Fornix Transection
Objective: To assess the necessity of hippocampal input for nucleus accumbens neuron activity state transitions by performing acute fornix transection and evaluating changes in neuronal activity patterns
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Equipment2
Materials1
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Protocol Steps
Baseline neuronal recording and characterization
Record from nucleus accumbens neurons using in vivo intracellular recording techniques to identify and characterize their activity states (silent, spontaneously firing at low constant rates, or bistable membrane potential)
Note: Bistable neurons characterized by alternating periods of activity and silence with transitions between two steady-state membrane potentials (average base: -77.3 ± 7.1 mV, plateau: -63.0 ± 7.4 mV)
View evidence from paper
“Neurons recorded in the accumbens displayed one of three activity states: (1) silent, (2) spontaneously firing at low, constant rates, or (3) a bistable membrane potential”
Test hippocampal afferent activation
Stimulate hippocampal afferents and observe effects on bistable accumbens neurons to establish baseline response patterns
Note: Activation of hippocampal afferents induces bistable cells to switch to the depolarized (active) state
View evidence from paper
“Activation of hippocampal afferents, but not cortical, amygdaloid, or thalamic afferents, induced bistable cells to switch to the depolarized (active) state”
Perform acute fornix transection
Surgically transect the fornix acutely to eliminate hippocampal input to the nucleus accumbens
Note: This is the critical intervention to test necessity of hippocampal input
View evidence from paper
“no bistable cells were encountered in the nucleus accumbens following an acute transection of the fornix”
Record neuronal activity post-transection
Continue in vivo intracellular recording from nucleus accumbens neurons after fornix transection to assess changes in activity state patterns
Note: Absence of bistable cells indicates hippocampal input is necessary for this activity state
View evidence from paper
“no bistable cells were encountered in the nucleus accumbens following an acute transection of the fornix”
Microinjection of lidocaine at fornix level
Perform microinjection of lidocaine in the vicinity of hippocampal afferents at the level of the fornix to reversibly inactivate hippocampal input
Note: This provides reversible confirmation of the transection results
View evidence from paper
“microinjection of lidocaine in the vicinity of the hippocampal afferents at the level of the fornix caused a reversible elimination of the plateau phase in bistable cells”
Assess plateau phase elimination
Record neuronal responses during lidocaine microinjection to confirm reversible elimination of the plateau phase in bistable cells
Note: Reversibility confirms the effect is due to hippocampal inactivation rather than tissue damage
View evidence from paper
“microinjection of lidocaine in the vicinity of the hippocampal afferents at the level of the fornix caused a reversible elimination of the plateau phase in bistable cells”