1,3-di-o-tolylguanidine

Neurotoxicity

Description of key information

Because 1,3-di-o-tolylguanidine is preferentially stored in the sigma-receptors in the brain, in particular in the brain stem, it is widely used in neuropharmacology as a model coumpound for studying disturbances in behaviour and movement (BG Chemie, 1999).

Key value for chemical safety assessment

Effect on neurotoxicity: via oral route

Link to relevant study records

Reference

Endpoint:

neurotoxicity

Remarks:

acute

Type of information:

experimental study

Adequacy of study:

other information

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Study well documented, meets generally accepted scientific principles, acceptable for assessment.

Qualifier:

no guideline followed

Principles of method if other than guideline:

A Forced Swimming (Porsolt's test) and a Open field test were performed on rats.

GLP compliance:

no

Limit test:

no

Species:

rat

Strain:

Wistar

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: no data
- Age at study initiation: no data
- Weight at study initiation: 250-300 g
- Fasting period before study: no data
- Housing: 6 per cage
- Diet (e.g. ad libitum): free access
- Water (e.g. ad libitum): free access
- Acclimation period: no data

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22+/-2°C
- Humidity (%): no data
- Air changes (per hr): no data

Route of administration:

intraperitoneal

Vehicle:

other: 1% aqueous solution of tween 80

Details on exposure:

Administration volume = 2 ml/kg

Analytical verification of doses or concentrations:

no

Duration of treatment / exposure:

3 injections

Frequency of treatment:

3 injections

Remarks:

Doses / Concentrations:
2.5 and 5 mg/kg
Basis:
nominal conc.

No. of animals per sex per dose:

Forced swimming test : 8 rats/ group
Open field test: 6 rats/group

Control animals:

not specified

Details on study design:

Forced swimming (Porsolt's) test
The animals were subjected to two trials during which they were forced to swim in a cylinder (40 cm high, 18 cm in diameter) filled with water (23-25°C) to a height of 15 cm. There was a 24-hour interval between the first and second trial; the first trial lasted 15 min, the second 5 min. The total duration (s) of immobility was measured throughout the second trial. DTG (2.5 and 5 mg/kg) was given separately or in combination with MEM (2.5 mg/kg) three times: at 24, 5, and 1 h before the test.

Open field test
The center of an open platform (divided into sectors, without walls) was illuminated with a 75 W bulb, hung directly 75 cm above it. During all experiments the rest of the laboratory room was dark. To start the test, animals were placed gently in the center of the platform and were allowed to explore it freely. Ambulation (the number of crossings of sector lines), peeping (the number of times the animals peeped down from the edge of the arena) or rearing and the time of walking were recorded directly for 5 min. Drug treatments were carried out according to the same experimental schedule as described above (three injections).

Statistics:

The data were evaluated by two-way ANOVA, followed, when appropriate, by individual com¬parisons with the control using Dunnett's test.

Details on results:

DTG (2.5 or 5 mg/kg) did not change the immobility time of rats. Co-administration of DTG with MEM induced antidepressant-like effect in Porsolt's test (at both dose used of DTG). These synergistic effects were not an expression of a general change in locomotor activity, since it was unaltered after co-administration of both sigma receptor ligands and MEM.
The antidepressant-like effect of DTG at a dose of 5 mg/kg, given jointly with MEM, was antagonized by progesterone (20 mg/kg).

Conclusions:

DTG (2.5 or 5 mg/kg) did not change the immobility time of rats.

Executive summary:

The obtained results show that DTG, the sigma1 and sigma2 receptor agonist, exerts a synergistic effect with memantine, an uncompetitive NMDA receptor antagonist, in the forced swimming test in rats, and that progesterone and BD 1047, the sigma1 receptor antagonists, counteract this effect. The results suggest that the sigma1receptor subtype may contrebute to the behavioral response induced by combined administration of DTG and memantine in Porsolt's test in rats.

 

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEL

30 mg/kg bw/day

Study duration:

subacute

Species:

rat

Quality of whole database:

The majority are acute studies performed on rats. These studies are reliable with a klimisch score of 2.

Effect on neurotoxicity: via inhalation route

Endpoint conclusion

Endpoint conclusion:

no study available

Effect on neurotoxicity: via dermal route

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

Several studies had analyzed the effect on DOTG on central nervous system.

Summary of specific studies :

DOTG is a compound hightly selective sigma receptor ligand; DTG has reported to bind for both the sigma1 and sigma2 receptor subtypes as an agonist (Nakazawa 1999). Results of study suggest that the receptors on which DTG acts are located on the mossy fiber terminals in the CA3 region and are absent in the CA1 region (Debonnel 1996).

DTG demontrated full concentration-dependent neuroprotection with a EC50 (neuroprotection) at 42.7 µM (DeCoster 1995).

DTG antagonize the apomorphine-induced aggression and climbing, but not affect the apomorphine stereotypy (Maj 1993).

DTG acts as a typical neuroleptic (antagonizes the apomorphine-induced aggression and climbing) and at the same time, as dopamine stimulants (antagonize neuroleptic-induced catalepsy). When given alone it exhibits no visible behavioural effects (Maj 1996).

DTG elicits a marked deviation of the head (torticollis) following microinjection into the red nucleus. An acute abnormal postural change (dystonia) was observed 1-5 min after injection of DOTG (Faherty 1997, Nakagawa 1999).

DOTG produces hypothermia in the rodent after s.c. and i.c.v. administrations (Bejanian 1991). This findings represents a potential confound of effects in nociceptive assays that use reactivity to thermal stimuli as an end point.

Consistent with a sigma receptor site of action, DOTG antinociception in the aforementioned study was blocked in a dose-dependent manner by rimcazole, a selective sigma receptor ligand and putative antagonist.

In the formalin test, DTG produced no visible signs of motor dysfunction or malaise alone or in combinaison with rimcazole.

DTG produced antinociception on the acute phase of the formalin test following systemic administration (Kest (b) 1995). The formalin test of nociception, in which a dilute volume of formaldehyde is injected subcutaneously is one model of tonic pain.

DTG (2.5 or 5 mg/kg) did not change the immobility time of rats (Skuza 2003).

Justification for selection of effect on neurotoxicity via oral route endpoint:
Several studies had analyzed the effect on DOTG on central nervous system.

Justification for classification or non-classification

No classification is justified.