Lateral Protocerebrum

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Structure of the lateral protocerebrum(LPC)

While the mushroom body is a conspicuous and well-separated neuropil compartment, the lateral protocerebral neuropil is mostly devoid of clear generally detectable landmarks. Antennal lobe PNs also project to the lateral protocerebum (in some species, the projection area is defined as the lateral horn). In the silkmoth, it could be shown that there is a specific topography of pheromone-sensitive PNs in their projection area in the inferior LPC. Here, the segregation of pheromone component information is preserved in some areas while colocalisation in other areas suggests integration. This was possible because bombykol-senseitive PNs happened to specifically produce cGMP as induced by NO [Seki et al., 2005]．The projection areas of pheromone-sensitive PNs and PNs sensitive to general odours are distinct in the LPC. A similar configuration has been shown to be present in the LPC of the fruit fly [Jefferis et al., 2007]．The projection areas of PNs from thermo- and hygrosensitive glomeruli are also distinct from those of other glomeruli [Nishino et al., 2003]．

Function of the lateral protocerebrum

The functions of the LPC are not so well understood. It is thought that the LPC is a site for multimodal integration, although integration within the olfactory modality does not appear to be pronounced [Tanaka et al 2004]. It appears that the AL-LPC pathways is necessary and sufficient for olfactory behaviours that do not rely on experience, which requires functional MBs [Heimbeck et al 2001; Kido & Ito 2002]. A specific group of cells in the LPC has been shown to play an important role in the initiation of mating behaviour [Broughton et al., 2004]. There appears to be a separation at the qualitative level in the olfactory system: While responses to attractive odorants are abolished when neurotransmission is blocked in the MBs, responses to repulsive odorants remain intact. Thus, the LPC may be particularly important in innate avoidance behaviours [Wang et al., 2003]．

Neurons of the LPC

One major input to the LPC, as already mentioned, are antennal projection neurons. Generally, these project both to the LPC as well as to the MB, although for some projections neurons, MB projections were not identified.
Neurons of the LPC are known to innervate the mushroom body calyx and lobes [Nishino et al., 1998; Strausfeld & Li 1999; Perez-Orive et al., 2002]. Other LPC neurons have been found to innervate other brain regions [Tanaka et al., 2004]. There is still little systematic knowledge concerning the output of the LPC.

References

Broughton SJ, Kitamoto T, Greenspan RJ (2004) Excitatory and inhibitory switches for courtship in the brain of Drosophila melanogaster. Curr Biol 14: 538-547

Heimbeck G, Bugnon V, Gendre N, Keller A, Stocker RF (2001) A central neural circuit for experience-independent olfactory and courtship behavior in Drosophila melanogaster. Proc Natl Acad Sci U S A 98: 15336-15341

Homberg U, Montague RA, Hildebrand JG (1988) antenno-cerebral pathways in the brain of the sphinx moth Manduca sexta. Cell Tissue Res 254:255-281.

Jefferis GS, Potter CJ, Chan AM, Marin EC, Rohlfing T, Maurer CR Jr, Luo L (2007) Comprehensive maps of Drosophila higher olfactory centers: spatially segregated fruit and pheromone representation. Cell 128:1187-1203.

Kido A, Ito K (2002) Mushroom bodies are not required for courtship behavior by normal and sexually mosaic Drosophila. J Neurobiol 52: 302-311

Malun D, Waldow U, Kraus D, Boeckh J (1993) Connections between the deutocerebrum and the protocerebrum, and neuroanatomy of several classes of deutocerebral projection neurons in the brain of male Periplaneta americana. J Comp Neurol 329:143-162.

Marin EC, Jefferis GS, Komiyama T, Zhu H, Luo L (2002) Representation of the glomerular olfactory map in the Drosophila brain. Cell 109:243-255.

Nishino H, Mizunami M (1998) Giant input neurons of the mushroom body: intracellular recording and staining in the cockroach. Neurosci Lett 246: 57-60

Nishino H, Yamashita S, Yamazaki Y, Nishikawa M, Yokohari F, Mizunami M (2003) Projection neurons originating from thermo- and hygrosensory glomeruli in the antennal lobe of the cockroach. J Comp Neurol 455: 40-55

Perez-Orive J, Mazor O, Turner GC, Cassenaer S, Wilson RI, Laurent G (2002) Oscillations and sparsening of odor representations in the mushroom body. Science 297: 359-365

Strausfeld NJ, Li Y (1999) Organization of olfactory and multimodal afferent neurons supplying the calyx and pedunculus of the cockroach mushroom bodies. J Comp Neurol 409: 603-625.

Wang Y, Chiang AS, Xia S, Kitamoto T, Tully T, Zhong Y (2003) Blockade of neurotransmission in Drosophila mushroom bodies impairs odor attraction, but not repulsion. Curr Biol 13: 1900-1904

Wong AM, Wang JW, Axel R (2002) Spatial representation of the glomerular map in the Drosophila protocerebrum. Cell 109:229-241.

Yamazaki Y, Nishikawa M, Mizunami M (1998) Three classes of GABA-like immunoreactive neurons in the mushroom body of the cockroach. Brain Res 788: 80-86