Serotonin receptor 1A knockout: An animal model of anxiety-related disorder

Abstract

To investigate the contribution of individual serotonin (5-hydroxytryptamine; 5-HT) receptors to mood control, we have used homologous recombination to generate mice lacking specific serotonergic receptor subtypes. In the present report, we demonstrate that mice without 5-HT1A receptors display decreased exploratory activity and increased fear of aversive environments (open or elevated spaces). 5-HT1A knockout mice also exhibited a decreased immobility in the forced swim test, an effect commonly associated with antidepressant treatment. The serotonin (5-hydroxytryptamine; 5-HT) receptor 1A is found on serotonergic neurons, where it acts as an autoreceptor, and on nonserotonergic neurons (1). 5-HT1A receptor agonists are currently used in the treatment of anxiety disorders (2), and antagonists of this receptor have been suggested to improve the efficacy of certain antidepressant drugs (3). However, the clinical value of these drugs, as well as their mechanism of action, is still unclear. To study the role of the 5-HT1A receptor in mood control, we have generated mice lacking this receptor by homologous recombination (see Methods). The disruption of the 5-HT1A receptor gene was verified by Southern blot analysis (not shown). Despite suggestions that 5-HT1A receptors play a role in development (4, 5), these knockout mice had normal growth and viability and did not display any obvious anatomical or behavioral abnormalities. MATERIALS AND METHODS5-HT1A Gene Targeting. The 5-HT1A gene was cloned from a 129͞Sv mouse genomic library (Lambda EMBL3, Stratagene) by using the human 5-HT1A gene as a probe (6). A KpnI fragment containing the 5-HT1A gene was cloned in pGEM-13(ϩ). The PGK-neo gene was inserted into an AscI site located after the third transmembrane domain of the 5-HT1A gene. W9.5 embryonic stem cells were electroporated (Bio-Rad Gene Pulser; 800 V and 3 F) with 30 g of the targeting construct. These embryonic stem cells were then plated onto mitomycin treated mouse embryonic fibroblasts for 1 week in the presence of G418 (150 g per ml of active substance). The G418-resistant clones were screened by Southern blot with a BglII digest and a 32 P-labeled outside probe (600-bp HindIII-KpnI fragment). Positive cells for the targeting event were injected into C57BL6͞J blastocysts. These blastocysts were reimplanted in B6CBAF1͞J foster mothers, which gave birth to chimeric mice. Chimeras were mated with 129͞Sv females to generate heterozygous mutant (ϩ͞Ϫ) mice on a pure 129͞Sv genetic background. The resulting heterozygous mice were bred and generated 25% homozygous mutant mice.Autoradiography Studies. Coronal cryostat sections (20 m) from three brains of adult male mice were thaw-mounted on gelatin-coated slides and stored at Ϫ20°C. 8-Hydroxy-2-(di-n-[ 3

Knockout Mice Reveal Opposite Roles for Serotonin 1A and 1B Receptors in Prepulse Inhibition

“…Some compensatory changes have also been reported in 1AKO mice. For example, 5-HT 1B receptors may be upregulated (Ramboz et al 1998), although there is little evidence for a behavioral consequence of this upregulation in the present experiments.The activation of 5-HT 1A receptors increases PPI in mice (Dulawa et al 1997(Dulawa et al , 1998, and decreases PPI in rats (Sipes and Geyer 1995; Rigdon and Weatherspoon 1992). Inconsistencies have also been reported regarding the effects of drugs on PPI in rats versus humans.…”

“…22 , NO . 6 Opposite Roles for 5-HT1A and 1B Receptors in Murine PPI 651 5-HT 1B knockout (1BKO) mice (Dulawa et al 1997), suggesting that 5-HT 1B receptors modulate both forms of startle plasticity in mice.The recent availability of 5-HT 1A knockout (1AKO) mice (Ramboz et al 1998;Heisler et al 1998;Parks et al 1998) and the selective 5-HT 1B agonist anpirtoline (Schlicker et al 1992) permits more precise dissection of the roles of 5-HT 1A and 5-HT 1B receptors in behaviors of interest. 5-HT 1A receptors are autoreceptors and heteroreceptors for serotonergic and nonserotonergic neurons and are located on cell bodies and dendrites, where they inhibit cell firing (Hamon et al 1990).…”

“…5-HT 1B receptors are most densely localized on striatal neuron terminals in the globus pallidus and substantia nigra, and on Purkinje neuron terminals in the deep cerebellar nuclei (Boschert et al 1994;Pazos et al 1988). Many of these brain regions, such as the hippocampus (Caine et al 1991), septum (Koch 1996, raphe (Sipes and Geyer 1995), and ventral pallidum (Swerdlow et al 1990(Swerdlow et al , 1992Sipes and Geyer 1997), are components of the neural circuitry involved in modulating PPI.We assessed the roles of 5-HT 1A and 5-HT 1B receptors in modulating PPI and habituation using WT, 1AKO, and 1BKO mice, which are without any obvious anatomical or behavioral abnormalities (Ramboz et al 1998;Saudou et al 1994). WT, 1AKO, and 1BKO mice received saline, the 5-HT 1A/1B agonist RU24969, which binds preferentially at 5-HT 1B sites (Sills et al 1984;Doods et al 1985), and the 5-HT 1A agonist 8-OH-DPAT.…”

Solubilization of Serotonin1AReceptors Heterologously Expressed in Chinese Hamster Ovary Cells

“…Serotonergic signaling appears to play a key role in the generation and modulation of various cognitive and behavioral functions including sleep, mood, pain, addiction, locomotion, sexual activity, depression, anxiety, alcohol abuse, aggression, and learning (Artigas et al, 1996;Ramboz et al, 1998). 5-Hydroxytryptamine or 5-HT is an intrinsically fluorescent , biogenic amine found in a wide variety of sites in the central and peripheral nervous systems.…”

“…5-Hydroxytryptamine or 5-HT is an intrinsically fluorescent , biogenic amine found in a wide variety of sites in the central and peripheral nervous systems. Disruptions in serotonergic systems have been implicated in the etiology of mental disorders such as schizophrenia, migraine, depression, suicidal behavior, infantile autism, eating disorders, and obsessive compulsive disorder (Heisler et al, 1998;Ramboz et al, 1998;Tecott et al, 1995).…”