Activation of the N-methyl-D-aspartate (NMDA) receptor is important for certain forms of activity-dependent synaptic plasticity, such as long-term potentiation (reviewed in ref. 1), and the patterning of connections during development of the visual system (reviewed in refs 2, 3). Several subunits of the NMDA receptor have been cloned: these are NMDAR1 (NR1), and NMDAR2A, 2B, 2C and 2D (NR2A-D). Based on heterologous co-expression studies, it is inferred that NR1 encodes an essential subunit of NMDA receptors and that functional diversity of NMDA receptors in vivo is effected by differential incorporation of subunits NR2A-NR2D. Little is known, however, about the actual subunit composition or heterogeneity of NMDA receptors in the brain. By co-immunoprecipitation with subunit-specific antibodies, we present here direct evidence that NMDA receptors exist in rat neocortex as heteromeric complexes of considerable heterogeneity, some containing both NR2A and NR2B subunits. A progressive alteration in subunit composition seen postnatally could contribute to NMDA-receptor variation and changing synaptic plasticity during cortical development.

It has been hypothesized that the direction of synaptic weight change elicited by synaptic activity depends on the magnitude of the activity-dependent rise in intracellular Ca2+ concentration. Several aspects of this hypothesis were examined at the Schaffer collateral CA1 synapse, where both long-term depression (LTD) and long-term potentiation (LTP) can be elicited and are Ca2+ dependent. Brief tetanic stimulation, which normally generated LTP, could induce LTD when Ca2+ entry via NMDA receptors was limited either by moderate concentrations of D-APV or by voltage clamping cells at negative membrane potentials. Repetitive activation of voltage-dependent Ca2+ channels in the absence of afferent stimulation could also elicit an LTD that was Ca2+ dependent and was occluded by prior generation of homosynaptic LTD using prolonged low evidence that the minimal requirements for inducing LTD involve simply a transient influx of Ca2+ into the postsynaptic cell, via either NMDA receptors or voltage-dependent Ca2+ channels.

Background Females exhibit more rapid escalation of cocaine use and enhanced cocaine-taking behavior as compared to males. While ovarian hormones likely play a role in this increased vulnerability, research has yet to examine the role of estradiol in affecting the behavioral and neurological response to cocaine in a brain region- and sex-specific way. Methods First, we examined stereotypy and locomotor sensitization after repeated cocaine administration (10 mg/kg i.p.) in intact (SHAM) and castrated (CAST) males, and ovariectomized (OVX) females treated with 5 μg estradiol benzoate (EB) or vehicle (OIL). Next, we used in vivo microdialysis to examine the effects of acute EB treatment on cocaine-induced DA in the regions mediating the display of these behaviors (i.e., the dorsolateral striatum, DLS; and the nucleus accumbens, NAc; respectively). Results We find that EB enhances sensitization of cocaine-induced stereotypy in OVX females after 12 days of cocaine treatment, and after a 10-day withdrawal. Similarly, the OVX/EB females show enhanced locomotor sensitization compared to the other three groups on the same days. Using in vivo microdialysis to assess the neurochemical response, we find that EB rapidly enhances cocaine-induced DA in DLS dialysate of OVX females but not CAST males, and has no effect in NAc of either sex. Conclusions With these experiments, we show that there are sex differences in the effects of estradiol to preferentially enhance the response to cocaine in the DLS over the NAc in females, which may contribute to the preferential sensitization of stereotypy in females.

The gonadal hormone estradiol modulates mesolimbic dopamine systems in the female rat. This modulatory effect is thought to be responsible for the observed effects of estradiol on motivated behaviors. Dopamine acting in the nucleus accumbens is thought to be important for the attribution of incentive motivational properties to cues that predict reward delivery, while dopamine in the striatum is associated with the expression of repetitive or stereotyped behaviors. Elevated concentrations of estradiol are associated with increased motivation for sex or cues associated with access to a mate, while simultaneously attenuating motivation for food. This shift in motivational salience is important for adaptive choice behavior in the natural environment. Additionally, estradiol’s adaptive effects on motivation can be maladaptive when increasing motivation for non-natural reinforcers, such as drugs of abuse. Here we discuss the effect of estradiol on mesotelencephalic dopamine transmission and subsequent effects on motivated behaviors.