Glutamate Decarboxylases in Nonneural Cells of Rat Testis and Oviduct: Differential Expression of GAD 65 and GAD 67

Γ-Aminobutyric acid (GABA) and its synthetic enzyme, glutamate decarboxylase (GAD), are not limited to the nervous system but are also found in nonneural tissues. The mammalian brain contains at least two forms of GAD (GAD 67 and GAD 65 ), which differ from each other in size, sequence, immunoreactivity, and their interaction with the cofactor pyridoxal 5′-phosphate (PLP). We used cDNAs and antibodies specific to GAD 65 and GAD 67 to study the molecular identity of GADs in peripheral tissues. We detected GAD and GAD mRNAs in rat oviduct and testis. In oviduct, the size of GAD, its response to PLP, its immunoreactivity, and its hybridization to specific RNA and DNA probes all indicate the specific expression of the GAD 65 gene. In contrast, rat testis expresses the GAD 67 gene. The GAD in these two reproductive tissues is not in neurons but in nonneural cells. The localization of brain GAD and GAD mRNAs in the mucosal epithelial cells of the oviduct and in spermatocytes and spermatids of the testis shows that GAD is not limited to neurons and that GABA may have functions other than neurotransmission.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66211/1/j.1471-4159.1992.tb09763.x.pd

Training locomotor networks

For a complete adult spinal rat to regain some weight-bearing stepping capability, it appears that a sequence of specific proprioceptive inputs that are similar, but not identical, from step to step must be generated over repetitive step cycles. Furthermore, these cycles must include the activation of specific neural circuits that are intrinsic to the lumbosacral spinal cord segments. For these sensorimotor pathways to be effective in generating stepping, the spinal circuitry must be modulated to an appropriate excitability level. This level of modulation is sustained from supraspinal input in intact, but not spinal, rats. In a series of experiments with complete spinal rats, we have shown that an appropriate level of excitability of the spinal circuitry can be achieved using widely different means. For example, this modulation level can be acquired pharmacologically, via epidural electrical stimulation over specific lumbosacral spinal cord segments, and/or by use-dependent mechanisms such as step or stand training. Evidence as to how each of these treatments can “tune” the spinal circuitry to a “physiological state” that enables it to respond appropriately to proprioceptive input will be presented. We have found that each of these interventions can enable the proprioceptive input to actually control extensive details that define the dynamics of stepping over a range of speeds, loads, and directions. A series of experiments will be described that illustrate sensory control of stepping and standing after a spinal cord injury and the necessity for the “physiological state” of the spinal circuitry to be modulated within a critical window of excitability for this control to be manifested. The present findings have important consequences not only for our understanding of how the motor pattern for stepping is formed, but also for the design of rehabilitation intervention to restore lumbosacral circuit function in humans following a spinal cord injury

Retraining the injured spinal cord

The present review presents a series of concepts that may be useful in developing rehabilitative strategies to enhance recovery of posture and locomotion following spinal cord injury. First, the loss of supraspinal input results in a marked change in the functional efficacy of the remaining synapses and neurons of intraspinal and peripheral afferent (dorsal root ganglion) origin. Second, following a complete transection the lumbrosacral spinal cord can recover greater levels of motor performance if it has been exposed to the afferent and intraspinal activation patterns that are associated with standing and stepping. Third, the spinal cord can more readily reacquire the ability to stand and step following spinal cord transection with repetitive exposure to standing and stepping. Fourth, robotic assistive devices can be used to guide the kinematics of the limbs and thus expose the spinal cord to the new normal activity patterns associated with a particular motor task following spinal cord injury. In addition, such robotic assistive devices can provide immediate quantification of the limb kinematics. Fifth, the behavioural and physiological effects of spinal cord transection are reflected in adaptations in most, if not all, neurotransmitter systems in the lumbosacral spinal cord. Evidence is presented that both the GABAergic and glycinergic inhibitory systems are up-regulated following complete spinal cord transection and that step training results in some aspects of these transmitter systems being down-regulated towards control levels. These concepts and observations demonstrate that (a) the spinal cord can interpret complex afferent information and generate the appropriate motor task; and (b) motor ability can be defined to a large degree by training

Effects of diet and/or exercise in enhancing spinal cord sensorimotor learning.

Given that the spinal cord is capable of learning sensorimotor tasks and that dietary interventions can influence learning involving supraspinal centers, we asked whether the presence of omega-3 fatty acid docosahexaenoic acid (DHA) and the curry spice curcumin (Cur) by themselves or in combination with voluntary exercise could affect spinal cord learning in adult spinal mice. Using an instrumental learning paradigm to assess spinal learning we observed that mice fed a diet containing DHA/Cur performed better in the spinal learning paradigm than mice fed a diet deficient in DHA/Cur. The enhanced performance was accompanied by increases in the mRNA levels of molecular markers of learning, i.e., BDNF, CREB, CaMKII, and syntaxin 3. Concurrent exposure to exercise was complementary to the dietary treatment effects on spinal learning. The diet containing DHA/Cur resulted in higher levels of DHA and lower levels of omega-6 fatty acid arachidonic acid (AA) in the spinal cord than the diet deficient in DHA/Cur. The level of spinal learning was inversely related to the ratio of AA:DHA. These results emphasize the capacity of select dietary factors and exercise to foster spinal cord learning. Given the non-invasiveness and safety of the modulation of diet and exercise, these interventions should be considered in light of their potential to enhance relearning of sensorimotor tasks during rehabilitative training paradigms after a spinal cord injury

The effect of TrkB IgG on PaWL and the levels of BDNF, CaMKII, CREB, and syntaxin 3 mRNA in the spinal cord.

<p>(A) Sequestering of BDNF protein with TrkB IgG significantly decreased spinal learning in mice that were on a DHA/Cur diet. Mean response durations were lower at 13 min and thereafter during the 30-min PaWL sessions in the group receiving TrkB IgG compared to the saline injected group. (B) Mean total response duration was lower in the group injected with TrkB IgG than in the saline injected group. BDNF (C), CaMKII (D), and CREB (E), but not syntaxin 3 (F), mRNA levels were lower in the group receiving TrkB IgG compared to the saline injected group. Values are mean ± SEM (n = 9/group). Mann-Whitney t-test. *: significant difference between Saline vs. TrkB IgG groups, at <i>P</i><0.05.</p

Spinal cord learning evaluated using the paw withdrawal learning paradigm.

<p>(A) The groups receiving DHA/Cur with and without Ex had longer mean response durations than both CtrlDiet groups, initially at the 12 min time bin and at almost all time points thereafter during the 30-min PaWL sessions. (B) Mean total response duration in the groups receiving DHA/Cur with and without Ex had longer total response durations than in both CtrlDiet groups. The DHA/Cur+Ex group had a longer mean total response duration than the DHA/Cur+Sed group, reflecting the complementary effect of exercise with the DHA/Cur diet. Values are mean ± SEM (n = 13/group). One-way ANOVA followed by Tukey's post-hoc test at <i>P</i><0.05. ^*, ^†, ^‡: Significantly different from CtrlDiet+Sed, CtrlDiet+Ex, and DHA/Cur+Sed, respectively.</p

Levels of DHA and AA fatty acids in the spinal cord.

<p>The levels of DHA were higher (A) and those of AA lower (C) in the two DHA/Cur groups compared to the two CtrlDiet groups. Consequently, the AA∶DHA ratio was lower (E) in the two groups treated with DHA/Cur compared to the two CtrlDiet groups. There was a significant positive correlation between response duration (spinal learning) and DHA levels in the spinal cord (B) and a significant negative correlation between response duration and AA levels in the spinal cord (D) and the AA∶DHA ratio (F) across groups. Values are mean ± SEM (n = 13/group). One-way ANOVA followed by Tukey's post-hoc test and Pearson product correlations between PaWL and mRNA levels. ^*, ^†, ^‡: significantly different from CtrlDiet+Sed, CtrlDiet+Ex, and DHA/Cur+Sed, respectively, at <i>P</i><0.05.</p

Effects of Diet and/or Exercise in Enhancing Spinal Cord Sensorimotor Learning

Given that the spinal cord is capable of learning sensorimotor tasks and that dietary interventions can influence learning involving supraspinal centers, we asked whether the presence of omega-3 fatty acid docosahexaenoic acid (DHA) and the curry spice curcumin (Cur) by themselves or in combination with voluntary exercise could affect spinal cord learning in adult spinal mice. Using an instrumental learning paradigm to assess spinal learning we observed that mice fed a diet containing DHA/Cur performed better in the spinal learning paradigm than mice fed a diet deficient in DHA/Cur. The enhanced performance was accompanied by increases in the mRNA levels of molecular markers of learning, i.e., BDNF, CREB, CaMKII, and syntaxin 3. Concurrent exposure to exercise was complementary to the dietary treatment effects on spinal learning. The diet containing DHA/Cur resulted in higher levels of DHA and lower levels of omega-6 fatty acid arachidonic acid (AA) in the spinal cord than the diet deficient in DHA/Cur. The level of spinal learning was inversely related to the ratio of AA∶DHA. These results emphasize the capacity of select dietary factors and exercise to foster spinal cord learning. Given the non-invasiveness and safety of the modulation of diet and exercise, these interventions should be considered in light of their potential to enhance relearning of sensorimotor tasks during rehabilitative training paradigms after a spinal cord injury