Localization and neurochemical identity of alpha1-adrenergic receptor-containing elements in the mouse locus coeruleus.

The locus coeruleus (LC) is the major source for norepinephrine (NE) in the brain and projects to areas involved in learning and memory, reward, arousal, attention, and autonomic functions related to stress. There are three types of adrenergic receptors that respond to NE: alpha1-, alpha2-, and beta-adrenergic receptors. Previous behavioral studies have shown the alpha1-adrenergic receptor (α1AR) to be present in the LC, however, with conflicting results. For example, it was shown that α1ARs in the LC are involved in some of the motivational effects of stimulation of the medial forebrain bundle, which was reduced by α1AR antagonist terazosin. Another study showed that during novelty-induced behavioral activation, the α1AR antagonist prazosin reduced c-fos expression in brain regions known to contain motoric α1ARs, except for the LC, where c-fos expression was enhanced. Despite new research delineating more specific connectivity of the neurons in the LC, and some roles of the adrenergic receptors, the α1ARs have not been localized at the subcellular level. Therefore, in order to gain a greater understanding of the aforementioned studies, we used immunohistochemistry at the electron microscopic (EM) level to determine which neuronal or glial elements in the LC express the α1AR. We hypothesized, based on previous work in the ventral periaqueductal gray area, that the α1AR would be found mainly presynaptically in axon terminals, and possibly in glial elements. Single labeling immunohistochemistry at the EM revealed that about 40% of labeled elements that contained the α1AR were glial elements, while approximately 50% of the labeled neuronal elements were axon terminals or small unmyelinated axons in the LC. Double labeling immunohistochemistry found the α1AR expressed in GFAP-labeled astrocytes, in both GABAergic and glutamatergic axon terminals, and in a portion of the α1AR dendrites, colocalized with tyrosine hydroxylase (TH, a marker for noradrenergic neurons). This study sheds light on the neuroanatomical framework underlying the effects of NE and pharmaceuticals acting directly or indirectly on α1ARs in the LC.

Olfactory dysfunction in the 3xTg-AD model of Alzheimer's disease.

Alzheimer's disease (AD) is an incurable neurodegenerative disease in which the risk of development increases with age. People with AD are plagued with deficits in their cognition, memory, and basic social skills. Many of these deficits are believed to be caused by the formation of amyloid-ß plaques and neurofibrillary tangles in regions of the brain associated with memory, such as the hippocampus. However, one of the early, preclinical symptoms of AD is the loss of olfactory detection and discrimination. To determine if a mouse model of AD expresses the same olfactory dysfunction seen in human AD, 3xTg-AD mice were given a buried food test and, unlike previous studies, compared to their background and parental strains. Results showed that over 52 weeks, the 3xTg-AD mice took significantly longer to find the buried food than the control strains. The olfactory bulbs of the 3xTg-AD mice were removed, sliced, and stained using Congo red for histological analysis. Amyloid deposits were observed predominantly in the granule layer of the olfactory bulb beginning at 13 weeks of age in 3xTg-AD mice, but not in the control strains of mice. Further examination of the buried food test data revealed that 3xTg-AD females had a significantly longer latency to detect the buried food than males beginning at 26 weeks of age. Overall, this study provides further validation of the 3xTg-AD mouse model of AD and supports the idea that simple olfactory testing could be part of the diagnostic process for human AD.

Two Scientists Share Nobel Prize for the First Time! A Case Study Developed for Exploring the History of Neuroanatomy.

In this case, students read a 'press release' that describes the awarding of the 1906 Nobel Prize in Physiology or Medicine to Camillo Golgi and Santiago Ramon y Cajal. The case was developed to highlight the historical significance of these first descriptions of the nervous system for an upper level undergraduate neuroanatomy course. The dialogue was presented in a way to pique the students' interest by focusing on the disagreement between the two scientists on the structure and arrangement of neurons in the brain and peripheral nervous system. In the middle of the case, there were two concept check questions to ensure that the students understood the conflicting theories put forth by Golgi and Ramon y Cajal. At the end of the narrative, the class was broken into groups and assigned a series of questions to engage the students in reading primary literature (e.g., the acceptance speeches of both scientists), as well as secondary review articles on both Golgi's and Ramon y Cajal's contributions to the field of neuroscience. A series of primary and secondary articles was provided to the class, although this could be optional (depending on the course/level of students). Students presented their answers to the class in the form of short presentations. The case could also be used in an introductory neuroscience class to present the foundations of neuroanatomy, controversies in scientific discovery, biases that have existed or still exist, and how scientific information was disseminated prior to the 21st century.

Noradrenergic Transmission at Alpha1-Adrenergic Receptors in the Ventral Periaqueductal Gray Modulates Arousal.

BACKGROUND: Dysregulation of arousal is symptomatic of numerous psychiatric disorders. Previous research has shown that the activity of dopamine (DA) neurons in the ventral periaqueductal gray (vPAG) tracks with arousal state, and lesions of vPAGDA cells increase sleep. However, the circuitry controlling these wake-promoting DA neurons is unknown. METHODS: This study combined designer receptors exclusively activated by designer drugs (DREADDs), behavioral pharmacology, electrophysiology, and immunoelectron microscopy in male and female mice to elucidate mechanisms in the vPAG that promote arousal. RESULTS: Activation of locus coeruleus projections to the vPAG or vPAGDA neurons induced by DREADDs promoted arousal. Similarly, agonist stimulation of vPAG alpha1-adrenergic receptors (α1ARs) increased latency to fall asleep, whereas α1AR blockade had the opposite effect. α1AR stimulation drove vPAGDA activity in a glutamate-dependent, action potential-independent manner. Compared with other dopaminergic brain regions, α1ARs were enriched on astrocytes in the vPAG, and mimicking α1AR transmission specifically in vPAG astrocytes via Gq-DREADDS was sufficient to increase arousal. In general, the wake-promoting effects observed were not accompanied by hyperactivity. CONCLUSIONS: These experiments revealed that vPAG α1ARs increase arousal, promote glutamatergic input onto vPAGDA neurons, and are abundantly expressed on astrocytes. Activation of locus coeruleus inputs, vPAG astrocytes, or vPAGDA neurons increase sleep latency but do not produce hyperactivity. Together, these results support an arousal circuit whereby noradrenergic transmission at astrocytic α1ARs activates wake-promoting vPAGDA neurons via glutamate transmission.

α1b-Adrenergic Receptor Localization and Relationship to the D1-Dopamine Receptor in the Rat Nucleus Accumbens.

The α1-adrenergic receptors (α1ARs) have been implicated in numerous actions of the brain, including attention and wakefulness. Additionally, they have been identified as contributing to disorders of the brain, such as drug addiction, and recent work has shown a role of these receptors in relapse to psychostimulants. While some functionality is known, the actual subcellular localization of the subtypes of the α1ARs remains to be elucidated. Further, their anatomical relationship to receptors for other neurotransmitters, such as dopamine (DA), remains unclear. Therefore, using immunohistochemistry and electron microscopy techniques, this study describes the subcellular localization of the α1b-adrenergic receptor (α1bAR), the subtype most tied to relapse behaviors, as well as its relationship to the D1-dopamine receptor (D1R) in both the shell and core of the rat nucleus accumbens (NAc). Overall, α1bARs were found in unmyelinated axons and axon terminals with some labeling in dendrites. In accordance with other studies of the striatum, the D1R was found mainly in dendrites and spines; therefore, colocalization of the D1R with the α1bAR was rare postsynaptically. However, in the NAc shell, when the receptors were co-expressed in the same neuronal elements there was a trend for both receptors to be found on the plasma membrane, as opposed to the intracellular compartment. This study provides valuable anatomical information about the α1bAR and its relationship to the D1R and the regulation of DA and norepinephrine (NE) neurotransmission in the brain which have been examined previously.

α-1 Adrenergic receptors are localized on presynaptic elements in the nucleus accumbens and regulate mesolimbic dopamine transmission.

Brainstem noradrenergic neurons innervate the mesocorticolimbic reward pathway both directly and indirectly, with norepinephrine facilitating dopamine (DA) neurotransmission via α1-adrenergic receptors (α1ARs). Although α1AR signaling in the prefrontal cortex (PFC) promotes mesolimbic transmission and drug-induced behaviors, the potential contribution of α1ARs in other parts of the pathway, such as the ventral tegmental area (VTA) and nucleus accumbens (NAc), has not been investigated before. We found that local blockade of α1ARs in the medial NAc shell, but not the VTA, attenuates cocaine- and morphine-induced locomotion. To determine the neuronal substrates that could mediate these effects, we analyzed the cellular, subcellular, and subsynaptic localization of α1ARs and characterized the chemical phenotypes of α1AR-containing elements within the mesocorticolimbic system using single and double immunocytochemical methods at the electron microscopic (EM) level. We found that α1ARs are found mainly extra-synaptically in axons and axon terminals in the NAc and are enriched in glutamatergic and dopaminergic elements. α1ARs are also abundant in glutamatergic terminals in the PFC, and in GABA-positive terminals in the VTA. In line with these observations, microdialysis experiments revealed that local blockade of α1ARs attenuated the increase in extracellular DA in the medial NAc shell following administration of cocaine. These data indicate that local α1ARs control DA transmission in the medial NAc shell and behavioral responses to drugs of abuse.

Functional and ultrastructural analysis of group I mGluR in striatal fast-spiking interneurons.

Striatal parvalbumin-containing fast-spiking (FS) interneurons provide a powerful feedforward GABAergic inhibition on spiny projection neurons, through a widespread arborization and electrical coupling. Modulation of FS interneuron activity might therefore strongly affect striatal output. Metabotropic glutamate receptors (mGluRs) exert a modulatory action at various levels in the striatum. We performed electrophysiological recordings from a rat striatal slice preparation to investigate the effects of group I mGluR activation on both the intrinsic and synaptic properties of FS interneurons. Bath-application of the group I mGluR agonist, (S)-3,5-dihydroxyphenylglycine (3,5-DHPG), caused a dose-dependent depolarizing response. Both (S)-(+)-alpha-amino-4-carboxy-2-methylbenzeneacetic acid (LY367385) and 7-(hydroxyimino)cyclopropa[b]chromen-1a-carboxylate ethyl ester (CPCCOEt), selective mGluR1 antagonists, significantly reduced the amplitude of the membrane depolarization caused by 3,5-DHPG application. Conversely, mGluR5 antagonists, 2-methyl-6-(phenylethylnyl)pyridine hydrochloride (MPEP) and 6-methyl-2-(phenylazo)-3-pyridinol (SIB1757), were unable to affect the response to 3,5-DHPG, suggesting that only mGluR1 contributes to the 3,5-DHPG-mediated excitatory action on FS interneurons. Furthermore, mGluR1 blockade significantly decreased the amplitude of the glutamatergic postsynaptic potentials, whereas the mGluR5 antagonist application produced a small nonsignificant inhibitory effect. Surprisingly, our electron microscopic data demonstrate that the immunoreactivity for both mGluR1a and mGluR5 is expressed extrasynaptically on the plasma membrane of parvalbumin-immunoreactive dendrites of FS interneurons. Together, these results suggest that despite a common pattern of distribution, mGluR1 and mGluR5 exert distinct functions in the modulation of FS interneuron activity.

Intra-VTA CART 55-102 reduces the locomotor effect of systemic cocaine in rats: an isobolographic analysis.

CART (cocaine- and amphetamine-regulated transcript) peptides appear to be mediators or modulators of psychostimulant drugs. An interesting result in the nucleus accumbens has been that injection of CART peptide has no effect by itself on locomotor activity, but it reduces the locomotor activity induced by cocaine or amphetamine. However, in the ventral tegmental area (VTA), injections of CART peptide have been shown to increase locomotor activity, although to a lesser degree [Kimmel, H.L., Gong, W., Vechia, S.D., Hunter, R.G., Kuhar, M.J., 2000. Intra-ventral tegmental area injection of rat cocaine and amphetamine-regulated transcript peptide 55-102 induces locomotor activity and promotes conditioned place preference. J. Pharmacol. Exp. Ther. 294, 784-792]. This study was carried out to clarify the interaction of intra-VTA CART 55-102 and systemic cocaine on locomotor activity. The CART-cocaine interaction has been examined using the rigorous isobolographic approach. This type of analysis permits an assessment of additivity, subadditivity, or synergism of two substances. By measuring locomotor activity and using a range of doses of CART peptide and cocaine, both alone and together, with different dosing strategies, clear evidence of subadditivity was found. CART reduced the locomotor activating effects of systemic cocaine, especially at higher doses of CART. These results imply that intra-VTA CART is not simply acting in the same manner as cocaine, and is likely to oppose the action of cocaine. This has implications for the physiological significance of CART-DA (dopamine) interactions and for medications development.

Comparative analysis of the subcellular and subsynaptic localization of mGluR1a and mGluR5 metabotropic glutamate receptors in the shell and core of the nucleus accumbens in rat and monkey.

Group I metabotropic glutamate receptors (mGluRs) play critical roles in synaptic plasticity and drug addiction. To characterize potential sites whereby these receptors mediate their effects in the ventral striatum, we studied the subcellular and subsynaptic localization of mGluR1a and mGluR5 in the shell and core of the nucleus accumbens in rat and monkey. In both species, group I mGluRs are mainly postsynaptic in dendrites and spines, with rare presynaptic labeling in unmyelinated axons. Minor, yet significant, differences in proportions of specific immunoreactive elements were found between the accumbens shell and the accumbens core in monkey. At the subsynaptic level, significant differences were found in the proportion of plasma membrane-bound mGluR5 labeling between species. In dendrites, spines, and unmyelinated axons, a significantly larger proportion of mGluR5 labeling was bound to the plasma membrane in rats (50-70%) than in monkeys (30-50%). Conversely, mGluR1a displayed the same pattern of immunogold labeling in the two species. Electron microscopic colocalization studies revealed 30% colocalization of mGluR1a and mGluR5 in dendrites and as much as 50-65% in spines in both compartments of the rat accumbens. Both group I mGluRs were significantly expressed in D1-immunoreactive dendritic processes (60-75% colocalization) and spines (30-50%) of striatal projection neurons as well as dendrites of cholinergic (30-70%) and parvalbumin-containing (70-85%) interneurons. These findings highlight the widespread expression of group I mGluRs in projection neurons and interneurons of the shell and core of the nucleus accumbens, providing a solid foundation for regulatory and therapeutic functions of group I mGluRs in reward-related behaviors and drug addiction.