Biomedical subjects

Rachel D Samson

Publications and source records attributed to Rachel D Samson.

4 recordsLinked to original sources

PubMed2005

Activity-dependent synaptic plasticity in the central nucleus of the amygdala.

Much evidence indicates that fear conditioning involves potentiation of some thalamic inputs to the lateral amygdala (LA). In turn, the LA would excite more neurons in the central nucleus (CE), leading to the generation of fear responses via their brainstem and hypothalamic projections. However, the posterior thalamus not only projects to LA but also to the medial sector of CE (CEm), suggesting that CEm might also be a site of plasticity. To test whether CEm also exhibits activity-dependent synaptic plasticity, we performed whole-cell recordings of CEm neurons in amygdala slices and stimulated thalamic axons coursing through the internal capsule and, as a control, the basolateral (BL) nucleus. High-frequency stimulation of thalamic inputs led to a long-lasting potentiation of thalamic responses, whereas BL-evoked responses remained unchanged. This thalamic long-term potentiation (LTP) developed even when slices were prepared with a cut severing the connections between the LA and CEm but was greatly reduced when an NMDA receptor antagonist was added to the perfusate shortly before and during LTP induction. Yet, intracellular dialysis with the NMDA receptor antagonist (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate did not prevent induction of the thalamic LTP, suggesting that presynaptic NMDA receptors are required for its induction. Consistent with this, the thalamic LTP also developed when the cells were dialyzed with a calcium chelator or kept hyperpolarized during induction. Finally, this thalamic LTP was associated with reduced amounts of paired-pulse facilitation, suggesting that it is expressed presynaptically. These results are consistent with the idea that the CEm plays an active role in fear conditioning.

2-Amino-5-phosphonovalerate↗

PubMed2005

Synaptic plasticity in the central nucleus of the amygdala.

In recent years, the amygdala has emerged as a critical site of plasticity for the acquisition of various forms of Pavlovian learning, either aversive or appetitive. In most of these models, the critical site of plasticity has been localized to the basolateral complex of the amygdala (BLA). In contrast, the central nucleus of the amygdala has emerged as a passive relay of potentiated BLA outputs toward downstream effectors. At odds with this view, however, recent studies suggest that the central nucleus may also be a site of plasticity and play an active role in some forms of Pavlovian learning. The present review summarizes the evidence supporting this possibility.

Amygdala↗

PubMed2003

Feedback inhibition defines transverse processing modules in the lateral amygdala.

The lateral amygdaloid (LA) nucleus is the main input station of the amygdala for sensory afferents. However, it is unclear how the lateral nucleus transforms these inputs, because its intrinsic connectivity is poorly understood. Here, we took advantage of the fact that glutamatergic neurons of the lateral nucleus send a primarily unidirectional projection to the basomedial nucleus. Consequently, it was possible to infer the targets of their intranuclear axons (projection cells vs inhibitory interneurons) by backfiring some projection neurons from the basomedial nucleus and analyzing evoked responses in other LA projection cells. Basomedial stimuli evoked markedly different synaptic responses depending on the orientation of the slices. In coronal slices (intact and decorticated), the prevalent response of LA neurons was an inhibition, regardless of the stimulation intensity. This inhibition was sensitive to GABA(A) and non-NMDA receptor antagonists, suggesting that it was mediated by the activation of GABAergic cells of the LA. In contrast, basomedial stimuli primarily evoked EPSPs in horizontal slices, regardless of the position of recorded neurons. In light of these findings, we conclude that the prevalent target of the intrinsic axon collaterals of projection cells depend on the rostrocaudal position of target neurons with respect to the parent cell body: inhibitory interneurons at rostrocaudal proximity versus other projection cells at a distance. Thus, feedback interneurons effectively divide the lateral nucleus in transverse processing modules that prevent runaway excitation within each module but allow intermixing of sensory information in the rostrocaudal plane.

Action Potentials↗

PubMed2002

Physiological properties of central amygdala neurons: species differences.

The connections of limbic structures are remarkably constant across species. However, different species express fear in distinct ways. Because the central amygdaloid nucleus is considered an important mediator of fear responses, we compared the physiological properties of central amygdala neurons in guinea pigs, rats and cats using whole-cell recordings in coronal slices in vitro. In guinea pigs, most central medial and lateral neurons displayed an outward rectification that delayed firing onset in response to depolarizing current pulses (hence the designation late-firing neurons). Late-firing neurons were also prevalent in the lateral sector of the cat central nucleus. In contrast, late-firing neurons were rare in the rat central nucleus and the cat central medial nucleus. There, most neurons generated Ni2+-sensitive low-threshold bursts of Na+ spikes and/or displayed pronounced inward rectification in the hyperpolarizing direction. Species differences in passive properties were also observed, but they were mainly related to the relative prevalence of late-firing cells. Indeed, late-firing cells had a significantly lower input resistance and more negative membrane potential than other types of central neurons. Thus, there are marked species differences in the physiological properties of central neurons. Because the synaptic responsiveness of neurons is constrained by their physiological properties, our findings raise the possibility that the contrasting behavioural responsiveness observed across species is partly dependent on the species-specific physiological properties of central neurons.

Action Potentials↗