Fear extinction is a process in which a learned fear response is reduced or eliminated through repeated exposure to the fear-inducing stimulus in the absence of any adverse consequences. Fear extinction specifically refers to the reduction of conditioned fear responses, such as freezing behavior, in rats that have been previously conditioned to associate a neutral stimulus (conditioned stimulus, CS) with an aversive outcome (unconditioned stimulus, US). NMDA receptor antagonists can facilitate fear extinction by affecting different stages of the fear extinction memory process:

1. **Initiation**: An NMDA antagonist impairs the initiation of fear extinction memory when administered before or shortly after the extinction session. This means that it interferes with the beginning of the process where the fear response starts to diminish.

2. **Consolidation**: An NMDA antagonist also disrupts the consolidation of fear extinction memory. This stage involves the stabilization of the reduced fear response over time. When an NMDA antagonist is given during this phase, it hinders the solidification of the reduced fear memory.

1. … . Initial studies were promising (Miserendino et al 1990). Infusion of APV prior to learning blocked fear conditioning, but infusion proior to testing had no effect. NMDA
2. … blockade of NMDA receptors induces epigenetic abnormalities in the adult medial prefrontal cortex: possible involvement in memory impairment in trace fear …
3. … in rats is mediated by neurons in the deep layers of the superior colliculus/deep mesencephalic nucleus of the rostral midbrain through the glutamate non-NMDA …
4. … of an NR2B-selective or an NR2A-preferring NMDA receptor antagonist differentially influence fear conditioning and expression in the fear-potentiated startle test
5. A critical role for VEGF and VEGFR2 in NMDA receptor synaptic function and fear-related behavior
6. A NMDA receptor antagonist, MK-801 impairs consolidating extinction of auditory conditioned fear responses in a Pavlovian model
7. A risk variant for alcoholism in the NMDA receptor affects amygdala activity during fear conditioning in humans
8. Acquisition of contextual Pavlovian fear conditioning is blocked by application of an NMDA receptor antagonist D, L-2-amino-5-phosphonovaleric acid to the …
9. Acquisition of fear extinction requires activation of NR2B-containing NMDA receptors in the lateral amygdala
10. Acquisition, extinction, and reinstatement of Pavlovian fear conditioning: the roles of the NMDA receptor and nitric oxide
11. Activity-induced synaptic delivery of the GluN2A-containing NMDA receptor is dependent on endoplasmic reticulum chaperone Bip and involved in fear …
12. Acute injections of the NMDA receptor antagonist memantine rescue performance deficits of the Ts65Dn mouse model of Down syndrome on a fear …
13. Alcohol inhibition of the NMDA receptor function, long-term potentiation, and fear learning requires striatal-enriched protein tyrosine phosphatase
14. Amygdalar NMDA receptors are critical for new fear learning in previously fear-conditioned rats
15. Amygdalar NMDA receptors are critical for the expression of multiple conditioned fear responses
16. An appetitive experience after fear memory destabilization attenuates fear retention: involvement GluN2B-NMDA receptors in the Basolateral Amygdala Complex
17. An appetitive experience after fear memory destabilization attenuates fear retention: involvement GluN2B-NMDA receptors in the Basolateral Amygdala Complex.
18. An NMDA–receptor antagonist, MK-801 blocks the suppressive vasopressin response to fear-but not to anxiety-related stimuli in the rat.
19. Aquaporin-4 deficiency facilitates fear memory extinction in the hippocampus through excessive activation of extrasynaptic GluN2B-containing NMDA receptors
20. Are fear memories made and maintained by the same NMDA receptor-dependent mechanisms?
21. ASIC1a regulates ventral hippocampal-infralimbic prefrontal plasticity and fear extinction via BDNF-NMDA receptor signaling
22. Bed nucleus of the stria terminalis NMDA receptors and nitric oxide modulate contextual fear conditioning in rats
23. Beyond attention: The role of amygdala NMDA receptors in fear conditioning
24. Blockade of Cav2. 1-mediated NMDA receptor signaling disrupts conditioned fear extinction
25. Blockade of NMDA receptors in the amygdala prevents latent inhibition of fear-conditioning
26. Blocking of acquisition but not expression of conditioned fear-potentiated startle by NMDA antagonists in the amygdala
27. Brief neonatal maternal separation alters extinction of conditioned fear and corticolimbic glucocorticoid and NMDA receptor expression in adult rats
28. Close linkage between calcium/calmodulin kinase II α/β and NMDA‐2A receptors in the lateral amygdala and significance for retrieval of auditory fear conditioning
29. Complex effects of NMDA receptor antagonist APV in the basolateral amygdala on acquisition of two-way avoidance reaction and long-term fear memory
30. Conditioning-strength dependent involvement of NMDA NR2B subtype receptor in the basolateral nucleus of amygdala in acquisition of auditory fear memory
31. Consolidation of auditory fear memories formed by weak unconditioned stimuli requires NMDA receptor activation and de novo protein synthesis in the …
32. Consolidation of fear extinction requires NMDA receptor-dependent bursting in the ventromedial prefrontal cortex
33. Decrease in NMDA receptor-signalling activity in the anterior cingulate cortex diminishes defensive behaviour and unconditioned fear-induced antinociception elicited …
34. Differential involvement of amygdala and cortical NMDA receptors activation upon encoding in odor fear memory
35. Differential involvement of amygdalar NMDA receptors across variants of contextual fear conditioning in adolescent rats
36. Differential involvement of amygdalar NMDA receptors in variants of adolescent contextual fear conditioning
37. Differentiating the contributions of NMDA receptor-mediated synaptic plasticity in basal and lateral nuclei of the amygdala during Pavlovian fear conditioning
38. Dorsal hippocampus and classical fear conditioning to tone and context in rats: Effects of local NMDA‐receptor blockade and stimulation
39. Dorsal hippocampus NMDA receptors differentially mediate trace and contextual fear conditioning
40. Effect of the NMDA antagonist MK-801 on latent inhibition of fear conditioning
41. Effects of agonists and antagonists of NMDA and ACh receptors on plasticity of bat auditory system elicited by fear conditioning
42. Effects of an NMDA–receptor antagonist, MK-801 on emotional memory associated with neurohypophysial responses to fear or anxiety stimuli in rats
43. Effects of NMDA receptor antagonists and sigma ligands on the acquisition of conditioned fear in mice
44. Effects of REM deprivation and an NMDA agonist on the extinction of conditioned fear
45. Effects of single prolonged stress and D-cycloserine on contextual fear extinction and hippocampal NMDA receptor expression in a rat model of PTSD
46. Elucidating the mechanisms of fear extinction in developing animals: a special case of NMDA receptor-independent extinction in adolescent rats
47. Endogenous co-agonists of the NMDA receptor modulate contextual fear in trace conditioning
48. Estradiol-induced enhancement of fear extinction in female rats: The role of NMDA receptor activation
49. Estradiol-induced enhancement of fear extinction in female rats: the role of NMDA receptor activation Running title: Estradiol, NMDAr activation, and fear …
50. Extinction of fear-potentiated startle: blockade by infusion of an NMDA antagonist into the amygdala
51. Extinction of fear-potentiated Startle: Blockade by Infusion of an NMDA Antagonist into the Amygdala
52. fear conditioning performance and NMDA receptor subtypes: NR2A differential expression in the striatum
53. fear memory extinction accelerated by simultaneous activation of GABA (B) and NMDA receptors
54. fear memory impairing effects of systemic treatment with the NMDA NR2B subunit antagonist, Ro 25-6981, in mice: attenuation with ageing
55. GABA and NMDA receptors in CRF neurons have opposing effects in fear acquisition and anxiety in central amygdala vs. bed nucleus of the stria terminalis
56. Glutamate NMDA receptors within the amygdala participate in the modulatory effect of glucocorticoids on extinction of conditioned fear in rats
57. Hippocampal NMDA receptor blockade impairs CREB phosphorylation in amygdala after contextual fear conditioning
58. Hippocampal NMDA receptor subunits differentially regulate fear memory formation and neuronal signal propagation
59. Hippocampal NMDA receptors are necessary for auditory trace fear conditioning measured with conditioned hypoalgesia in rats
60. Hypofunction of the dorsal hippocampal NMDA receptors impairs retrieval of memory to partially presented foreground context in a single-trial fear conditioning in rats
61. Impairment of conditioned contextual fear of C57BL/6J mice by intracerebral injections of the NMDA receptor antagonist APV
62. Induction-and conditioning-protocol dependent involvement of NR2B-containing NMDA receptors in synaptic potentiation and contextual fear memory in the …
63. Infusion of the NMDA receptor antagonist, DL-APV, into the basolateral amygdala disrupts learning to fear a novel and a familiar context as well as relearning to fear …
64. Infusion of the non-NMDA receptor antagonist CNQX into the amygdala blocks the expression of fear-potentiated startle
65. Injections of the NMDA receptor antagonist aminophosphonopentanoic acid into the lateral nucleus of the amygdala block the expression of fear-potentiated startle …
66. Interaction between glutamatergic–NMDA and cholinergic–muscarinic systems in classical fear conditioning
67. Intra-amygdala blockade of the NR2B subunit of the NMDA receptor disrupts the acquisition but not the expression of fear conditioning
68. Involvement of NMDA receptors within the amygdala in short-versus long-term memory for fear conditioning as assessed with fear-potentiated startle.
69. Lack of a temporal gradient of retrograde amnesia following NMDA-induced lesions of the basolateral anygdala assessed with the fear-potentiated startle paradigm.
70. Latent inhibition of cued fear conditioning: an NMDA receptor‐dependent process that can be established in the presence of anisomycin
71. Loss of NMDA receptor function in corticotrophin-releasing factor neurons sex-dependently enhances fear and increases sensitivity to social stress, yet reduces social …
72. Mapping and deciphering neural codes of NMDA receptor-dependent fear memory engrams in the hippocampus
73. Neonatal ethanol exposure impairs trace fear conditioning and alters NMDA receptor subunit expression in adult male and female rats
74. Neonatal treatment with a competitive NMDA antagonist results in response-specific disruption of conditioned fear in preweanling rats
75. Newly acquired and reactivated contextual fear memories are more intense and prone to generalize after activation of prelimbic cortex NMDA receptors
76. Nicotine ameliorates NMDA receptor antagonist-induced deficits in contextual fear conditioning through high-affinity nicotinic acetylcholine receptors in the …
77. Nitric oxide signalling in the basolateral complex of the amygdala: an extension of NMDA receptor activation during Pavlovian fear conditioning and expression
78. NMDA and AMPA/kainate glutamatergic receptors in the prelimbic medial prefrontal cortex modulate the elaborated defensive behavior and innate fear-induced …
79. NMDA and dopaminergic contributions to context fear memory reconsolidation
80. NMDA and muscarinic receptor modulation of latent learning in Pavlovian fear conditioning.
81. NMDA currents and receptor protein are downregulated in the amygdala during maintenance of fear memory
82. NMDA GluN2A and GluN2B receptors play separate roles in the induction of LTP and LTD in the amygdala and in the acquisition and extinction of conditioned fear
83. NMDA processes mediate anterograde amnesia of contextual fear conditioning induced by hippocampal damage: immunization against amnesia by context …
84. NMDA receptor antagonism in the basolateral but not central amygdala blocks the extinction of Pavlovian fear conditioning in rats
85. NMDA receptor antagonist MK-801 blocks learning of conditioned stimulus-unconditioned stimulus contiguity but not fear of conditioned stimulus in goldfish …
86. NMDA receptor blockade and hippocampal neuronal loss impair fear conditioning and position habit reversal in C57Bl/6 mice
87. NMDA receptor mediated expression of Arc in dorsal and ventral hippocampus contributes to the acquisition of contextual and trace fear conditioning
88. NMDA receptor-and ERK-dependent histone methylation changes in the lateral amygdala bidirectionally regulate fear memory formation
89. NMDA receptor-dependent LTD is required for consolidation but not acquisition of fear memory
90. NMDA receptor-mediated Arc expression in dorsal and ventral hippocampus contributes to the acquisition of trace and contextual fear conditioning
91. NMDA receptors and fear extinction: implications for cognitive behavioral therapy
92. NMDA receptors and L-type voltage-gated calcium channels contribute to long-term potentiation and different components of fear memory formation in the lateral …
93. NMDA receptors and the ontogeny of post‐shock and retention freezing during contextual fear conditioning
94. NMDA receptors are critical for unleashing consolidated auditory fear memories
95. NMDA receptors are essential for the acquisition, but not expression, of conditional fear and associative spike firing in the lateral amygdala
96. NMDA receptors in retrosplenial cortex are necessary for retrieval of recent and remote context fear memory
97. NMDA receptors in the CeA and BNST differentially regulate fear conditioning to predictable and unpredictable threats
98. NMDA receptors in the pontine brainstem are necessary for fear potentiation of the startle response
99. NMDA-mediated social learning of fear-induced conditioned analgesia to biting flies
100. NR2A-and NR2B-containing NMDA receptors in the prelimbic medial prefrontal cortex differentially mediate trace, delay, and contextual fear conditioning
101. NR2B subunit-specific NMDA antagonist Ro25-6981 inhibits the expression of conditioned fear: a comparison with the NMDA antagonist MK-801 and fluoxetine
102. PACAP modulates the consolidation and extinction of the contextual fear conditioning through NMDA receptors
103. Pharmacological evidence that a failure to recruit NMDA receptors contributes to impaired fear extinction retention in adolescent rats
104. Plasticity of NMDA receptors at Ventral Hippocampal Synapses in the Infralimbic Cortex Regulates Cued fear
105. Potentiation of GluN2C/D NMDA receptor subtypes in the amygdala facilitates the retention of fear and extinction learning in mice
106. Pre-training prevents context fear conditioning deficits produced by hippocampal NMDA receptor blockade
107. Prefrontal NMDA receptors expressed in excitatory neurons control fear discrimination and fear extinction
108. Prenatal kynurenine exposure in rats: age-dependent changes in NMDA receptor expression and conditioned fear responding
109. Pretraining NMDA receptor blockade in the basolateral complex, but not the central nucleus, of the amygdala prevents savings of the conditional fear.
110. Role of NMDA receptors and MAP kinase in the amygdala in extinction of fear: clinical implications for exposure therapy
111. ROLE OF PREFRONTAL CORTICAL NMDA NR2B SUBTYPE receptor IN fear-AND WORKING-MEMORY
112. Role of the basolateral amygdala and NMDA receptors in higher-order conditioned fear
113. Role of the basolateral amygdala and NMDA receptors in the acquisition and extinction of higher-order conditioned fear
114. Roles of NMDA NR2B subtype receptor in prefrontal long-term potentiation and contextual fear memory
115. Second-order fear conditioning prevented by blocking NMDA receptors in amygdala
116. Studies of GluN2C-containing NMDA receptors in schizophrenia-like behaviors and fear learning; Relevance to the glutamate hypofunction hypothesis of …
117. Surface expression of hippocampal NMDA GluN2B receptors regulated by fear conditioning determines its contribution to memory consolidation in adult rats
118. Targeting the NMDA receptor for fear-related disorders
119. Temporal-difference prediction errors and Pavlovian fear conditioning: role of NMDA and opioid receptors.
120. The effect of hippocampal NMDA receptor blockade by MK-801 on cued fear extinction
121. The effect of the mGlu5 negative allosteric modulator MTEP and NMDA receptor partial agonist D-cycloserine on Pavlovian conditioned fear
122. The effect of the NMDA receptor antagonist MK-801 on the acquisition and extinction of learned fear in the developing rat
123. The effects of intra-hippocampal microinfusion of D-cycloserine on fear extinction, and the expression of NMDA receptor subunit NR2B and neurogenesis in the …
124. The expression of contextual fear conditioning involves activation of a NMDA receptor-nitric oxide-cGMP pathway in the dorsal hippocampus of rats
125. The expression of contextual fear conditioning involves activation of an NMDA receptor–nitric oxide pathway in the medial prefrontal cortex
126. The importance of having Arc: expression of the immediate-early gene Arc is required for hippocampus-dependent fear conditioning and blocked by NMDA receptor …
127. The innate defensive behaviour and unconditioned fear-induced antinociception evoked by NMDA receptor activation in the medial hypothalamus are modulated by …
128. The nitric oxide donor SIN-1-produced panic-like behaviour and fear-induced antinociception are modulated by NMDA receptors in the anterior hypothalamus
129. The NMDA agonist D-cycloserine facilitates fear memory consolidation in humans
130. The NMDA antagonist MK-801 blocks the extinction of Pavlovian fear conditioning.
131. The NMDA receptor antagonist MK-801 renders pavlovian fear conditioning state-dependent
132. The role of dorsal hippocampus and basolateral amygdala NMDA receptors in the acquisition and retrieval of context and contextual fear memories.
133. The role of GluN2B-containing NMDA receptors in short-and long-term fear recall
134. The role of NMDA glutamate receptors, PKA, MAPK, and CAMKII in the hippocampus in extinction of conditioned fear
135. Trace and contextual fear conditioning require neural activity and NMDA receptor-dependent transmission in the medial prefrontal cortex
136. Trace fear conditioning depends on NMDA receptor activation and protein synthesis within the dorsal hippocampus of mice
137. US habituation, like CS extinction, produces a decrement in conditioned fear responding that is NMDA dependent and subject to renewal and reinstatement
138. Vagus nerve stimulation enhances extinction of conditioned fear in rats and modulates Arc protein, CaMKII, and GluN2B-containing NMDA receptors in the …
139. Vorinostat ameliorates impaired fear extinction possibly via the hippocampal NMDA-CaMKII pathway in an animal model of posttraumatic stress disorder
140. Vorinostat, a histone deacetylase inhibitor, facilitates fear extinction and enhances expression of the hippocampal NR2B-containing NMDA receptor gene