A role for TrkA during maturation of striatal and basal forebrain cholinergic neurons in vivo - PubMed (original) (raw)

A role for TrkA during maturation of striatal and basal forebrain cholinergic neurons in vivo

A M Fagan et al. J Neurosci. 1997.

Abstract

Nerve growth factor (NGF), acting via the TrkA receptor, has been shown to regulate the survival and maturation of specific neurons of the peripheral nervous system. Furthermore, exogenous NGF has potent actions on TrkA-expressing cholinergic neurons of the basal forebrain (BFCNs) and striatum. However, initial analysis of mice lacking NGF or TrkA revealed that forebrain cholinergic neurons were present in these animals through the fourth postnatal week. Because of the potential effects of NGF/TrkA interactions on these developing neurons, we have analyzed quantitatively the striatal and basal forebrain cholinergic neurons in trkA knock-out mice. By postnatal day (P) 7/8, forebrain cholinergic neurons are smaller in trkA (-/-) mice than those in wild-type littermate controls. However, cholinergic neuron number and fiber density in the hippocampus, a target region of BFCNs, are grossly intact. Interestingly, by P20-P25 trkA knock-outs contain significantly fewer (20-36%) and smaller cholinergic neurons in both the striatum and septal regions, as compared with controls. Cholinergic fiber density within the hippocampus also is depleted in knock-outs by the end of the second postnatal week. Contrary to some predictions, despite expression of p75(NTR) in the absence of trkA in BFCNs of these knock-out mice, many cells, although smaller, are still alive at P25. Our data suggest that, in the absence of NGF/TrkA signaling, striatal cholinergic neurons and BFCNs do not mature fully and that BFCNs begin to atrophy and/or die surrounding the time of target innervation.

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Figures

Fig. 1.

Striatal neurons of wild-type and_trk_A (−/−) mice stained with antibodies to ChAT or NADPH-d histochemistry. A, ChAT immunoreactivity identifies cholinergic neurons in the striatum of wild-type mice at P7.B, trk_A (−/−) mice exhibit ChAT-positive cells in the striatum at P7, but many cells are smaller (see insets in A and B), and immunolabeling intensity in both cell bodies and neuropil is generally less than that observed in wild-type mice of the same age.C, By P22, cholinergic neurons in the wild-type striatum are large and stain darkly with antibodies to ChAT. A plexus of immunoreactive fibers also can be observed throughout the striatal neuropil. D, ChAT-positive cells in the_trk_A (−/−) striatum at P22 are smaller (inset in D) than those in wild-type animals (inset in C) and often exhibit reduced ChAT immunoreactivity. Cholinergic fiber staining in the striatal neuropil also is reduced in knock-outs at this age.E, Noncholinergic neurons of the striatum, which stain for NADPH-d, are observed throughout the wild-type striatum at P22.F, Neurons stained for NADPH-d in P22_trk_A (−/−) mice appear indistinguishable in size and staining intensity from those of wild-type animals. Scale bar in_A, 100 μm.

Fig. 2.

Quantitative analysis of the number and size of neurons in the striatum of wild-type and _trk_A (−/−) mice during development. A, Unbiased counting methods were used to determine the total number of striatal neurons stained with antibodies to choline acetyltransferase (ChAT) and NADPH-diaphorase (NADPH-d) at P7/8 and P20–P25. Although the mean number of ChAT-positive cells in wild-type (n = 4) and_trk_A knock-out (n = 4) mice was not different at P7/8, _trk_A (−/−) mice (n = 6) at P20–P25 exhibited fewer ChAT-immunoreactive neurons than wild-type controls (n = 5; ¥, p = 0.059). The number of striatal neurons stained for NADPH-d did not differ between the groups at P20–P25. B, The mean cross-sectional area of striatal profiles stained for ChAT and NADPH-d was determined. ChAT-immunoreactive neuronal profiles in the striatum of_trk_A (−/−) mice were significantly smaller than those of wild-type animals at P7/8 and P20–P25. However, cells stained for NADPH-d were of similar size in the two groups of animals at P20–P25.Asterisk indicates statistical significance,p < 0.05. Error bars, SEM.

Fig. 3.

Neurons in the medial septum of P7 and P22 wild-type and trk_A (−/−) mice stained with antibodies to ChAT. A, ChAT-immunoreactive neurons in the medial septum of P7 wild-type mice appear larger (compare_insets in A and B) and stain more darkly with the ChAT antibody than those in_trk_A (−/−) mice (B) of the same age. By P22, the difference in medial septal cell size and ChAT immunostaining intensity between wild-type (C) and trk_A knock-out (D) mice is even clearer than at the earlier time point. ChAT-immunoreactive processes also appear more complex in the wild-type, as compared with the knock-out mice (see insets in C and_D). In addition, there appear to be reduced numbers of ChAT-positive neurons in the medial septum of knock-out animals at this age. Scale bar in A, 100 μm.

Fig. 4.

Quantitative analysis of the number and size of cholinergic neurons in the medial septum of wild-type and_trk_A (−/−) mice during development. A, Unbiased counting methods were used to determine the total number of septal neurons stained with antibodies to ChAT at P7/8 and P20–P25. Although the mean number of ChAT-positive cells in wild-type (n = 4) and _trk_A knock-out (n = 4) mice was not different at P7/8,_trk_A (−/−) mice (n = 6) at P20–P25 exhibited significantly fewer immunoreactive neurons than wild-type controls (n = 5). B, The mean cross-sectional area of ChAT-positive profiles in the medial septum of _trk_A knock-out mice and wild-type controls was determined. At P7, ChAT-positive neuronal profiles in knock-out animals were smaller than those in wild-type mice (§, p = 0.053). By P20–P25, immunoreactive cells in the knock-out septum were significantly atrophic, as compared with wild-type controls.Asterisk indicates statistical significance,p < 0.05. Error bars, SEM.

Fig. 5.

Counts of TUNEL-positive profiles in four tissue sections through the septal region of _trk_A (−/−) mice and littermate controls. _Trk_A (−/−) mice exhibited significantly greater numbers of TUNEL-positive nuclei in the septal region at P7 than were observed in littermate controls. This indicates that at this time point there is likely to be an increase over baseline in the amount of naturally occurring cell death in _trk_A knock-out animals. By P13, both groups of mice displayed few TUNEL-stained profiles in the septal region. _Asterisk_indicates statistical significance, p < 0.05. Error bars, SEM.

Fig. 6.

Immunoreactivity for p75NTR in the hippocampus of wild-type and _trk_A (−/−) mice at P7. A, p75NTR-immunoreactive fibers are observed in the hippocampus of wild-type mice at P7.B, A similar pattern of fiber staining is observed in_trk_A knock-outs at this time. At higher magnification, individual fibers can be seen in many regions of the wild-type (C, E, G) and trk_A (−/−) (D, F, H) hippocampus, including the stratum oriens (C, D), stratum radiatum (E, F), and molecular layer of the dentate gyrus (G, H). Fiber density in these regions is not markedly different in the two groups of animals at this time. gl, Granular layer;ml, molecular layer; or, stratum oriens;pyr, pyramidal layer; rad, stratum radiatum. Scale bars: in A, B, 100 μm; in_C–H, 20 μm.

Fig. 7.

Immunoreactivity for p75NTR in the hippocampus of wild-type and _trk_A (−/−) mice at P25. A, The adult laminated pattern of cholinergic p75NTR-positive fibers in the hippocampus is observed in wild-type mice at P25. In contrast, fiber staining is reduced markedly in _trk_A (−/−) mice of the same age (B). Differences in fiber staining are observed in all regions of the hippocampus, including the stratum oriens (C, D), stratum radiatum (E, F), and molecular layer of the dentate gyrus (G, H). Loss of fiber staining in the trk_A knock-out mice (B, D, F, H) likely does not merely reflect a simple downregulation of p75NTR protein expression because the cell bodies of these projecting neurons in the medial septum, although clearly atrophic at this time (compare_insets in A and B), stain darkly with antibodies to p75NTR. gl, Granular layer; ml, molecular layer; or, stratum oriens; pyr, pyramidal layer;rad, stratum radiatum. Scale bars: in A, B, 100 μm; in C–H, 20 μm.

References

1. Albers KM, Wright DE, Davis BM. Overexpression of nerve growth factor in epidermis of transgenic mice causes hypertrophy of the peripheral nervous system. J Neurosci. 1994;14:1422–1432. -PMC -PubMed
1. Alcantara S, Frisen J, Del Rio JA, Soriano E, Barbacid M, Silos-Santiago I. TrkB signaling is required for postnatal survival of CNS neurons and protects hippocampal and motor neurons from axotomy-induced death. J Neurosci. 1997;17:3623–3633. -PMC -PubMed
1. Alderson RF, Alterman AL, Barde YA, Lindsay RM. Brain-derived neurotrophic factor increases survival and differentiated functions of rat septal cholinergic neurons in culture. Neuron. 1990;5:297–306. -PubMed
1. Anderson KJ, Dam D, Lee S, Cotman CW. Basic fibroblast growth factor prevents death of lesioned cholinergic neurons in vivo. Nature. 1988;332:360–361. -PubMed
1. Barbacid M. The Trk family of neurotrophin receptors. J Neurobiol. 1994;25:1386–1403. -PubMed

A role for TrkA during maturation of striatal and basal forebrain cholinergic neurons in vivo - PubMed (original) (raw)