Excitotoxic median raphe lesions aggravate working memory storage performance deficits caused by scopolamine infusion into the dentate gyrus of the hippocampus in the inhibitory avoidance task in rats

Abstract

The interactions between the median raphe nucleus (MRN) serotonergic system and the septohippocampal muscarinic cholinergic system in the modulation of immediate working memory storage performance were investigated. Rats with sham or ibotenic acid lesions of the MRN were bilaterally implanted with cannulae in the dentate gyrus of the hippocampus and tested in a light/dark step-through inhibitory avoidance task in which response latency to enter the dark compartment immediately after the shock served as a measure of immediate working memory storage. MRN lesion per se did not alter response latency. Post-training intrahippocampal scopolamine infusion (2 and 4 µg/ side) produced a more marked reduction in response latencies in the lesioned animals compared to the sham-lesioned rats. Results suggest that the immediate working memory storage performance is modulated by synergistic interactions between serotonergic projections of the MRN and the muscarinic cholinergic system of the hippocampus. Correspondence

Cellular, molecular, and genetic substrates underlying the impact of nicotine on learning

“…Much research has focused on determining the behavioral contributions that the dentate gyrus makes to learning and memory. Numerous studies have shown that the DG is critical for spatial reference memory (Barbosa, Pontes, Ribeiro, Ribeiro, and Silva, 2012; Beselia, Maglakelidze, Chkhikvishvili, Burjanadze, and Dashniani, 2010; Gilbert, Kesner, and Lee, 2001; Hernandez-Rabaza, Hontecillas-Prieto, Velazquez-Sanchez, Ferragud, Perez-Villaba, Arcusa, Barcia, Trejo, and Canales, 2008; Hunsaker, Mooy, Swift, and Kesner, 2007; Jeltsch, Bertrand, Lazarus, and Cassel, 2001; Lee, Hunsaker, and Kesner, 2005a; Xavier, Oliveira-Filho, and Santos, 1999) and spatial working memory (Babar, Melik, and Ozgunen, 2002; Babar, Melik, Ozgunen, and Polat, 2002; Costa, Bueno, and Xavier, 2005; Hernandez-Rabaza, Barcia, Llorens-Martin, Trejo, and Canales, 2007; Jeltsch et al, 2001; Niewoehner, Single, Hvalby, Jensen, Meyer zum Alten Borgloh, Seeburg, Rawlins, Sprengel, and Bannerman, 2007; Xavier et al, 1999). In addition, the DG is involved in contextual learning and memory; manipulations that impair DG function lead to deficits in contextual memory and context discrimination (Daumas, Ceccom, Halley, Frances, and Lassalle, 2009; Hernandez-Rabaza et al, 2008; Lee and Kesner, 2004; McHugh, Jones, Quinn, Balthasar, Coppari, Elmquist, Lowell, Fanselow, Wilson, and Tonegawa, 2007).…”

Dorsal and median raphe neuronal firing dynamics characterized by non-linear metrics

“…DRN contains the greatest density of serotonergic neurons, with around 11500 in the rat, and MRN follows it with approximately 1100 [1]. A large body of evidence supports the role of the DRN and MRN in an extensive array of important functions, including stress response [2][3][4][5], pain control [6][7][8][9], reproductive functions and behaviour [10], food intake and obesity [11,12], aggressiveness [13,14], social interaction [15], motivation and reward [16,17], fear [18,19], learning and memory [20][21][22][23], motor activity [12], and the sleep-wake cycle physiology [24][25][26]. Additionally, the raphe nuclei play an important role in the physiopathology of several diseases, including major depression [27][28][29], anxiety, panic, obsessive compulsive disorder, eating disorders, phobias, drug addiction, and post-traumatic stress [30].…”