Synaptic plasticity in the hippocampal area CA1-subiculum projection: Implications for theories of memory

Abstract

This paper reviews investigations of synaptic plasticity in the major, and underexplored, pathway from hippocampal area CA1 to the subiculum. This brain area is the major synaptic relay for the majority of hippocampal area CA1 neurons, making the subiculum the last relay of the hippocampal formation prior to the cortex. The subiculum thus has a very major role in mediating hippocampal‐cortical interactions. We demonstrate that the projection from hippocampal area CA1 to the subiculum sustains plasticity on a number of levels. We show that this pathway is capable of undergoing both long‐term potentiation (LTP) and paired‐pulse facilitation (PPF, a short‐term plastic effect). Although we failed to induce long‐term depression (LTD) of this pathway with low‐frequency stimulation (LFS) and two‐pulse stimulation (TPS), both protocols can induce a “late‐developing” potentiation of synaptic transmission. We further demonstrate that baseline synaptic transmission can be dissociated from paired‐pulse stimulation of the same pathway; we also show that it is possible, using appropriate protocols, to change PPF to paired‐pulse depression, thus revealing subtle and previously undescribed mechanisms which regulate short‐term synaptic plasticity. Finally, we successfully recorded from individual subicular units in the freely‐moving animal, and provide a description of the characteristics of such neurons in a pellet‐chasing task. We discuss the implications of these findings in relation to theories of the biological consolidation of memory. Hippocampus 10:447–456, 2000 © 2000 Wiley‐Liss, Inc.

A two-week period of detraining reduces hippocampal volume in regularly active young adults: a structural MRI study

“…CA1 has been closely linked to episodic memory [49,50] and spatial navigation [51]. Likewise, the subiculum plays a signi cant role in memory consolidation processes [52]. The reduction in MVPA observed in our sample appears to be associated, on one hand, with a decreased demand for spatial processing and motor control, functions that are largely dependent on hippocampal pyramidal neurons [53].…”

A two-week period of detraining reduces hippocampal volume in regularly active young adults: a structural MRI study

“…CA1 has been closely linked to episodic memory [49,50] and spatial navigation [51]. Likewise, the subiculum plays a signi cant role in memory consolidation processes [52]. The reduction in MVPA observed in our sample appears to be associated, on one hand, with a decreased demand for spatial processing and motor control, functions that are largely dependent on hippocampal pyramidal neurons [53].…”

Long‐term effects of chronic nicotine on emotional and cognitive behaviors and hippocampus cell morphology in mice: comparisons of adult and adolescent nicotine exposure

“…It is possible that the atrophy in the CA1 region of the hippocampus of mice exposed to nicotine during adolescence results in altered signaling to the subiculum. The subiculum receives input from the CA1 region of the hippocampus and acts as a relay between the hippocampus and other parts of the cortex (O'Mara et al ., ). Lesions to this region result in impaired acquisition and recall of contextual fear (Maren, ), as well as disruption of latent inhibition which is context dependent and mediated through the hippocampus (Quintero et al ., ).…”

Novel neurosteroid hypnotic blocks T-type calcium channel-dependent rebound burst firing and suppresses long-term potentiation in the rat subiculum

“…15 Here, we confirm the hypnotic and T-channel-blocking properties of 3b-OH in juvenile rats and, furthermore, report on its differential effects at two hippocampal synapses important for memory processing: CA3-CA1 4 and CA1-subiculum. 30 First, we detected isolated T-currents in subicular neurones with minimal differences in biophysical properties compared with rat pups, 11 which clearly showed a dominant expression of the Ca V 3.1 T-channel isoform. However, here we report an increase in mRNA expression of Ca V 3.3 isoform compared with rat pups.…”

A two-week period of detraining reduces hippocampal volume in regularly active young adults: a structural MRI study

“…CA1 has been closely linked to episodic memory [49,50] and spatial navigation [51]. Likewise, the subiculum plays a signi cant role in memory consolidation processes [52]. The reduction in MVPA observed in our sample appears to be associated, on one hand, with a decreased demand for spatial processing and motor control, functions that are largely dependent on hippocampal pyramidal neurons [53].…”

Long‐term effects of chronic nicotine on emotional and cognitive behaviors and hippocampus cell morphology in mice: comparisons of adult and adolescent nicotine exposure

“…It is possible that the atrophy in the CA1 region of the hippocampus of mice exposed to nicotine during adolescence results in altered signaling to the subiculum. The subiculum receives input from the CA1 region of the hippocampus and acts as a relay between the hippocampus and other parts of the cortex (O'Mara et al ., ). Lesions to this region result in impaired acquisition and recall of contextual fear (Maren, ), as well as disruption of latent inhibition which is context dependent and mediated through the hippocampus (Quintero et al ., ).…”

Novel neurosteroid hypnotic blocks T-type calcium channel-dependent rebound burst firing and suppresses long-term potentiation in the rat subiculum

“…15 Here, we confirm the hypnotic and T-channel-blocking properties of 3b-OH in juvenile rats and, furthermore, report on its differential effects at two hippocampal synapses important for memory processing: CA3-CA1 4 and CA1-subiculum. 30 First, we detected isolated T-currents in subicular neurones with minimal differences in biophysical properties compared with rat pups, 11 which clearly showed a dominant expression of the Ca V 3.1 T-channel isoform. However, here we report an increase in mRNA expression of Ca V 3.3 isoform compared with rat pups.…”

A two-week period of detraining reduces hippocampal volume in regularly active young adults: a structural MRI study

“…CA1 has been closely linked to episodic memory [49,50] and spatial navigation [51]. Likewise, the subiculum plays a signi cant role in memory consolidation processes [52]. The reduction in MVPA observed in our sample appears to be associated, on one hand, with a decreased demand for spatial processing and motor control, functions that are largely dependent on hippocampal pyramidal neurons [53].…”

Long‐term effects of chronic nicotine on emotional and cognitive behaviors and hippocampus cell morphology in mice: comparisons of adult and adolescent nicotine exposure

“…It is possible that the atrophy in the CA1 region of the hippocampus of mice exposed to nicotine during adolescence results in altered signaling to the subiculum. The subiculum receives input from the CA1 region of the hippocampus and acts as a relay between the hippocampus and other parts of the cortex (O'Mara et al ., ). Lesions to this region result in impaired acquisition and recall of contextual fear (Maren, ), as well as disruption of latent inhibition which is context dependent and mediated through the hippocampus (Quintero et al ., ).…”

Novel neurosteroid hypnotic blocks T-type calcium channel-dependent rebound burst firing and suppresses long-term potentiation in the rat subiculum

“…15 Here, we confirm the hypnotic and T-channel-blocking properties of 3b-OH in juvenile rats and, furthermore, report on its differential effects at two hippocampal synapses important for memory processing: CA3-CA1 4 and CA1-subiculum. 30 First, we detected isolated T-currents in subicular neurones with minimal differences in biophysical properties compared with rat pups, 11 which clearly showed a dominant expression of the Ca V 3.1 T-channel isoform. However, here we report an increase in mRNA expression of Ca V 3.3 isoform compared with rat pups.…”