A área de transição amígdalo-piriforme (APir) está situada na confluência dos córtices piriforme, periamigdalóide e entorrinal lateral (ENTl). Com técnicas de rastreamento retrógrado foi observado que as principais aferências da APir se originam do bulbo olfativo, dos córtices piriforme, insular disgranular e agranular posterior, perirrinal, da formação hipocampal e da amígdala. Outras estruturas como o núcleo da banda diagonal de Broca, o pálido ventral, a substância inominada sublenticular, o tálamo da linha média, o núcleo dorsal da rafe, o locus coeruleus e a área parabraquial são fontes de aferências mais modestas a esta área de transição. A APir e o ENTl diferem no que diz respeito à origem de suas aferências mesocorticais, amigdalianas e talâmicas. Assim, a APir está em condições de integrar informações olfativas, gustativas, interoceptivas gerais e polissensoriais complexas e, através de suas projeções para a amígdala expandida, striatum ventral e formação hipocampal, influenciar a expressão de comportamentos motivados. / The amygdalo-piriform transition area (APir) lies at the junction of the piriform, periamygdaloid and entorhinal cortices. The afferent connections of this olfactory district were studied with retrograde tracing methods using the cholera toxin B subunit and Fluoro-Gold as tracers. Our retrograde experiments showed that the main input sources to APir derive from the olfactory bulb, mesocortical and allocortical areas including the dysgranular insular, posterior part of the agranular insular, piriform, lateral entorhinal and perirhinal cortices, temporal field CA1 of Ammon horn, ventral subiculum, as well as the endopiriform nucleus and the amygdaloid complex (anterior basomedial, posterior basolateral and anterior, posterolateral, posteromedial cortical nuclei). Several other structures among which the diagonal band, ventral pallidum, sublenticular substantia inominatta, midline thalamic nuclei, dorsal raphe nucleus, locus coeruleus and parabrachial area provide more modest inputs to APir. Our results suggest in addition that projections from mesocortical areas, hippocampal formation and the posterior basolateral amygdaloid nucleus to APir are topographically organized. Fluoro-Gold injections in the ventrolateral entorhinal cortex indicate that the afferent connections of this district differ in many regards from the afferent connections of APir. Cortical and amygdaloid inputs suggest tha APir is chiefly involved in the processing of olfactory, gustatory, visceral and somesthesic information, whereas the ventrolateral entorhinal cortex seems to be more crucially related with visual and auditory processes. APir is also less densely projected upon by midline thalamic nuclei than the lateral entorhinal cortex. Taken as a whole our results suggest that APir is in position to relay highly integrated olfactory, gustatory, interoceptive and somesthesic information to the extended amygdala, ventral striatum and ventral subiculum, and as such modulate the expression of motivated and emotional behavior.

A área de transição amígdalo-piriforme (APir) está situada na confluência dos córtices piriforme, periamigdalóide e entorrinal lateral (ENTl). Com técnicas de rastreamento retrógrado foi observado que as principais aferências da APir se originam do bulbo olfativo, dos córtices piriforme, insular disgranular e agranular posterior, perirrinal, da formação hipocampal e da amígdala. Outras estruturas como o núcleo da banda diagonal de Broca, o pálido ventral, a substância inominada sublenticular, o tálamo da linha média, o núcleo dorsal da rafe, o locus coeruleus e a área parabraquial são fontes de aferências mais modestas a esta área de transição. A APir e o ENTl diferem no que diz respeito à origem de suas aferências mesocorticais, amigdalianas e talâmicas. Assim, a APir está em condições de integrar informações olfativas, gustativas, interoceptivas gerais e polissensoriais complexas e, através de suas projeções para a amígdala expandida, striatum ventral e formação hipocampal, influenciar a expressão de comportamentos motivados. / The amygdalo-piriform transition area (APir) lies at the junction of the piriform, periamygdaloid and entorhinal cortices. The afferent connections of this olfactory district were studied with retrograde tracing methods using the cholera toxin B subunit and Fluoro-Gold as tracers. Our retrograde experiments showed that the main input sources to APir derive from the olfactory bulb, mesocortical and allocortical areas including the dysgranular insular, posterior part of the agranular insular, piriform, lateral entorhinal and perirhinal cortices, temporal field CA1 of Ammon horn, ventral subiculum, as well as the endopiriform nucleus and the amygdaloid complex (anterior basomedial, posterior basolateral and anterior, posterolateral, posteromedial cortical nuclei). Several other structures among which the diagonal band, ventral pallidum, sublenticular substantia inominatta, midline thalamic nuclei, dorsal raphe nucleus, locus coeruleus and parabrachial area provide more modest inputs to APir. Our results suggest in addition that projections from mesocortical areas, hippocampal formation and the posterior basolateral amygdaloid nucleus to APir are topographically organized. Fluoro-Gold injections in the ventrolateral entorhinal cortex indicate that the afferent connections of this district differ in many regards from the afferent connections of APir. Cortical and amygdaloid inputs suggest tha APir is chiefly involved in the processing of olfactory, gustatory, visceral and somesthesic information, whereas the ventrolateral entorhinal cortex seems to be more crucially related with visual and auditory processes. APir is also less densely projected upon by midline thalamic nuclei than the lateral entorhinal cortex. Taken as a whole our results suggest that APir is in position to relay highly integrated olfactory, gustatory, interoceptive and somesthesic information to the extended amygdala, ventral striatum and ventral subiculum, and as such modulate the expression of motivated and emotional behavior.

Glutamat ist der wichtigste exzitatorische Neurotransmitter im Zentralnervensystem der Säugetiere. Die präzise Kontrolle des extrazellulären Glutamatspiegels ist für eine normale synaptische Transmission wichtig und erforderlich, um die Neurone vor Exzitotoxizität zu schützen. Im Gehirn sorgen vor allem verschiedene hochaffine Na+-abhängige Glutamattransporter für diese Kontrolle. In der vorliegenden Arbeit wurde deshalb untersucht, welchen Einfluß die Inhibition der Glutamattransporter auf die exzitatorische synaptische Transmission in Schicht III, einer Region in der bei Alzheimer-Demenz, Schizophrenie und Epilepsie häufig Zellschädigungen und Zellverluste beobachtet werden, und Schicht V des medialen entorhinalen Kortex (mEC) hat. Extrazelluläre Messungen in den Schichten III und V der Ratte zeigten, daß die verwendeten Transport-Inhibitoren signifikant die negativen Feldpotentialkomponenten beider Schichten reduzierten. Schichtspezifische Unterschiede konnten dabei nicht festgestellt werden, was auf eine ähnliche Glutamatregulation in beiden Schichten schließen läßt. Für die anschließenden intrazellulären und patch-clamp Messungen wurden aus diesem Grund nur noch Neurone der Schicht III untersucht. Beide Transport-Inhibitoren (L-trans-2,4-PDC und DL-TBOA) reduzierten die Amplituden der pharmakologisch isolierbaren EPSPs/EPSCs ohne die Kinetik zu beeinflussen. Diese reduzierende Wirkung konnte durch trans-(±)-ACPD, einen Agonisten der Gruppe I und II metabotropen Glutamatrezeptoren (mGluRs), nachgeahmt werden. Die Vorinkubation der Hirnschnitte mit dem unspezifischen Gruppe I und II mGluR-Antagonisten MCPG verhinderte die durch trans-(±)-ACPD hervorgerufene Amplitudenreduktion und auch den reduzierenden Effekt der beiden Transport-Inhibitoren. In nachfolgenden Experimenten mit dem spezifischen Gruppe II mGluR-Antagonisten EGLU konnte dieser zwar die durch L-trans-2,4-PDC hervorgerufene Wirkung verhindern, nicht aber den durch DL-TBOA vermittelten Effekt, was auf eine Aktivierung von Gruppe I mGluRs hinweist. Zusätzlich führte die Applikation von DL-TBOA zu einer signifikanten Veränderung des Doppelpuls-Index, was auf einen präsynaptischen Wirkmechanismus hinweist. Die Applikation von L-trans-2,4-PDC hingegen hatte keinen Effekt auf den Doppelpuls-Index. Die Ergebnisse der vorliegenden Arbeit sprechen dafür, daß beide Transport-Inhibitoren die erregende synaptische Transmission über eine Aktivierung präsynaptischer metabotroper Glutamatrezeptoren der Gruppen I und II hemmen. Dabei konnte festgestellt werden, daß diese Hemmung unter Applikation von DL-TBOA die präsynaptische Transmitterausschüttung über einen negativen Rückkopplungsmechanismus durch Aktivierung von Gruppe I mGluRs vermindert, während L-trans-2,4-PDC seine Wirkung vor allem über eine Aktivierung der Gruppe II vermittelt. Dabei kann davon ausgegangen werden, daß L-trans-2,4-PDC in der benutzten Konzentration die mGluRs der Gruppe II direkt aktivieren kann und der Effekt nicht nur präsynaptisch vermittelt wird. / Glutamate is the primary excitatory neurotransmitter in the mammalian central nervous system. The precise control of extracellular glutamate is crucial for the maintenance of normal synaptic transmission and the prevention of excitotoxicity. High-affinity glutamate transporters ensure termination of glutamatergic neurotransmission and keep the synaptic glutamate concentration below excitotoxic levels. In layer III, a region that is especially prone to cell damage in Alzheimer's disease, schizophrenia and epilepsy, and layer V of the medial entorhinal cortex (mEC) effects of blocking glutamate uptake on excitatory synaptic transmission were studied. Extracellular recordings in rat brain slices revealed that application of glutamate uptake inhibitors significantly reduced stimulus-induced negative field potentials in both, layer III and V of the mEC. This effect showed no significant differences in both layers suggesting a similar glutamate regulation in layer III and V. Therefore, only layer III neurons of the mEC were used for the subsequent intracellular and patch-clamp recordings. Two competitive glutamate transporter antagonists, DL-TBOA and L-trans-2,4-PDC, reduced the amplitude of pharmacologically isolated EPSPs/EPSCs without changing the time course of the events. This effect was mimicked by trans-(±)-ACPD, an agonist of group I and II metabotropic glutamate receptors (mGluRs). The competitive group I and II mGluR antagonist MCPG blocked the depression of the EPSC amplitude induced by trans-(±)-ACPD and also masked the effect of either DL-TBOA or L-trans-2,4-PDC. Furthermore, EGLU, which selectively antagonizes group II mGluRs, masked the effect of L-trans-2,4-PDC but not that of DL-TBOA, indicating an involvement of group I mGluRs in the latter case. Finally, DL-TBOA significantly enhanced the paired-pulse index, suggesting a presynaptic mechanism for the depression of EPSP/EPSC amplitude, whereas application of L-trans-2,4-PDC had no significant effect on the paired-pulse behaviour. The present study shows that both transport inhibitors depress pharmacologically isolated EPSPs/EPSCs in layer III neurons of the mEC in combined entorhinal-hippocampal slices. This effect seems to be mediated via activation of different groups of mGluRs. The results suggest that DL-TBOA causes a negative feedback on glutamate release via indirect activation of presynaptic group I mGluRs, possibly due to an accumulation of glutamate, whereas application of L-trans-2,4-PDC most likely leads to an activation of presynaptic group II mGluRs reducing Ca2+-independent release. The latter might be due to a direct action of L-trans-2,4-PDC at these receptors. The present data suggest that blockade of glutamate transport in the mEC does not lead to an excessive accumulation of glutamate because of a counteractive autoinhibiting mechanism.