LQ % whereas the remaining rats (n = 6) were injected(i.p.) with 5HT1A agonist, 8-OH DPAT, and LQ % wascorrelated with concentrations of NE, DA and 5-HT inthe hypothalamus and amygdala. Data show that in con-trast to OVX rats DZ treatment of intact rats led to toler-ance to DZ. However in those primed with OB + P,development of tolerance to DZ was inconsistent. Groupsof intact, DZ-tolerant and OVX and DZ treated rats whentested for sexual receptivity showed an LQ of 17 and 20%,respectively. In animals that were OVX, DZ-tolerant andOB + P primed, the LQ was 62%. When injected with5HT1A agonist, 8-OH-DPAT, LQ % decreased (p < 0.01)in OVX, DZ-treated and OB + P primed rats. DA and 5-HT concentrations in the hypothalamus were raised(p < 0.001) in OVX, DZ-tolerant but OB + P primed ratswith no change in NE concentrations in all groups. Thissuggests that DA and 5-HT in the hypothalamus underthe influence of a specific steroid milieu play a modulatoryrole in regulation of anxiety and sexual behavior as LQ inthe DZ-tolerant rats was directly proportional to 5-HTconcentrations in the hypothalamus. (Pakistan ScienceFoundation, Islamabad, Pakistan.)

doi:10.1016/j.yfrne.2006.03.243

Brain aromatase activity and mRNA expression in a fish with

male sexual polymorphism

David Goncalves, Joao Alpedrinha, Ana Domingues, Magda

Teles, Rui F. Oliveira

ISPA, Rua Jardim do Tabaco 34, 1149-041 Lisboa, Portugal

In a small intertidal fish, the peacock blenny Salariapavo, large males with fully developed secondary sexualcharacters defend nests and reproduce by attractingfemales to their nests with male courtship displays. Femaleslay their eggs in the nest and the male takes care of the eggsuntil they hatch. Small ‘‘sneaker’’ males are unable to com-pete with the larger males for nests and reproduce using analternative tactic. These males mimic female appearanceand courtship displays in order to deceive and approachthe nests of larger males. Once close to the nest, sneakersrelease sperm and fertilize part of the eggs in the nest. Thus,in this species two male classes with distinct reproductivebehaviors, male and female-like, occur. In this study, aro-matase activity and mRNA expression in the brain of thetwo male morphs and females was quantified. Aromataseis a key enzyme responsible for the conversion of andro-gens into estrogens in several tissues, including the brain,and its role in sexual behavior has been well establishedin many vertebrates. Thus, aromatase may mediate someof the behavioral differences observed between male mor-phs. Whole brain aromatase activity (AA) was higher infemales than in both male morphs, as measured by a radio-metric assay. Nesting males had higher levels than sneakersbut this difference was marginally non-significant

(p = 0.08). In these same samples, whole brain mRNA aro-matase expression was measured by real-time RT-PCR.Females had higher aromatase mRNA expression thanboth male morphs but no significant differences were foundbetween nesting males and sneakers. In a second sample,brains were divided into macroareas and AA was mea-sured. Females had the highest levels of AA in the cerebel-lum, significantly higher than nesting males and sneakers.Both male morphs had their highest AA levels in the dien-cephalon, but in nesting males these levels were approxi-mately 4-fold higher than in sneakers. Thus, differences inaromatase activity between the male morphs occurredmainly in the diencephalon, an area known to be involvedin the control of reproductive behaviors. The high levels ofAA in this area of nesting males suggests that male repro-ductive behaviors may be facilitated by the synthesis ofestrogens from androgens by aromatization.

doi:10.1016/j.yfrne.2006.03.244

Quantitative comparison of the topographical organization

of the axonal projections from the medial and lateral zones of

the caudal hypothalamus to the periaqueductal gray in rats

Cara F. Harley, Loretta M. Flanagan-Cato

Neuroscience Graduate Group, Department of Psychology

and Institute of Neurological Sciences, University of

Pennsylvania, Philadelphia, PA, USA

The hypothalamus integrates neuroendocrine functionwith affiliated motivated behaviors. The functional organi-zation of the hypothalamus has been difficult to conceptu-alize because it is populated by many small nuclei withdisparate functions. One proposed scheme includes a dis-tinction between the medial and lateral zones of the hypo-thalamus. In this proposed system, the nuclei in the medialzone subserve specific motivated behaviors. The ventrome-dial nucleus of the hypothalamus (VMH) is an example ofa nucleus in the medial zone that is associated with a spe-cific motivated behavior, namely female sexual behavior.In contrast, nuclei in the lateral zone, such as the lateralhypothalamus (LH) may exert more general arousal effects.An important target of the axons arising from both themedial and lateral zones of the hypothalamus is the peri-aqueductal grey (PAG), mediating both behavioral andautonomic effects. Based on anatomical and functional evi-dence, the PAG has been subdivided into longitudinal col-umns. There have been no quantitative studies ofcomparing the innervation of these PAG columns arisingfrom different hypothalamic zones. We have employedthe anterograde tracer phaseolus vulgaris leucoagglutinin(PHA-L) to compare projections to the PAG arising fromthe VMH (n = 6) and the LH (n = 3). PHA-L was ionto-phoretically injected into the VMH or LH, and then thePAG was analyzed for PHA-L immunoreactivity to deter-mine the amount of innervation. Optical density of the

142 Abstracts / Frontiers in Neuroendocrinology 27 (2006) 141–147