Comparison of the behavioural effects of infusion of carbachol and acetylcholinesterase into the rat substantia nigra

Characterization of a Bioactive Peptide T14 in the Human and Rodent Substantia Nigra: Implications for Neurodegenerative Disease

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.

Circling behavior and [14C]2-deoxyglucose mapping in rats: possible implications for autistic repetitive behaviors

Repetitive behaviors (such as circling) are one of the defining features of autism. The substantia nigra (SN) is involved in circling. We used unilateral SN pars reticulata (SNR) infusions of the GABA agonist muscimol to induce circling and deoxyglucose autoradiography mapping in adult and postnatal day (PN) 15 male and female rats to determine its substrates. In adults, muscimol infusions in posterior SNR induced a higher circling rate than in anterior SNR, after which males displayed faster circling than females. In contrast, PN15 female rats circled faster than PN15 male rats. Autoradiograms demonstrated age- and sex-specific alterations of deoxyglucose uptake in the SN pars compacta (SNC) associated with highest circling rates. The data suggest that there is a close relationship of the GABAergic SNR and dopaminergic SNC in the induction of circling; there is a topographic organization of the SNR in terms of circling behavior and associated deoxyglucose uptake, which is dependent on age and sex.