title: Influence of the hippocampus on amino acid utilizing and cholinergic neurons within the nucleus accumbens is promoted by histamine via H₁ receptors.
abstract: OBJECTIVE
  The influence of the neurotransmitter histamine on spontaneous and stimulation-evoked release of glutamate, aspartate, GABA and ACh in the nucleus accumbens (NAc) was investigated in vivo.
  
  
  METHODS
  Using the push-pull superfusion technique, histaminergic compounds were applied to the NAc and neurotransmitter release was assessed. In some experiments, the fornix/fimbria of the hippocampus was electrically stimulated by a microelectrode and evoked potentials were monitored in the NAc.
  
  
  RESULTS
  Superfusion of the NAc with the H1 receptor antagonist triprolidine (50 μM) decreased spontaneous outflow of glutamate, aspartate and ACh, while release of GABA remained unaffected. Superfusion with histamine elevated release of ACh, without influencing that of the amino acids. Electrical stimulation of the fornix/fimbria enhanced the output of amino acids and ACh within the NAc. The evoked outflow of glutamate and ACh was diminished on superfusion with triprolidine, while release of aspartate and GABA was not affected. Superfusion of the NAc with histamine intensified the stimulation-evoked release of glutamate and Ach. Histamine also elevated the stimulation-induced release of aspartate, without influencing that of GABA. Presuperfusion with triprolidine abolished the reinforced effect of histamine on stimulation-evoked transmitter release within the NAc.
  
  
  CONCLUSIONS
  Neuronal histamine activates H1 receptors and increases spontaneous release of glutamate, aspartate and ACh within the NAc. Stimulation of the hippocampal fornix/fimbria tract also enhances release of glutamate and ACh within the NAc and this effect is intensified by H1 receptor stimulation within the NAc. The latter effects, which are mediated by hippocampal afferences, might play an important role in mnemonic performance and in emotional processes such as anxiety and stress disorders.
authors.affiliation: Department of Pharmacology and Toxicology, University of Innsbruck, Innsbruck.
authors.forename: M M
authors.initials: MM
authors.lastname: Kraus
authors.forename: H
authors.initials: H
authors.lastname: Prast
authors.forename: A
authors.initials: A
authors.lastname: Philippu
mesh_terms: D000109:Acetylcholine / Q000378:metabolism; D000818:Animals; D001224:Aspartic Acid / Q000378:metabolism; D059329:Cholinergic Neurons / Q000378:metabolism; D004558:Electric Stimulation; D005071:Evoked Potentials; D018698:Glutamic Acid / Q000378:metabolism; D006624:Hippocampus / Q000378:metabolism; D006632:Histamine / Q000378:metabolism*; D006634:Histamine H1 Antagonists / Q000494:pharmacology; D008297:Male; D008839:Microelectrodes; D009474:Neurons / Q000378:metabolism*; D009714:Nucleus Accumbens / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011969:Receptors, Histamine H1 / Q000187:drug effects / Q000378:metabolism*; D014311:Triprolidine / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
chemical_list: D006634:Histamine H1 Antagonists; D011969:Receptors, Histamine H1; D014311:Triprolidine; D001224:Aspartic Acid; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid; D006632:Histamine; D000109:Acetylcholine
keywords: H1 receptor antagonist; Histamine; acetylcholine; amino acids; electrical stimulation; hippocampal afferences to nucleus accumbens; push-pull superfusion