Nair-Roberts Radha G, Erichsen Jonathan T, Reboreda Juan C, Kacelnik Alex
Department of Zoology, Oxford University, UK.
J Comp Neurol. 2006 Jun 10;496(5):610-26. doi: 10.1002/cne.20915.
Parasitic cowbirds monitor potential hosts' nests and return to lay when appropriate, a task that is likely to involve spatial recall. Seasonal and sexual behavioral variations in the cowbirds correlate with anatomical changes in the hippocampal formation. During the breeding season, parasites have larger hippocampal formations than nonparasites. In parasitic species in which females alone perform nest bookkeeping, females have larger hippocampal formations than males. We investigated the distribution of the neuropeptide substance P (SP) in three sympatric cowbirds: two obligate parasites (shiny cowbird and screaming cowbird) and one nonparasite (bay-winged cowbird). Distribution of SP was similar to that in other songbirds, except for a previously undescribed field of dense SP-rich terminals within the hippocampus that we call the hippocampal SP terminal field (SPh). We found robust species differences in the volume of this new area, measured relative to the remainder of the telencephalon. SPh was largest in the generalist parasite (shiny cowbird) and smallest in the nonparasitic species (bay-winged cowbird). In the specialist parasite (screaming cowbird), SPh was smaller than in the generalist parasite but larger than in the nonparasitic species. SPh overlaps with two subdivisions described in the pigeon that have been related to the mammalian dentate gyrus and subiculum. The area containing SPh receives a major input from the lateral mammillary nucleus, which is probably the avian equivalent of the mammalian supramammillary nucleus (SUM), the main source of extrinsic SP input to mammalian hippocampus. SPh may be the termination of a pathway homologous to the SP-rich projection from SUM to the hippocampus in mammals.
寄生牛鹂会监测潜在宿主的巢穴，并在合适的时候回来产卵，这一任务可能涉及空间记忆。牛鹂的季节性和性行为变化与海马结构的解剖学变化相关。在繁殖季节，寄生牛鹂的海马结构比非寄生牛鹂的更大。在仅由雌性进行巢穴管理的寄生种类中，雌性的海马结构比雄性的更大。我们研究了神经肽P物质（SP）在三种同域分布的牛鹂中的分布：两种专性寄生牛鹂（辉拟鹂和啸声牛鹂）和一种非寄生牛鹂（湾翅牛鹂）。SP的分布与其他鸣禽相似，只是在海马体内有一个以前未描述过的富含SP的密集终末区域，我们称之为海马SP终末场（SPh）。我们发现，相对于端脑的其余部分，这个新区域的体积存在显著的物种差异。SPh在泛性寄生牛鹂（辉拟鹂）中最大，在非寄生种类（湾翅牛鹂）中最小。在专性寄生牛鹂（啸声牛鹂）中，SPh比泛性寄生牛鹂小，但比非寄生种类大。SPh与鸽子中描述的两个亚区重叠，这两个亚区与哺乳动物的齿状回和下托有关。包含SPh的区域接受来自外侧乳头体核的主要输入，外侧乳头体核可能相当于哺乳动物的乳头体上核（SUM），而SUM是哺乳动物海马体外部SP输入的主要来源。SPh可能是与哺乳动物中从SUM到海马体的富含SP的投射同源的一条通路的终点。
