Evidence for serotonin involvement in the NANC excitatory neurotransmission in the catfish intestine.
1. Four putative neurotransmitters (serotonin, substance P, ATP (alpha-beta-methylene-ATP), and vasoactive intestinal peptide, VIP) of the non-adrenergic non-cholinergic (NANC) innervation were examined for their role in the NANC excitatory neurotransmission in channel catfish intestine after adrenergic and cholinergic blockade. 2. VIP at concentrations ranging from 10(-12)M to 10(-4)M did not produce either a relaxant or a contractile response in these segments. 3. Serotonin, substance P and alpha-beta-methyl-ATP produced contractile responses in a dose-dependent manner. Their EC50 values were 5 x 10(-7)M, 5 x 10(-9)M and 5 x 10(-9)M and 5 x 10(-6)M, respectively. 4. Electrical field stimulation of the intestinal segments produced a predominant excitatory response after complete blockade of adrenergic and cholinergic divisions, suggesting a predominant NANC excitatory innervation. 5. Three types of serotonin receptor antagonists, namely methiothepin (predominantly a 5-HT1 antagonist), ketanserin (a selective 5-HT2 antagonist), methysergide and cyproheptadine (predominantly 5-HT2 blockers) and metoclopramide (a selective 5-HT3 blocker) were tested for their effectiveness against serotonin and EFS-induced contractions. Methiothepin, methysergide, cyproheptadine and metoclopramide produced significant blockade of the response to serotonin, whereas only methiothepin and cyproheptadine produced blockade of EFS-induced response. 6. Three agents tested for substance P blockade, namely spantide, 4-11 fragment of substance P, and methysergide (also a serotonin blocker), did not produce significant inhibition of the response to either substance P or EFS. 7. Suramin at a dose that blocked the ED50 concentration of ATP did not produce a significant blockade of the response to EFS suggesting that ATP-involvement in the NANC-e neurotransmission is unlikely. 8. This study confirmed the involvement of serotonin in the expression of non-adrenergic non-cholinergic excitatory response of the channel catfish intestine.
Venugopalan
C S
CS
Department of Veterinary Physiology, Pharmacology and Toxicology, School of Veterinary Medicine, Louisiana State University, Baton Rouge 70803, USA.
Holmes
E P
EP
Kleinow
K M
KM
D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001341:Autonomic Nervous System / Q000187:drug effects / Q000502:physiology*; D004558:Electric Stimulation; D007059:Ictaluridae; D066298:In Vitro Techniques; D007422:Intestines / Q000187:drug effects / Q000294:innervation*; D012701:Serotonin / Q000494:pharmacology / Q000502:physiology*; D013373:Substance P / Q000494:pharmacology; D009435:Synaptic Transmission; D014660:Vasoactive Intestinal Peptide / Q000494:pharmacology
D012701:Serotonin; D013373:Substance P; D014660:Vasoactive Intestinal Peptide; D000255:Adenosine Triphosphate; C002630:alpha,beta-methyleneadenosine 5'-triphosphate