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ARS Home » Pacific West Area » Dubois, Idaho » Range Sheep Production Efficiency Research » Research » Publications at this Location » Publication #138384
Title: NEUROANATOMICAL CORRELATES OF SEX AND SEXUAL PARTNER PREFERENCE IN SHEEP

Author
item LARKIN, K. - OREGON HEALTH SCI. UNIV.
item RESKO, J. - OREGON HEALTH SCI. UNIV
item STORMSHAK, F. - OREGON STATE UNIV.
item Stellflug, John
item ROSELLI, C. - OREGON HEALTH SCI. UNIV.

Submitted to: Society for Neuroscience Abstracts and Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 5/4/2002
Publication Date: 11/1/2002
Citation: Society of Neuroscience 28. 2002. Program #383. p. 10.

Interpretive Summary: A sexually dimorphic nucleus (SDN) can be distinguished within the medial preoptic area (MPOA) that is specifically larger in males than in females. The SDN has been implicated in both motor aspects of copulation and expression of sexual partner preferences in experimental animal and humans. Six to ten percent of rams prefer male sexual partners (male-oriented rams, MORs) in contrast to the majority of rams that prefer female partners (female-oriented rams, FORs). This study was designed to determine whether an analog of the SDN is present in the sheep brain and to test the hypothesis that size of this cell group correlates with sexual partner preference. We identified a cell group in the caudal MPOA of Nissl-stained sections from sheep that corresponds positionally to the SDN. In situ hybridization revealed that neurons in this nucleus express high levels of aromatase mRNA, which was used to define its rostral-caudal extent. Quantitative comparisons of morphologic features of the SDN were made among adult FORs (n=4), MORs (n=3) and luteal phase ewes (n=4). The mean volume of this cell group was larger in FORs (1.81±0.18 mm3) than in ewes (0.44±0.1 mm3, p<0.05) or in MORs (0.44±0.01 mm3, p<0.05); MORs and ewes were not different. Average total cell numbers paralleled the findings for volumes (FORs 4126±764.76; ewes 973.13±299.13, p<0.05; and MORs 802.50±78.38, p<0.05). Mean cell size and cell density were the same among all groups. Quantitative analysis of the aromatase mRNA signal on adjacent sections revealed a similar trend in mean volumes (FORs 5.45±0.49 mm3; ewes 2.48±1.14 mm3; and MORs 1.54±0.11 mm3, p<0.05). These findings indicate that a SDN exists in sheep MPOA and that this dimorphism correlates with sexual partner preference suggesting that mate preference in sheep has a biological substrate. (Supported by NIH grant R01 RR14270).

Technical Abstract: A sexually dimorphic nucleus (SDN) can be distinguished within the medial preoptic area (MPOA) that is specifically larger in males than in females. The SDN has been implicated in both motor aspects of copulation and expression of sexual partner preferences in experimental animal and humans. Six to ten percent of rams prefer male sexual partners (male-oriented rams, MORs) in contrast to the majority of rams that prefer female partners (female-oriented rams, FORs). This study was designed to determine whether an analog of the SDN is present in the sheep brain and to test the hypothesis that size of this cell group correlates with sexual partner preference. We identified a cell group in the caudal MPOA of Nissl-stained sections from sheep that corresponds positionally to the SDN. In situ hybridization revealed that neurons in this nucleus express high levels of aromatase mRNA, which was used to define its rostral-caudal extent. Quantitative comparisons of morphologic features of the SDN were made among adult FORs (n=4), MORs (n=3) and luteal phase ewes (n=4). The mean volume of this cell group was larger in FORs (1.81±0.18 mm3) than in ewes (0.44±0.1 mm3, p<0.05) or in MORs (0.44±0.01 mm3, p<0.05); MORs and ewes were not different. Average total cell numbers paralleled the findings for volumes (FORs 4126±764.76; ewes 973.13±299.13, p<0.05; and MORs 802.50±78.38, p<0.05). Mean cell size and cell density were the same among all groups. Quantitative analysis of the aromatase mRNA signal on adjacent sections revealed a similar trend in mean volumes (FORs 5.45±0.49 mm3; ewes 2.48±1.14 mm3; and MORs 1.54±0.11 mm3, p<0.05). These findings indicate that a SDN exists in sheep MPOA and that this dimorphism correlates with sexual partner preference suggesting that mate preference in sheep has a biological substrate. (Supported by NIH grant R01 RR14270).