4. 4 Limitations
The study owns some limitations such as, firstly, the focus on
ionotropic glutamate signaling and not, for instance, on the potential
role of metabotropic mGluR5 receptors as suggested by EE-induced mGluR5
enhancement of hippocampal LTP (Buschler & Manahan-Vaughan, 2017).
Therefore, ad-hoc molecular studies are needed on the entire
glutamatergic components, as well as on other neurochemical pathways
(e.g., BDNF, 5-HT) and brain regions (e.g., amygdala) relevant to
rewarding and learning. Further, we did not investigate the mechanism
underlying the expression change, whether due to changes in synthesis or
degradation. We measured the glutamatergic changes only at 2 hours after
the end of the brief EE exposure: we are aware that a series of
timepoint assessments may provide a better understanding. We are also
aware that only detecting protein expression cannot establish a causal
relationship and that protein expression alone may not reflect
functional mechanisms. Our rats were kept isolated thus raising the
possibility that housing conditions may indeed influence the response of
the glutamatergic synapse. For instance, we recently demonstrated in
adult male mice that living environment (i.e., social vs isolation
housing) influences the efficacy of EE/fluoxetine interaction in
inhibiting relapse to sucrose (Pintori et al. , 2022b). Finally,
we used only male rats in our study and, therefore, we do not know if
our findings can be extended to female rats.