Region- and peptide-specific regulation of the neurotrophins by estrogen

Molecular Brain Research 85 (2000) 77–84 www.elsevier.com / locate / bres

Research report

Region- and peptide-specific regulation of the neurotrophins by estrogen M.K. Jezierski, F. Sohrabji* Department of Human Anatomy and Medical Neurobiology, The Texas A& M University System Health Science Center, 228 Reynolds Medical Building, College Station, Texas TX 77843 -1114, USA Accepted 26 September 2000

Abstract We have previously shown that estrogen increases the expression of brain-derived neurotrophic factor (BDNF) mRNA in the olfactory bulb and cingulate cortex. Here we report that estrogen regulation of BDNF protein and the structurally related peptides nerve growth factor (NGF) and neurotrophin (NT)-4 is region- and peptide-specific. The olfactory bulb and cingulate cortex are both estrogen-sensitive targets and each receives a separate projection from neurons in the horizontal limb of the diagonal band of Broca (hlDBB). Furthermore, neurotrophins are retrogradely transported from the bulbar and cortical targets to the hlDBB. Four weeks of estrogen replacement to ovariectomized animals increased BDNF expression in the olfactory bulb, but decreased BDNF in the cingulate cortex. On the other hand, estrogen increased NT-4 expression in the cingulate cortex, but not in the olfactory bulb. NGF expression was not affected by estrogen in either region studied. In the hlDBB, estrogen increased BDNF but decreased NT-4, suggesting that estrogen differentially affects retrograde accumulation of these peptides. While both estrogen receptor alpha and beta have been identified in the olfactory bulb and cingulate cortex, our results indicate that estrogen receptor alpha expression is relatively higher in the olfactory bulb as compared to the cortex. Since the two estrogen receptors have been shown to stimulate different signaling pathways, we hypothesize that estrogen acting through specific receptors may differentially influence the extent and direction of neurotrophin expression.  2000 Elsevier Science B.V. All rights reserved. Theme: Development and regeneration Topic: Neurotrophic factors: expression and regeneration Keywords: Cingulate cortex; Olfactory bulb; Basal forebrain; Horizontal limb; Neurotrophin; Estrogen receptor

1. Introduction Basal forebrain cholinergic neurons have been implicated in learning and memory functions. Experimentallyinduced degeneration of these neurons results in impaired task acquisition and recall [55,79,80] and the loss of these neurons is thought to contribute to the cognitive losses that accompany dementias such as Alzheimer’s disease (AD) [82,83]. In rodents, an age-dependent decline has been observed in cholinergic function [23,62], often accompanied by learning impairment [13,33,43]. Exogenous treatment with the neurotrophin NGF appears to attenuate

*Corresponding author. Tel.: 11-409-845-4072; fax: 11-409-8450790. E-mail address: [email protected] (F. Sohrabji).

the atrophy of cholinergic neurons and memory impairment in aged animals [14,15]. The neurotrophins, including nerve growth factor (NGF) and brain derived neurotrophic factor (BDNF), have been shown to promote survival and differentiation of basal forebrain neurons in vitro [1,30,31] and protect adult cholinergic neurons against lesion-induced cell death [20,29,32,44,45,53]. Although poorly synthesized locally [50,61], basal forebrain neurons acquire NGF and BDNF via receptor-specific transport from targets such as the olfactory bulb, cortex and the hippocampus. Thus, maintaining neurotrophin availability in the target may be crucial for basal forebrain function. Previous work has shown that the gonadal hormone estrogen regulates neurotrophin systems in the forebrain. In the developing forebrain, cholinergic neurons express estrogen receptors [76], and estrogen receptor mRNA is

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colocalized to basal forebrain neurons that express p75, the universal neurotrophin receptor, as well as trkA and trkB, the peptide specific tyrosine kinase receptors [51,52]. Furthermore, estrogen receptor mRNA is also colocalized to NGF and BDNF mRNA-expressing cells in basal forebrain efferent targets such as the cortex and hippocampus [52]. These observations suggest the presence of a biological substrate necessary for hormonal regulation of the neurotrophin system. Our previous work also indicates that, in the adult ovariectomized rat, acute (4 h) estradiol treatment increases the expression of BDNF mRNA in the cingulate cortex and the olfactory bulb [71]. Anatomical studies have shown that both these regions receive a separate projection from basal forebrain neurons located in the the horizontal limb of the diagonal band of Broca (hlDBB) [22]. Using these two hlDBB circuits, we determined whether chronic estrogen treatment would regulate protein expression of key neurotrophins in the two forebrain targets and their accumulation in the hlDBB. Our data indicate that 4 weeks of estrogen deprivation differentially affected BDNF and NT4 expression in the olfactory bulb and cingulate cortex and their accumulation in the hlDBB, but did not affect NGF. Using estrogen receptor specific antibodies, we observed that estrogen receptors were expressed in both the olfactory bulb and the cingulate region although the relative expression of the two currently known forms of the estrogen receptor was different in both regions. Regional differences in the ratio of the two estrogen receptors may contribute to the regional differences in neurotrophin regulation by estrogen, and thus influence the extent of neurotrophic support afforded by each target area for a specific population of afferent cells.

2. Materials and methods Adult Sprague Dawley rats (200 g, 2.5 months of age, Harlan laboratories, IN) were maintained on a 12 h light / 12 h dark cycle with lights on at 6 a.m. and with food and water available ad libitum. One group of animals was anesthetized with metofane while bilateral ovariectomies were performed using a dorsal midline incision inferior to the palpated rib cage and kidneys. Ovaries and surrounding tissue were removed and 28-day time-release 17-b estradiol pellets (E2; 0.5 mg) or placebo pellets (PLC; Innovative Research, 28-day release) were inserted subcutaneously before closing the incision. A second group of animals that were included in estrogen receptor expression assays were not ovariectomized (INTACT) and maintained in the same way for 4 weeks. A 4-week end-point was used for these studies since our pilot studies indicated that 3 weeks or less of estrogen deprivation does not significantly alter neurotrophin expression. Rats were sacrificed by decapitation and plasma was collected for

estimation of estradiol content by radioimmunoassay (Diagnostic systems Laboratories, TX). All brain dissections were performed by the same individual (MJ) to ensure consistency in microdissected regions. The olfactory bulbs were rapidly removed to 2808C and the horizontal bands of Broca were dissected in the following manner. Bilateral hippocampi were removed to expose the septal-diagonal band complex. A fresh razor blade was used to separate the diagonal band from the ventral pallidum (see [58]). Next, the brain was sliced caudal to the septum-diagonal band and cranial to the anterior commisure. The most lateral portion of the hlDBB (see Fig. 1 in [2]) was removed and saved at 2808C. Proteins were isolated using lysis buffer (50 mM Tris (pH 7.4), 150 mM NaCl, 10% glycerol, 1 mM EGTA, 1 mM sodium orthovanadate (pH 10), 5 mM ZnCl 2 , 100 mM NaF, 10 mg / ml Aprotinin, 1 mg / ml Leupeptin, 1 mM PMSF in DMSO, 1% Triton X-100). Protein concentrations were determined using the BCA protein assay kit (Pierce, IL).

2.1. Neurotrophin analysis Commercial ELISA kits for BDNF, NGF, and NT4 (Promega, IL) were used to determine neurotrophin expression. Briefly, primary antibodies were diluted in Na 2 CO 3 / NaHCO 3 buffer and coated on 96-well plates overnight at 48C. Protein samples and human recombinant standards were incubated with primary antibody for 2 h (BDNF) or 6 h (NGF, NT4) at room temperature. Plate was sequentially incubated with a second primary antibody and HRP-conjugated secondary antibody. Antigen-antibody complexes were detected with a peroxidase substrate. Plates were read at 450 nm on a microplate reader (BioTek, VT). Standard curves were determined from optical measurements of wells containing human recombinant standard protein. Neurotrophin content of sample wells was calculated by interpolation from the peptide standard curve using KC3 software (Bio-Tek, VT) and normalized to total protein.

2.2. Estrogen receptor analysis Western blot analysis was used to determine the relative expression of ERa and ERb protein in the olfactory bulb and cingulate cortex of intact and ovariectomized animals. Equivalent amounts (100 mg) of total protein from tissue lysates were resolved on a 12% polyacrylamide gel. Proteins were then transferred to a nylon membrane (Hybond Super C, Amersham, IL) and blocked for 1 h with a 5% milk in 13Tris Buffered Saline10.05% Tween (TTBS) solution followed by incubation with the primary antibody in non-fat dry milk / TTBS (1 / 200 ERa, Neo Markers, CA; 1 / 500 ERb / ERa Affinity BioReagents, CO[PA1-310) overnight at 48C. Blots were washed with TTBS (30 min) and primary antibody was detected using appropriate secondary in TTBS for 1 h at room tempera-

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ture. After a final wash step, an enzyme-catalyzed chemiluminescent reagent (Renaissance; NEN, MA) was used for immunodetection. Signal was detected using Xray film; bands were quantified by densitometric analysis (Bio-Rad Gel Doc 1000; version 1.4.1). Samples were subjected to Western analysis at least twice for confirmational data.

2.3. Statistical analyses Group differences were evaluated by t-tests. Means were considered significantly different if P,0.05. All data shown are mean6S.E.M.

3. Results

3.1. Plasma estradiol Ovariectomized animals replaced with an estrogen containing pellet (E2) had an average plasma estradiol level similar to that seen at proestrus in the cycling rat (average594.5367.1 pg / ml). In contrast, ovariectomized, placebo-replaced animals (PLC) had low levels of estrogen (average516.9961.67 pg / ml).

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3.2. Estrogen regulation of neurotrophin protein in the olfactory bulb and cortex Neurotrophin protein in the olfactory bulbs and cingulate cortices was assessed by ELISA assay. NGF, BDNF and NT-4 were detected in both olfactory bulb and cingulate cortex, although the relative expression of the three neurotrophins varied considerably by region. NGF was highly expressed in both the cortex and bulb, while NT-4 was least abundant in both regions. Comparatively more BDNF was expressed, relative to total protein, in the olfactory bulb than in the cingulate cortex. In the olfactory bulb, estrogen treatment increased BDNF levels 2-fold (Fig. 1a) but did not affect protein expression of NT4 (Fig. 1b) or NGF (Fig. 1c). Alternately, in the cingulate cortex, estrogen treatment resulted in a 50% reduction in BDNF concentration (Fig. 1d) while increasing NT4 expression 2-fold (Fig. 1e). Finally, as in the olfactory bulb, NGF expression was refractory to 4 weeks of estrogen treatment (Fig. 1f).

3.3. Estrogen regulation of NT4 and BDNF in the horizontal limb Due to the enhanced NT-4 expression in the cingulate cortex and BDNF in the olfactory bulb as a result of estrogen treatment, we used ELISA assays to determine

Fig. 1. Estrogen regulation of neurotrophin protein in the olfactory bulb and cingulate cortex. Olfactory bulb and cingulate cortex lysates from estrogen-replaced (E2) or placebo-treated (PLC) rats were assayed for BDNF, NT4 and NGF by ELISA. In the olfactory bulb, estrogen significantly increased (a) BDNF expression but did not enhance (b) NT4 or (c) NGF. In the cortex, estrogen decreased (d) BDNF while increasing (e) NT4 protein. Estrogen did not affect (f) NGF in the cortex (*P,0.05; n56).

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Fig. 2. Estrogen regulation of NT4 and BDNF in the basal forebrain. Protein lysates from the hlDBB of estrogen-replaced (E2) or placebotreated (PLC) rats were assayed for NT4 and BDNF by ELISA. Estrogen significantly decreased (a) NT4 peptide while increasing (b) BDNF in the hlDBB. (*P,0.05; n56).

whether NT-4 and BDNF levels were altered in their basal forebrain afferent, the hlDBB. NT4 accumulation in the hlDBB was 50% lower in the estrogen-replaced condition compared to the placebo-treated (Fig. 2a) while estradiol significantly increased BDNF accumulation in the hlDBB (Fig. 2b).

3.4. Expression of estrogen receptor in the olfactory bulb and cortex In view of the differential effects of estrogen on cortical and bulbar expression of neurotophins, we examined the expression of the estrogen receptor (ER) in these regions. As shown in Fig. 3, there were differences in the compara-

tive expression of estrogen receptors in the cortex and olfactory bulb. Estrogen receptor protein expression was evaluated by Western immunoblot assays, using two different antibodies in separate assays to confirm regional expression in the olfactory bulb and the cingulate cortex. The first antibody (Affinity Bioreagents, CO) recognized a 67 kD band in commercially available recombinant ERa protein, rat ovary and sample lysates. This antibody also recognized the 55 kD recombinant ERb protein and a size-appropriate band in sample lysates (Fig. 2a). Using this antibody, ERa was more highly expressed in the olfactory bulb while ERb was higher in the cingulate cortex. The second receptor-specific antibody recognized the hsp90-binding site of the ERa receptor but did not recognize ERb (Neomarkers, CA; Fig. 2b). Gonadallyintact and ovariectomized rats both exhibited higher levels of ERa in the olfactory bulb than the cortex. Together these data indicate that while ERa is present in both regions, the ratio of ERa and ERb may be different in the two regions.

4. Discussion The present data reveal a complex region- and peptidespecific regulation of the neurotrophins by estrogen in the adult forebrain. These observations extend our previous findings that estrogen increases neurotrophin mRNA in the olfactory bulb [71] and forward the hypothesis that re-

Fig. 3. Estrogen receptor alpha and beta expression in the forebrain. Olfactory bulb (OB) and cingulate cortex (CTX) lysates were assayed for ERa and ERb protein using Western immunoblot assays. Equivalent amounts of total protein were resolved on polyacrylamide gels and proteins were detected as described in Methods. (a) In gonadally intact animals, two bands were identified using an antibody which recognized both ERa and ERb: a 67 kD band corresponding to the ERa control peptide and ovary control and 55 kD band matching the ERb control peptide. ERa expression was higher in the olfactory bulb than in the cingulate cortex and the size appropriate band for ERb protein was greater in the cingulate cortex. (b) An ERa-specific antibody corresponding to the hsp90-binding site recognized recombinant ERa peptide but not recombinant ERb peptide. ERa expression was higher in the olfactory bulb of both intact (INTACT) and ovariectomized (PLACEBO) rats.

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gional differences in hormonal action on growth factors may be due, in part, to the differential expression of ER subtypes. In this study, chronic estrogen replacement for 4 weeks differentially regulated neurotrophin protein expression in the olfactory bulb and the cingulate cortex, two independent targets of the hlDBB portion of the basal forebrain [22]. While the olfactory bulb and cingulate cortex have distinctive cognitive and sensory roles, neurons in both regions provide trophic support for basal forebrain neurons. The bulb and cingulate cortex express estrogen receptors [48,60,65,67], contain neurotrophin-producing cells which are targets of basal forebrain neurons [9,24,28,34,61] and estrogen has been shown to increase neurotrophin mRNA in both regions [71]. NGF is not regulated in either brain region following estrogen deprivation. NGF is the most abundantly expressed of the three neurotrophins studied here, and due to its high constitutive expression, discrete modulations due to estrogen may not be easily observed. Alternately, a longer period of estrogen deprivation may be required to detect hormonal regulation of this peptide. In fact, in a related experiment from our laboratory, where ovariectomized rats received 6-weeks of estrogen or placebo replacement, hormone deprivation resulted in a decrease in NGF in the olfactory bulb as compared to hormone-replaced rats [72]. The most striking regional contrast is seen in estrogen regulation of BDNF and NT4. Both BDNF and NT-4 bind the p75 receptor as well the tyrosine kinase receptor, trkB [40,73]. TrkB facilitates axonal transport of both BDNF and NT4 and mediates signal transduction involving the pro-survival Ras / MAP-K and PI-3 kinase pathways [17,39]. In the present studies, BDNF expression is increased by estrogen in the olfactory bulb, but decreased in the cingulate cortex. While hormone-mediated increases in bulbar BDNF were predicted based on our previous observations that estrogen increases BDNF mRNA in this region, down-regulation of this peptide in the cortex was surprising. Estrogen increases BDNF mRNA in cingulate [71] and frontal cortex [68], consequently the decrease in cortical BDNF protein due to estrogen suggests that the hormone may exert translational and post-translational modifications that change the basal expression of the peptide. Alternatively, estrogen may differentially affect the turnover or stability of this neurotrophin, or cause rapid translocation of this peptide to its afferent and efferent targets. Regional differences are also seen in NT-4 regulation by estrogen. NT-4 mRNA is synthesized in the olfactory bulb [75] and our data indicate that low levels of NT-4 protein is expressed in this region. Estrogen does not affect the expression of this peptide in the bulb. In contrast, estrogen significantly increases the expression of NT-4 in the cingulate cortex. Estrogen-dependent changes in neurotrophin accumulation in the hlDBB may be best interpreted in terms of

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hormonal regulation of neurotrophin transport. Although little direct evidence is available that trk / p75 expressing hlDBB terminals contact neurotrophin synthesizing cells, other indirect evidence suggests that neurotrophins are retrogradely transported to the hlDBB from the olfactory bulb and cortex. For example, hlDBB neurons express neurotrophin receptors necessary for this transport [3,84], and terminate on cell layers known to contain neurotrophin-synthesizing neurons in the olfactory bulb [28]. Moreover, neurotrophins such as NGF and BDNF injected into the olfactory bulb are retrogradely transported to the hlDBB [2,16]. Estrogen-induced increases in BDNF in the hlDBB may be related to the increased transport of BDNF from its targets to the hlDBB. In a related study, we found that estrogen enhances the retrograde translocation of exogenous BDNF from the olfactory bulb to the hlDBB [37]. This increased transport may be related to an increased expression of bulbar trkB [37], the tyrosine kinase receptor that promotes retrograde transport of BDNF [73,74]. Decreased NT-4 levels in the estrogen-exposed hlDBB presents an intriguing paradox, especially since target levels of NT-4 are either unchanged (as in the olfactory bulb) or increased (as in the cortex). Even if the increased NT-4 levels occurs in cortical neurons not contacted by the hlDBB, (and therefore not available for retrograde transport), target NT-4 levels should likely remain unchanged. One possible explanation for this decrease may be the presence of other hlDBB targets that produce NT-4, which are adversely affected by estradiol treatment. For example, the suprachiasmatic nucleus of the hypothalamus also receives a projection from the hlDBB [7] and had been shown to synthesize neurotrophins [49]. Thus, decreased NT-4 synthesis in response to estrogen at targets other than the olfactory bulb and cortex may affect NT-4 accumulation in the hlDBB. Alternately, estrogens may affect another component of the NT-4 transport system, such as the receptors. Recent studies in the peripheral nervous system reveal that both p75 and trkB are needed for efficient NT4 transport [11,35,63]. Hence unlike BDNF, NT-4 transport may be hindered by conditions where p75 expression is changed. In several cell types, estrogen has been shown to decrease p75 mRNA [69,70] and protein [37], which is consistent with the hypothesis that NT-4 transport to the basal forebrain may be impeded by estrogen. Collectively these observations suggest that estrogen may discretely alter neurotrophin synthesis and provide a specific combination of trophic support for basal forebrain neurons. Regional differences in the relative expression of estrogen receptor alpha and beta isoforms may limit transcriptional and post-transcriptional changes in estrogensensitive genes. Two forms of the estrogen receptor have been identified, ERa [26,27] and the more recently cloned ERb [46,54,77]. Our data indicate that, in the intact adult female, ERa protein is more prevalent in the bulb than in

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the cortex, while ERb is expression is higher in the cortex as compared to the bulb. The higher ERb expression in the cortex is corroborated by other reports in the literature describing greater relative expression of ERb mRNA than ERa mRNA in the rodent cortex [65,66]. In the case of the adult olfactory bulb, only one other report is currently available, which reports significantly more ERb mRNA as compared to ER-a mRNA [65] in this region. Further studies will be needed to determine whether both receptor mRNAs are translated in the olfactory bulb, and whether the differences in mRNA are reflected in the protein as well. Both receptors bind most known estrogenic ligands with varying affinities [4,47]. The estrogen receptors are ligandactivated transcription factors capable of regulating genes by forming homo- or heterodimers and binding DNA regulatory sequences [21,41,81]. Recent evidence indicates that alpha homodimers may regulate genes differently from beta homodimers and that heterodimers may behave differently [10,56,59]. In the present study it was possible to confirm the relative expression of ERa in these two regions using an ERa specific antibody, however, at the present time, there does not appear to be an antibody that unequivocally recognizes only ERb (unpublished observations). Irrespective of ERb expression in these two regions, it does appear that ERa is differentially expressed in the olfactory bulb and cingulate cortex of both the intact and ovariectomized animal, indicating that the ratio of ERa and ERb will vary regionally. This spatial variation in estrogen receptor ratios may contribute to the present regional differences in neurotrophin modulation. It is also possible that a longer duration of hormonal loss may alter the profile of these receptors and their ratio. In fact, related studies from our lab show that ERa expression changes as a result of reproductive senescence [38] and is correlated with changes in neurotrophin regulation. Collectively, these data support the hypothesis that the relative expression of estrogen receptors may define the pattern of neurotrophin regulation. Although 17b-estradiol used in this study binds both receptors with similar affinity [47], it may be possible to test the relative contribution of each receptor using receptor-specific ligands in future studies. Region-specific differences in neurotrophin regulation by estrogen may also be closely tied to developmental diversity. Developmental peaks of BDNF-, NT3-, and NT4 / 5- induced Trk-phosphorylation in specific regions are coincident with neuronal differentiation, and declines with maturation [42]. Regional differences in neurotrophin regulation by estrogen may reflect differences in the pattern of neuronal differentiation. For instance, in the olfactory bulb, where neuronal differentiation occurs throughout life [5,25], BDNF is upregulated by estrogen, while in the cingulate cortex, which differentiates prenatally [6], BDNF does not respond to estrogen. In view of the differential roles for neurotrophins, peptide specific regulation by estrogen suggests an intricate

role for steroid / neurotrophin interactions in maintaining basal forebrain neurons. For instance, each neurotrophin displays distinct expression patterns [28,34] as well as specific patterns of retrograde transport in the brain [12]. In addition, each uniquely regulates survival and function [18], responds independently to injury [19,64,78], and utilizes different signal transduction pathways [36], which induce distinguishable down-stream outputs, as in the case of differentiation patterns in PC12 cells [36] and in the formation of Ras-GTP [8]. If specific neurotrophin combinations are required to maintain a healthy environment for local and afferent neurons, then regional variations in hormonal regulation of specific peptides may be necessary for the normal function of forebrain circuits.

Acknowledgements We thank Leia Brundige, Olga Marroquin, Joseph Newman and Trichelle Trombatore for technical assistance. This work supported by NINDS NS36297.

References [1] R.F. Alderson, A.L. Alterman, Y.-A. Barde, R.M. Lindsay, Brainderived neurotrophic factor increases survival and differentiated functions of rat septal cholinergic neurons in culture, Neuron 5 (1990) 297–306. [2] C.A. Altar, C. Bakhit, Receptor-mediated transport of human recombinant nerve growth factor from olfactory bulb to forebrain cholinergic nuclei, Brain Res. 541 (1991) 82–88. [3] C.A. Altar, J.A. Siuciak, P. Wright, N.Y. Ip, R.M. Lindsay, S.J. Weigand, In situ hybridization of trkB and trkC receptor mRNA in the rat forebrain and association with high affinity binding of 125BDNF, 123NT-4 / 5 and 125NT-3, Euro. J. Neurosci. 6 (1994) 1389–1405. [4] T. Barkhem, B. Carlsson, Y. Nilsson, E. Enmark, J. Gustafsson, S. Nilsson, Differential response of estrogen receptor and estrogen receptor to partial estrogen agonists / antagonists, Mol. Pharm. 54 (1998) 105–112. [5] S.A. Bayer, [ 3 H]Thymidine-radiographic studies of neurogenesis in the rat olfactory bulb, Exper. Brain Res. 50 (1983) 329–340. [6] S.A. Bayer, J. Altman, Neocortical Development, Raven Press, New York, 1991. [7] K.G. Bina, B. Rusak, K. Semba, Localization of cholinergic neurons in the forebrain and brainstem that project to the suprachiasmatic nucleus of the hypothalamus in rat, J. Comp. Neurol 335 (1993) 295–307. [8] B.D. Carter, U. Zirrgiebel, Y.-A. Barde, Differential regulation of p21ras activation in neurons by nerve growth factor and brainderived neurotrophic factor, J. Biological Chem. 270 (1995) 21751– 21757. [9] J.M. Conner, S. Varon, Developmental profile of NGF immunoreactivity in the rat brain: a possible role of NGF in the establishment of cholinergic terminal fields in the hippocampus and cortex, Brain Res. Developmental Brain Res. 101 (1997) 67–79. [10] S.M. Cowley, S. Hoare, S. Mosselman, M.G. Parker, Estrogen receptors and form heterodimers on DNA, J. Biol. Chem. 272 (1997) 19858–19862. [11] R. Curtis, K.M. Adryan, J.L. Stark, J.S. Park, D.L. Compton, G. Weskamp, L.J. Huber, M.V. Chao, R. Jaenisch, K.-F. Lee, R.M.

M.K. Jezierski, F. Sohrabji / Molecular Brain Research 85 (2000) 77 – 84

[12]

[13]

[14]

[15]

[16]

[17] [18]

[19]

[20]

[21]

[22]

[23]

[24]

[25]

[26]

[27]

[28]

[29]

[30]

Lindsay, P.S. DiStephano, Differential role of the low affinity neurotrophin receptor (p75) in retrograde axonal transport, Neuron 14 (1995) 1201–1211. P.S. DiStephano, B. Friedman, C. Radziejewski, C. Alexander, P. Boland, C.M. Schick, R.M. Lindsay, S.J. Wiegand, The neurotrophins BDNF, NT-3, and NGF display distinct patterns of retrograde axonal transport in peripheral and central neurons, Neuron 8 (1992) 983–993. W. Fischer, F.H. Gage, A. Bjorklund, Degenerative changes in forebrain chholinergic nuclei correlate with cognitive impairments in aged rats, Eur. J. Neurosci. 1 (1989) 34–45. W. Fischer, A. Sirevaag, S. Wiegand, R. Lindsay, A. Bjorklund, Reversal of spatial memory impairments in aged rats by nerve growth factor and neurotrophins 3 and 4 / 5 but not by brain-derived neurotrophic factor, Proc. Natl. Acad. Sci. USA 91 (1994) 8607– 8611. W. Fischer, K. Chen, F. Gage, A. Bjorklund, Progressive decline in spatial learning and integrity of forebrain cholinergic neurons during aging, Neurobiol. Aging 13 (1992) 2–23. L. Frank, S.J. Weigand, J.A. Siuciak, R.M. Lindsay, J.S. Rudge, Effects of BDNF infusion on the regulation of trkB protein and message in the rat adult brain, Exp. Neurol. 145 (1997) 62–70. W.J. Friedman, L.A. Greene, Neurotrophin signaling via trks and p75, Exp. Cell Res. 253 (1999) 131–142. W.J. Friedman, C.F. Ibanez, F. Hallbook, H. Persson, L.D. Cain, C.F. Dreyfus, I.B. Black, Differential actions of neurotrophins in the locus coeruleus and basal forebrain, Exp. Neurol. 119 (1993) 72–78. H. Funakoshi, J. Frisen, B. Gisela, T. Timmusk, O. Zachrisson, V.M.K. Verge, H. Persson, Differential expression of mRNAs for neurotrophins and their receptors after axotomy of the sciatic nerve, J. Cell Biol. 123 (1993) 455–465. F.H. Gage, D.M. Armstrong, L.R. Williams, S. Varon, Morphological response of axotomized septal neurons to nerve growth factor, J. Comp. Neurol. 269 (1988) 147–155. M.P. Gaub, M. Bellard, I. Scheuer, P. Chambon, P. Sassone-Corsi, Activation of the ovalbumin gene by the estrogen receptor involves the fos–jun complex, Cell 63 (1990) 1267–1276. R.P.A. Gaykema, P.G.M. Luiten, C. Nyakas, J. Traber, Cortical projection patterns of the medial septum-diagonal band complex, J. Compar. Neurol. 293 (1990) 103–124. G.M. Gilad, J.M. Rabey, Y. Tizabi, V.H. Gilad, Age-dependent loss and compensatory changes of septohippocampal cholinergic neurons in two rat strains differing in logevity and response to stress, Brain Res. 436 (1987) 311–322. Q. Gong, M.S. Bailey, S.K. Pixley, M. Ennis, W. Liu, M.T. Shipley, Localization and regulation of low affinity nerve growth factor receptor expression in the rat olfactory system during development and regeneration, J. Compar. Neurol. 344 (1994) 336–348. P.P.C. Graziadei, G.A. Montigraziadei, Neurogenesis and neuron regeneration in the olfactory system of mammals. III. Deafferentation and reinnervation of the olfactory bulb following section of the fila olfactoria in rat, J. Neurocytology 9 (1980) 145–162. G.L. Green, P. Gilna, M. Waterfield, A. Baker, Y. Hort, J. Shine, Sequence and expression of human estrogen receptor complementary DNA, Science 231 (1986) 1150–1154. S. Green, P. Walter, V. Kumar, A. Krust, J.-M. Bornert, P. Argos, P. Chambon, Human oestrogen receptor cDNA: sequence, expression, and homology to v-erb-A, Nature 320 (1986) 134–139. K.M. Guthrie, C.M. Gall, Differential expression of mRNAs for the NGF family of neurotrophic factors in the adult rat central olfactory system, J. Compar. Neurol. 313 (1991) 95–102. T. Hagg, B. Fass-Holmes, H.L. Vahlsing, M. Manthorpe, J.M. Conner, S. Varon, Nerve growth factor (NGF) reverses axotomyinduced decreases in choline acetyltransferase, NGF receptor and size of medial septum cholinergic neurons, Brain Res. 505 (1989) 29–38. J. Hartikka, F. Hefti, Development of septal cholinergic neurons in

[31]

[32]

[33]

[34]

[35] [36]

[37]

[38]

[39] [40]

[41]

[42]

[43]

[44]

[45] [46]

[47]

[48]

[49]

83

culture: plating density and glial cells modulate effects of NGF on survival, fiber growth, and expression of transmitter-specific enzymes, J. Neurosci. 8 (1988) 2967–2985. H. Hatanaka, H. Tsukui, I. Nihonmatsu, Developmental change in the nerve growth factor action from induction of choline acetyltransferase to promotion of cell survival in cultured basal forebrain cholinergic neurons from postnatal rats, Developmental Brain Res. 39 (1988) 85–95. F.H. Hefti, J. Hartikka, B. Knusel, Function of neurotrophic factors in the adult and aging brain and their possible use in the treatment of neurodegenerative diseases, Neurobiol. Aging 10 (1989) 515–533. R. Hellweg, W. Fischer, C. Hock, F.H. Gage, A. Bjorklund, H. Thoenen, Nerve growth factor levels and choline acetyltransferase activity in the brain of aged rats with spatial memory impairments, Brain Res. 537 (1990) 123–130. M. Hofer, S.R. Pagliusi, A. Hohn, J. Leibrock, Y.-A. Barde, Regional distribution of brain-derived neurotrophic factor mRNA in the adult mouse brain, EMBO J. 9 (1990) 2459–2464. ´˜ C.F. Ibanez, Neurotrophin-4: The odd one out in the neurotrophin family, Neurochem. Res. 21 (1996) 787–793. Y. Iwasaki, M. Ishikawa, N. Okada, S. Koizumi, Induction of a distinct morphology and signal transduction in trkB / PC12 cells by nerve growth factor and brain-derived neurotrophic factor, J. Neurochem. 68 (1997) 927–934. M.K. Jezierski, S. Neela, F. Sohrabji, Estrogen regulates retrograde transport of brain-derived neurotrophic factor in the forebrain, In review (2000). M.K. Jezierski, F. Sohrabji, Neurotrophin expression in the reproductively senescent forebrain is refractory to estrogen stimulation, Neurobiology of Aging, (2000) in press. D.R. Kaplan, Studying signal transduction in neuronal cells: The Trk / NGF system, Prog. Brain Res. 117 (1998) 35–46. R. Klein, F. Lamballe, S. Bryant, M. Barbacid, The trkB tryrosine protein kinase is a receptor for neurotrophin-4, Neuron 8 (1992) 1–20. L. Klein-Hitpass, M. Schorpp, U. Wagner, G.U. Ryffel, An estrogenresponsive element derived from the 59 flanking region of the Xenopus vitellogenin A2 gene functions in transfected human cells, Cell 46 (1986) 1053–1061. B. Knusel, S.J. Rabin, F. Hefti, D.R. Kaplan, Regulated neurotrophin receptor responsiveness during neuronal migration and early differentiation, J. Neurosci. 14 (1994) 1542–1554. S. Koh, P. Chang, T.J. Collier, R. Loy, Loss of NGF receptor immunoreactivity in basal forebrain neurons of aged rats: correlation with spatial memory impairment, Brain Res. 498 (1989) 397–404. V.E. Koliatsos, D.L. Price, G.K. Gouras, M.H. Cayouette, L.E. Burtin, J.W. Winslow, Highly selective effects of nerve growth factor, brain derived neurotrophic factor and neurotrophin-3 on intact and injured basal forebrain magnocellular neurons, J. Comp. Neurol. 343 (1994) 247–262. L. Kromer, Nerve growth factor after brain injury prevents neuronal death, Science 235 (1987) 214–216. G.G.J.M. Kuiper, E. Enmark, M. Pelto-Huikko, S. Nilsson, J.-A. Gustafsson, Cloning of a novel estrogen receptor expressed in rat prostrate and ovary, Proc. Natl. Acad. Sci. USA 93 (1996) 5925– 5930. G.G.J.M. Kuiper, B. Carlsson, K. Grandien, E. Enmark, J. Haggblad, S. Nilsson, J.-A. Gustafsson, Comparison of the ligand binding specificity and transcript tissue distribution of estrogen receptors a and b, Endocrinology 138 (1997) 863–870. N. Laflamme, R.E. Nappi, D. Guy, C. Labrie, S. Rivest, Expression and neuropeptidergic characterization of estrogen receptors (ERa and ERb) throughout the rat brain: anatomical evidence of distinct roles of each subtype, J. Neurobiol. 36 (1998) 357–378. F.-Q. Liang, F. Sohrabji, R. Miranda, B. Earnest, D. Earnest, Expression of brain-derived neurotrophic factor and its cognate receptor, TrkB, in the rat suprachiasmatic nucleus, Exp. Neurology 151 (1998) 184–193.

84

M.K. Jezierski, F. Sohrabji / Molecular Brain Research 85 (2000) 77 – 84

[50] R.C. Miranda, F. Sohrabji, C.D. Toran-Allerand, Neuronal colocalization of mRNAs for neurotrophins and their receptors in the developing central nervous system suggests a potential for autocrine interactions, Proc. Natl. Acad. Sci. USA 90 (1993) 6439–6443. [51] R.C. Miranda, F. Sohrabji, C.D. Toran-Allerand, Presumptive estrogen target neurons express mRNAs for both the neurotrophins and neurotrophin receptors: A basis for potential developmental interactions of estrogen with the neurotrophins, Mol. Cell. Neurosci. 4 (1993) 510–525. [52] R.C. Miranda, F. Sohrabji, C.D. Toran-Allerand, Intractions of estrogen with the neurotrophins and their receptors during neural development, Hormones and Behav. 28 (1994) 367–375. [53] J.K. Morse, S.J. Weigand, K. Anderson, Y. You, N. Cai, J. Carnahan, J. Miller, P. DiStephano, C.A. Altar, R.M. Lindsay, R.P. Alderson, Brain-derived neurotrophic factor (BDNF) prevents the degeneration of medial septal cholinergic neurons following fimbria transection, J. Neurosci. 13 (1993) 4146–4156. [54] S. Mosselman, J. Polman, R. Dijkema, ER beta: identification and characterization of a novel human estrogen receptor, FEBS Lett. 247 (1996) 49–53. [55] O.G. Nilsson, G. Leanza, C. Rosenblad, D.A. Lappi, R.G. Wiley, A. Bjorklund, Spatial learning impairment in rats with selective immunolesion of the forebrain cholinergic system, Neuroreport 3 (1992) 1005–1008. [56] S. Ogawa, S. Inoue, T. Watanabe, H. Hisahiko, O. Akira, T. Hosoi, Y. Ouchi, M. Masami, The complete primary structure of human estrogen receptor (her) and its heterodimerization with Er in vivo and in vitro, Biochem. Biophys. Res. Comm. 243 (1998) 122–126. [58] G. Paxinos, C. Watson, in: The Rat Brain in Stereotaxic Coordinates, 2nd Edition, Academic Press, San Diego, CA, 1986, pp. 11–15. [59] K. Pettersson, K. Grandien, G.G. Kuiper, J.A. Gustafsson, Mouse estrogen receptor beta forms estrogen respnse element-binding heterodimers with estrogen receptor alpha, Mol. Endocrinol. 11 (1997) 1486–1496. [60] D. Pfaff, M. Keiner, Atlas of estradiol-concentrating cells in the central nervous system of the female rat, J. Comp. Neur. 151 (1973) 121–158. [61] H.S. Phillips, J.M. Hains, G.F. Laramee, A. Rosenthal, J.W. Winslow, Widespread expression of BDNF but not NT3 by target areas of basal forebrain cholinergic neurons, Science 250 (1990) 290– 294. [62] B.V. Rama Sastry, V.E. Janson, N. Jaiswal, O.S. Tayeb, Changes in enzyms of the cholinergic system and acetylcholine release in the cerebra of aging male Fischer rats, Pharmacology 46 (1983) 61–72. ´ J. Murray-Rust, D. Glass, L.L. Ilag, M. Trupp, G.D. [63] M. Ryden, ´˜ Yancopoulos, N.Q. McDonald, C.F. Ibanez, Functional analysis of mutant neurotrophins deficient in low-affinity binding reveals a role for p75LNFR in NT-4 signaling, EMBO J. 14 (1995) 1979–1990. [64] H. Shen, J.M. Chung, K. Chung, Expression of neurotrophin mRNAs in the dorsal root ganglion after spinal nerve injury, Mol. Brain Res. 64 (1999) 186–192. [65] P.J. Shughrue, M.V. Lane, I. Merchenthaler, Comparative distribution of estrogen receptor- and estrogen receptor-mRNA in the rat central nervous system, J. Compar. Neurol. 388 (1997) 507–525. [66] P.J. Shughrue, P.J. Scrimo, I. Merchenthaler, Evidence for the colocalization of estrogen receptor-beta mRNA and estrogen receptor-alpha immunoreactivity in neurons of the rat forebrain, Endocrinology 139 (1998) 5267–5270. [67] R.B. Simerly, C. Chang, M. Muramatsu, L.W. Swanson, Distribution of androgen and estrogen receptor mRNA-containing cells in the rat brain: an in situ hybridization study, J. Comp. Neurol. 294 (1990) 76–95. [68] M. Singh, E.M. Meyer, J.W. Simpkins, The effect of ovariectomy and estradiol replacement on brain-derived neurotrophic factor messenger ribonucleic acid expression in cortical and hippocampal brain regions of female Sprague–Dawley rats, Endocrinology 136 (1995) 2320–2324.

[69] F. Sohrabji, L.A. Greene, R.C. Miranda, C.D. Toran-Allerand, Reciprocal regulation of estrogen and NGF receptors by their ligands in PC-12 cells, J. Neurobiol. 25 (1994) 974–988. [70] F. Sohrabji, R.C. Miranda, C.D. Toran-Allerand, Estrogen differentially regulates estrogen and nerve growth factor receptor mRNAs in adult sensory neurons, J. Neurosci. 14 (1994) 459–471. [71] F. Sohrabji, R.C.G. Miranda, C.D. Toran-Allerand, Identification of a putative estrogen response element in the gene encoding brainderived neurotrophic factor, Proc. Natl. Acad. Sci. USA 92 (1995) 11110–11114. [72] F. Sohrabji, K.W. Peeples, O.A. Marroquin, Local and cortical effects of olfactory bulb lesions on trophic support and cholinergic function and their modulation by estrogen, J. Neurobiol. 45 (2000) 61–74. [73] D. Soppet, E. Escandon, J. Maragos, D.S. Middlemas, S.W. Reid, J. Blair, L.E. Burton, B.R. Stanton, D.R. Kaplan, T. Hunter, K. Nikolics, L.F. Parada, The neurotrophic factors brain-derived neurotrophic factor and neurotrophin-3 are ligands for trkB tyrosine kinase receptor, Cell 65 (1991) 895–903. [74] S.P. Squinto, T.N. Stitt, R.H. Aldrich, S. Davis, S.M. Bianco, C. Radziejewski, D.J. Glass, P. Masiakowski, M.E. Furth, D.M. Valenzuela, P.S. DiStefano, G.D. Yancopoulous, trkB encodes a funtional receptor for brain-derived neurotrophic factor and neurotrophin-3 but not nerve growth factor, Cell 65 (1991) 885–893. [75] T. Timmusk, N. Belluardo, M. Metsis, H. Persson, Widespread and developmentally regulated expression of neurotrophin-4 mRNA in rat brain and peripheral tissues, Eur. J. Neurosci. 5 (1993) 605–613. [76] C.D. Toran-Allerand, R. Miranda, W. Bentham, W.F. Sohrabji, T.J. Brown, R.B. Hochberg, N.J. MacLusky, Estrogen receptors colocalize with low-affinity nerve growth factor receptors in cholinergic neurons of the basal forebrain, Proc. Natl. Acad. Sci. USA 89 (1992) 4668–4672. [77] G.B. Tremblay, A. Tremblay, N.G. Copeland, D.J. Gilbert, N.A. ` Jenkins, F. Labrie, V. Giguere, Cloning, chromosomal localization and functional analysis of the murine estrogen receptor, Mol. Endocrinol. 11 (1997) 352–365. [78] J. Truettner, R. Schmidt-Kastner, R. Busto, O.F. Alonso, J.Y. Loor, W.D. Dietrick, M.D. Ginsberg, Expression of brain-derived neurotrophic factor, nerve growth factor, and heat shock protein HSP70 following fluid percussion brain injury in rats, J. Neurotrauma 16 (1999) 471–486. [79] J.J. Waite, A.D. Chen, M.L. Wardlow, R.G. Wiley, A. Lappi, L.J. Thal, 192-immunoglobulin g-saporin produces graded behavioral and biochemical changes accompanying the loss of cholinergic neurons of the basal forebrain and cerebellar Purkinje cells, Neuroscience 65 (1995) 463–476. [80] J.J. Waite, M.L. Wardlow, A.D. Chen, A. Lappi, R.G. Wiley, L.J. Thal, Time course in cholinergic and and monoaminergic changes in the rat brain after immunolesioning with 192 IgG-saporin, Neurosci. Lett. 169 (1994) 154–158. [81] A. Weisz, R. Rosales, Identification of an estrogen response element upstream of the human c-fox gene that binds the estrogen receptor and the AP-1 transcription factor, Nucl. Acid Res. 18 (1990) 5097–5106. [82] P. Whitehouse, D. Price, A. Clark, J. Coyle, M. Delong, Alzheimer’s disease: evidence for selective loss of cholinergic neurons in the nucleus basalis, Ann. Neurol. 10 (1981) 122–126. [83] P. Whitehouse, D. Price, R. Struble, A. Clark, J. Coyle, M. Delong, Alzheimer’s disease and senile dementia: loss of neurons in the basal forebrain, Science 215 (1981) 1237–1239. [84] T. Sobreviela, M. Pagcatipunan, J.S. Kroin, E.J. Mufson, Retrograde transport of brain-derived neurotrophic factor (BDNF) following infusion in neo- and limbic cortex in rat: relationship to BDNF mRNA expressing neurons, J. Comp. Neurol. 375 (1996) 417–444.