Reconsideration of 5-Hydroxytryptamine (5-HT)7Receptor Distribution Using [3H]5-Carboxamidotryptamine and [3H]8-Hydroxy-2-(di-n-propylamino)tetraline: Analysis in Brain of 5-HT1A Knockout and 5-HT1A/1B Double-Knockout Mice (original) (raw)

Research ArticleNEUROPHARMACOLOGY

, Diane Nepomuceno, Annette Kwok, Wenying Chai, Xavier Langlois, Rene Hen, Kimberly Stark, Nicholas Carruthers and Timothy W. Lovenberg

Journal of Pharmacology and Experimental Therapeutics July 2002, 302 (1) 240-248; DOI: https://doi.org/10.1124/jpet.302.1.240

Abstract

The characterization and anatomical distribution of 5-hydroxytryptamine (5-HT)7 receptor binding sites in brain tissue has been hampered by the lack of a specific radioligand. In the present autoradiographic study, we took advantage of 5-HT1Aknockout and 5-HT1A/1B double-knockout mice to revisit the pharmacological characterization and anatomical localization of 5-HT7 binding sites in mouse brain using [3H]5-carboxamidotryptamine (5-CT) and [3H]8-hydroxy-2-(di-_n_-propylamino)tetraline (8-OH-DPAT). The distribution pattern of [3H]5-CT binding sites (2 nM) in the brain of mice lacking the 5-HT1A/1Breceptor was scarce and confined to the septum, globus pallidus, thalamus, hypothalamus, amygdala, cortex, and substantia nigra. The low densities of [3H]5-CT binding sites detected in septum, thalamus, hypothalamus, amygdala, and cortex were displaced by 10 μM of the selective 5-HT7 receptor antagonist (R)-3-(2-(2-(4-methylpiperidin-1-yl) ethyl)pyrrolidine-1-sulfonyl) phenol (SB-269970). The SB-269970-insensitive [3H]5-CT binding sites detected in globus pallidus and substantia nigra of 5-HT1A/1B knockout mice were displaced by_N_-[3-(2-dimethylamino)ethoxy-4-methoxy-phenyl]-2′-methyl-4′- (5-methyl-1,2,4-oxadiazol-3-yl)-(1,1′-biphenyl)-4-carboxamide hydrochloride (SB-216641) (1 μM), demonstrating the 5-HT1D nature of these binding sites. In contrast to the low densities of [3H]5-CT binding sites, high-to-moderate densities of [3H]8-OH-DPAT binding sites (10 nM) were found throughout the brain of 5-HT1A and 5-HT1A/1B knockout mice (olfactory system, septum, thalamus, hypothalamus, amygdala, CA3 field of the hippocampus, cortical mantle, and central gray). These [3H]8-OH-DPAT binding sites were displaced by 10 μM SB-269970, risperidone, and methiothepin but not by pindolol,_N_-tert-butyl-3-[4-(2-methoxyphenyl)piperazin-1-yl]-2-phenylpropanamide (WAY- 100135), or citalopram. We conclude that despite its high affinity for the 5-HT7 receptor in tissue homogenates, [3H]5-CT is not a good tracer for measuring 5-HT7 receptor binding sites autoradiographically. Also, the lower affinity ligand [3H]8-OH-DPAT is a much better tracer for autoradiographic studies at the 5-HT7 receptor binding sites.

Footnotes

• Abbreviations:
  5-HT
  5-hydroxytryptamine
  5-CT
  5-carboxamidotryptamine
  8-OH-DPAT
  8-hydroxy-2-(di-_n_-propylamino)tetraline
  SB-269970
  (R)-3-(2-(2-(4-methylpiperidin-1-yl)ethyl)pyrrolidine-1-sulfonyl) phenol
  WAY-100135
  _N_-tert-butyl-3-[4-(2-methoxyphenyl)piperazin-1-yl]-2-phenylpropanamide
  GR125743
  _N_-[4-methoxy-3-(4-methyl piperazin-1-yl)phenyl]-3-methyl-4-(4-pyridyl)benzamide
  SB-216641
  _N_-[3-(2-dimethylamino)ethoxy-4-methoxy-phenyl]-2′-methyl-4′-(5-methyl-1,2,4-oxadiazol-3-yl)-(1,1′-biphenyl)-4-carboxamide hydrochloride

• • Received January 10, 2002.
  • Accepted March 6, 2002.

• The American Society for Pharmacology and Experimental Therapeutics

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