Neuropeptide Y and Epilepsy

Abstract

It is a central tenet of the epilepsy field that seizures result from the imbalance of excitation over inhibition (1). The bulk of excitation is mediated by the neurotransmitter glutamate, whereas inhibition results mainly from the actions of ␥ -aminobutyric acid (GABA).europeptide Y (NPY) is a 36-amino acid peptide made by neurons throughout the brain and by other secretory cells of the body. NPY has been associated with a number of physiologic processes in the brain, including the regulation of energy balance, memory and learning, and epilepsy. In the hippocampus and neocortex, NPY is made by neurons that almost all express ␥ -aminobutyric acid (GABA). Many NPYcontaining interneurons also coexpress somatostatin (3). NPY receptors are densely concentrated in the strata radiatum and oriens of Ammon's horn of rats (3) and humans (4).Early investigations focused on the actions of NPY in the hippocampus. We (5-7,) and others (8) observed that application of NPY to freshly prepared slices of rat hippocampus maintained in vitro potently and selectively reduced synaptic excitation mediated by glutamate release (Fig. 1A). Further work showed that the action of NPY was highly selective, inhibiting only excitatory inputs onto pyramidal cell throughout Ammon's horn in the rat, but not affecting either synaptic inhibition (7,8) or inputs to dentate granule cells (9), despite the very high levels of NPY in the molecular layer of the dentate (10). The receptor or receptors involved in these actions belong to the G protein-coupled superfamily (11; see later).Detailed studies of the action of NPY were consistent with an entirely presynaptic site in rat hippocampus. Specifically, in neurons whose glutamatergic inputs were suppressed by NPY, the peptide did not affect the postsynaptic responses to glutamate application (6,12). Consistent with this, the release of glutamate from hippocampal slices was shown to be suppressed by NPY (13). Further studies showed that NPY suppressed N-type Ca 2 ϩ currents at presynaptic terminals in neuronal cultures (14) and N-, P/Q-, and other types of Ca 2 ϩ currents in presynaptic terminals of freshly prepared hippocampal slices (15). Once the sites and mechanisms of action were clear, the next question was what role NPY actually played in the physiology and pathophysiology of the hippocampus.It appears that elevated activity in hippocampal circuitry, such as that accompanying epileptiform discharges, results in increased NPY expression in interneurons and dentate granule cells, but that prolonged overstimulation in some epilepsy models and in humans ablates NPY (and other) interneurons. Thus several laboratories determined that NPY peptide and messenger RNA (mRNA) expression was increased in epilepsy models in vivo (16)(17)(18). At about the same time, it was reported that NPY/GABA interneurons in the hippocampus were selectively ablated in rat epilepsy models in vivo (19,20) and in epilepsy patients (21), although it was recently questioned whether NPY cells are indeed selectively vulnerable in...

Receptors of Peptides as Therapeutic Targets in Epilepsy Research

“…A large body of information provided evidence that exogenously applied NPY has anti-epileptic activity in both in vitro models (bursting without Mg 2+ , picrotoxin and stimulus-train induced bursting in hippocampal slices), and in vivo models of partial seizures such as different kindling models and kainate-induced seizures reviewed previously [60,61]. Although less extensively studied, NPY may also be beneficial in models of generalized seizures, the pentylenetetrazole [62] and the electroconvulsive seizures [63], and models of absence epilepsy [28].…”

“…There are 4 different neuropeptide receptors identified in human, Y1, Y2, Y4 and Y5, of which Y1, Y2 and Y5 may be involved in epilepsy [61]. These receptors signal through G i proteins that inhibit adenylate cyclase and decrease intracellular Ca 2+ levels [69].…”

Changes in neuropeptide Y protein expression following photothrombotic brain infarction and epileptogenesis

“…In models of temporal lobe epilepsy (TLE), increased NPY mRNA and protein expression has been demonstrated in neocortical and limbic regions, particularly in GABAergic inhibitory interneurons and following its de novo synthesis in dentate granule cells and transport through mossy fibers to their terminals (Causing et al, 1996;Gruber et al, 1994;Marksteiner et al, 1989Marksteiner et al, , 1990Marksteiner and Sperk, 1988;McCarthy et al, 1998;Schwarzer et al, 1995;Tu et al, 2005). In the epileptic brain, presynaptic release of NPY can reduce epileptiform discharges and inhibit hippocampal seizures (Colmers and El Bahh, 2003;Tu et al, 2005;Woldbye et al, 1996), whereas transgenic mice lacking endogenous NPY exhibit hyperexcitability at the cellular level and increased sensitivity to seizure activity (Baraban et al, 1997;DePrato Primeaux et al, 2000).…”

Substance P and Neuropeptide Y as Potential Biomarkers for Diagnosis of Acute Myocardial Infarction in Korean Patients

“…It regulates energy usage, and is involved in learning, memory processing, and epilepsy. 36 It has been shown that NPY is expressed in the mammalian myocardium and that it co-localizes with norepinephrine in perivascular sympathetic neurons. NPY is released together with norepinephrine during conditions of high sympathetic activity and it contributes to the regulation of myocardial contractility through NPY receptor type 1 and type 2.…”