The effects of strychnine, bicuculline, and ketamine on 'immersion-inhibited' dorsal horn convergent neurons in intact and spinalized rats

Neuroprotective effect of geraniol on neurological disorders: a review article

BACKGROUND

Neurological disorders are structural, biochemical, and electrical abnormalities that affect the peripheral and central nervous systems. Paralysis, muscle weakness, tremors, spasms, and partial or complete loss of sensation are some symptoms of these disorders. Neurorehabilitation is the main treatment for neurological disorders. Treatments can improve the quality of life of patients. Neuroprotective substances of natural origin are used for the treatments of these disorders.

METHODS AND RESULTS

Online databases, such as Google Scholar, PubMed, ScienceDirect, and Scopus were searched to evaluate articles from 1981-2021 using the Mesh words of geraniol (GER), neurological disorders, epilepsy, spinal cord injury (SCI), Parkinson's diseases (PD), and depression. A total of 87 studies were included in this review. GER with antioxidant, anti-inflammatory, and neuroprotective effects can improve the symptoms and reduce the progression of neurological diseases. GER exhibits neuroprotective effects by binding to GABA and glycine receptors as well as by inhibiting the activation of nuclear factor kappa B (NF-κB) pathway and regulating the expression of nucleotide-binding oligomerization of NLRP3 inflammasome. In this study, the effect of GER was investigated on neurological disorders, such as epilepsy, SCI, PD, and depression.

CONCLUSION

Although the medicinal uses of GER have been reported, more clinical and experimental studies are needed to investigate the effect of using traditional medicine on improving lifethreatening diseases and the quality of life of patients.

Anticonvulsant activity of methanolic extract of Withania cogulans in mice

Mental and neurological diseases including depression, Parkinson's disease, dementia, epilepsy, anxiety disorders and bipolar disorders account for a considerable amount of the world's disease burden. Unfortunately, drugs used in the treatment of neurological diseases are expensive, symptomatic and they produce undesirable side effects. People from different cultures prefer to use medicinal plants for the treatment of various ailments ranging from plain to perplex disorders because they are most affordable, cost effective and easily accessible source of treatment in the primary healthcare system throughout the world. Withania coagulans, an erect grayish under-shrub belongs to family Solanaceae. It is common in Pakistan, East India, Iran and Afghanistan. The objective of this study was to analyze the anti-seizure activity of crude methanolic extract of Withania coagulans fruits (MeWc). For screening of this activity, maximal electroshock seizures model (MES) and chemically-induced seizures models were used. In maximal electroshock seizures test MeWc showed significant dose dependent percent protection against hind-limb tonic extension; significant and dose-dependent increase in latency to myoclonic jerks and tonic clonic convulsions and decrease in seizures duration were observed in PTZ-induced seizures. In strychnine-induced convulsions MeWc significantly increased latency to hind-limb tonic extension and percent protection from death in a dose-dependent manner. Thus, it was inferred from the experiments that extract of Withania coagulans showed anticonvulsant activity.

Distinct temporal filtering mechanisms are engaged during dynamic increases and decreases of noxious stimulus intensity

Offset analgesia could be activated with a feedback-controlled near-infrared laser system. Larger and delayed response to temperature decrease than to temperature increase was observed.

Physical stimuli are subject to pronounced temporal filtering during afferent processing such that changes occurring at certain rates are amplified and others are diminished. Temporal filtering of nociceptive information remains poorly understood. However, the phenomenon of offset analgesia, where a disproportional drop in perceived pain intensity is caused by a slight drop in noxious heat stimulation, indicates potent temporal filtering in the pain pathways. To develop a better understanding of how dynamic changes in a physical stimulus are constructed into an experience of pain, a transfer function between the skin temperature and the perceived pain intensity was modeled. Ten seconds of temperature-controlled near-infrared (970 nm) laser stimulations above the pain threshold with a 1°C increment, decrement, or constant temperature were applied to the dorsum of the hand of healthy human volunteers. The skin temperature was assessed by an infrared camera. Offset analgesia was evoked by laser heat stimulation. The estimated transfer functions showed shorter latencies when the temperature was increased by 1°C (0.53 seconds [0.52-0.54 seconds]) than when decreased by 1°C (1.15 seconds [1.12-1.18 seconds]) and smaller gains (increase: 0.89 [0.82-0.97]; decrease: 2.61 [1.91-3.31]). The maximal gain was observed at rates around 0.06 Hz. These results show that temperature changes occurring around 0.06 Hz are best perceived and that a temperature decrease is associated with a larger but slower change in pain perception than a comparable temperature increase. These psychophysical findings confirm the existence of differential mechanisms involved in temporal filtering of dynamic increases and decreases in noxious stimulus intensity.

Opioid-independent mechanisms supporting offset analgesia and temporal sharpening of nociceptive information

The mechanisms supporting temporal processing of pain remain poorly understood. To determine the involvement of opioid mechanisms in temporal processing of pain, responses to dynamic noxious thermal stimuli and offset analgesia were assessed after administration of naloxone, a μ-opioid antagonist, and on a separate day, during and after intravenous administration of remifentanil, a μ-opioid agonist, in 19 healthy human volunteers. Multiple end points were sampled from real-time computerized visual analog scale ratings (VAS, 1 to 10) to assess thermal sensitivity, magnitude and duration of offset analgesia, and painful after sensations. It was hypothesized that the magnitude of offset analgesia would be reduced by direct opioid antagonism and during states of acute opioid-induced hypersensitivity (OIH), as well as diminished by the presence of exogenous opioids. Surprisingly, the magnitude of offset analgesia was not altered after naloxone administration, during remifentanil infusion, or after the termination of remifentanil infusion. Because thermal hyperalgesia was observed after both drugs, 8 of the original 19 subjects returned for an additional session without drug administration. Thermal hyperalgesia and increased magnitude of offset analgesia were observed across conditions of remifentanil, naloxone, and no drug within this subset analysis, indicating that repeated heat testing induced thermal hyperalgesia, which potentiated the magnitude of offset analgesia. Thus, it is concluded that the mechanisms subserving temporal processing of nociceptive information are largely opioid-independent, but that offset analgesia may be potentiated by heat-induced thermal hyperalgesia in a proportion of individuals.

Comparative anticonvulsant activities of the essential oils (EOs) from Cymbopogon winterianus Jowitt and Cymbopogon citratus (DC) Stapf. in mice

The fresh leaves of Cymbopogon citratus are a good source of an essential oil (EO) rich in citral, and its tea is largely used in the Brazilian folk medicine as a sedative. A similar source of EO is Cymbopogon winterianus, rich in citronellal. The literature presents more studies on the EO of C. citratus and their isolated bioactive components, but only a few are found on the EO of C. winterianus. The objective of the present study was then to study, in a comparative way, the effects of both EOs on three models of convulsions (pentylenetetrazol, pilocarpine, and strychnine) and on the barbiturate-induced sleeping time on male Swiss mice. The animals (20-30 g) were acutely treated with 50, 100, and 200 mg kg(-1), intraperitoneally, of each EO, and 30 min later, the test was initiated. The observed parameters were: latency to the first convulsion and latency to death in seconds. Furthermore, the in vitro effects of the EOs were also studied on myeloperoxidase (MPO; a biomarker for inflammation) and lactate dehydrogenase (LDH; an index of cytotoxicity) releases from human neutrophils. The EOs radical-scavenging activities were also evaluated by the 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay. The results showed that both EOs were more active on the pentylenetetrazol-induced convulsion model, and C. citratus was even more efficient in increasing latency to the first convulsion and latency to death. Both parameters were potentiated in the presence of a lower dose of diazepam (reference drug) when associated to a lower dose of each EO (25 mg kg(-1)). Besides, their anticonvulsant effects were blocked by flumazenil, a known benzodiazepine antagonist. This effect was somewhat lower on the pilocarpine-induced convulsion, and better effects were seen only with the EOs' higher doses (200 mg kg(-1)). A similar result was observed on the strychnine-induced convulsion model. Both EOs potentiated the barbiturate-induced sleeping time. However, C. citratus was more efficient. Interestingly, both EOs completely blocked the MPO release from human neutrophils and showed no cytotoxic effect on the LDH release from human neutrophils. On the other hand, only a very low or no effect on the DPPH assay was observed with C. winterianus and C. citratus, respectively, indicating that the radical scavenging activity did not play a role on the EOs' effects. We conclude that the mechanism of action of the anticonvulsant effect of the EOs studied is, at least in part, dependent upon the GABAergic neurotransmission. In addition, their effects on inflammatory biomarkers can also contribute to their central nervous system activity.

Phythochemical screening and anticonvulsant activity of Cymbopogon winterianus Jowitt (Poaceae) leaf essential oil in rodents

Cymbopogon winterianus (Poaceae) is used for its analgesic, anxiolytic and anticonvulsant properties in Brazilian folk medicine. This report aimed to perform phythochemical screening and to investigate the possible anticonvulsant effects of the essential oil (EO) from fresh leaves of C. winterianus in different models of epilepsy. The phytochemical analysis of EO showed presence of geraniol (40.06%), citronellal (27.44%) and citronellol (10.45%) as the main compounds. A behavioral screening demonstrated that EO (100, 200 and 400mg/kg; ip) caused depressant activity on CNS. When administered concurrently, EO (200 and 400mg/kg, ip) significantly reduced the number of animals that exhibited PTZ- and PIC-induced seizures in 50% of the experimental animals (p<0.05). Additionally, EO (100, 200 and 400mg/kg, ip) significantly increased (p<0.05) the latencies of clonic seizures induced by STR. Our results demonstrated a possible activity anticonvulsant of the EO.

Spinal ventral root after-discharges as a pain index: Involvement of NK-1 and NMDA receptors

Nociceptive signals are transmitted to the spinal dorsal horn via primary afferent fibers, and the signals induce withdrawal reflexes by activating spinal motoneurons in the ventral horn. Therefore, nociceptive stimuli increase motoneuronal firing and ventral root discharges. This study was aimed to develop a method for the study of pain mechanisms and analgesics by recording ventral root discharges. Spinalized rats were laminectomized in the lumbo-sacral region. The fifth lumbar ventral root was sectioned and placed on a pair of wire electrodes. Multi unit efferent discharges from the ventral root were increased by mechanical stimulation using a von Frey hair applied to the plantar surface of the hindpaw. The low-intensity mechanical stimuli increased the discharges during stimulation (during-discharges) without increasing the discharges after cessation of stimulation (after-discharges), and the high-intensity mechanical stimuli increased both during- and after-discharges. Pretreatment with resiniferatoxin, an ultrapotent analogue of capsaicin, halved during-discharges and eliminated after-discharges, suggesting that after-discharges are generated by heat- and mechanosensitive polymodal nociceptors. Ezlopitant, a neurokinin-1 (NK-1) receptor antagonist, but not its inactive enantiomer, selectively reduced the after-discharges. Ketamine, an N-methyl-D-aspartate (NMDA) receptor antagonist, preferentially reduced the after-discharges, demonstrating that NK-1 and NMDA receptors mediate the after-discharges. Morphine reduced the after-discharges without affecting during-discharges. By contrast, mephenesin, a centrally acting muscle relaxant, reduced both during- and after-discharges. There results suggest that simultaneous recordings of during- and after-discharges are useful to study pain mechanisms and analgesics as well as to discriminate the analgesic effects from the side effects such as muscle relaxant effects.

Switching-on and -off of bistable spontaneous discharges in rat spinal deep dorsal horn neurons

Somatosensory deep dorsal horn spinal neurons were previously shown to present in vitro a bistable state of activity in which a fixed firing rate is maintained over prolonged periods in the absence of stimulation. Those periods of enhanced spinal spontaneous discharge may play a role in the genesis or maintenance of hyperalgesic states, where episodes of durable spontaneous pain are commonly reported. Here we show in vivo that a small percentage of deep spinal neurons (4% of the recorded population) are capable of rapidly shifting between low-frequency and high-frequency levels of spontaneous activity. At least one of the transitions between the two states was induced by stimulation of the receptive field, making this an interesting and unique case in which stable firing rates are switched-on or -off by somatosensory stimuli.

Electrophysiological studies on the role of the NMDA receptor in nociception in the developing rat spinal cord

The present study investigated the effects of spinally applied N-methyl-D-aspartate (NMDA) antagonists 2-amino-5-phosphonovaleric acid (AP5) and ketamine on convergent neurones in the deep dorsal horn of rats, in vivo at different postnatal ages (P) 14, 21, 28, and 56 days. AP5 inhibited the primary afferent fibre input, the C fibre, post-discharge and windup evoked responses in a dose-dependent manner at each age, and was significantly more effective in the pups than adult rats (P<0.03 at 100-microg dose). AP5 100 microg abolished windup almost completely in the pups, whilst the adults required 10-fold higher doses. In contrast there was no difference in ketamine potency between age groups. Windup in the ketamine groups was reduced in a dose-dependent manner equally across all the age groups. The differential inhibitory effects of AP5 and ketamine may be due to postnatal changes in density, localisation and receptor subunit composition, altering receptor affinity and kinetics.