Neurons under genetic control: What are the next steps towards the treatment of movement disorders?

Optogenetic approaches for neural tissue regeneration: A review of basic optogenetic principles and target cells for therapy

Optogenetics has revolutionized the field of neuroscience by enabling precise control of neural activity through light-sensitive proteins known as opsins. This review article discusses the fundamental principles of optogenetics, including the activation of both excitatory and inhibitory opsins, as well as the development of optogenetic models that utilize recombinant viral vectors. A considerable portion of the article addresses the limitations of optogenetic tools and explores strategies to overcome these challenges. These strategies include the use of adeno-associated viruses, cell-specific promoters, modified opsins, and methodologies such as bioluminescent optogenetics. The application of viral recombinant vectors, particularly adeno-associated viruses, is emerging as a promising avenue for clinical use in delivering opsins to target cells. This trend indicates the potential for creating tools that offer greater flexibility and accuracy in opsin delivery. The adaptations of these viral vectors provide advantages in optogenetic studies by allowing for the restricted expression of opsins through cell-specific promoters and various viral serotypes. The article also examines different cellular targets for optogenetics, including neurons, astrocytes, microglia, and Schwann cells. Utilizing specific promoters for opsin expression in these cells is essential for achieving precise and efficient stimulation. Research has demonstrated that optogenetic stimulation of both neurons and glial cells-particularly the distinct phenotypes of microglia, astrocytes, and Schwann cells-can have therapeutic effects in neurological diseases. Glial cells are increasingly recognized as important targets for the treatment of these disorders. Furthermore, the article emphasizes the emerging field of bioluminescent optogenetics, which combines optogenetic principles with bioluminescent proteins to visualize and manipulate neural activity in real time. By integrating molecular genetics techniques with bioluminescence, researchers have developed methods to monitor neuronal activity efficiently and less invasively, enhancing our understanding of central nervous system function and the mechanisms of plasticity in neurological disorders beyond traditional neurobiological methods. Evidence has shown that optogenetic modulation can enhance motor axon regeneration, achieve complete sensory reinnervation, and accelerate the recovery of neuromuscular function. This approach also induces complex patterns of coordinated motor neuron activity and promotes neural reorganization. Optogenetic approaches hold immense potential for therapeutic interventions in the central nervous system. They enable precise control of neural circuits and may offer new treatments for neurological disorders, particularly spinal cord injuries, peripheral nerve injuries, and other neurodegenerative diseases.

Patterned Stimulation of the Chrimson Opsin in Glutamatergic Motor Thalamus Neurons Improves Forelimb Akinesia in Parkinsonian Rats

Parkinson's disease (PD) is a motor disorder charactertised by altered neural activity throughout the basal ganglia-thalamocortical circuit. Electrical deep brain stimulation (DBS) is efficacious in alleviating motor symptoms, but has several notable side-effects, most likely reflecting the non-specific nature of electrical stimulation and/or the brain regions targeted. We determined whether specific optogenetic activation of glutamatergic motor thalamus (Mthal) neurons alleviated forelimb akinesia in a chronic rat model of PD. Parkinsonian rats (unilateral 6-hydroxydopamine injection) were injected with an adeno-associated viral vector (AAV5-CaMKII-Chrimson-GFP) to transduce glutamatergic Mthal neurons with the red-shifted Chrimson opsin. Optogenetic stimulation with orange light at 15 Hz tonic and a physiological pattern, previously recorded from a Mthal neuron in a control rat, significantly increased forelimb use in the reaching test (p < 0.01). Orange light theta burst stimulation, 15 Hz and control reaching patterns significantly reduced akinesia (p < 0.0001) assessed by the step test. In contrast, forelimb use in the cylinder test was unaffected by orange light stimulation with any pattern. Blue light (control) stimulation failed to alter behaviours. Activation of Chrimson using complex patterns in the Mthal may be an alternative treatment to recover movement in PD. These vector and opsin changes are important steps towards translating optogenetic stimulation to humans.

Basal Forebrain Impairment: Understanding the Mnemonic Function of the Septal Region Translates in Therapeutic Advances

The basal forebrain is one of the three major brain circuits involved in episodic memory formation together with the hippocampus and the diencephalon. The dysfunction of each of these regions is known to cause anterograde amnesia. While the hippocampal pyramidal neurons are known to encode episodic information and the diencephalic structures are known to provide idiothetic information, the contribution of the basal forebrain to memory formation has been exclusively associated with septo-hippocampal cholinergic signaling. Research data from the last decade broadened our understanding about the role of septal region in memory formation. Animal studies revealed that septal neurons process locomotor, rewarding and attentional stimuli. The integration of these signals results in a systems model for the mnemonic function of the medial septum that could guide new therapeutic strategies for basal forebrain impairment (BFI). BFI includes the disorders characterized with basal forebrain amnesia and neurodegenerative disorders that affect the basal forebrain. Here, we demonstrate how the updated model of septal mnemonic function can lead to innovative translational treatment approaches that include pharmacological, instrumental and behavioral techniques.