The spino-bulbar-cerebellar pathway: organization and neurochemical properties of spinal cells that project to the lateral reticular nucleus in the rat

Abstract

In addition to classical spinocerebellar pathways, the cerebellum receives information from the spinal cord indirectly via spino-bulbar-cerebellar systems. One of the structures in this pathway is the lateral reticular nucleus (LRt). We performed series of experiments to investigate the organization and neurotransmitter content of spinoreticular tract (SRT) neurons in the lumbar spinal cord that project to the LRt. Three rats received injections of the b subunit of Cholera toxin (CTb) or Fluorogold (FG) within the left and right LRt. The majority of SRT cells (56–61%) were found within the contralateral medial intermediate gray matter where small numbers (7–10%) of double-labeled cells were also present on both sides of the cord. Six rats received unilateral spinal injections of CTb to label spinal projections to the LRt. Injections of FG were made also into the anterior lobe of the cerebellum to label LRt pre-cerebellar neurons. Terminals were found mainly ipsilateral to spinal injection sites within the central and ventrolateral regions of the LRt. Immunocytochemical analysis of SRT terminals revealed that the majority (75%) were contained vesicular glutamate transporter 2 but a minority (20%) contained the vesicular GABA transporter. The inhibitory subpopulation was found to be GABAergic, glycinergic, or contained both transmitters. Inhibitory and excitatory terminals were present within overlapping regions of the nucleus. Most CTb terminals contacting LRt pre-cerebellar neurons were excitatory (80%) whereas a minority were inhibitory and most cells (88%) received contacts from both inhibitory and excitatory terminals. This study shows that SRT axons in the LRt have the capacity to exert direct excitatory and inhibitory actions on LRt pre-cerebellar neurons. Thus spinal cord input has the capacity to facilitate or depress the activity of individual LRt cells which in turn adjust activity in the cerebellum to produce coordinated motor behaviors.

Corneal Sensitivity to Hyperosmolar Eye Drops: A Novel Behavioral Assay to Assess Diabetic Peripheral Neuropathy

“…29,30 Pertinent to our study are expression and sensitivity of TRPM8 because Quallo et al 7 demonstrated that TRPM8 is a neuronal osmo-sensor that regulates blinking in mice. Alamri et al 31 demonstrated that approximately 45% of corneal afferent neurons expressed TRPV1, 28% expressed Piezo2 (a marker of putative pure mechano-nociceptors), and 8% expressed TRPM8, with 6% of TRPV1 neurons coexpressing TRPM8 (a marker for of cold-sensing neurons); TRPM8 cold-sensing neurons are activated by menthol and hyperosmotic stimuli. 7,32 Our studies confirm that sensory nerves in the subepithelial layer and nerves penetrating the epithelial layer of the cornea express TRPM8.…”

Altered anterior‐posterior connectivity through the arcuate fasciculus in temporal lobe epilepsy

“…The AF extending to the midtemporal cortex may be relevant to the evolution of language in the human brain because this pathway is absent in nonhuman primates [Rilling et al, 2008]. In addition, this pathway is more dominant in the left hemisphere than the right hemisphere in the healthy human brain [Catani et al, 2007; Takaya et al, 2015]. Our results indicate that the AF extending to the midtemporal cortex, which may play a substantial role during language-related processing in the healthy human brain, is likely to be affected in patients with left TLE.…”

“…In contrast, the left inferior prefrontal cortex, including Broca’s area, may serve as a central executive for retrieving and evaluating semantic information and making decisions, presumably via top-down signals to the temporal cortex [Badre et al, 2005; Binder et al, 1997; Bookheimer, 2002; Demb et al, 1995; Thompson-Schill et al, 1997; Wagner et al, 2001; Whitney et al, 2011]. In particular, the semantic classification task requires functional interaction between Broca’s area and the left midtemporal cortex, supposedly through the AF [Demb et al, 1995; Glasser and Rilling, 2008; Takaya et al, 2015; Wang et al, 2014; Whitney et al, 2011]. In the current study, structural and task-modulated functional connectivity with Broca’s area decreased in the left midtemporal cortices.…”

“…We first examined the change in structural connectivity with Broca’s area/the right Broca’s homologue through the AF in the inferior parietal and lateral temporal cortices in patients with left TLE, using a surface-based structural connectivity analysis that we have developed [Takaya et al, 2015]. This method allows visualizing the cortical regions that show changes in structural connectivity of a specific fiber pathway.…”

“…To evaluate cortical function during cognitive processing, we used a single-word semantic classification task that is known to activate both Broca’s area and the lateral temporal cortex in the left hemisphere. This task is used to identify the language-dominant hemisphere prior to temporal lobectomy and is thought to require functional interaction between the frontal and temporal language-related cortices, purportedly through the AF [Demb et al, 1995; Desmond et al, 1995; Glasser and Rilling, 2008; Takaya et al, 2015; Wang et al, 2014; Whitney et al, 2011]. …”