of gestation. These levels were compared to levels measured in adult male and female brains (evaluated at different stages of the estrous cycle). Neither the brain levels of parent hormones nor of their 5 alpha-reduced metabolites varied as a function of fetal sex or of gestational age. Therefore, the data from the two sexes were combined. In fetal brains, the levels of the progesterone reduced metabolites were 20-fold higher than levels of progesterone itself whereas levels of testosterone reduced metabolites were 10-fold lower than testosterone levels. In contrast to fetal brain, conversion of progesterone to reduced metabolites was much lower in adult brain, but the level of 5 alpha-reduced androgens was 3-10-fold higher than the level of testosterone in all adult tissue, indicating more conversion of androgen to 5 alpha-reduced metabolites in adult than in fetal brains. These results imply that the reduction of progesterone to reduced metabolites may play a critical role in brain development.

Membrane receptors for steroid hormones: a case for specific cell surface binding sites for vitamin D metabolites and estrogens

Steroid hormones, including vitamin D metabolites and estrogens, activate target cells through specific receptors that discriminate among ligands based upon recognition of distinct structural features. For both classes of ligands, cell surface and nuclear receptors co-exist in many target cells. Upon ligand binding, these receptors generate both rapid and long lasting responses. While the structure of the nuclear receptors and their function as transcriptional activators of specific target genes is generally understood, the identity of the membrane receptors remains elusive. Using pharmacological, functional and biochemical approaches, new insights are being gained into nature of the cell surface receptors for both vitamin D metabolites and estrogens.

Estrous hormones enhance coupled, rhythmic olivary discharge in correlation with facilitated limb stepping

Synchronized oscillatory behaviour of neurons within the dorsal accessory olive of the rat were monitored across spontaneous changes in rapid, co-ordinated limb movements associated with the estrous (hormone) and circadian cycles as well as following local administration of estradiol. Facilitation of rapid alterations in limb movement is observed following increases in circulating estradiol and progesterone on the night of behavioural estrus, as assessed by the ability of a rat to maintain a consistent position on a treadmill in response to variable changes in acceleration. Synchronized olivary activity was determined using chronically implanted bundles of microwires (50 microns diameter) to record from as many as 23 individual olivary neurons simultaneously across several four to five day estrous cycles, and in some cases after injection of the estrous hormones, estradiol and/or progesterone, either by systemic or local administration. Rats were tested during non-movement, constant speed locomotion or using a variable acceleration paradigm. Olivary oscillations were most commonly observed during treadmill locomotion with variable changes in acceleration. Local administration of estradiol, in combination with systemic progesterone administration, enhanced rhythmic olivary oscillations during this paradigm. At this time, at least a six-fold increase in the size of the coupled cluster of rhythmically discharging olivary neurons was observed compared with values obtained on diestrus, a low hormone state. Similar facilitating effects on olivary oscillations were observed on estrus, or following systemic injection of both estrous hormones. Administration of either steroid alone was not as effective. During the dark phase of the light:dark cycle, the oscillatory behaviour of these neurons was enhanced more than five-fold than during the light phase, and coupling diameter was maximal on the night of behavioural estrus. The synchronized oscillatory discharge of neurons within the olive is a putative timing mechanism which may underlie hormone-associated facilitation of rapid limb movements. The results from the present study provide evidence that both hormonal and circadian factors can enhance olivary rhythmicity in association with behavioural rhythmicity.

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.

Developmental changes in motor function in girls with Turner syndrome

The Turner syndrome phenotype is characterized by a particular neurocognitive profile of normal verbal skills, impaired visuospatial and/or visuoperceptual abilities, and difficulty with motor function. We investigated motor function in non-estrogen-treated girls (ages 7-9 and 10-12 years) with Turner syndrome and age-matched female controls. Our goal was to delineate the differences in motor performance between girls with Turner syndrome (n = 78) and control girls (n = 145). Cognitive and motor tasks were administered, as well as nonspatial, repetitive motor tasks, and spatially mediated motor tasks. Questionnaires were also administered. Turner subjects performed less well than the controls on the motor tasks with the greatest spatial demands, particularly in the older age group (age 10-12.9 years). The older control group, unlike the older Turner syndrome group, had significantly increased speed on most of the motor tasks, suggesting a Turner syndrome-associated deficiency in motoric development. The superior performance of the dominant (right) versus the nondominant (left) hand was similar for the Turner syndrome and control groups. In general, the girls with Turner syndrome had evidence of a decreased sense of athletic ability and physical self-image. A likely explanation for motoric deficiency in the older Turner syndrome group relates to their gonadal dysgenesis and estrogen deficiency. In addition to the obvious physical benefits of estrogen replacement, estrogen treatment may have a positive impact on motor function; this will be the subject of future investigations.

The estrous cycle and the olivo-cerebellar circuit. I. Contrast enhancement of sensorimotor-correlated cerebellar discharge

Neuromodulation of Purkinje (Pnj) cell responses by monoamines and estrous hormones is well characterized in the cerebellum at the cellular level, but not at the level of neuronal circuits in the awake behaving animal. In the present study, simultaneous recordings of up to 16 single neurons from within the olivo-cerebellar circuit were obtained through chronically implanted microwire electrode bundles: arrays of Pnj cell like neurons (Pnj cln) in the paravermal cerebellum and neurons within the afferent source of its climbing fiber input, the rostral dorsal accessory olive (rDAO), were recorded simultaneously across 3-20 consecutive estrous cycles during constant or variable speed treadmill locomotion performance tasks. Over 90% of Pnj cln recorded during treadmill locomotion exhibited significant increases (80%) or decreases (10%) in activity correlated with the stance phase of locomotion. In contrast, cells from the rDAO increased activity during speed changes or when the rat failed to maintain the treadmill speed (position slip). On the night of behavioral estrus, which is triggered by elevations in circulating levels of 17 beta-estradiol and progesterone, the magnitude of both increases and decreases in stance-correlated Pnj cln activity increased by 85-115%. These results are consistent with our previous findings that 17 beta-estradiol and progesterone enhance excitatory and inhibitory responses of single Pnj cells to locally applied glutamate and GABA, respectively. This dual enhancement of both excitatory and inhibitory effects, apparently paradoxical at the cellular level, produced a marked heightening of the contrast of the neural population "signal" at the neuronal ensemble level. Furthermore, the stance-correlated discharge of Pnj cln during estrus preceded that during diestrus by approximately 120 ms. Frame-by-frame video analysis also suggested that the swing phase of the step cycle was shortened on estrus compared with diestrus (low hormone state). In addition, rDAO discharge correlated with speed change or position slip was also significantly increased (P < 0.05) on the night of behavioral estrus versus diestrus. Thus, estrus was associated with changes in both the amplitude and the timing of Pnj cln and rDAO discharge correlated with specific behavioral events. These estrous-associated changes in Pnj cell activity were well correlated (r = 0.84) with faster responses to random changes in treadmill speed, a motor performance task. Together, these findings suggest that the increases in the contrast of stance-correlated Phj cln discharge observed following peak circulating levels of sex steroid hormones are associated with improved motor performance on a randomly moving treadmill.

The effects of aging on cerebellar beta-adrenergic receptor activation and motor learning in female F344 rats

Female Fischer 344 (F344) rats were tested for age-related differences in both cerebellar beta-adrenergic receptor activation and motor learning. Three and 20 month old rats were tested on a motor learning paradigm that required the rats to adjust their gait to navigate a runway of unevenly spaced pegs. Rates of acquisition were compared between age groups. After behavioral testing, cerebellar beta-adrenergic receptor function was assessed using extracellular recordings of Purkinje cells during iontophoresis of GABA and isoproterenol (ISO). Aged female rats showed deficits in motor learning and in beta-adrenergic receptor activation. In young rats, ISO modulated GABAergic inhibition of Purkinje cell firing in more cells compared with aged rats. Thus, aging produces deficits in both motor learning and in beta-adrenergic receptor activation in aged female F344 rats.

Hormonal regulation of CREB phosphorylation in the anteroventral periventricular nucleus

The anteroventral periventricular nucleus (AVPV) is a nodal point in neural circuits regulating secretion of gonadotropin and contains sexually dimorphic populations of hormonally regulated dopamine-, dynorphin-, and enkephalin-containing neurons. Because the tyrosine hydroxylase (TH), prodynorphin (PDYN), and proenkephalin (PENK) genes contain cAMP response elements that control their expression in their promoters, we used histochemical methods to determine whether ovarian steroids alter expression of the cAMP response element-binding protein (CREB) in the AVPV. Because the ability of CREB to activate transcription depends on phosphorylation at Ser133, we also evaluated the effects of acute steroid treatment on levels of phosphorylated CREB (pCREB) in AVPV neurons by using an antibody that differentiates between CREB and pCREB. Treatment of ovariectomized rats with estradiol treatments caused a significant induction in the number of pCREB-immunoreactive nuclei within 30 min that was maintained for at least 4 hr, but did not alter CREB immunostaining in the AVPV. Pretreatment with the estrogen antagonist Nafoxidine blocked this induction. In contrast, acute administration of progesterone to estrogen-primed animals suppressed and then increased pCREB staining in the ASVPV at 30 and 60 min, respectively; no significant differences between experimental and control animals were apparent by 2 hr after progesterone treatment. Double-labeling experiments showed that pCREB was colocalized with PDYN, PENK, or TH mRNA in the AVPV, suggesting that pCREB may mediate the effect of steroid hormones on gene expression in these neurons.

Estrus- and steroid-induced changes in circadian rhythms in a diurnal rodent, Octodon degus

Diurnal Octodon degus exhibited marked alterations in activity and temperature in conjunction with the 3 wk estrous cycle when housed in LD12:12 light cycle. On the day of estrus, mean daily activity increases 109%, mean core temperature rises .4 degree C, activity onset is advanced 2 h, and amplitudes of both rhythms decline compared with the 3 days prior to estrus. On the day following estrus, activity onset was delayed 4.9 h, and mean activity and core temperature fell below that of the preestrus period. Ovariectomy significantly reduced mean temperature (.98 degree C) but did not significantly alter mean activity, and eliminated cyclic effects of estrus. Estrogen replacement led to a nonsignificant elevation in mean activity and core temperature with no change in the phase angle of entrainment. Progesterone replacement significantly reduced mean core temperature and mean activity, while only the phase angle difference between temperature minimum and activity onset was significantly altered. Intact degus maintained in constant darkness displayed only transient fluctuations in activity onset and temperature minimum during and after estrus. Estrogen or progesterone treatment of ovariectomized, free-running degus altered mean temperature and activity levels, but did not influence tau. Changes in phase angle of entrainment during estrus are not the result of hormone effects on the circadian clock but likely reflect increased or decreased levels of activity.

Ullrich-Turner syndrome: neurodevelopmental changes from childhood through adolescence

Our objective was to investigate whether the previously-described neurocognitive pattern in girls with Ullrich-Turner syndrome is found in childhood and adolescence; we used a prospective, controlled study of neurocognitive development in girls with Ullrich-Turner syndrome. The patients included 56 girls with Ullrich-Turner syndrome, and 100 normal age- and verbal IQ-matched female control subjects, whose ages ranged from 6-14 years. All girls with Ullrich-Turner syndrome and the normal control girls received a battery of neurocognitive tests designed to evaluate the following domains: general cognition, memory, academic achievement, language, visual-spatial/perceptual skills, visual-motor skills, attention, and affect recognition. Our results demonstrated consistent findings in Ullrich-Turner syndrome girls across the age range studied. In general, the Ullrich-Turner girls resembled control subjects in terms of verbal and language abilities. We found relatively depressed performance IQ and a significant verbal IQ-performance IQ difference. Significant differences were observed on examination of nonverbal abilities. The Ullrich-Turner girls performed more poorly than control girls on 1) tests of visual-motor skills including the Beery Test of Visual-Motor Integration, the Perceptual Organization Factor, and the Rey-Osterrieth Figures; 2) tests of visual-spatial skills, including the Motor-Free Visual Perception Test; 3) tests of attention, including the Freedom From Distractibility Factor; and 4) the Affective Prosody Affect Recognition Test. Ullrich-Turner subjects showed evidence of multifocal or diffuse right cerebral dysfunction and deficits generally involving nonverbal skills that may be due to X chromosome monosomy, gonadal dysgenesis, or both. Future studies will examine the role of estrogen replacement on cognitive function in Ullrich-Turner syndrome individuals.

Emerging diversities in the mechanism of action of steroid hormones

The classical genomic action of steroid hormones acting through intracellular receptors is well recognized. Within this concept of action, questions regarding the ultimate fate of the hormone and lack of a tight correlation between tissue uptake and biological activity with receptor binding remain unanswered. Evidence has accumulated that steroid hormones can exert non-classical action that is characterized by rapid effect of short duration. In most of these cases, the hormone effects occurs at the membrane level and is not associated with entry into the cell. The possible mechanisms for these non-classical actions are: (a) changes in membrane fluidity; (b) steroid hormone acting on receptors on plasma membranes; (c) steroid hormones regulating GABAA receptors on plasma membranes; and (d) activation of steroid receptors by factors such as EGF, IGF-1 and dopamine. Data have also been obtained indicating that receptor-mediated insertion of steroid hormones into DNA may take place with the steroid acting as a transcription factor. These new proposed mechanism of action of steroid hormones should not be viewed as a challenge to the classical mechanism. These diverse modes of action provide for an integrated action of hormones which may be rapid and of short duration or prolonged to address the physiological needs of the individual.

Altered stressor-induced changes in GABAA receptor function in the cerebral cortex of adult rats exposed in utero to diazepam

Prenatal administration of the anxiolytic drug diazepam (DZP), 2.5 mg/kg) to the pregnant rat over gestational days 14-20 altered function and stressor-induced responsiveness of the GABAA receptor in the cerebral cortex of exposed animals as adults. In Experiment 1, the impact of 15 min of restraint on chloride-facilitated benzodiazepine binding was evaluated in male and female rats at 70-90 days of age. Early exposure to DZP led to an enhanced potency of chloride on binding in both males and females. In Experiment 2, GABA stimulation of 36chloride uptake was measured in male rats at 35 or 70 days of age following 10 min of forced swimming at ambient temperature. In control animals, stressor-induced changes in receptor function were not evident until 70 days, and in DZP-exposed rats the stressor had no effect on receptor function at either age. These changes in GABAA receptor responsiveness induced by early exposure to DZP may underlie the disrupted behavioral responses to environmental challenge that have been previously reported.

Sexual dimorphism in the hamster cerebellum demonstrated by glial fibrillary acidic protein (GFAP) and vimentin immunoreactivity

Male and female hamsters aged 1, 4, and 10 postnatal weeks were used to study the distribution of vimentin and glial fibrillary acidic protein (GFAP) in the cerebellum. Vimentin immunoreactivity exceeded that of GFAP during the first postnatal week, although GFAP was also observed in all cerebellar layers. Immunoperoxidase analysis revealed that by the fourth postnatal week vimentin was only detected in Bergmann fibers and the very scarce fibrous astrocytes located in the inner white matter. The Purkinje cell bodies were only coated with GFAP-immunopositive processes. At 10 weeks, vimentin immunoreactivity was reduced to thin Bergmann glial processes, whereas GFAP immunoreactivity had greatly increased in the whole cerebellum. The GFAP immunostaining was denser in males than in females; however, in females, the Bergmann fibers were heavily immunostained with anti-vimentin in contrast to the males. The results described in the present paper indicate a sex difference in vimentin and GFAP immunoreactivities in the cerebellar astrocytes at 4 weeks of age, which persisted in the oldest hamsters in this study. The existence of sexual dimorphism might suggest that the expression of both gliofilament proteins could be influenced by circulating sex steroids.

Leu-enkephalin, tamoxifen and ethanol interactions: effects on motility and hepatic ethanol metabolizing enzymes

1. Short-term treatment with tamoxifen (a nonsteroidal antiestrogen) decreased mouse spontaneous locomotor activity compared to controls. 2. Short-term pretreatment with tamoxifen prior to an acute sedative dose of ethanol potentiated ethanol-medicated behavioral depression in the mouse. 3. Injection of a small dose of Leu-enkephalin, which is devoid of effect on mouse motility, prior to an acute sedative dose of ethanol to tamoxifen pretreated female mice counteracted ethanol-produced suppression of motor activity. 4. Mouse liver aldehyde dehydrogenase was inhibited by the short-term administration of tamoxifen when given alone or preceding acute dosages of Leu-enkephalin. Concomitantly, there was an increase in blood plasma ethanol concentration from corresponding control. 5. The results of the behavioral performance test used suggest that tamoxifen possesses depressant property and exerts synergestic effect with Leu-enkephalin in antagonizing ethanol-produced behavioral depression in the mouse. 6. The enzymatic part of the study indicates an adverse metabolic influence by tamoxifen on hepatic metabolism of ethanol-derived acetaldehyde which could contribute to the potentiation of the sedative effect of ethanol.

Locally applied estrogens potentiate glutamate-evoked excitation of cerebellar Purkinje cells

Ongoing studies in our laboratory have demonstrated that systemically administered sex steroids 17 beta-estradiol (E2) and progesterone (P) alter cerebellar Purkinje cell responses to the amino acid neurotransmitter glutamate (Glu) in the urethane-anesthetized, ovariectomized adult rat. In the present study, we have examined the effects of locally pressure ejected E2 (0.5 microM) on Purkinje cell responsiveness to microiontophoretically applied Glu. The inactive stereoisomer of E2, 17 alpha-E2 (0.5 microM), estradiol benzoate (EB, 0.5 microM), and estrone (E1, 0.5 microM) were also tested (vehicle: 0.01% propylene glycol-saline, pH 7.4). Extracellular activity of single Purkinje neurons was recorded using multibarrel glass micropipets. Spontaneous firing rate and neuronal responses to microiontophoretic pulses (10 s every 40 s at 10-50 nA) of Glu were examined before, during and after continuous local pressure application of the steroids (1-5 psi, 10-15 min). Local E2 administration increased Glu response by 86% within 2-3 min after the onset of steroid application, with no recovery apparent by 30 min after termination of steroid administration. As such, local E2 application mimicked the effect of systemic injection of this steroid. The inactive estrogen isomer, 17 alpha-E2, failed to significantly enhance Glu responsiveness. Both EB and E1, however, significantly potentiated Glu responsiveness in a manner similar to locally applied E2. In addition, EB administration produced long-lasting increases in background discharge, unlike E2, and eventual recovery of Glu responses to control pre-steroid levels. In summary, this study provides a demonstration of local sex steroid actions on neuronal responsiveness in a model extrahypothalamic CNS area. These effects were specific, as the inactive 17 alpha-E2 isomer did not alter neuronal physiology. The results presented here suggest that the neuronal effects of systemic estrogen may be mediated by local actions of E2 or E1.