Limited inhibition of 5-HT 1A receptor expression in the rat brain by antisense RNA and oligodesoxynucleotides Youssef Sari a , Carla Sibella a,1 , Daniel Verge ´ a , Michel Hamon b , Marie-Christine Miquel a, * a De ´ partement de Neurobiologie des Signaux Intercellulaires, Institut des Neurosciences, CNRS UMR 7624, Universite ´ Pierre et Marie Curie, 7 quai Saint-Bernard, 75005 Paris, France b Laboratoire de Neuropsychopharmacologie Mole ´ culaire, Cellulaire et Fonctionnelle INSERM U288, CHU Pitie ´ -Salpe ˆ trie ` re, 75013 Paris, France Received 9 October 1998; received in revised form 9 November 1998; accepted 13 November 1998 Abstract The efficiency of antisense approaches to produce a selective regional inhibition of the expression of brain 5-HT 1A receptors was tested in the rat. In vivo ICV injections of modified antisense oligodesoxynucleotides yielded at most an 18% specific decrease in 5-HT 1A receptor expression in the hippocampus only, as measured by [ 3 H]8-OH-DPAT autoradiographic labeling. In vitro, when 5-HT 1A receptors were transiently expressed in LLC-PK1 cells, co-transfection with antisense RNA encoding plasmids resulted in a marked reduction (50–70%) in the density of 5-HT 1A binding sites. In vivo stereotaxic injections of the same constructs into the hippocampus, but not in the raphe, which contains 5-HT 1A autoreceptors, were shown to produce a ~20% reduction in local 5-HT 1A receptor density. These data show that antisense strategies could be used to inhibit 5-HT 1A receptors expression in the rat hippocampus, but with a limited efficacy.  1999 Elsevier Science Ireland Ltd. All rights reserved Keywords: Rat brain nucleic acid injection; Antisense oligodesoxynucleotides; Antisense RNA encoding plasmids; 5-HT 1A receptors Among the variety of central serotonin (5-HT) receptors, the G-protein-coupled 5-HT 1A receptors have been exten- sively studied and proven to play a role in numerous phy- siological functions [19], as well as in some psychiatric disorders, including anxiety and depression [8]. Anatomical and functional studies have led to the identification of both postsynaptic 5-HT 1A receptors and 5-HT 1A autoreceptors [17]. Their respective roles in each of these localizations are not fully understood, particularly in the above-men- tioned psychiatric pathologies [8]. In spite of some differ- ences in their physico-chemical properties [17] and physiological coupling mechanisms [4], no structural differ- ence has ever been demonstrated between 5-HT 1A autore- ceptors and post-synaptic 5-HT 1A receptors. Indeed, the 5- HT 1A receptor protein is encoded by a unique intronless gene [1] and no isoform has been cloned so far. Therefore, a selective, local and direct blockade of the expression of the 5-HT 1A receptor protein seemed very pro- mising for the analysis of the respective role of the soma- todendritic 5-HT 1A autoreceptors and post-synaptic 5-HT 1A receptors. With this aim, we have applied the now-common anti- sense strategy [6,20] using stereotaxic injections of anti- sense oligodesoxynucleotides (ODNs), as well as plasmid encoded antisense RNAs. The resulting inhibition of 5-HT 1A receptors expression was assessed by quantitative [ 3 H]8- OH-DPAT autoradiographic labeling and by immunoautor- adiography using specific anti-5-HT 1A receptor antibodies [14]. The ODN sequence, chosen after a search for potentially hairpin-rich regions in the rat 5-HT 1A receptor sequence [1] with the Palingol software [3] and comparison to the Gen- bank data base, was complementary to a region encompass- ing the initiation codon (bases 1–18): 5′AAAACT- Neuroscience Letters 259 (1999) 191–195 0304-3940/99/$ - see front matter  1999 Elsevier Science Ireland Ltd. All rights reserved PII S0304-3940(98)00925-2 * Corresponding author. Tel.: +33 1 44273146; fax: +33 1 44272508; e-mail: marie-christine.miquel@snv.jussieu.fr 1 De ´partement de Physiopathologie, Unite ´ de Pharmacologie Neu- roImmuno-Endocrinienne, Institut Pasteur, 75015 Paris, France.