Neuronal localization of M2 muscarinic receptor immunoreactivity in the rat amygdala

Abstract

Muscarinic cholinergic neurotransmission in the amygdala is critical for memory consolidation in emotional/motivational learning tasks, but little is known about the neuronal distribution of different receptor subtypes. Immunohistochemistry was used in the present investigation to localize the m2 receptor (M2R). Differential patterns of M2R-immunoreactivity (m2R-ir) were observed in the somata and neuropil of the various amygdalar nuclei. Neuropilar m2R-ir was strongest in rostral portions of the basolateral nuclear complex (BLC). M2R+ somata were seen in low numbers in all nuclei of the amygdala. Most M2R+ neurons associated with the BLC were in the lateral nucleus and external capsule. These cells were nonpyramidal neurons that contained glutamatic acid decarboxylase (GAD), somatostatin (SOM) and neuropeptide Y (NPY), but not parvalbumin (PV), calretinin (CR), or cholecystokinin (CCK). Little or no M2R-ir was observed in GAD+, PV+, CR+, or CCK+ axons in the BLC, but was seen in some SOM+ axons and many NPY+ axons. M2R-ir was found in a small number of spiny and aspiny neurons of the central nucleus that were mainly located along the lateral and ventral borders of its lateral subdivision. Many of these cells contained SOM and NPY. M2R+ neurons were also seen in the medial nucleus, including a distinct subpopulation of neurons that surrounded its anteroventral subdivision. The latter neurons were negative for all neuronal markers analyzed. The intercalated nuclei (IN) were associated with two types of large M2R+ neurons, spiny and aspiny. The small principal neurons of the INs were M2R-negative. The somata and dendrites of the large spiny neurons, which were actually found in a zone located just outside of the rostral INs, expressed SOM and NPY, but not GAD. These findings indicate that acetylcholine can modulate a variety of discrete neuronal subpopulations in various amygdalar nuclei via M2Rs, especially neurons that express SOM and NPY.

Evidence for M2 muscarinic receptor modulation of axon terminals and dendrites in the rodent basolateral amygdala: An ultrastructural and electrophysiological analysis

“…2A). M 2 R-ir in the BLa was very dense in the neuropil, but virtually all cell bodies appeared unstained as in previous studies in the rat (McDonald and Mascagni 2011, Muller et al 2016) (Fig. 2B).…”

“…No immunostaining was observed in M 2 R knockout mice (Jositsch et al, 2009). The pattern of M 2 R immunohistochemical labeling with this antibody in the rat brain, including the amygdala (McDonald and Mascagni, 2011), is identical to that seen with other M 2 R antibodies developed by the Levey laboratory (Levey et al, 1995). …”

“…In the present study we demonstrated that some of these M 2 R+ terminals belong to dendrite-targeting PV+ INs. However, many of the M 2 R+/PV-negative terminals that targeted dendritic shafts in the present study probably contain somatostatin (SOM) or neuropeptide Y (NPY), since in our previous immunofluorescence study in the rat many M 2 R+ axon terminals in the neuropil exhibited SOM-ir or NPY-ir (McDonald and Mascagni, 2011). It is well established that SOM+ axon terminals mainly synapse with distal dendrites and spines of PNs (Muller et al, 2007; Wolff et al, 2014).…”

Impact of Basal Forebrain Cholinergic Inputs on Basolateral Amygdala Neurons

“…In both the neocortex and BLA, a subpopulation of interneurons expresses muscarinic type-2 (M2) receptors (Levey et al, 1991;McDonald and Mascagni, 2011) whereas principal cells express M1 receptors (Mrzljak et al, 1993;McDonald and Mascagni, 2010;Yamasaki et al, 2010). Pharmacological activation of muscarinic receptors elicits similar responses in principal neurons of the neocortex and BLA.…”

Elevated Hippocampal Cholinergic Neurostimulating Peptide precursor protein (HCNP-pp) mRNA in the amygdala in major depression

“…The amygdala receives cholinergic input from the Nucleus Basalis of Meynert (Schafer et al, 1998) and expresses both muscarinic and nicotinic receptors (Klein and Yakel, 2006; McDonald and Mascagni, 2010; 2011). However, the cholinergic system in the amygdala has not been studied in detail in MDD subjects.…”