Research ReportIdentification and distribution of projections from monoaminergic and cholinergic nuclei to functionally differentiated subregions of prefrontal cortex
Introduction
The PFC is associated with several higher order cognitive functions such as rule-based and goal-directed behaviors, working memory, decision-making and reward seeking (Brown and Bowman, 2002, Dalley et al., 2004, Furuyashiki and Gallagher, 2007, Fuster, 2000, Ongur and Price, 2000, Passetti et al., 2002, Robbins, 2000). The connectivity and intrinsic organization of this region of the brain is optimal for its role in abstract behavioral and executive processes (Dalley et al., 2004, Fuster, 2000, Hoover and Vertes, 2007, Passetti et al., 2002). The PFC is composed of several anatomically and functionally distinct subregions, including OFC, mPFC, and ACC. In the rodent, OFC is implicated in reversal learning and lower order sensory discriminations (Dalley et al., 2004, Furuyashiki and Gallagher, 2007, Kolb et al., 2004, Murray et al., 2007, Rushworth et al., 2009, Schoenbaum et al., 2007, Sul et al., 2010), while mPFC is involved in higher order sensory-based discriminations, behavioral flexibility and sustained attention (Dalley et al., 2004, Floresco et al., 2008, McGaughy et al., 2008, Newman et al., 2008), and ACC is implicated in behavioral impulse control and regulation (Bussey et al., 1997). Importantly, functional, and to a lesser degree, anatomical, homology exists between rodent and human PFC (Dalley et al., 2004). These regions are each unique in their afferent and efferent connections (Dalley et al., 2004, Hoover and Vertes, 2007); however, several ascending neuromodulatory pathways all converge in these regions to regulate network activity. The purpose of this study was to identify the organization and distribution of cells in NB, VTA, DRN and LC that project to functionally and anatomically distinct subregions of PFC.
The NB is the primary source of cholinergic input to the cerebral cortex (Sarter and Bruno, 2000, Wenk, 1997) and has been implicated in arousal, learning, attention and memory (McGaughy et al., 2000, McGaughy and Sarter, 1998, McGaughy and Sarter, 1999, Nieto-Escamez et al., 2002, Sarter and Bruno, 2000, Wenk, 1997). A rough topography has been identified in the primate analog of NB, nucleus basalis of Meynert, such that anteromedial portions of the nucleus project to the medial surface of the cortex, anterolateral regions project to frontal and parietal cortices and amygdala, intermediate regions project to prefrontal, insular and posterior parietal cortices, and caudal portions project to the superior and temporal cortex (Pang et al., 1993). This nucleus is less well defined in rodent and its cholinergic projection neurons are more scattered (Sarter and Bruno, 2000, Wenk, 1997); however, it similarly stains intensely for cholinergic markers, is situated in roughly the same region of the brain, and has also been implicated in the modulation of higher order cognitive processes (Lehmann et al., 1980, McGaughy and Sarter, 1998, McGaughy and Sarter, 1999, Nieto-Escamez et al., 2002, Sarter and Bruno, 2000, Wenk, 1997). This group of cells has also been given the designation Ch4 by Mesulam and colleagues (Mesulam et al., 1983).
The VTA is similarly involved in several higher order cognitive processes such as reward seeking and working memory (Carr et al., 1999, Chambers et al., 2010, Greene, 2006, Grimm et al., 2004, Li et al., 2009, Pang et al., 1993, Schultz, 1998, Vucetic et al., 2010, Wang et al., 2010). Previous accounts of the VTA projection system indicate that its efferents do not collateralize extensively (Loughlin and Fallon, 1984, Sobel and Corbett, 1984). Furthermore, these cells have been shown to be topographically ordered with respect to their projection targets (Beckstead et al., 1979, Carter and Fibiger, 1977, Fallon et al., 1978, Fallon and Loughlin, 1982, Fallon and Moore, 1978a, Fallon and Moore, 1978b, Loughlin and Fallon, 1984, Sobel and Corbett, 1984) such that medial cell groups innervate more medial and rostral structures, while laterally positioned cells innervate more lateral and caudal structures (Loughlin and Fallon, 1984).
The DRN is one of several midbrain serotonergic nuclei, and the primary source of serotonin to the forebrain. It is involved in the regulation of mood, sleep and waking cycles (Mamounas and Molliver, 1988, Moore and Halaris, 1975, Moore et al., 1978, O'Hearn and Molliver, 1984). The DRN displays a rough topographical organization (Abrams et al., 2004, Vertes, 1991) such that more rostral structures are innervated by more rostral portions of DRN whereas caudal structures receive input from more caudal clusters of cells (Abrams et al., 2004). Cortical structures receive input primarily from cells located along the midline and dorsal to the medial longitudinal fasciculus, whereas subcortical structures receive projections from cells located in the lateral wings (Kirifides et al., 2001, O'Hearn and Molliver, 1984, Van Bockstaele et al., 1993, Villar et al., 1988, Waterhouse et al., 1986, Waterhouse et al., 1993). Furthermore, it has been shown that DRN cells collateralize more extensively to forebrain structures than do those projecting from VTA (Sobel and Corbett, 1984, Van Bockstaele et al., 1993) and that axons emanating from individual DRN neurons tend to send collaterals to multiple functionally related targets simultaneously (Abrams et al., 2004, Simpson et al., 1997, Van Bockstaele et al., 1993). The projections from DRN to various subregions of PFC have not been characterized (Table 1, Table 2, Table 3, Table 4).
The LC is the only source of norepinephrine-containing fibers to the PFC (Berridge and Waterhouse, 2003, Sara, 2009) and, in addition, exerts a widespread influence on neuronal circuitries involved in sensory processing, motor behavior, arousal and cognitive processes (Berridge and Waterhouse, 2003, Cain et al., 2011, Devilbiss et al., 2006, Devilbiss and Waterhouse, 2000, Devilbiss and Waterhouse, 2004, Hurley et al., 2004, McGaughy et al., 2008, McGaughy and Sarter, 1998, Moxon et al., 2007, Newman et al., 2008, Sara, 2009). Previous reports that describe LC anatomy suggest that this nucleus is highly divergent with only minimal efferent topographic organization (Fallon and Loughlin, 1982, Loughlin et al., 1982, Waterhouse et al., 1983, Waterhouse et al., 1993), although some LC cells send axon collaterals to multiple target structures along the same sensory pathway (Simpson et al., 1997, Simpson et al., 1999, Simpson et al., 2006). However, the nature of the projection from LC to the major subregions of PFC subregions has not yet been explored.
The purpose of the present study was to examine in greater detail the projections from NB, VTA, DRN and LC to OFC, mPFC and ACC with particular focus on efferent topographic relationships and patterns of axonal collateralization within these projection systems. As all of these modulatory pathways are involved in complex behavioral and cognitive processes, become dysfunctional in many forms of neuropsychiatric and neurodegenerative disease, and are targeted by many classes of CNS drugs, it is critically important to understand the efferent connectivity of the neurons comprising these pathways. A preliminary report describing the organizing principles of the LC- and NB-PFC projections has appeared previously in a theoretical review article (Chandler and Waterhouse, 2012); only new analyses of the data related to these nuclei are presented here.
Section snippets
Results
Data are reported from 9 of 10 animals where injections were confirmed to be within the anatomical boundaries of OFC, mPFC and ACC. Fig. 1A shows representative fluorescent photomicrographs of injected PFC subregions from a single animal and the extent of tracer diffusion. All subsequent representative photomicrographs were generated from the same animal. Fig. 1B shows the boundaries of the largest (lighter color) and smallest (darker color) injections in each representative section (taken from
Discussion
This study is the first of its kind to actively compare the distribution and collateralization of projections arising from the major brainstem neuromodulatory systems and terminating in subregions of the PFC. We used multiple, counterbalanced fluorescent retrograde tracer injections in single animals to identify and compare the distributions and relative size of the populations of neurons comprising these projection systems. We further characterized the degree of axonal collateralization among
Conclusions
Based on their anatomical properties, neurons in VTA, DRN and LC appear to be anatomically aligned to promote independent modulation of OFC, mPFC and ACC. This may suggest the existence of a previously unidentified segregation of prefrontal cortical function within these nuclei. Whether or not these nuclei are physiologically capable of such independent modulatory actions, and the consequence of such an organization on prefrontal network properties however, remains to be explored. Conversely,
Retrograde tracing
The Drexel University College of Medicine Institutional Animal Care and Use Committee (IACUC) approved all animal procedures and protocols. Ten young adult male Sprague-Dawley rats (Taconic), weighing between 250 and 350Β g were used in this study. Each rat was deeply anesthetized through isoflurane inhalation (4%) and placed in a stereotaxic frame. Isoflurane concentration was decreased to 2.5% after reaching a surgical plane of anesthesia. Body temperatures were monitored and controlled
Funding
This work is supported by National Institutes on Drug Abuse (DA017960) and National Institutes of Mental Health (MH087921) and an award from the Drexel University Human Cognition Enhancement Program.
Acknowledgments
We would like to acknowledge Dr. Brian Clark for his assistance in the statistical analysis of data, and Miss Ashley Smith for her technical assistance.
References (106)
- et al.
Rhythms, synchrony and electrical coupling in the Locus coeruleus
Respir. Physiol. Neurobiol.
(2004) - et al.
Efferent connections of the substantia nigra and ventral tegmental area in the rat
Brain Res.
(1979) - et al.
The locus coeruleus-noradrenergic system: modulation of behavioral state and state-dependent cognitive processes
Brain Res. Brain Res. Rev.
(2003) - et al.
Cholinergic projections from the basal forebrain to frontal, parietal, temporal, occipital, and cingulate cortices: a combined fluorescent tracer and acetylcholinesterase analysis
Brain Res. Bull.
(1982) - et al.
Rodent models of prefrontal cortical function
Trends Neurosci.
(2002) - et al.
Atomoxetine facilitates attentional set shifting in adolescent rats
Dev. Cogn. Neurosci.
(2011) - et al.
Ascending projections of presumed dopamine-containing neurons in the ventral tegmentum of the rat as demonstrated by horseradish peroxidase
Neuroscience
(1977) - et al.
Prefrontal executive and cognitive functions in rodents: neural and neurochemical substrates
Neurosci. Biobehav. Rev.
(2004) - et al.
Medial prefrontal cortex receives input from dorsal raphe nucleus neurons targeted by hypocretin1/orexinA-containing axons
Neuroscience
(2011) - et al.
Monoamine innervation of the forebrain: collateralization
Brain Res. Bull.
(1982)
Inactivation of the medial prefrontal cortex of the rat impairs strategy set-shifting, but not reversal learning, using a novel, automated procedure
Behav. Brain Res.
From the Golgi-Cajal mapping to the transmitter-based characterization of the neuronal networks leading to two modes of brain communication: wiring and volume transmission
Brain Res. Rev.
The role of the locus coeruleus in the development of Parkinson's disease
Neurosci. Biobehav. Rev.
A matter of focus: monoaminergic modulation of stimulus coding in mammalian sensory networks
Curr. Opin. Neurobiol.
Plasticity and functions of the orbital frontal cortex
Brain Cogn.
The nucleus basalis magnocellularis: the origin of a cholinergic projection to the neocortex of the rat
Neuroscience
Neuronal projections from ventral tegmental area to forebrain structures in rat studied by manganese-enhanced magnetic resonance imaging
Magn. Reson. Imaging
Substantia nigra and ventral tegmental area projections to cortex: topography and collateralization
Neuroscience
Locus coeruleus projections to cortex: topography, morphology and collateralization
Brain Res. Bull.
Evidence for dual serotonergic projections to neocortex: axons from the dorsal and median raphe nuclei are differentially vulnerable to the neurotoxin p-chloroamphetamine (PCA)
Exp. Neurol.
The role of cortical cholinergic afferent projections in cognition: impact of new selective immunotoxins
Behav. Brain Res.
Noradrenergic, but not cholinergic, deafferentation of prefrontal cortex impairs attentional set-shifting
Neuroscience
Differential response of the central noradrenergic nervous system to the loss of locus coeruleus neurons in Parkinson's disease and Alzheimer's disease
Brain Res.
GABAergic suppression prevents the appearance and subsequent fatigue of an NMDA receptor-mediated potential in neocortex
Brain Res.
Influence of norepinephrine on somatosensory neuronal responses in the rat thalamus: a combined modeling and in vivo multi-channel, multi-neuron recording study
Brain Res.
Cholinergic receptor blockade in prefrontal cortex and lesions of the nucleus basalis: implications for allocentric and egocentric spatial memory in rats
Behav. Brain Res.
Organization of raphe-cortical projections in rat: a quantitative retrograde study
Brain Res. Bull.
Locus coeruleus neurones in vitro: pH-sensitive oscillations of membrane potential in an electrically coupled network
Respir. Physiol.
Individual cells in the nucleus basalisβdiagonal band complex have restricted axonal projections to the cerebral cortex in the rat
Brain Res.
Identification of connexin36 in gap junctions between neurons in rodent locus coeruleus
Neuroscience
General mechanisms for making decisions?
Curr. Opin. Neurobiol.
On the use of retrograde tracers for identification of axon collaterals with multiple fluorescent retrograde tracers
Neuroscience
Axonal branching of ventral tegmental and raphe projections to the frontal cortex in the rat
Neurosci. Lett.
Distinct roles of rodent orbitofrontal and medial prefrontal cortex in decision making
Neuron
A comprehensive analysis of the effect of DSP4 on the locus coeruleus noradrenergic system in the rat
Neuroscience
Topography of serotonin neurons in the dorsal raphe nucleus that send axon collaterals to the rat prefrontal cortex and nucleus accumbens
Brain Res.
Expression of connexins during development and following manipulation of afferent input in the rat locus coeruleus
Neurochem. Int.
Recent techniques for tracing pathways in the central nervous system of developing and adult mammals
Brain Res. Bull.
Early life protein restriction alters dopamine circuitry
Neuroscience
Anatomic and functional topography of the dorsal raphe nucleus
Ann. N. Y. Acad. Sci.
Functional coupling between neurons and glia
J. Neurosci.
Vesicular acetylcholine transporter (VAChT) protein: a novel and unique marker for cholinergic neurons in the central and peripheral nervous systems
J. Comp. Neurol.
Adaptive gain and the role of the locus coeruleus-norepinephrine system in optimal performance
J. Comp. Neurol.
An integrative theory of locus coeruleus-norepinephrine function: adaptive gain and optimal performance
Annu. Rev. Neurosci.
Ultrastructure of the periaqueductal gray-matter of the ratβan electron-microscopic and horseradish-peroxidase study
J. Comp. Neurol.
Dissociable effects of cingulate and medial frontal cortex lesions on stimulus-reward learning using a novel Pavlovian autoshaping procedure for the rat: implications for the neurobiology of emotion
Behav. Neurosci.
Cholinergic projections from the basal forebrain to the basolateral amygdaloid complex: a combined retrograde fluorescent and immunohistochemical study
J. Comp. Neurol.
Dopamine terminals in the rat prefrontal cortex synapse on pyramidal cells that project to the nucleus accumbens
J. Neurosci.
Ventral and dorsal striatal dopamine efflux and behavior in rats with simple vs. co-morbid histories of cocaine sensitization and neonatal ventral hippocampal lesions
Psychopharmacology (Berlin)
Evidence for broad versus segregated projections from cholinergic and noradrenergic nuclei to functionally and anatomically discrete subregions of prefrontal cortex
Front. Behav. Neurosci.
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