The substantia nigra is generally considered to show significant cell loss not only in Parkinson’s but also in Alzheimer’s disease, conditions that share several neuropathological traits. An interesting feature of this nucleus is that the pars compacta dopaminergic neurons contain acetylcholinesterase (AChE). Independent of its enzymatic role, this protein is released from pars reticulata dendrites, with effects that have been observed in vitro, ex vivo and in vivo. The part of the molecule responsible for these actions has been identified as a 14-mer peptide, T14, cleaved from the AChE C-terminus and acting at an allosteric site on alpha-7 nicotinic receptors, with consequences implicated in neurodegeneration. Here, we show that free T14 is co-localized with tyrosine hydroxylase in rodent pars compacta neurons. In brains with Alzheimer’s pathology, the T14 immunoreactivity in these neurons increases in density as their number decreases with the progression of the disease. To explore the functional implications of raised T14 levels in the substantia nigra, the effect of exogenous peptide on electrically evoked neuronal activation was tested in rat brain slices using optical imaging with a voltage-sensitive dye (Di-4-ANEPPS). A significant reduction in the activation response was observed; this was blocked by the cyclized variant of T14, NBP14. In contrast, no such effect of the peptide was seen in the striatum, a region lacking the T14 target, alpha-7 receptors. These findings add to the accumulating evidence that T14 is a key signaling molecule in neurodegenerative disorders and that its antagonist NBP14 has therapeutic potential.

The basal forebrain has received much attention due to its involvement in multiple cognitive functions, but little is known about the basic neuronal mechanisms underlying its development, nor those mediating its primary role in Alzheimer’s disease. We have previously suggested that a novel 14-mer peptide, ‘T14’, could play a pivotal role in Alzheimer’s disease, via reactivation of a developmental signaling pathway. In this study, we have characterized T14 in the context of post-natal rat brain development, using a combination of different techniques. Ex-vivo rat brain slices containing the basal forebrain, at different stages of development, were used to investigate large-scale neuronal network activity in real time with voltage-sensitive dye imaging. Subsequent Western blot analysis revealed the expression profile of endogenous T14, its target alpha7 nicotinic receptor and the familiar markers of Alzheimer’s: amyloid beta and phosphorylated Tau. Results indicated maximal neuronal activity at the earliest ages during development, reflected in a concomitant profile of T14 peptide levels and related proteins. In conclusion, these findings show that the peptide, already implicated in neurodegenerative events, has an age-dependent expression, suggesting a possible contribution to the physiological mechanisms underlying brain maturation.

Despite the many attempts to understand the aetiology of Alzheimer's disease, the basic mechanisms accounting for the progressive cycle of neuronal loss are still unknown. Previous work has suggested that the pivotal molecule mediating neurodegeneration could be an independently acting peptide cleaved from acetylcholinesterase. This previously unidentified agent acts as a signalling molecule in selectively vulnerable groups of cells where erstwhile developmental mechanisms are activated inappropriately to have a toxic effect in the context of the mature brain. We have previously shown that the toxic actions of this peptide, whose level is doubled in the Alzheimer brain, can be blocked by a cyclised variant (NBP14). However, the size and properties of NBP14 would render it unlikely as a feasible therapeutic candidate. Here therefore we test a synthetic peptidomimetic (NB-0193), modelled on the binding of NBP14 to the target alpha-7 nicotinic receptor, and benchmarked against it to screen for reversal effects using real-time optical imaging in rat brain slices. The blocking action of NB-0193 was confirmed by testing its effect against peptide-induced calcium influx in cell cultures, where it showed a dose-dependent profile over a trophic-toxic range. Moreover, NB-0193 presented promising pharmacokinetic characteristics and could therefore prompt a new therapeutic approach against Alzheimer's disease.