A nerve growth factor mimetic TrkA antagonist causes withdrawal of cortical cholinergic boutons in the adult rat

Abstract

Cholinergic neurons respond to the administration of nerve growth factor (NGF) in vivo with a prominent and selective increase of choline acetyl transferase activity. This suggests the possible involvement of endogenous NGF, acting through its receptor TrkA, in the maintenance of central nervous system cholinergic synapses in the adult rat brain. To test this hypothesis, a small peptide, C(92-96), that blocks NGF-TrkA interactions was delivered stereotactically into the rat cortex over a 2-week period, and its effect and potency were compared with those of an anti-NGF monoclonal antibody (mAb NGF30). Two presynaptic antigenic sites were studied by immunoreactivity, and the number of presynaptic sites was counted by using an image analysis system. Synaptophysin was used as a marker for overall cortical synapses, and the vesicular acetylcholine transporter was used as a marker for cortical cholinergic presynaptic sites. No significant variations in the number of synaptophysin-immunoreactive sites were observed. However, both mAb NGF30 and the TrkA antagonist C(92-96) provoked a significant decrease in the number and size of vesicular acetylcholine transporter-IR sites, with the losses being more marked in the C(92-96) treated rats. These observations support the notion that endogenously produced NGF acting through TrkA receptors is involved in the maintenance of the cholinergic phenotype in the normal, adult rat brain and supports the idea that NGF normally plays a role in the continual remodeling of neural circuits during adulthood. The development of neurotrophin mimetics with antagonistic and eventually agonist action may contribute to therapeutic strategies for central nervous system degeneration and trauma.Nerve growth factor (NGF) is the first well characterized member of a family of neurotrophic factors (NTFs) (1) that includes brain-derived neurotrophic factor, neurotrophin 3, and neurotrophin 4 (2, 3). These neurotrophins are known to regulate the survival, differentiation, and phenotypic maintenance of specific neuronal populations, but their role in neuronal plasticity is not fully understood. Investigations in newborn and adult rats have shown that cholinergic neurons in the corpus striatum and those in the basal forebrain projecting to the hippocampus and cortex respond to exogenous NGF with a selective and prominent increase of choline acetyl transferase (ChAT) activity (4-8). These areas are the major targets of ascending projections from cholinergic basal forebrain neurons that retrogradely transport NGF from these areas to the cholinergic cell bodies of the basal forebrain (9, 10). The intracerebral application of NGF prevents the downregulation of cholinergic markers in septal cholinergic neurons after axotomy (11) and ameliorates both cholinergic and behavioral deficits after basalocortical lesions (12, 13).Another cholinergic phenotype-specific protein is the vesicular acetylcholine transporter (VAChT) (14). This molecule mobilizes cytosolic acetylcholine (ACh) into the synaptic vesicle...

In the Adult Hippocampus, Chronic Nerve Growth Factor Deprivation Shifts GABAergic Signaling from the Hyperpolarizing to the Depolarizing Direction

“…Interestingly, in the present experiments, the reduced expression of Kcc2 mRNA and protein was associated with a severe impairment of cholinergic function not only in the hippocampus but also in the basal forebrain cholinergic neurons. These neurons are known to critically depend on NGF for their survival and differentiation (Hefti, 1986;Li et al, 1995;Molnar et al, 1998;Cattaneo et al, 1999;Debeir et al, 1999) and previous studies from AD11 mice have unveiled a selective loss of cholinergic neurons in the basal forebrain (Capsoni et al, 2000a) associated with a severe deficit of the cholinergic function Sola et al, 2006). Therefore, it is likely that changes in GABAergic signaling observed here are dependent on the severe deficit in nicotine cholinergic activity induced by chronic NGF deprivation.…”

Identification of a low–molecular weight TrkB antagonist with anxiolytic and antidepressant activity in mice

“…We recently developed a highly potent small peptide that allosterically inhibits TrkB signaling in neurons and that is active in vivo after systemic delivery (20). Our in vivo study, together with others' studies (21)(22)(23), demonstrates the feasibility of developing heterocyclic ligands that can modulate TrkB activity in living animals. However, peptide-derived ligands have the problem of being proteolytically unstable, which potentially decreases their efficiency under therapeutic conditions.…”

Long-Lasting Rescue of Age-Associated Deficits in Cognition and the CNS Cholinergic Phenotype by a Partial Agonist Peptidomimetic Ligand of TrkA

“…The density of VAChT-immunoreactive (IR) or synaptophysin-IR presynaptic boutons in lamina V of the parietal cortex (bregma coordinates: lateral, 4.7-5.7 mm; ventral, 3.0 -4.2 mm) and the size and density of the VAChT-IR neurons at the nucleus basalis (lateral, 2.3-3.1 mm; anteroposterior, Ϫ1.2 to Ϫ1.8 mm; ventral, 6.3-7.3 mm) per 1000 m 2 were measured using a BH-2 Olympus microscope connected to an image analysis system (MCID Elite; Imaging Research, St. Catharines, Ontario, Canada) as described (Debeir et al, 1999). Briefly, five images per area, from both hemispheres, were taken from five different slices per rat (50 images per rats for each region basalis and cortex).…”

“…These neurons express NGF receptors (Backman et al, 1997) and are dependent for their health and cholinergic phenotype on NGF receptor activation (Debeir et al, 1999;Sofroniew et al, 2001). In aging and cognitive disorders such as Alzheimer's disease (AD), CBF neurons undergo atrophy and eventually degenerate (Turrini et al, 2001;Casu et al, 2002).…”