Developmental age and biological sex influence muscarinic receptor function and neuron morphology within layer VI of the medial prefrontal cortex

Abstract

Acetylcholine (ACh) neurotransmission within the medial prefrontal cortex (mPFC) plays an important modulatory role to support mPFC-dependent cognitive functions. This role is mediated by ACh activation of its nicotinic (nAChR) and muscarinic (mAChR) classes of receptors, which are both present on mPFC layer VI pyramidal neurons. While the expression and function of nAChRs have been characterized thoroughly for rodent mPFC layer VI neurons during postnatal development, mAChRs have not been characterized in detail. We employed whole-cell electrophysiology with biocytin filling to demonstrate that mAChR function is greater during the juvenile period of development than in adulthood for both sexes. Pharmacological experiments suggest that each of the M1, M2, and M3 mAChR subtypes contributes to ACh responses in these neurons in a sex-dependent manner. Analysis of dendrite morphology identified effects of age more often in males, as the amount of dendrite matter was greatest during the juvenile period. Interestingly, a number of positive correlations were identified between the magnitude of ACh/mAChR responses and dendrite morphology in juvenile mice that were not present in adulthood. To our knowledge, this work describes the first detailed characterization of mAChR function and its correlation with neuron morphology within layer VI of the mPFC.

Xanomeline restores endogenous nicotinic acetylcholine receptor signaling in mouse prefrontal cortex

“…There was an effect of sex, with greater responses seen in females (F 1,180 = 4.6, P = 0.03). The difference is consistent with existing work showing sex differences in layer 6 pyramidal cholinergic responses [41,53]. However, it is a modest difference compared to the strong and significant effect of age group, where opto-ACh responses are decreased in older relative to younger mice (F 1,180 = 23.5, P < 0.0001).…”

“…Here, we identify an age-related selective postsynaptic nicotinic receptor deficit in functional prefrontal cholinergic neurotransmission. This finding is consistent with earlier preclinical research showing age-dependent cortical decreases in nicotinic receptor binding [40,70,72,75] and in response to exogenous agonist [41]. A parallel decline in cortical nicotinic receptor binding is observed in older humans [17,18,76], underscoring the translational relevance of this work.…”

“…However, previous work has not examined the impact of age on these complex synapses. The need to study the integrated impact of adult age-related changes on endogenous cholinergic signaling is underscored by research suggesting that cholinergic receptor expression is dynamic [40,41] and there may be interactions across receptor subtypes [42][43][44].…”

Cell-Type Specific Neuromodulation of Excitatory and Inhibitory Neurons via Muscarinic Acetylcholine Receptors in Layer 4 of Rat Barrel Cortex

“…In the neocortex, both receptor types show layerspecific distributions and effects (Obermayer et al, 2017;Radnikow and Feldmeyer, 2018). In general, ACh increases the excitability of pyramidal cells located in different cortical layers by activating both nAChRs and mAChRs (Gulledge et al, 2007;Zolles et al, 2009;Bailey et al, 2010;Tian et al, 2014;Hay et al, 2016;Yang et al, 2020;Patel et al, 2021). In a minor fraction of deep L2/3 and a subset of L5/6 pyramidal cells, ACh induces an initial small and transient hyperpolarisation followed by a sustained depolarisation mediated by muscarinic M1/3 mAChRs (Gulledge and Stuart, 2005;Gulledge et al, 2007;Eggermann and Feldmeyer, 2009;Patel et al, 2021).…”

“…In general, ACh increases the excitability of pyramidal cells located in different cortical layers by activating both nAChRs and mAChRs (Gulledge et al, 2007;Zolles et al, 2009;Bailey et al, 2010;Tian et al, 2014;Hay et al, 2016;Yang et al, 2020;Patel et al, 2021). In a minor fraction of deep L2/3 and a subset of L5/6 pyramidal cells, ACh induces an initial small and transient hyperpolarisation followed by a sustained depolarisation mediated by muscarinic M1/3 mAChRs (Gulledge and Stuart, 2005;Gulledge et al, 2007;Eggermann and Feldmeyer, 2009;Patel et al, 2021). In contrast, excitatory neurons located in layer 4 are persistently hyperpolarised by ACh activating M4 mAChRs (Eggermann and Feldmeyer, 2009;Dasgupta et al, 2018).…”