Vesicular acetylcholine transporter–immunoreactive axon terminals enriched in the pontine nuclei of the mouse

Differential cholinergic innervation of lemniscal versus non-lemniscal regions of the inferior colliculus

The inferior colliculus (IC), a midbrain hub for integration of auditory information, receives dense cholinergic input that could modulate nearly all aspects of hearing. A key step in understanding cholinergic modulation is to identify the source(s) and termination patterns of cholinergic input. These issues have not been addressed for the IC in mice, an increasingly important model for study of hearing. We examined cholinergic inputs to the IC in adult male and female mice. We used retrograde tracing and immunochemistry to identify three sources of cholinergic innervation of the mouse IC: the pedunculopontine tegmental nucleus (PPT), the laterodorsal tegmental nucleus (LDT) and the lateral paragigantocellular nucleus (LPGi). We then used Cre-dependent labeling of cholinergic neurons in normal-hearing ChAT-Cre mice to selectively label the cholinergic projections to the IC from each of the cholinergic sources. Labeling of cholinergic projections from the PPT and LDT revealed cholinergic axons and boutons terminating throughout the IC, with the ipsilateral projection being denser. Electron microscopic examination showed that these cholinergic axons can form traditional synaptic junctions with IC neurons. In separate experiments, selective labeling of cholinergic projections from the LPGi revealed bilateral projections to the IC. The LPGi axons exhibited relatively equal densities on ipsilateral and contralateral sides, but on both sides the terminations were largely restricted to the non-lemniscal regions of the IC (i.e., the dorsal cortex, lateral cortex and intercollicular tegmentum). We conclude first that cholinergic axons can form traditional synapses in the IC. In addition, lemniscal and non-lemniscal regions of the IC receive different patterns of cholinergic innervation. The lemniscal IC (IC central nucleus) is innervated by cholinergic neurons in the PPT and the LDT whereas the non-lemniscal "shell" areas of the IC are innervated by the PPT and LDT and by cholinergic neurons in the LPGi. DATA AVAILABILITY: Data will be made available on request.

Structural basis for cholinergic regulation of neural circuits in the mouse olfactory bulb

Odor information is regulated by olfactory inputs, bulbar interneurons, and centrifugal inputs in the olfactory bulb (OB). Cholinergic neurons projecting from the nucleus of the horizontal limb of the diagonal band of Broca and the magnocellular preoptic nucleus are one of the primary centrifugal inputs to the OB. In this study, we focused on cholinergic regulation of the OB and analyzed neural morphology with a particular emphasis on the projection pathways of cholinergic neurons. Single-cell imaging of a specific neuron within dense fibers is critical to evaluate the structure and function of the neural circuits. We labeled cholinergic neurons by infection with virus vector and then reconstructed them three-dimensionally. We also examined the ultramicrostructure of synapses by electron microscopy tomography. To further clarify the function of cholinergic neurons, we performed confocal laser scanning microscopy to investigate whether other neurotransmitters are present within cholinergic axons in the OB. Our results showed the first visualization of complete cholinergic neurons, including axons projecting to the OB, and also revealed frequent axonal branching within the OB where it innervated multiple glomeruli in different areas. Furthermore, electron tomography demonstrated that cholinergic axons formed asymmetrical synapses with a morphological variety of thicknesses of the postsynaptic density. Although we have not yet detected the presence of other neurotransmitters, the range of synaptic morphology suggests multiple modes of transmission. The present study elucidates the ways that cholinergic neurons could contribute to the elaborate mechanisms involved in olfactory processing in the OB. J. Comp. Neurol. 525:574-591, 2017. © 2016 Wiley Periodicals, Inc.

Stimulation of the subthalamic nucleus engages the cerebellum for motor function in parkinsonian rats

Deep brain stimulation (DBS) is effective in managing motor symptoms of Parkinson's disease in well-selected individuals. Recently, research has shown that DBS in the basal ganglia (BG) can alter neural circuits beyond the traditional basal ganglia-thalamus-cortical (BG-TH-CX) loop. For instance, functional imaging showed alterations in cerebellar activity with DBS in the subthalamic nucleus (STN). However, these imaging studies revealed very little about how cell-specific cerebellar activity responds to STN stimulation or if these changes contribute to its efficacy. In this study, we assess whether STN-DBS provides efficacy in managing motor symptoms in Parkinson's disease by recruiting cerebellar activity. We do this by applying STN-DBS in hemiparkinsonian rats and simultaneously recording neuronal activity from the STN, brainstem and cerebellum. We found that STN neurons decreased spiking activity by 55% during DBS (P = 0.038), which coincided with a decrease in most pedunculopontine tegmental nucleus and Purkinje neurons by 29% (P < 0.001) and 28% (P = 0.003), respectively. In contrast, spike activity in the deep cerebellar nuclei increased 45% during DBS (P < 0.001), which was likely from reduced afferent activity of Purkinje cells. Then, we applied STN-DBS at sub-therapeutic current along with stimulation of the deep cerebellar nuclei and found similar improvement in forelimb akinesia as with therapeutic STN-DBS alone. This suggests that STN-DBS can engage cerebellar activity to improve parkinsonian motor symptoms. Our study is the first to describe how STN-DBS in Parkinson's disease alters cerebellar activity using electrophysiology in vivo and reveal a potential for stimulating the cerebellum to potentiate deep brain stimulation of the subthalamic nucleus.

Localization of pre- and postsynaptic cholinergic markers in rodent forebrain: a brief history and comparison of rat and mouse

Rat and mouse models are widely used for studies in cognition and pathophysiology, among others. Here, we sought to determine to what extent these two model species differ for cholinergic and cholinoceptive features. For this purpose, we focused on cholinergic innervation patterns based on choline acetyltransferase (ChAT) immunostaining, and the expression of muscarinic acetylcholine receptors (mAChRs) detected immunocytochemically. In this brief review we first place cholinergic and cholinoceptive markers in a historic perspective, and then provide an overview of recent publications on cholinergic studies and techniques to provide a literature survey of current research. Next, we compare mouse (C57Bl/J6) and rat (Wistar) cholinergic and cholinoceptive systems simultaneously stained, respectively, for ChAT (analyzed qualitatively) and mAChRs (analyzed qualitatively and quantitatively). In general, the topographic cholinergic innervation patterns of both rodent species are highly comparable, with only considerable (but region specific) differences in number of detectable cholinergic interneurons, which are more numerous in rat. In contrast, immunolabeling for mAChRs, detected by the monoclonal antibody M35, differs markedly in the forebrain between the two species. In mouse brain, basal levels of activated and/or internalized mAChRs (as a consequence of cholinergic neurotransmission) are significantly higher. This suggests a higher cholinergic tone in mouse than rat, and hence the animal model of choice may have consequences for cholinergic drug testing experiments.