Extracellular levels of NPY in the dorsal hippocampus of freely moving rats are markedly elevated following a single electroconvulsive stimulation, irrespective of anticonvulsive Y1 receptor blockade
Introduction
Although electroconvulsive therapy (ECT) has been used in the treatment of psychiatric and neurological disorders for more than 50 years, its therapeutic mechanism(s) of action has not been identified. Neuropeptide Y (NPY), is a highly conserved 36 amino acid peptide (Tatemoto et al., 1982), proposed to play a role in affective and anxiety-related disorders (Widerlöv et al., 1988), stress-susceptibility (Thorsell et al., 2000) and limbic epileptic seizures (Woldbye et al., 1997). Specifically, NPY has been suggested to act as an endogenous anticonvulsant since NPY knock-out and knock-down mice display an increased vulnerability to seizures (DePrato et al., 2000; Baraban et al., 1997; Erickson et al., 1996). In rats, a series of electroconvulsive stimulations (ECS), an experimental model of ECT, is known to increase hippocampal levels of preproNPY mRNA, tissue concentrations of NPY-like immunoreactivity (LI) as well as extracellular levels of NPY-LI, while NPY-sensitive binding sites are down-regulated (Husum et al., 2000; Madsen et al., 2000; Mathé et al., 1998; Greisen et al., 1997; Zachrisson et al., 1995; Mikkelsen et al., 1994; Stenfors et al., 1989). Surprisingly, the effects of single ECS on NPY activity in the hippocampus are largely unexplored.
Five NPY receptors, the Y1 (Herzog et al., 1992), Y2 (Rose et al., 1995), Y4 (Lundell et al., 1996), Y5 (Gerald et al., 1996), and Y6 (Gregor et al., 1996), have been identified and cloned and are all, except Y6, present in rat brain. In the hippocampus, Y1, Y2, and Y5 receptors have been implicated in the modulation of seizure activity. For example, NPY can inhibit the release of glutamate acting via an Y2 receptor (Weiser et al., 2000; Colmers and Bleakman, 1994; Greber et al., 1994; Klapstein and Colmers, 1993; Colmers et al., 1991), while the Y5 receptor has been implicated in the inhibition of kainic acid-induced seizures in rats (Woldbye et al., 1997). On the other hand, excitatory effects of NPY in cultured dentate granule cells have also been reported (Brooks et al., 1987) and intrahippocampal injections of BIBP3226, a selective non-peptide Y1 receptor antagonist (Rudolf et al., 1994), attenuated kainic acid and penetylenetetrazole-induced seizure activity in rats (Vezzani et al., 2000a; Vezzani et al., 2000b; Gariboldi et al., 1998). These studies suggest a possible excitatory effect of NPY mediated by the Y1 receptor subtype, which may contribute to the excessive hippocampal activity occurring during seizures. Indeed, the Y1 receptor was recently suggested to modulate glutamate release from a presynaptic site and to function as an autoreceptor on NPY expressing neurons in the hippocampus (St-Pierre et al., 2000). Consequently, the aim of the present study was to investigate, in the dorsal hippocampus of freely moving rats, the effects of (1) potassium stimulation and calcium-free conditions on extracellular levels of NPY, (2) a single ECS on extracellular levels of NPY-LI in the dorsal hippocampus, (3) BIBP3226 pretreatment on NPY outflow during and after a single ECS and on the duration of the ECS-induced seizure.
Section snippets
Animals
Male Sprague–Dawley rats weighing 300–350 g (B&K Universal, Sollentuna, Sweden) were used in the present study. The animals arrived one week prior to the initiation of the experiments and were kept five in a cage in a 12 h light:dark cycle (lights on at 06:00) with free access to chow and tap water. The experiments were approved by the Stockholm’s Ethical Committee for Protection of Animals and were conducted in accordance with the Karolinska Institutet’s Guidelines for the Care and Use of
Effect of KCl on extracellular NPY-LI levels
Basal NPY-LI levels were 5.61±1.8 pmol/L in dialysates collected prior to the KCl stimulation (Fig. 1). Administration of 60 mM KCl in the perfusion medium for 20 min caused an 85% increase in extracellular NPY-LI yielding dialysate levels of 10.4±0.68 pmol/L (P<0.01, n=6). The depolarizing effect of KCl was transient as the dialysate NPY-LI levels were not different from baseline in the following two fractions.
Effects of calcium on extracellular NPY-LI levels during baseline and KCl-depolarizing conditions
As also shown in Fig. 1, NPY-LI levels were highly sensitive to the presence of calcium.
Discussion
In the present study, the release of NPY in the dorsal hippocampus of freely moving animals was studied by means of microdialysis. A 20 min application of 60 mM KCl caused a significant, transient increase in dialysate NPY-LI levels. This effect of KCl was abolished during calcium-free conditions and basal levels of NPY-LI were significantly reduced compared to normal conditions. These results show a strong calcium-dependency of dialysate NPY-LI levels which is in line with studies on NPY-release
Acknowledgements
This study was supported by the Swedish Medical Research Council, Grant 10414, the NAMI Research Institute–Stanley Foundation Bipolar Network, Ivan Nielsens Fond and the Karolinska Institutet.
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2020, iScienceCitation Excerpt :Of note, the increase in NPY intensity that we have reported in the striatum and hippocampus of mutant mice may be secondary to the occurrence of epileptic seizures in these mice. Indeed, epileptic seizures are known to increase the expression of NPY in various brain regions, including the hippocampus (Husum et al., 2002; Vezzani and Sperk, 2004). The epileptic phenotype induced in mice by expressing a Thra mutation in GABAergic neurons is highly relevant to human pathology, as a history of epilepsy has been reported for several of the rare patients with a THRA mutation (Moran and Chatterjee, 2016).
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2016, NeuropeptidesCitation Excerpt :This is in line with the NPY-induced impairment of presynaptic glutamate release and long-term potentiation (LTP), likely to be mediated via Y2 receptors (Greber et al., 1994; Whittaker et al., 1999; Sørensen et al., 2008). Likewise, increased NPY release and synthesis associated with seizures (Husum et al., 1998, 2002; Mikkelsen and Woldbye, 2006) could contribute to retrograde amnesia seen in epilepsy patients or in patients undergoing a course of electroconvulsive therapy for severe depression. In addition, several studies have tested mice deficient in NPY or its receptors.