Reproductive system of the genus Crasiella (Gastrotricha, Macrodasyida)

Crasiella diplura from Sweden and Crasiella sp. from Italy were studied alive and with transmission electron microscopy (TEM). The two species are simultaneous hermaphrodites and share the same reproductive system lay-out: paired ovaries extend along the posterior part of the intestine and join mid-dorsally, while bilateral,club-shaped testes lie at the sides of the anterior gut, extending as deferentia that fuse on the mid-ventral plane and open into a single pore; gametes mature in a caudocephalicand centripetal direction. The bulky, sac-like, frontal organ is lined by a simple epithelium and lies dorsolaterally to the intestine, on the left side of the body.The spindle-shaped caudal organ is musculo-glandular and is located ventrolaterally to the gut on the right side. It is characterized by the presence of a roughly Y-shapedinternal channel that opens into two pores close to each other, which function for the intake and outlet of the (auto)sperm, respectively. The spermatozoa, which arepeculiar and similar in the two species, are characterized by a long and complex acrosome consisting of four ultrastructurally distinct regions, three of which findequivalence in other gastrotrich species. The flagellum lacks a striated cylinder. Anatomy and ultrastructure enable us to hypothesize a modality of sperm transfer in Crasiellathat is similar to that observed in Macrodasys

Functional expression of the GABA A receptor α2 and α3 subunits at synapses between intercalated medial paracapsular neurons of mouse amygdala

In the amygdala, GABAergic neurons in the intercalated medial paracapsular cluster (Imp) have been suggested to play a key role in fear learning and extinction. These neurons project to the central (CE) amygdaloid nucleus and to other areas within and outside the amygdala. In addition, they give rise to local collaterals that innervate other neurons in the Imp. Several drugs, including benzodiazepines (BZ), are allosteric modulators of GABA A receptors. BZ has both anxiolytic and sedative actions, which are mediated through GABA A receptors containing α2/α3 and α1 subunits, respectively. To establish whether α1 or α2/α3 subunits are expressed at Imp cell synapses, we used paired recordings of anatomically identified Imp neurons and high resolution immunocytochemistry in the mouse. We observed that a selective α3 subunit agonist, TP003 (100 nM), significantly increased the decay time constant of the unitary IPSCs. A similar effect was also induced by zolpidem (10 μM) or by diazepam (1 μM). In contrast, lower doses of zolpidem (0.1-1 μM) did not significantly alter the kinetics of the unitary IPSCs. Accordingly, immunocytochemical experiments established that the α2 and α3, but not the α1 subunits of the GABA A receptors, were present at Imp cell synapses of the mouse amygdala. These results define, for the first time, some of the functional GABA A receptor subunits expressed at synapses of Imp cells. The data also provide an additional rationale to prompt the search of GABA A receptor α3 selective ligands as improved anxiolytic drugs. © 2012 Geracitano, Fischer, Kasugai, Ferraguti and Capogna

Cell-Type-Specific Recruitment of Amygdala Interneurons to Hippocampal Theta Rhythm and Noxious Stimuli In Vivo

Neuronal synchrony in the basolateral amygdala (BLA) is critical for emotional behavior. Coordinated theta-frequency oscillations between the BLA and the hippocampus and precisely timed integration of salient sensory stimuli in the BLA are involved in fear conditioning. We characterized GABAergic interneuron types of the BLA and determined their contribution to shaping these network activities. Using in vivo recordings in rats combined with the anatomical identification of neurons, we found that the firing of BLA interneurons associated with network activities was cell type specific. The firing of calbindin-positive interneurons targeting dendrites was precisely theta-modulated, but other cell types were heterogeneously modulated, including parvalbumin-positive basket cells. Salient sensory stimuli selectively triggered axo-axonic cells firing and inhibited firing of a disctinct projecting interneuron type. Thus, GABA is released onto BLA principal neurons in a time-, domain-, and sensory-specific manner. These specific synaptic actions likely cooperate to promote amygdalo-hippocampal synchrony involved in emotional memory formation

Individual contribution of metabotropic glutamate receptor (mGlu) 2 and 3 to c-Fos expression pattern evoked by mGlu2/3 antagonism

Objectives and materials and methods: The aims of the present study were (1) to determine the neuronal activation pattern elicited by the group II mGlu antagonist LY341495 and (2) to evaluate the contribution of each group II mGlu subtype by using wild-type (WT) and knockout (KO) mice lacking either mGlu2 or mGlu3. c-Fos expression was used as a marker of neuronal activation. Results and discussion: In WT mice, LY341495 induced widespread c-Fos expression in 68 out of 92 brain areas, including limbic areas such as the amygdala, septum, prefrontal cortex, and hippocampus. LY341495-induced c-Fos response was markedly decreased in the medial part of the central amygdala (CeM) and lateral septum (LS) in mGlu3-KO mice, as well as in the lateral parabrachial nucleus (LPB) in both KO strains. In the majority of investigated areas, LY341495-induced c-Fos expression was similar in KO and WT mice. Analysis of the cellular and subcellular distribution of mGlu2 and mGlu3 revealed a prevailing presence of mGlu3-immunoreactivity in the CeM in glial processes and in postsynapstic neuronal elements, whereas only rare presynaptic axon terminals were found immunoreactive for mGlu2. Conclusion: In conclusion, our data indicate that group II mGlu blockade increases neuronal activation in a variety of brain areas, including many stress- and anxiety-related areas. The activation of two key brain areas, the CeM and LS, is mediated via mGlu3, while activation in the LPB involves both subtypes. Moreover, in the majority of investigated areas, LY341495-mediated neuronal activation appears to require a complex cross talk between group II mGlu subtypes or the action of LY341495 on additional receptors. © 2008 The Author(s)

Kv4.2 potassium channels segregate to extrasynaptic domains and influence intrasynaptic NMDA receptor NR2B subunit expression

Neurons of the intercalated cell clusters (ITCs) represent an important relay site for information flow within amygdala nuclei. These neurons receive mainly glutamatergic inputs from the basolateral amygdala at their dendritic domains and provide feed-forward inhibition to the central nucleus. Voltage-gated potassium channels type-4.2 (Kv4.2) are main players in dendritic signal processing and integration providing a key component of the A currents. In this study, the subcellular localization and distribution of the Kv4.2 was studied in ITC neurons by means of light- and electron microscopy, and compared to other types of central principal neurons. Several ultrastructural immunolocalization techniques were applied including pre-embedding techniques and, most importantly, SDS-digested freeze-fracture replica labeling. We found Kv4.2 densely expressed in somato-dendritic domains of ITC neurons where they show a differential distribution pattern as revealed by nearest neighbor analysis. Comparing ITC neurons with hippocampal pyramidal and cerebellar granule cells, a cell type- and domain-dependent organization in Kv4.2 distribution was observed. Kv4.2 subunits were localized to extrasynaptic sites where they were found to influence intrasynaptic NMDA receptor subunit expression. In samples of Kv4.2 knockout mice, the frequency of NR1-positive synapses containing the NR2B subunit was significantly increased. This indicates a strong, yet indirect effect of Kv4.2 on the synaptic content of NMDA receptor subtypes, and a likely role in synaptic plasticity at ITC neurons. © 2012 The Author(s)

Hippocampal Theta Input to the Amygdala Shapes Feedforward Inhibition to Gate Heterosynaptic Plasticity

The dynamic interactions between hippocampus and amygdala are critical for emotional memory. Theta synchrony between these structures occurs during fear memory retrieval and may facilitate synaptic plasticity, but the cellular mechanisms are unknown. We report that interneurons of the mouse basal amygdala are activated during theta network activity or optogenetic stimulation of ventral CA1 pyramidal cell axons, whereas principal neurons are inhibited. Interneurons provide feedforward inhibition that transiently hyperpolarizes principal neurons. However, synaptic inhibition attenuates during theta frequency stimulation of ventral CA1 fibers, and this broadens excitatory postsynaptic potentials. These effects are mediated by GABAB receptors and change in the Cl- driving force. Pairing theta frequency stimulation of ventral CA1 fibers with coincident stimuli of the lateral amygdala induces long-term potentiation of lateral-basal amygdala excitatory synapses. Hence, feedforward inhibition, known to enforce temporal fidelity of excitatory inputs, dominates hippocampus-amygdala interactions to gate heterosynaptic plasticity. Video Abstract: Hippocampal-amygdala interactions are critical for emotional memory, but the cellular mechanisms are unknown. In this paper, Bazelot, Bocchio et al. functionally demonstrate that GABAergic neurons of the basal amygdala gate principal neuron firing and heterosynaptic plasticity in the mouse amygdala