Malonate-induced cortico-motoneuron death is attenuated by NT-4, but not by BDNF or NT-3

Neurotrophins are promising candidates to slow the progression of amyotrophic lateral sclerosis (ALS), a neurodegenerative disease in which spinal and cortical motoneurons selectively degenerate. In a long-term in vitro model, malonate-induced toxicity and cell death of motoneurons have been demonstrated. Here we studied the neuroprotective effect of BDNF, NT-3, and NT-4 on the cell death of cortical motoneurons in an organotypic culture model after chronic mitochondrial inhibition with malonate. Our data show that NT-4 completely prevents malonate-induced toxicity, whereas BDNF or NT-3 had no neuroprotective effect. In clinical trials for ALS, predominantly focussed on the survival of spinal motoneurons, BDNF has already been tested with disappointing results; our results suggest that NT-4 may be a better neurotrophin to prevent motoneuron loss.     

NGF, BDNF and NT-5, but not NT-3 protect against MPP toxicity and oxidative stress in neonatal animals

A growing body of evidence suggests that neurotrophic factors can protect neurons against neuronal death. In the present study we examined whether systemic administration of members of the neurotrophin family, nerve growth factor (NGF), brain derived neurotrophic factor (BDNF), neurotrophin 3 (NT-3) and neurotrophin 5 (NT-5) and basic fibroblast growth factor (bFGF) could protect against 1-methyl-4-phenylpyridinium (MPP⁺) induced striatal damage in neonatal rats. Systemic administration of NGF, BDNF and NT-5 produced significant neuroprotective effects, whereas NT-3 was ineffective. Systemic administration of bFGF had significant neuroprotective effects as assessed by T₂-weighted magnetic resonance imaging and measurements of n-acetylaspartate and lactate using chemical shift magnetic resonance imaging. Systemic administration of NGF, BDNF and bFGF, but not NT-3 attenuated MPP⁺ induced increases in hydroxyl radical generation as assessed by the conversion of salicylate to 2,3- or 2,5-dihydroxybenzoic acid (DHBA). These results show that systemic administration of several neurotrophins and bFGF can attenuate neuronal damage induced by chemical hypoxia in vivo by a mechanism which may involve attenuation of oxidative stress.     

BDNF and NT-3, but not NGF, Prevent Axotomy-induced Death of Rat Corticospinal Neurons In Vivo

Brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) have been identified as survival factors for adult axotomized rat corticospinal neurons (CSN) in vivo. Axotomy of corticospinal neurons at the level of the internal capsule induced death of 46% of the CSN within the first week after axotomy. The surviving population of CSN displayed severe atrophy with mean cross-sectional area 49% of their unlesioned contralateral counterparts 7 days after axotomy. Using in situ hybridization to assess the expression of the receptors for the family of neurotrophins, we found trkB and trkC but not trkA mRNA expression in CSN. Intraparenchymal application of BDNF or NT-3 at doses of 12 μg/day for 7 days via an osmotic minipump fully prevented the axotomy-induced death of CSN. Interestingly, no neuronal atrophy was seen after BDNF application while NT-3 had only a partial effect on the size of the axotomized CSN. Nerve growth factor did not prevent death or cell atrophy, consistent with the lack of trkA mRNA expression in these neurons. These findings show that BDNF and NT-3 are survival factors for adult rat CSN in vivo , and may contribute to the development of therapeutic strategies aiming at the prevention of CSN degeneration in human motor neuron diseases.     

BDNF and NT-4, but not NT-3, promote development of inhibitory synapses in the absence of neuronal activity

Development of the full complement of inhibitory synapses in cerebellar cultures requires the presence of neuronal activity. The neurotrophins, BDNF, NT-3 and NT-4, were applied to cerebellar explants during activity blockade. Control numbers of inhibitory Purkinje cell axosomatic synapses developed in the presence of the TrkB receptor ligands, BDNF and NT-4, but not the TrkC receptor ligand, NT-3. The results suggest that BDNF and NT-4 have a role in the promotion of activity-dependent inhibitory synaptogenesis.     

Monoamine-activated α2-macroglobulin inhibits choline acetyltransferase of embryonic basal forebrain neurons and reversal of the inhibition by NGF and BDNF but not NT-3

Monoamine-activated α₂-macroglobulin (α₂M) has recently been shown to inhibit the growth and survival of cholinergic neurons of the basal forebrain (Liebl and Koo: J Neurosci Res 35:170–182, 1993). The mechanism of this inhibitory effect is believed to involve the regulation of growth factor activities by α₂M. The objectives of this study are to determine whether monoamine-activated α₂M can inhibit choline acetyltransferase (ChAT) activity of cholinergic basal forebrain neurons, and whether some common neurotrophins in the CNS can reverse the inhibition. This study demonstrates that both methylamine-activated α₂M (MA-α₂M) and serotonin-activated α₂M (5HT-α₂M) can dose-dependently suppress the expression of normal basal levels of ChAT activity in embryonic rat basal forebrain cells in vitro, while normal α₂M has little or no effect. As little as 0.35 μM monoamine-activated α₂M can suppress the ChAT activity, whereas either nerve growth factor (NGF) or brain-derived neurotrophic factor (BDNF), but not neurotrophin-3 (NT-3), stimulates ChAT expression of these cells. The addition of either NGF or BDNF to the α₂M-suppressed cells can increase ChAT activity back to its normal levels, while NT-3 can not. These results demonstrate that (1) monoamine-activated α₂M is a potent non-cytotoxic inhibitor of the ChAT activity in cholinergic basal forebrain neurons, and (2) NGF and BDNF are capable of not only stimulating the ChAT activity but can also specifically reverse the α₂M inhibition. The potential physiological role of monoamine-activated α₂M and neurotrophins in the degeneration and regeneration of cholinergic neurons is discussed. In addition, we propose that α₂M may serve as an important tool for evaluating the roles of growth factors in the nervous system. © 1994 Wiley-Liss, Inc.     

Corticosterone regulates expression of BDNF and trkB but not NT-3 and trkC mRNA in the rat hippocampus

Corticosterone has profound effects on growth, differentiation, and synaptic transmission of hippocampal neurons by activation of mineralocorticoid receptors (MRs) and glucocorticoid receptors (GRs). In the present study we tested if neurotrophins can be implicated in these effects. For this purpose we injected 30, 300, and 1,000 μg corticosterone s.c. (per kg body weight) in adrenalectomized rats and measured the mRNA levels of brain-derived neurotrophic factor (BDNF), tyrosine receptor kinase (trk)B, neurotrophin (NT)-3, and trkC in hippocampal cell fields at 6 hr after steroid administration by in situ hybridization. NT-3 and trkC mRNA did not show significant changes in any hippocampal region after the various doses of conticosterone. BDNF mRNA decreased after corticosterone administration dose dependently, resulting in a maximal suppression of 35, 20, and 50% in dentate gyrus, CA3, CA1, respectively. Interestingly, trkB responded to corticosterone in an inverted U-shaped fashion in CA3 and dentate gyrus: the low dose of corticosterone increased trkB mRNA expression in both regions by approximately 30%, while the effect of the two higher doses was not different from the vehicle injected controls. In conclusion, we found differential effects of low and high doses of corticosterone on BDNF and trkB expression in hippocampus, which suggests involvement of a coordinated MR- and GR-mediated action. J. Neurosci. Res. 48:334–341, 1997. © 1997 Wiley-Liss, Inc.     

BDNF, but not NT-3, promotes long-term survival of axotomized adult rat corticospinal neurons in vivo

Axotomy-induced death of corticospinal neurons (CSN) is prevented by intracotrical infusions of BDNF or NT-3 within the first week after axotomy. The present study examined whether this represents merely a delay of CSN death or whether BDNF and NT-3 can promote long-term survival of these neurons in vivo. The neurotrophins were infused for an initial period of 14 days to lesioned CSN which was followed by 28 days without treatment. BDNF was able to promote CSN survival for at least 42 days while NT-3 had no significant effect. These results suggest that initial BDNF treatment induces an endogamous mechanism that promotes survival of axotomized CSN without further exogenous neurotrophic factor supply. These findings may be important for the design of therapeutic strategies for motoneuron disease.     

Thyroid hormone regulation of NGF, NT-3 and BDNF RNA in the adult rat brain.

The effects of peripherally administered thyroid hormone (TH; 500 micrograms/kg; i.p.; q.d.) on the relative abundances of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin-3 (NT-3) RNA were determined by rtPCR in the cortex and hippocampus of young adult rats. Corresponding changes in choline acetyltransferase (ChAT) activity were measured since NGF and BDNF have been shown to enhance the expression of this marker enzyme of central cholinergic pathways. Abundance levels of NGF and NT-3, relative to cyclophilin (cycl), were increased significantly (+50%, P < 0.05) in the hippocampus following TH treatment. Despite enhanced abundance of NGF in the hippocampus, ChAT activity was unchanged, whereas ChAT activity was modestly increased by 28% in the cortex without corresponding changes in NGF, NT-3 or BDNF. These results demonstrate that TH administration is capable of inducing the accumulation of NT-3, in addition to NGF but that the induction levels of RNA cannot be directly correlated with responsivity of the cholinergic system as measured by ChAT activity.     

Dynamic patterns of BDNF expression in injured sensory neurons: differential modulation by NGF and NT-3

It has been suggested that altered retrograde neurotrophin support contributes to the phenotypic switch observed in BDNF expression in injured sensory neurons. Thus, modulatory influences of NGF and NT-3 on BDNF expression in injured adult rat DRG neurons were examined using in situ hybridization and immunohistochemical approaches. Quantitative analysis reveals a biphasic response to sciatic nerve injury, whereby in the first day following injury, BDNF expression is up-regulated in approximately 83% of injured neurons including all small neurons, and a larger pool of trkB expressing neurons than in intact. By 1 week and up to 3 weeks later expression is still seen in approximately 66% of injured neurons, but the characteristic phenotypic switch in the subpopulations expressing BDNF occurs, whereby expression in the trkA population is reduced and expression in trkB- and in trkC-positive neurons is elevated. NGF infusion results in elevated levels of BDNF expression in both intact and injured trkA-positive neurons, accompanied by reduced trkB expression. NT-3 acts in an opposite fashion effecting a down-regulation in BDNF expression in intact neurons and preventing/reducing the injury-associated increases in BDNF expression in both trkC- and nontrkC-expressing subpopulations of injured neurons. These effects suggest NGF can regulate BDNF expression in trkA-expressing neurons regardless of the axonal state and that elevated levels of BDNF may contribute to the down-regulation in trkB expression associated with these states. Furthermore, the findings demonstrate that NT-3 can act in an antagonistic fashion to NGF in the regulation of BDNF expression in intact neurons, and mitigate BDNF's expression in injured neurons.     

BDNF, NT-3 and NGF induce distinct new Ca2+ channel synthesis in developing hippocampal neurons

Neurotrophins exert short- and long-term effects on synaptic transmission. The mechanism underlying these forms of synaptic plasticity is unknown although it is likely that intracellular Ca2+ and presynaptic Ca2+ channels play a critical role. Here we show that BDNF, NGF and NT-3 (10-100 ng/mL) exhibit a selective long-term up-regulation of voltage-gated Ca2+ current densities in developing hippocampal neurons of 6-20 days in culture. NGF and NT-3 appear more effective in up-regulating L-currents, while BDNF predominantly acts on non-L-currents (N, P/Q and R). The effects of the three neurotrophins were time- and dose-dependent. The EC50 was comparable for BDNF, NGF and NT-3 (10-16 ng/mL) while the time of half-maximal activation was significantly longer for NGF compared to BDNF (58 vs. 25 h). Despite the increased Ca2+ current density, the neurotrophins did not alter the voltage-dependence of channel activation, the kinetics parameters or the elementary properties of Ca2+ channels (single-channel conductance, probability of opening and mean open time). Neurotrophin effects were completely abolished by coincubation with the nonspecific Trk-receptor inhibitor K252a, the protein synthesis blocker anisomycin and the MAP-kinase inhibitor PD98059, while cotreatment with the PLC-gamma blocker, U73122, was without effect. Immunocytochemistry and Western blotting revealed that neurotrophins induced an increased MAP-kinase phosphorylation and its translocation to the nucleus. The present findings suggest that on a long time scale different neurotrophins can selectively up-regulate different Ca2+ channels. The action is mediated by Trk-receptors/MAP-kinase pathways and induces an increased density of newly available Ca2+ channels with unaltered gating activity.     

NT-4/5 and LIF,but not NT-3 and BDNF,promote NPY mRNA expression in cortical neurons in the absence of spontaneous bioelectrical activity

Epigenetic factors are known to influence the differentiation of neocortical neurons. The present study analyses the role of spontaneous bioelectrical activity (SBA) and neurotrophic factors on the expression of neuropeptide Y (NPY) in rat visual cortical neurons using organotypic monocultures prepared from newborn animals and in situ hybridization to detect the NPY messenger ribonucleic acid (mRNA). Spontaneously active cortex cultures display NPY mRNA expression in about 7% of all cortical neurons from 10 days in vitro (DIV) on. Blocking the SBA by chronic application of 10 mm Mg²⁺ for 3–30 DIV reduces the percentage of NPY neurons to about 2%. Allowing an initial phase of SBA (1–20 DIV) followed by an SBA blockade (for 21–50 DIV) results in 2% labelled neurons, indicating a dramatic reduction of NPY mRNA expression in the absence of SBA. Surprisingly, the reverse experiment (a period of SBA blockade for 1–20 DIV followed by a period of SBA recovery for 21–40 DIV) does not cause an upregulation of NPY mRNA expression. However, allowing cultures to differentiate as spontaneously active cultures, then applying a transient period of SBA blockade which is followed by a second period of SBA, does rescue the NPY mRNA expression in 7% of the cortical neurons. We conclude that SBA is a main trigger for NPY mRNA expression and it is particularly important during an early postnatal period of differentiation. We then analysed whether neurotrophic factors known to modulate cortical neuropeptide expression are able to do so in the absence of SBA. Supplementing chronically blocked cultures with the neurotrophins, brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), neurotrophin-4/5 (NT-4/5) and the cytokine, leukaemia inhibitory factor (LIF), reveals that BDNF and NT-3 are unable to increase the percentage of NPY neurons. In contrast, LIF and NT-4/5 increase the percentage of NPY neurons to 4 and 6–7%, respectively. Moreover, neurons treated with NT-4/5 display a very high level of NPY mRNA expression in somata and in the dendritic trees. The data suggest a complex interplay and a hierarchy of epigenetic factors in regulating the neurochemical architecture of the developing neocortex.     

NGF, NT-3 and Trk C mRNAs, but not TrkA mRNA, are upregulated in the paraventricular structures in experimental hydrocephalus

OBJECTS: This study was designed to detect possible alterations in the expression of neurotrophins and trks in kaolin-induced hydrocephalus by in situ hybridization. METHODS AND RESULTS: Sixteen rats were treated by injection of 25 mg kaolin suspended in 0.1 ml of physiological saline into the cisterna magna. Four rats were injected with saline and served as controls. The kaolin-treated rats were divided into two groups studied 1 and 4 weeks after treatment. Rats were anesthetized and killed, and their brains were rapidly dissected and frozen. DNA oligonucleotide probes for nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and trkA, trkB, and C were labeled with [(35)S]dATP using terminal deoxyribonucleotidyl transferase for in situ hybridization. Hydrocephalic brains were also classified according to the degree of ventricular enlargement. The results observed were as follows. (1) The medial septal and striatal NGF mRNA levels increased with severity in animals. (2) Hippocampal trkB and BDNF mRNA levels increased with time in animals with moderate ventricular enlargement. (3) Expression of hippocampal trkB, trkC, and NT-3 mRNA increased in animals with moderate ventricular enlargement, while it apparently decreased in the large ventricular enlargement group reaching normal ranges. (4) In the corpus callosum there was an apparent increase in NGF, NT-3 and trkC mRNA, but not in trkA, in hydrocephalic animals. NT-3 EIA confirmed the presence of NT-3 protein increases in corpus callosum. It is therefore possible that simultaneous NGF, NT-3, and trkC receptor upregulation occurred in glial elements of the white matter. CONCLUSIONS: These results demonstrate that neurotrophins and their receptors are overexpressed in many damaged structures of the severely hydrocephalic brain. There were discrepancies in the distribution of NGF and trkA mRNA, and we hypothesize that NGF mRNA in the damaged white matter structure might be due to the reduced availability of other receptors, such as the low-affinity NGF receptors.     

BDNF，NT—3对体外培养的胚鼠脊髓AChE和NADPH—d阳性神经元生长发育的影响

利用AChE和NADPH d酶组织化学染色法研究了脑源性神经营养因子 (brain derivedneurotrophicfac tor ,BDNF)和神经营养因子 3(neurotrophin 3,NT 3)对离体培养的胚胎大鼠脊髓胆碱能神经元和一氧化氮能神经元生长发育的影响。结果显示 :BDNF处理组和NT 3处理组AChE阳性神经元数和NADPH d阳性神经元数均显著高于对照组 (P <0 .0 5 )。BDNF组AChE阳性神经元和NADPH d阳性神经元胞体平均直径、每细胞突起数和最长突起长度均显著高于对照组 (P <0 .0 5 )。NT 3组NADPH d阳性神经元的生长发育与对照组无明显差异 ,仅AChE阳性神经元的每细胞突起数和最长突起长度显著高于对照组 (P <0 .0 5 ) ,对胞体发育无影响。结果提示 :BDNF ,NT 3促进脊髓神经元的存活和生长发育 ,二者的作用具有选择性和特异性。     

Granule cell mRNA levels for BDNF, NGF, and NT-3 correlate with neuron losses or supragranular mossy fiber sprouting in the chronically damaged and epileptic human hippocampus

This study determined in temporal lobe epilepsy patients if there were correlations among hippocampal granule cell expression of neurotrophin mRNAs, aberrant supragranular mossy fiber sprouting, and neuron losses. Consecutive surgically resected hippocampi (n=9) and comparison tissue from autopsies (n=3) were studied for:

1. Granule cell mRNA levels usingin situ hybridization for brainderived neurotrophic factor (BDNF), nerve growth factor (NGF), and neurotrophin-3 (NT-3);
2. neo-Timm supragranular mossy fiber sprouting; and
3. Ammon’s horn neuron densities.

Clinically, patients were classified into those with hippocampal sclerosis (HS;n=7) and non-HS cases (i.e., mass lesions and autopsies;n=5). Results showed that compared to non-HS cases, HS patients showed increased granule cell mRNA levels for BDNF, NGF, and NT-3 (p=0.035,p=0.04,p=0.045 respectively; one-tail directional test). Moreover, granule cell BDNF mRNA levels correlated inversely with Ammon’s horn neuron densities (p=0.02) and correlated positively with greater supragranular mossy fiber sprouting (p=0.02). NGF mRNA levels correlated inversely with Ammon’s horn neuron densities (p=0.02), and TN-3 mRNA levels correlated inversely with age at surgery (p=0.04) and correlated positively with greater mossy fiber sprouting (p=0.026). These results indicate in the chronically damaged human hippocampus that granule cells express neurotrophin mRNAs, and mRNA levels correlate with either hippocampal neuron losses or aberrant supragranular mossy fiber sprouting. These data support the hypothesis that in the epileptic human hippocampus, there may be pathophysiologic associations among mossy fiber synaptic plasticity, hippocampal neuron damage, and granule cell mRNA neurotrophin levels.     

NGF but not GDNF or neurturin enhance acetylcholine tissue levels in striatal organotypic brain slices

Trophic factors play important roles in survival and nerve fiber growth of cholinergic interneurons in the striatum in vivo and in vitro. In this study an organotypic slice model was used to investigate the effects of nerve growth factor and the novel factors glial cell line-derived neurotrophic factor and neurturin as well as other trophic factors on the striatal acetylcholine tissue levels. During culturing over 2 weeks acetylcholine tissue levels markedly decreased, representing degeneration of cholinergic neurons. When striatal slices were cultured for 2 weeks in the presence of 100 ng\ml nerve growth factor tissue levels of acetylcholine and the expression of choline acetyltransferase-like immunoreactivity and mRNA, as well as the muscarinic M2 autoreceptor mRNA were markedly enhanced compared to slices cultured without or with 10 ng\ml nerve growth factor. A single administration of nerve growth factor had no effect on acetylcholine tissue levels suggesting that nerve growth factor does not directly increase acetylcholine synthesis. All other trophic factors (glial cell line-derived neurotrophic factor, neurturin, brain-derived neurotrophic factor, neurotrophin-3 and -4\5, fibroblast growth factor-2, insulin like growth factor-I) had no effects on acetylcholine tissue levels. Thus, the organotypic slice model is a suitable system to study the effects of trophic factors and it is concluded that nerve growth factor selectively enhances acetylcholine tissue levels, indicating protection of cholinergic interneurons in the dorsal striatum.     

NGF rescues substance P expression but not neurofilament or tubulin gene expression in axotomized sensory neurons.

A reduction in the supply of retrogradely transported NGF has been proposed as a possible signal for the axotomy response in dorsal root ganglion (DRG) neurons. Components of the axotomy response that have previously been well characterized in axotomized DRG cells include changes in cytoskeletal gene expression and changes in the expression of neurotransmitters/neuromodulators such as substance P. In this study, we examined the role of NGF in the axotomy response by examining protein synthesis and mRNA levels of the low-MW neurofilament protein (NF-L) and beta-tubulin in DRG cells at 1, 7, and 12 d after axotomy with and without continuous administration of exogenous NGF. We also examined substance P levels in the DRG by immunocytochemistry under the same experimental conditions. Sciatic nerves of adult male rats were unilaterally transected at the midthigh level, and the proximal nerve stumps were placed into Silastic tubes connected to osmotic minipumps that were filled with biologically active NGF. NGF (0.5 mg/ml in saline) was continuously infused (0.5 microliter/hr) onto the proximal stumps of transected sciatic nerves for 1-12 d. Control animals were prepared in an identical fashion except that the nerves were treated with saline alone. At death, DRGs were removed from the animals; the L4 experimental DRGs (axotomized) and contralateral L4 DRGs (uninjured) were used immediately for protein synthesis experiments, while the experimental and contralateral L5 DRGs were fixed in 4% paraformaldehyde and subsequently used for in situ hybridization and immunocytochemistry. From another set of experimental animals, the L4 and L5 DRGs were harvested and used for total RNA isolation and RNA blotting experiments. Immunocytochemical studies using a polyclonal antibody to substance P showed that the immunodetectable levels of this peptide decreased to undetectable levels in DRG neurons after axotomy and saline administration. However, in axotomized neurons treated with NGF, the level of immunodetectable substance P did not decrease, but instead, increased over even that present in normal DRG neurons. Pulse labeling of DRGs with 35S-methionine:cysteine followed by 2-dimensional (2D) gel electrophoresis and fluorography revealed that the synthesis of neurofilament (NF) proteins was decreased, while that of tubulin was increased, 12 d after sciatic nerve transection. NGF administration to axotomized neurons did not alter this pattern. Quantitative analysis of in situ hybridizations of DRG neurons and RNA blot analysis with cDNA probes specific for NF-L and beta-tubulin mRNAs showed that NGF treatment of axotomized DRGs did not significantly affect cytoskeletal gene expression at the mRNA level.(ABSTRACT TRUNCATED AT 400 WORDS)     

NT‐3, but not BDNF, prevents atrophy and death of axotomized spinal cord projection neurons

Following spinal cord injury, projection neurons are frequently axotomized and many of the cells subsequently die. One goal in spinal injury research is to preserve damaged neurons so that ultimately they are accessible to regeneration‐promoting strategies. Here we ask if neurotrophin treatment can prevent atrophy and death of axotomized sensory projection neurons. In adult rats, a hemisection was made in the thoracic spinal cord and axotomized neurons were retrogradely labelled with Fluoro‐Gold. Four distinct populations of cells were identified in the lumbar spinal cord, and both numbers and sizes of labelled cells were assessed at different time points postlesion. A progressive and significant degeneration was observed over time with severe atrophy apparent in all cell populations and significant cell loss evident by 4 weeks postlesion. This time point was used to assess neurotrophin effects. Hemisected rats were treated with either neurotrophin 3 (NT‐3) or brain‐derived neurotrophic factor (BDNF, 12 μg/day for each), or a vehicle solution, delivered continuously to the lesion site via an osmotic minipump. Treatment with NT‐3, but not BDNF, completely reversed cell atrophy in three of the four cell populations and also induced a significant increase in the number of surviving cells. In situ hybridization experiments showed trkB and trkC mRNA to be expressed in the majority of ascending spinal projection neurons, suggesting that these cells should be responsive to both BDNF and NT‐3. However, only NT‐3 treatment was neuroprotective, indicating that BDNF may not have reached the cell bodies of injured neurons. These results demonstrate that NT‐3 may be of benefit in preventing the secondary cell loss that occurs following spinal injury.     

Levels of trkA and BDNF mRNA, but not NGF mRNA, fluctuate across the estrous cycle and increase in response to acute hormone replacement

Recent studies suggest that hormone replacement therapy can help to reduce the risk and severity of Alzheimer's-related dementia in postmenopausal women. We have hypothesized that these effects are due, in part, to the ability for estrogen and progesterone to enhance hippocampal function, as well as the functional status of cholinergic projections to the hippocampus and cortex, by influencing the expression of specific neurotrophins and neurotrophin receptors. In the present study, quantitative in situ hybridization techniques were used to determine whether the levels of trkA mRNA in the basal forebrain, and nerve growth factor (NGF) mRNA and brain-derived neurotrophic factor (BDNF) mRNA in the hippocampus, are significantly affected by physiological changes in circulating gonadal steroids. Gonadally intact animals were sacrificed at different stages of the estrous cycle and ovariectomized animals were sacrificed at different times following the administration of either estrogen or estrogen plus progesterone. In gonadally intact animals, significant fluctuations in the levels of trkA mRNA in the medial septum (MS), and BDNF mRNA in regions CA1 and CA3/4 of the hippocampus, were detected across the estrous cycle. In animals that received hormone replacement, a significant increase (30.4%) in trkA mRNA was detected in the MS of animals sacrificed 24 h following estrogen administration. Levels of trkA mRNA in the MS declined to control levels over the next 48 h; however, a single injection of progesterone administered 48 h after estradiol appeared to prevent any further decline in trkA mRNA over the next 24 h. In addition, significant increases in BDNF mRNA were detected in the dentate granule cell layer (73.4%), region CA1 (28.1%), and region CA3/4 (76.9%) of animals sacrificed 53 h after receiving estrogen and 5 h after receiving progesterone. No significant changes in trkA mRNA were detected in the nucleus basalis magnocellularis, and no significant changes in NGF mRNA were detected in the hippocampus. These data demonstrate that levels of trkA mRNA in the MS, and BDNF mRNA in the hippocampus, are affected by physiological changes in the levels of circulating gonadal steroids and are elevated in response to acute hormone replacement. The relevance of these effects to the ability for estrogen replacement to enhance cholinergic activity and hippocampal function, and thereby reduce the risk and severity of Alzheimer's-related dementia in postmenopausal women, is discussed.     

Intracerebroventricular injection of muscimol, baclofen or nipecotic acid stimulates food intake in layer-type, but not meat-type, chicks

This study was designed to compare the effects of muscimol (GABA(A) agonist), baclofen (GABA(B) agonist) and nipecotic acid (GABA uptake inhibitor) on food intake in two chicken strains (meat-type and layer-type chicks). The intracerebroventricular (ICV) injection of all GABA agents induced hyperphagia in layer-type chicks. However, in broiler chicks, there were similar tendencies with muscimol and nipecotic acid but not significantly different. Conversely, ICV injection of baclofen depressed feeding of broiler chicks. These results suggest that there are some differences in central GABAergic systems between these strains of chicks, but GABAergic systems have an important role in the regulation of food intake in neonatal chicks.     

Memory consolidation and amnesia modify 5-HT6 receptors expression in rat brain: an autoradiographic study

Traditionally, the search for memory circuits has been centered on examinations of amnesic and AD patients, cerebral lesions and, neuroimaging. A complementary alternative might be the use of autoradiography with radioligands. Indeed, ex vivo autoradiographic studies offer the advantage to detect functionally active receptors altered by pharmacological tools and memory formation. Hence, herein the 5-HT(6) receptor antagonist SB-399885 and the amnesic drugs scopolamine or dizocilpine were used to manipulate memory consolidation and 5-HT(6) receptors expression was determined by using [(3)H]-SB-258585. Thus, memory consolidation was impaired in scopolamine and dizocilpine treated groups relative to control vehicle but improved it in SB-399885-treated animals. SB-399885 improved memory consolidation seems to be associated with decreased 5-HT(6) receptors expression in 15 out 17 brain areas. Scopolamine or dizocilpine decreased 5-HT(6) receptors expression in nine different brain areas and increased it in CA3 hippocampus or other eight areas, respectively. In brain areas thought to be in charge of procedural memory such basal ganglia (i.e., nucleus accumbens, caudate putamen, and fundus striate) data showed that relative to control animals amnesic groups showed diminished (scopolamine) or augmented (dizocilpine) 5-HT(6) receptor expression. SB-399885 showing improved memory displayed an intermediate expression in these same brain regions. A similar intermediate expression occurs with regard to amygdala, septum, and some cortical areas in charge of explicit memory storage. However, relative to control group amnesic and SB-399885 rats in the hippocampus, region where explicit memory is formed, showed a complex 5-HT(6) receptors expression. In conclusion, these results indicate neural circuits underlying the effects of 5-HT(6) receptor antagonists in autoshaping task and offer some general clues about cognitive processes in general.