The vasopressin 1b receptor is prominent in the hippocampal area CA2 where it is unaffected by restraint stress or adrenalectomy

Abstract

The vasopressin 1b receptor (Avpr1b) is one of two principal receptors mediating the behavioral effects of vasopressin (Avp) in the brain. Avpr1b has recently been shown to strongly influence social forms of aggression in mice and hamsters. This receptor appears to play a role in social recognition and motivation as well as in regulating the hypothalamic-pituitary-adrenal axis. Most of these studies have been performed in knockout mice, a species in which the localization of the Avpr1b has not been described, thus precluding correlations with the behaviors. We performed in situ hybridization histochemistry (ISHH) with specific probes and found especially prominent expression within the CA2 pyramidal neurons of the hippocampus, with much lower expression in the hypothalamic paraventricular nucleus and amygdala. Reverse transcriptase-polymerase chain reaction (RT-PCR) confirmed expression in those as well other areas in which the ISHH was not sensitive enough to detect labeled cells (e.g. piriform cortex, septum, caudate-putamen and lower brainstem areas). Mouse Avpr1b transcript levels were not altered in the CA2 field by restraint stress or adrenalectomy. Finally, ISHH and RT-PCR showed expression of the Avpr1b gene in the rat and human hippocampi as well. We suggest that the CA2 field may form or retrieve associations (memories) between olfactory cues and social encounters.

Figure 1

Avpr1b transcripts are present in cells of the mouse (A), rat (B) and human (C) anterior pituitaries as revealed using the 3′ probes. The mouse and rat photomicrographs are brightfield and the human photomicrograph darkfield illuminations. The 3′ probe was used for this ISHH and exposures were for 1 month.

Figure 2

In mice, brightfield (A,C,D) and darkfield (B,E) photomicrographs showing Avpr1b transcripts in the CA2 pyramidal cells of the far rostral (~1.1 mm behind the bregma; A,B) and slightly more caudal dorsal (~2.0 mm behind the bregma; C–F) hippocampus in coronal sections. Panels C and F show higher magnification of CA2 pyramidal cells from adjacent sections probed with antisense and sense probes, respectively. The 3′ probe was used for this ISHH and exposures were for 4 months. The small arrows show the CA2–CA3 pyramidal cell borders and the large arrow the CA1–CA2 pyramidal cell border. DG is the dentate gyrus. At the rostral level (A,B), the hippocampal topography places the CA3 area between portions of the CA2 area, in agreement with observations by Lein et al. (Lein et al., 2005) who nicely demonstrate this unfamiliar arrangement.

Figure 3

Cells containing Avpr1b transcripts are found occasionally in the mouse paraventricular nucleus of the hypothalamus (A) and rarely in the anterior amygdaloid area (B). The 3′ probe was used for this ISHH and exposures were for 4 months.

Figure 4

Reverse transcriptase-polymerase chain reaction examination of total RNA isolated from various mouse brain regions and peripheral tissues (wildtype mice unless noted otherwise). The RNA for each sample was divided equally between 2 reactions, one for Avpr1b and one for β-actin to which reaction mix and the appropriate primers pairs were added. The RT-PCR reactions were run in the same 48-well plate and subsequently paired on the same two-comb gels. Specific products are 322 and 266 bp in length for the Avpr1b (top row of each pair) and β-actin (bottom row of each pair) bands, respectively. Row A: 1, cervical spinal cord; 2, medulla; 3, trigeminal ganglion; 4, cerebellum; 5, pons; 6, midbrain; 7, caudate-putamen; 8, septum; 9, hypothalamus; 10, piriform cortex; 11, amygdala. Row B: 12, thalamus; 13, dorsal hippocampus; 14, parietal cortex; 15, olfactory bulb; 16, adrenal; 17, kidney; 18, pituitary; 19, knockout pituitary; 20, vomeronasal organ; 21, liver; 22, no RNA.

Figure 5

Avpr1b transcripts in rat hippocampal CA2 field shown in brightfield (A) and darkfield (B) photomicrographs. The small arrow shows the lateral CA2–CA3 pyramidal cell border and the large arrow the medial CA1–CA2 pyramidal cell border. The exposure was for 4 months.

Figure 6

Several cells in the human hippocampus contain vasopressin 1b receptor transcripts (arrows in panel A). A single labeled CA2 neuron in the human hippocampus at higher magnification shows the typical association with a corpus amylacea (B). This carbohydrate rich accumulation is in the homogenous structure to the left of the cell nucleus (the arrow indicates the lower boundary between the nucleus and the corpus amylacea). The exposure was for 4 months.