Lesions of the nucleus basalis magnocellularis (Meynert) induce enhanced somatosensory responses and tactile hypersensitivity in rats

Tonic Electrical Stimulation of the Locus Coeruleus Enhances Cortical Sensory-Evoked Responses via Noradrenaline α1 and β Receptors

The locus coeruleus (LC) neurons send extensive projections to the somatosensory cortex and release noradrenaline (NA) at synaptic terminals, which is thought to regulate the activation of sensory-related cells by acting on three types of receptors (α1, α2 and β). Although previous studies have examined the effects of LC stimulation on single-unit sensory neurons, their impact on somatosensory evoked potentials (SEPs) and their temporal variations, as well as the specific roles of NA receptors, remain unclear. Herein, we investigated how SEPs are modulated by tonic LC stimulation at physiological frequencies (0.1, 1 and 4 Hz) and identified the receptors involved in these changes. Forepaw stimulation-induced amplitudes in SEP were enhanced in response to 1 Hz stimulation of the LC but not in response to 0.1 and 4 Hz stimulation. Interestingly, the enhancement of SEPs after LC stimulation persisted for tens of minutes following the cessation of stimulation. Optical imaging using a voltage-sensitive dye showed an increase in the depolarizing response in the somatosensory cortex after 1 Hz stimulation. Prazosin (α1 receptor antagonist) and propranolol (β receptor antagonist) inhibited SEP enhancement following 1 Hz LC stimulation, whereas yohimbine (α2 receptor antagonist) had no effect. This suggests that the enhancement in SEP observed is primarily mediated by the activation of cortical excitatory α1 and β receptors. These findings provide insight into the impact of the NA system on sensory information processing and the pathophysiology of sensory disorders related to the disruption of the NA system.

Impaired Basal Forebrain Cholinergic Neuron GDNF Signaling Contributes to Perioperative Sleep Deprivation-Induced Chronicity of Postsurgical Pain in Mice Through Regulating Cholinergic Neuronal Activity, Apoptosis, and Autophagy

AIMS

This study investigated the roles of lateral basal forebrain glial cell line-derived neurotrophic factor (GDNF) signaling and cholinergic neuron activity, apoptosis, and autophagy dysfunction in sleep deprivation-induced increased risk of chronic postsurgical pain (CPSP) in mice.

METHODS

Sleep deprivation (6 h per day from -1 to 3 days postoperatively) was administered to mice receiving skin/muscle incision and retraction (SMIR) to determine whether perioperative sleep deprivation induces mechanical and thermal pain hypersensitivity, increases the risk of chronic pain, and causes changes of basal forebrain neurons activity (c-Fos immunostaining), apoptosis (cleaved Caspase-3 expression), autophagy (LC3 and p62 expression) and GDNF expression. Adeno-associated virus (AAV)-GDNF was microinjected into the basal forebrain to see whether increased GDNF expression could reverse sleep deprivation-induced changes in pain duration and cholinergic neuron apoptosis and autophagy. Cholinergic neurons were further depleted by mu p75-SAP to examine whether the pain-prolonging effects of sleep deprivation still exist.

RESULTS

Perioperative sleep deprivation enhanced pain sensation and prolonged pain duration in SMIR mice, which was accompanied by decreased cholinergic neuron activity and GDNF expression, increased apoptosis, and autophagy dysfunction in the substantia innominata (SI), magnocellular preoptic nucleus (MCPO), and horizontal diagonal band Broca (HDB) (hereafter lateral basal forebrain). Normalizing cholinergic neuron GDNF expression by AAV-GDNF in the lateral basal forebrain inhibited apoptosis and autophagy dysfunction and mitigated sleep deprivation-induced pain maintenance. Mice with selective lesion of lateral basal forebrain cholinergic neurons were resistant to the pain-enhancing and prolonging effects of sleep deprivation and the pain-alleviating effects of AAV-GDNF therapy.

CONCLUSIONS

Perioperative sleep deprivation promotes chronicity of postsurgical pain possibly through decreasing basal forebrain GDNF signaling and causing cholinergic neuronal apoptosis and autophagy dysfunction.

Effects of focal cortical cooling on somatosensory evoked potentials in rats

Although the focal brain cooling technique is widely used to examine brain function, the effects of cortical temperature at various levels on sensory information processing and neural mechanisms remain underexplored. To elucidate the mechanisms of temperature modulation in somatosensory processing, this study aimed to examine how P1 and N1 deflections of somatosensory evoked potentials (SEPs) depend on cortical temperature and how excitatory and inhibitory inputs contribute to this temperature dependency. SEPs were generated through electrical stimulation of the contralateral forepaw in anesthetized rats. The SEPs were recorded while cortical temperatures were altered between 17-38 °C either without any antagonists, with a gamma-aminobutyric acid type A (GABAA) receptor antagonist (gabazine), with an aminomethylphosphonic acid (AMPA) receptor antagonist (NBQX), or with an N-Methyl-D-aspartic acid (NMDA) receptor antagonist ([R]-CPP). The effects of different gabazine concentrations (0, 1, and 10 µM) were examined in the 35-38 °C range. The P1/N1 amplitudes and their peak-to-peak differences plotted against cortical temperature showed an inverted U relationship with a maximum at approximately 27.5 °C when no antagonists were administered. The negative correlation between these amplitudes and temperatures of ≥ 27.5 °C plateaued after gabazine administration, which occurred progressively as the gabazine concentration increased. In contrast, the correlation remained negative after the administration of NBQX and (R)-CPP. These results suggest that GABAergic inhibitory inputs contribute to the negative correlation between SEP amplitude and cortical temperature around the physiological cortical temperature.

The role of the nucleus basalis of Meynert in neuromodulation therapy: a systematic review from the perspective of neural network oscillations

As a crucial component of the cerebral cholinergic system and the Papez circuit in the basal forebrain, dysfunction of the nucleus basalis of Meynert (NBM) is associated with various neurodegenerative disorders. However, no drugs, including existing cholinesterase inhibitors, have been shown to reverse this dysfunction. Due to advancements in neuromodulation technology, researchers are exploring the use of deep brain stimulation (DBS) therapy targeting the NBM (NBM-DBS) to treat mental and neurological disorders as well as the related mechanisms. Herein, we provided an update on the research progress on cognition-related neural network oscillations and complex anatomical and projective relationships between the NBM and other cognitive structures and circuits. Furthermore, we reviewed previous animal studies of NBM lesions, NBM-DBS models, and clinical case studies to summarize the important functions of the NBM in neuromodulation. In addition to elucidating the mechanism of the NBM neural network, future research should focus on to other types of neurons in the NBM, despite the fact that cholinergic neurons are still the key target for cell type-specific activation by DBS.