Blockade of voltage-sensitive Na(+) channels by the 5-HT(1A) receptor agonist 8-OH-DPAT: possible significance for neuroprotection

Environmental enrichment, alone or in combination with various pharmacotherapies, confers marked benefits after traumatic brain injury

Traumatic brain injury (TBI) is a significant health care issue that affects over ten million people worldwide. Treatment options are limited with numerous failures resulting from single therapies. Fortunately, several preclinical studies have shown that combination treatment strategies may afford greater improvement and perhaps can lead to successful clinical translation, particularly if one of the therapies is neurorehabilitation. The aim of this review is to highlight TBI studies that combined environmental enrichment (EE), a preclinical model of neurorehabilitation, with pharmacotherapies. A series of PubMed search strategies yielded only nine papers that fit the criteria. The consensus is that EE provides robust neurobehavioral, cognitive, and histological improvement after experimental TBI and that the combination of EE with some pharmacotherapies can lead to benefits beyond those revealed by single therapies. However, it is noted that EE can be challenged by drugs such as the acetylcholinesterase inhibitor, donepezil, and the antipsychotic drug, haloperidol, which attenuate its efficacy. These findings may help shape clinical neurorehabilitation strategies to more effectively improve patient outcome. Potential mechanisms for the EE and pharmacotherapy-induced effects are also discussed. This article is part of the Special Issue entitled "Neurobiology of Environmental Enrichment".

5-hydroxytryptamine1A (5-HT1A) receptor agonists: A decade of empirical evidence supports their use as an efficacious therapeutic strategy for brain trauma

Traumatic brain injury (TBI) is a significant and enduring health care issue with limited treatment options. While several pre-clinical therapeutic approaches have led to enhanced motor and/or cognitive performance, the benefits of these treatments have not translated to the clinic. One plausible explanation is that the therapies may not have been rigorously evaluated, thus rendering the bench-to-bedside leap premature and subsequently unsuccessful. An approach that has undergone considerable empirical research after TBI is pharmacological targeting of 5-HT1A receptors with agonists such as repinotan HCl, 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT), and buspirone. The goal of this review is to integrate and interpret the findings from a series of studies that evaluated the efficacy of 5-HT1A receptor agonists on functional, histological, and molecular outcome after acquired brain injury. The overwhelming consensus of this exhaustive review is that a decade of empirical evidence supports their use as an efficacious therapeutic strategy for brain trauma. This article is part of a Special Issue entitled SI:Brain injury and recovery.

Agonist of 5-HT1A/7 receptors but not that of 5-HT2 receptors disinhibits tracheobronchial-projecting airway vagal preganglionic neurons of rats

The vagus nerves supply the major cholinergic tone to airway smooth muscles physiologically and play critical roles in the genesis of airway hyperreactivity under some pathological conditions. Postganglionic airway cholinergic tone relies largely on the ongoing activity of medullary airway vagal preganglionic neurons (AVPNs), of which the tracheobronchial-projecting ones are primarily located in the external formation of the nucleus ambiguus (eNA). AVPNs are regulated by 5-HT, and 5-HT(1A/7) and 5-HT(2) receptors have been indicated to be involved. But the mechanisms at synaptic level are unknown. In the present study, tracheobronchial-projecting AVPNs (T-AVPNs) were retrogradely labeled from the trachea wall; fluorescently labeled T-AVPNs in the eNA were recorded with whole-cell voltage patch clamp; and the effects of 5-HT(1A/7) receptor agonist (±)-8-Hydroxy-2-(dipropylamino) tetralin hydrobromide (8-OH-DPAT) (1 μmol L(-1)) and 5-HT(2) receptor agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) (10 μmol L(-1)) on the synaptic inputs were examined. 8-OH-DPAT significantly inhibited the GABAergic and glycinergic spontaneous inhibitory postsynaptic currents (sIPSCs) of T-AVPNs in both the frequency and amplitude but had no effect on the GABAergic and glycinergic miniature inhibitory postsynaptic currents (mIPSCs). The 8-OH-DPAT inhibition of the GABAergic and glycinergic sIPSCs was prevented by 5-HT(1A/7) receptor antagonist N-[2-[4-(2-Methoxyphenyl)-1-piperazinyl] ethyl]-N-2-pyridinylcyclohexanecarboxamide maleate salt (WAY-100635) (1 μmol L(-1)). 8-OH-DPAT had no effect on the glutamatergic spontaneous excitatory postsynaptic currents (sEPSCs) and caused no alterations in the baseline current and input resistance of T-AVPNs. DOI had no effect on any types of the synaptic inputs of T-AVPNs. These results suggest that 5-HT(1A/7) receptor agonist causes "disinhibition" of T-AVPNs, which might, in part, account for the reflex increase of airway resistance.

5-HT1A/7 receptor agonist excites cardiac vagal neurons via inhibition of both GABAergic and glycinergic inputs

AIM

To study the synaptic mechanisms involved in the 5-hydroxytryptamine1A/7 (5-HT1A/7) receptor-mediated reflex control of cardiac vagal preganglionic neurons (CVPN).

METHODS

CVPN were retrogradely labeled and identified in brain stem slices of newborn rats, and their synaptic activity was examined using whole-cell patch-clamp.

RESULTS

8-Hydroxy-2-(di-N-propylamino) tetralin (8-OH-DPAT), an agonist of 5-HT1A/7 receptors, had no effect on the glutamatergic inputs of CVPN. In contrast, it significantly decreased the frequency and the amplitude of both the GABAergic and the glycinergic spontaneous inhibitory postsynaptic currents (sIPSC). 8-OH-DPAT also caused significant amplitude decrease of the GABAergic currents evoked by stimulation of the nucleus tractus solitarius. Both the frequency inhibition and the amplitude inhibition of the GABAergic and the glycinergic sIPSC by 8-OH-DPAT had dose-dependent tendencies and could be reversed by WAY-100635, an antagonist of 5-HT1A/7 receptors. In the pre-existence of tetrodotoxin, 8-OH-DPAT had no effect on the GABAergic or the glycinergic miniature inhibitory postsynaptic currents, and had no effect on the GABAergic or the glycinergic currents evoked by exogenous GABA or glycine.

CONCLUSION

The 5-HT1A/7 receptor agonist excites CVPN indirectly via the inhibition of both the GABAergic and glycinergic inputs. These findings have at least in part revealed the synaptic mechanisms involved in the 5-HT1A/7 receptor-mediated reflex control of cardiac vagal nerves in intact animals.

The neurobehavioral benefit conferred by a single systemic administration of 8-OH-DPAT after brain trauma is confined to a narrow therapeutic window

The 5-HT(1A) receptor agonist 8-OH-DPAT (0.5mg/kg) enhances behavioral recovery when administered 15min after experimental traumatic brain injury (TBI). To determine if benefits are still attainable at clinically relevant times, treatment was delayed 1 and 2h post-TBI and motor/cognitive performance was compared to early (i.e., 15min) administration. No differences were observed among the vehicle and 8-OH-DPAT groups treated at 1 and 2h, but all three were significantly impaired versus early 8-OH-DPAT. The data suggest that an early and narrow critical period exists for the behavioral recovery afforded by a single 8-OH-DPAT treatment paradigm. The critical window corresponds to the well documented TBI-induced glutamate increase, suggesting that 8-OH-DPAT may be conferring neuroprotection by attenuating this acute deleterious surge.

Acute treatment with the 5-HT(1A) receptor agonist 8-OH-DPAT and chronic environmental enrichment confer neurobehavioral benefit after experimental brain trauma

Acute treatment with the 5-HT(1A) receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) or chronic environmental enrichment (EE) hasten behavioral recovery after experimental traumatic brain injury (TBI). The aim of this study was to determine if combining these interventions would confer additional benefit. Anesthetized adult male rats received either a cortical impact or sham injury followed 15min later by a single intraperitoneal injection of 8-OH-DPAT (0.5mg/kg) or saline vehicle (1.0mL/kg) and then randomly assigned to either enriched or standard (STD) housing. Behavioral assessments were conducted utilizing established motor and cognitive tests on post-injury days 1-5 and 14-18, respectively. Hippocampal CA(1)/CA(3) neurons were quantified at 3 weeks. Both 8-OH-DPAT and EE attenuated CA(3) cell loss. 8-OH-DPAT enhanced spatial learning in a Morris water maze (MWM) as revealed by differences between the TBI+8-OH-DPAT+STD and TBI+VEHICLE+STD groups (P=0.0014). EE improved motor function as demonstrated by reduced time to traverse an elevated narrow beam in both the TBI+8-OH-DPAT+EE and TBI+VEHICLE+EE groups versus the TBI+VEHICLE+STD group (P=0.0007 and 0.0016, respectively). EE also facilitated MWM learning as evidenced by both the TBI+8-OH-DPAT+EE and TBI+VEHICLE+EE groups locating the escape platform quicker than the TBI+VEHICLE+STD group (P's<0.0001). MWM differences were also observed between the TBI+8-OH-DPAT+EE and TBI+8-OH-DPAT+STD groups (P=0.0004) suggesting that EE enhanced the effect of 8-OH-DPAT. However, there was no difference between the TBI+8-OH-DPAT+EE and TBI+VEHICLE+EE groups. These data replicate previous results from our laboratory showing that both a single systemic administration of 8-OH-DPAT and EE improve recovery after TBI and extend those findings by elucidating that the combination of treatments in this particular paradigm did not confer additional benefit. One explanation for the lack of an additive effect is that EE is a very effective treatment and thus there is very little room for 8-OH-DPAT to confer additional statistically significant improvement.

Endogenous monoamine receptor activation is essential for enabling persistent sodium currents and repetitive firing in rat spinal motoneurons

The spinal cord and spinal motoneurons are densely innervated by terminals of serotonin (5-HT) and norepinephrine (NE) neurons arising mostly from the brain stem, but also from intrinsic spinal neurons. Even after long-term spinal transection (chronic spinal), significant amounts (10%) of 5-HT and NE (monoamines) remain caudal to the injury. To determine the role of such endogenous monoamines, we blocked their action with monoamine receptor antagonists and measured changes in the sodium currents and firing in motoneurons. We focused on persistent sodium currents (Na PIC) and sodium spike properties because they are critical for enabling repetitive firing in motoneurons and are facilitated by monoamines. Intracellular recordings were made from motoneurons in the sacrocaudal spinal cord of normal and chronic spinal rats (2 mo postsacral transection) with the whole sacrocaudal cord acutely removed and maintained in vitro (cords from normal rats termed acute spinal). Acute and chronic spinal rats had TTX-sensitive Na PICs that were respectively 0.62 +/- 0.76 and 1.60 +/- 1.04 nA, with mean onset voltages of -63.0 +/- 5.6 and -64.1 +/- 5.4 mV, measured with slow voltage ramps. Application of 5-HT2A, 5-HT2C, and alpha1-NE receptor antagonists (ketanserin, RS 102221, and WB 4101, respectively) significantly reduced the Na PICs, and a combined application of these three monoamine antagonists completely eliminated the Na PIC, in both acute and chronic spinal rats. Likewise, reduction of presynaptic transmitter release (including 5-HT and NE) with long-term application of cadmium also eliminated the Na PIC. Associated with the elimination of the Na PIC in monoamine antagonists, the motoneurons lost their ability to fire during slow current ramps. At this point, the spike evoked by antidromic stimulation was not affected, suggesting that activation of the transient sodium current was not impaired. However, the spike evoked after a slow ramp depolarization was slightly reduced in height and rate-of-rise, suggesting decreased sodium channel availability as a result of increased channel inactivation. These results suggest that endogenous monoamine receptor activation is critical for enabling the Na PIC and decreasing sodium channel inactivation, ultimately enabling steady repetitive firing in both normal and chronic spinal rats.

Neuroprotective efficacy of repinotan HCl, a 5-HT1A receptor agonist, in animal models of stroke and traumatic brain injury

Repinotan is a highly potent 5-HT1A receptor agonist with strong neuroprotective efficacy in animal models of middle cerebral artery occlusion and traumatic brain injury. In this study, we characterized the time window for neuroprotective effects of repinotan in animal models. In the permanent middle cerebral artery occlusion model, repinotan showed neuroprotective efficacy when administered as a triple bolus injection (0.3-100 microg/kg) or an intravenous infusion (0.3-100 microg/kg per hour). A 73% reduction in infarct volume was observed with a 3 microg/kg intravenous bolus, and a 65% reduction was observed with a 3 and 10 microg/kg per hour intravenous infusion. When delayed until 5 hours after occlusion, repinotan (10 microg/kg per hour) reduced infarct volume by 43%. In the transient middle cerebral artery occlusion model, repinotan (10 microg/kg per hour) administered immediately after occlusion reduced infarct volume by 97%, and a delay to 5 hours reduced infarct volume by 81%. In the acute subdural hematoma model, repinotan (3 and 10 microg/kg per hour) reduced infarct volume by 65%. In this model, repinotan (3 microg/kg per hour) administered 5 hours after occlusion reduced infarct volume by 54%. The favorable neuroprotective efficacy, broad dose-response curve, and prolonged therapeutic window observed in all models strongly suggest that repinotan is a promising candidate for treating acute ischemic stroke in humans.

Stimulation of 5-HT1A receptor with 8-OH-DPAT inhibits hydrogen peroxide-induced neurotoxicity in cultured rat cortical cells

We investigated the effect of 8-hydroxy-2-(N,N-dipropylamino)tetralin (8-OH-DPAT), a specific 5-HT(1A) receptor agonist, on H(2)O(2)-induced neuronal cell death in cultured rat cortical cells. H(2)O(2) produced a concentration-dependent reduction of cell viability, which was significantly reduced by (5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d] cyclohepten-5,10-imine (MK-801), an N-methyl-d-aspartate (NMDA) receptor antagonist. Pretreatment of 8-OH-DPAT over the concentration range of 1-100 microM significantly inhibited the H(2)O(2) (100 microM)-induced neuronal cell death as assessed by a MTT assay and the number of apoptotic nuclei, evidenced by Hoechst 33342 staining. The protective effect of 8-OH-DPAT (100 microM) was completely blocked by the simultaneous treatment of 1-(2-methoxyphenyl)-4-[4-(2-phthalimideo)butyl]piperazine (NAN-190, 10muM), a selective 5-HT(1A) receptor antagonist, but not in the presence of the dopamine receptor blocker spiperone (10 microM), indicating that the protective effect of 8-OH-DPAT was mediated via 5-HT(1A) receptors. In addition, 8-OH-DPAT inhibited the H(2)O(2)-induced elevation of glutamate release into the medium and cytosolic Ca(2+) concentration ([Ca(2+)](c)), generation of reactive oxygen species (ROS), and caspase-3 activity. These results suggest that the activation of 5-HT(1A) receptor with 8-OH-DPAT may ameliorate an oxydative stress-induced apoptosis of neuronal cell by interfering with the increase of [Ca(2+)](c), and then by inhibiting glutamate release, generation of ROS and caspase activity.

A review of the neuroprotective properties of the 5-HT1A receptor agonist repinotan HCl (BAYx3702) in ischemic stroke

Repinotan HCl (repinotan, BAYx3702), a highly selective 5-HT1A receptor agonist with a good record of safety was found to have pronounced neuroprotective effects in experimental models that mimic various aspects of brain injury. Repinotan caused strong, dose-dependent infarct reductions in permanent middle cerebral artery occlusion, transient middle cerebral artery occlusion, and traumatic brain injury paradigms. The specific 5-HT1A receptor antagonist WAY 100635 blocked these effects, indicating that the neuroprotective properties of repinotan are mediated through the 5-HT1A receptor. The proposed neuroprotective mechanisms of repinotan are thought to be the result of neuronal hyperpolarization via the activation of G protein-coupled inwardly rectifying K+ channels upon binding to both pre- and post-synaptic 5-HT1A receptors. Hyperpolarization results in inhibition of neuron firing and reduction of glutamate release. These mechanisms, leading to protection of neurons against overexcitation, could explain the neuroprotective efficacy of repinotan per se, but not necessarily the efficacy by delayed administration. The therapeutic time window of repinotan appeared to be at least 5 h in in vivo animal models, but may be even longer at higher doses of the drug. Experimental studies indicate that repinotan affects various mechanisms involved in the pathogenesis of brain injury. In addition to the direct effect of repinotan on neuronal hyperpolarization and suppression of glutamate release this compound affects the death-inhibiting protein Bcl-2, serotonergic glial growth factor S-100beta and Nerve Growth Factor. It also suppresses the activity of caspase-3 through MAPK and PKCalpha; this effect may contribute to its neuroprotective efficacy. The dose- and time-dependent neuroprotective efficacy of repinotan indicates that the drug is a promising candidate for prevention of secondary brain damage in brain-injured patients suffering from acute ischemic stroke. Unfortunately, however, the first, randomized, double blind, placebo-controlled clinical trial did not demonstrate the efficacy of repinotan in acute ischemic stroke.

The 5HT1A receptor agonist, 8-OH-DPAT, protects neurons and reduces astroglial reaction after ischemic damage caused by cortical devascularization

Serotonin 1A (5HT1A) receptor agonists have shown neuroprotective properties in different models of central nervous system injury. Activation of neuronal 5HT1A receptors appears to be involved in the neuroprotective effects. It remains to be elucidated if astroglial cells are responsive to the 5HT1A neuroprotective effects. The participation of astroglial S100B trophic factor has been proposed since 5HT1A activation leads to S100B release and nanomolar concentration level of this molecule showed pro-survival activity in neuronal cultures. Using the cortical devascularization model (CD; unilateral pial disruption), a procedure that results in localized ischemia without producing direct physical damage to brain tissue, we tested the effects of a full 5HT1A agonist, 8-OH-DPAT, or the antagonist WAY-100635 on cortical neuronal survival, astroglial cell response and S100B expression. Wistar rats were subjected to CD lesion which consisted of a craniotomy followed by physical damage to the underlying pial blood vessels. Two and twenty-four hours after the CD lesion, animals received intraperitoneally 8-OH-DPAT (1 mg/kg), WAY-100635 (1 mg/kg) or vehicle (sterile saline). At 3, 7 or 14 days post-lesion, animals were sacrificed and their brains processed for immunohistochemistry to detect GFAP, vimentin, MAP-2, S100B and nuclear Hoechst staining. S100B level in the brain cortex and serum was quantified by an ELISA assay. Serum S100B was considered an index of S100B release. 8-OH-DPAT treatment reduced neuronal death, dendrite loss, astroglial hypertrophy and hyperplasia. In contrast, WAY-100635 treatment increased these parameters of damage. S100B intracellular immunoreactivity in astrocytes and total S100B level showed long-lasting changes after the CD lesion and subsequent treatments depending on the 5HT1A activity. The level of serum S100B was increased in 8-OH-DPAT-treated animals. Increased damage observed in WAY-100635-treated animals supports the hypothesis that the protective 8-OH-DPAT action may be mediated by specific 5HT1A receptors. The reduction in astroglial hypertrophy and hyperplasia as well as long-term changes in S100B immunoreactivity and increased S100B release that we observed allows us to hypothesize that astroglial cells may play an important role in 5HT1A-mediated neuroprotection.

Synthesis and Structure−Activity Relationship Studies for Hydantoins and Analogues as Voltage-Gated Sodium Channel Ligands

We previously developed a preliminary 3-D QSAR model for the binding of 14 hydantoins to the neuronal voltage-gated sodium channel; this model was successful in designing an effective non-hydantoin ligand. To further understand structural features that result in optimum binding, here we synthesized a variety of compound classes and evaluated their binding affinities to the neuronal voltage-gated sodium channel using the [3H]-batrachotoxinin A 20-alpha-benzoate ([3H]BTX-B) binding assay. In order to understand the importance of the hydantoin ring for good sodium channel binding, related non-hydantoins such as hydroxy amides, oxazolidinediones, hydroxy acids, and amino acids were included. Two major conclusions were drawn: (1) The hydantoin ring is not critical for compounds with long alkyl side chains, but it is important for compounds with shorter side chains. (2) Relative to Khodorov's pharmacophore, which contains two hydrophobic regions, a third hydrophobic region may enhance binding to provide nanomolar inhibitors.

The therapeutic efficacy conferred by the 5-HT(1A) receptor agonist 8-Hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) after experimental traumatic brain injury is not mediated by concomitant hypothermia

We recently reported that the 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) attenuated traumatic brain injury (TBI)-induced cognitive deficits and histopathology. However, 8-OH-DPAT also produced mild hypothermia (Hypo), which may have contributed to the benefit. To clarify this issue, we conducted an experiment similar to the previous, but included an 8-OH-DPAT group that was maintained at 37 +/- 0.5 degrees C (normothermia; Normo). Isoflurane-anesthetized rats received either a cortical impact (2.7-mm deformation at 4 m/sec) or sham injury and then were randomly assigned to two saline (Sham/Vehicle, n = 5; Injury/Vehicle, n = 10) or three 8-OH-DPAT (Sham/DPAT, n = 5; Injury/DPAT + Normo, n = 10; Injury/DPAT + Hypo, n = 10) groups. 8-OH-DPAT (0.5 mg/kg) or a comparable volume of saline was administered intraperitoneally 15 min after cortical impact or sham injury. Core temperatures were taken prior to treatment and every 15 min thereafter for 2 h. Function was assessed by established motor and cognitive tasks on post-operative days 1-5 and 14-20, respectively. Hippocampal CA1/CA3 cell survival and cortical lesion volume were quantified at 4 weeks. Both the Injury/DPAT + Normo and Injury/DPAT + Hypo groups exhibited enhanced cognitive performance (spatial acquisition and retention) and reduced histopathology (CA3 cell loss and cortical lesion volume) versus the Injury/ Vehicle group (P < 0.05), but did not differ from one another despite a rapid (15 min), mild (34.4-34.9 degrees C), and transient (~1 h) hypothermic effect in the latter. These data confirm that a single systemic administration of 8-OH-DPAT confers neurological protection after TBI, and demonstrate that the beneficial effect is not mediated by concomitant hypothermia. The mechanisms for the protective effects of 8-OH-DPAT after TBI require further inquiry.

5HT1A serotonin receptor agonists inhibit Plasmodium falciparum by blocking a membrane channel

To identify new leads for the treatment of Plasmodium falciparum malaria, we screened a panel of serotonin (5-hydroxytryptamine [5HT]) receptor agonists and antagonists and determined their effects on parasite growth. The 5HT1A receptor agonists 8-hydroxy-N-(di-n-propyl)-aminotetralin (8-OH-DPAT), 2,5-dimethoxy-4-iodoamphetamine, and 2,5-dimethoxy-4-bromophenylethylamine inhibited the growth of P. falciparum in vitro (50% inhibitory concentrations, 0.4, 0.7, and 1.5 microM, respectively). In further characterizing the antiparasitic effects of 8-OH-DPAT, we found that this serotonin receptor agonist did not affect the growth of Leishmania infantum, Trypanosoma cruzi, Trypanosoma brucei brucei, or Trichostrongylus colubriformis in vitro and did not demonstrate cytotoxicity against the human lung fibroblast cell line MRC-5. 8-OH-DPAT had similar levels of growth inhibition against several different P. falciparum isolates having distinct chemotherapeutic resistance phenotypes, and its antimalarial effect was additive when it was used in combination with chloroquine against a chloroquine-resistant isolate. In a patch clamp assay, 8-OH-DPAT blocked a P. falciparum surface membrane channel, suggesting that serotonin receptor agonists are a novel class of antimalarials that target a nutrient transport pathway. Since there may be neurological involvement with the use of 8-OH-DPAT and other serotonin receptor agonists in the treatment of falciparum malaria, new lead compounds derived from 8-OH-DPAT will need to be modified to prevent potential neurological side effects. Nevertheless, these results suggest that 8-OH-DPAT is a new lead compound with which to derive novel antimalarial agents and is a useful tool with which to characterize P. falciparum membrane channels.

Short posterior ciliary artery, central retinal artery, and choroidal hemodynamics in brimonidine-treated primary open-angle glaucoma patients

PURPOSE

Malfunction in peripapillary hemodynamics has been suggested to play a major part in the pathogenesis of primary open-angle glaucoma (POAG). The aim of this study was to determine whether topically applied brimonidine can influence blood hemodynamic characteristics associated with the perioptic short posterior ciliary arteries (SPCAs), central retinal artery (CRA), and choroidal vascular system in POAG patients.

DESIGN

Randomized clinical trial. In this prospective, institutional, double-masked, vehicle-controlled, randomized clinical trial, the intraocular pressure (IOP) and vascular dynamics of the SPCAs, CRA, and choroidal vascular system were analyzed in both eyes of 17 POAG patients, before and after treatment with 0.2% brimonidine for 4 weeks.

RESULTS

Mean IOP reduction was significant (18.7%) following treatment with brimonidine. However, no clear changes were recorded with respect to blood perfusion parameters (peak systolic velocity, end-diastolic velocity, pulsatility, and resistance indices) associated with the SPCAs and CRA or the choroidal ocular pulse amplitude.

CONCLUSIONS

Topical treatment of brimonidine to POAG patients causes a significant reduction of IOP, but blood hemodynamic properties associated with the SPCAs, CRA, and choroidal vascular systems appeared unaffected. Topically applied brimonidine, therefore, appears not to constrict or dilate peripapillary blood vessels.

Post-lesion administration of 5-HT1A receptor agonist 8-OH-DPAT protects cholinergic nucleus basalis neurons against NMDA excitotoxicity

Recent evidence indicates that serotonin (5-HT)1A receptor agonists may abrogate excitotoxic brain damage. We investigated whether a single i.p. injection of the 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT), at a dose of 2.5 mg/kg, protects cholinergic neurons of the rat magnocellular nucleus basalis (MBN) against NMDA excitotoxicity when administered at post-injury intervals ranging from 6 to 96 h. Drug effects on passive avoidance learning and on the density of cortical cholinergic innervation, a measure of neuronal survival in the damaged MBN, were analyzed. Our results demonstrate that 8-OH-DPAT, when administered up to 24 h post-lesion, significantly attenuates both behavioral and neuroanatomical consequences of NMDA excitotoxicity on cholinergic MBN neurons; and support the hypothesis that 5-HT1A receptor agonists may interfere with delayed neuronal death in vivo that is of significance in the pharmacological treatment of neurological disorders associated with excitotoxic neuronal damage.

Protective effects of the 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin against traumatic brain injury-induced cognitive deficits and neuropathology in adult male rats

To further investigate the efficacy of 5-HT(1A) receptor agonism on functional and histological outcome in traumatically-brain injured (TBI) rats, a single intraperitoneal injection of 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT; 0.1, 0.5, or 1.0 mg/kg) or vehicle was given 15 min after controlled cortical impact or sham injury. Function was assessed by established motor and cognitive tests on post-operative days 1-5 and 14-18, respectively. Cortical lesion volume and hippocampal CA(1)/CA(3) cell survival were quantified at 4 weeks. The administration of 8-OH-DPAT (0.5 mg/kg) attenuated spatial acquisition deficits and reduced hippocampal CA(3) cell loss vs. vehicle (P < 0.05). These data augment published reports that 5-HT(1A) receptor agonists confer neuroprotective effects after experimental TBI.

The selective 5-HT(1A) receptor agonist repinotan HCl attenuates histopathology and spatial learning deficits following traumatic brain injury in rats

The selective 5-HT(1A) receptor agonist Repinotan HCl (BAY x3702) has been reported to attenuate cortical damage and improve functional performance in experimental models of cerebral ischemia and acute subdural hematoma. Using a clinically relevant contusion model of traumatic brain injury, we tested the hypothesis that a 4-h continuous infusion of Repinotan HCl (10 microg/kg/h i.v.) commencing 5 min post-injury would ameliorate functional outcome and attenuate histopathology. Forty isoflurane-anesthetized male adult rats were randomly assigned to receive either a controlled cortical impact (2.7 mm tissue deformation, 4 m/s) or sham injury (Injury/Vehicle=10, Injury/MK-801=10, Injury/Repinotan HCl=10, Sham/Vehicle=10), then tested for vestibulomotor function on post-operative days 1-5 and for spatial learning on days 14-18. Neither Repinotan HCl nor the non-competitive N-methyl-D-aspartate receptor antagonist MK-801, which served as a positive control, improved vestibulomotor function on beam balance and beam walk tasks relative to the Injury/Vehicle group, but both did significantly attenuate spatial learning and memory deficits on a water maze task. Repinotan HCl also reduced hippocampal CA(1) and CA(3) neuronal loss, as well as cortical tissue damage, compared to the Injury/Vehicle group at 4 weeks post-trauma. No significant difference in histological outcome was revealed between the Repinotan HCl- and MK-801-treated groups.These findings extend the therapeutic efficacy of Repinotan HCl to a contusion model of experimental brain injury and demonstrate for the first time that 5-HT(1A) receptor agonists confer neuroprotection and attenuate spatial learning deficits following controlled cortical impact injury. This treatment strategy may be beneficial in a clinical context where memory impairments are common following human traumatic brain injury.