The aim of this study was to investigate whether prenatal exposure to the cannabinoid CB1 receptor agonist WIN 55,212-2 (WIN) at a daily dose devoid of overt signs of toxicity and/or gross malformations (0.5 mg/kg, gestation days 5-20), influences cortical glutamatergic neurotransmission, learning and emotional reactivity in rat offspring. Basal and K+-evoked extracellular glutamate levels were significantly lower in cortical cell cultures obtained from pups exposed to WIN during gestation with respect to those measured in cultures obtained from neonates born from vehicle-treated dams. The addition of NMDA to cortical cell cultures from neonates born from vehicle-treated dams concentration-dependently increased glutamate levels, and this was absent in cell cultures obtained from WIN-exposed pups. WIN-exposed rats also revealed a poorer performance in homing (10-12 days of age) and active avoidance tests (80 days of age) as well as a decrease in the rate of separation-induced ultrasonic emission (10 days of age). Finally, prenatal exposure to WIN induced a reduction in the number of cortical neuronal population. These findings (i) provide evidence for a deficit in cortical glutamatergic neurotransmission and behaviour in the rat neonate following prenatal exposure to WIN; and (ii) suggest that the reduction in cortical glutamatergic neurotransmission, NMDA receptor activity and alterations in neuronal development might underlie, at least in part, the learning deficit and decreased emotional reactivity observed in the offspring.

Cannabinoids have been proposed as clinically promising neuroprotective molecules, as they are capable to reduce excitotoxicity, calcium influx, and oxidative injury. They are also able to decrease inflammation by acting on glial processes that regulate neuronal survival and to restore blood supply to injured area by reducing the vasoconstriction produced by several endothelium-derived factors. Through one or more of these processes, cannabinoids may provide neuroprotection in different neurodegenerative disorders including Parkinson's disease and Huntington's chorea, two chronic diseases that are originated as a consequence of the degeneration of specific nuclei of basal ganglia, resulting in a deterioration of the control of movement. Both diseases have been still scarcely explored at the clinical level for a possible application of cannabinoids to delay the progressive degeneration of the basal ganglia. However, the preclinical evidence seems to be solid and promising. There are two key mechanisms involved in the neuroprotection by cannabinoids in experimental models of these two disorders: first, a cannabinoid receptor-independent mechanism aimed at producing a decrease in the oxidative injury and second, an induction/upregulation of cannabinoid CB2 receptors, mainly in reactive microglia, that is capable to regulate the influence of these glial cells on neuronal homeostasis. Considering the relevance of these preclinical data and the lack of efficient neuroprotective strategies in both disorders, we urge the development of further studies that allow that the promising expectatives generated for these molecules progress from the present preclinical evidence till a real clinical application.

Primary cultures of cortical neurons were employed to investigate the modulatory effects of neurotensin on glutamate excitotoxicity and the possible neuroprotective actions of the neurotensin receptor antagonist SR48692. NT(1-13) and its biologically active fragment NT(8-13) at 10 nM (30 min) increased endogenous glutamate levels. The inactive fragment NT(1-7) (10-100 nM; 30 min) was ineffective. SR48692, applied 20 min before NT and maintained in contact with cells during NT exposure as well as a low calcium medium (from the onset of the experiment) prevented the NT(1-13)-induced increase in extracellular glutamate levels. The addition of NMDA (0.01-10 micro M; 10 min) to the medium concentration-dependently increased extracellular glutamate levels. When 0.1 nM NT(1-13) was added in combination with 0.01 micro M NMDA, in concentrations by themselves ineffective, a significant increase in glutamate levels was observed. SR48692 at 100 nM counteracted the increase in glutamate levels induced by 0.1 nM NT(1-13) plus 0.01 micro M NMDA. The inhibitor of the protein kinase C (PKC) calphostin C (0.1 micro M; 10 min before NT) prevented the increase in glutamate levels induced by the combined treatments. The morphological analysis indicated that 10 nM NT(1-13) enhanced the glutamate (10 min)-induced apoptosis. The peptide was added 30 min prior to glutamate and maintained in contact with cells during the glutamate exposure. The presence of 100 nM SR48692 (20 min before NT) antagonized this effect of NT(1-13). These findings support the view of a pathophysiological role for NT in the cerebral cortex. Thus, under pathological conditions NT by enhancing glutamate outflow and by amplifying the NMDA-mediated glutamate signaling may be involved in increasing the degeneration of cortical neurons.

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The present study investigated the neurotensin (NT) receptor subtype (NTR) involved in the antagonistic neurotensin modulation of striatal dopamine D2 receptors observed in vitro and in vivo. The NT induced increase of the IC50 values of dopamine (DA) competition for [125I]iodosulpiride binding sites was counteracted by the NTR1-like antagonist SR48692 in rat striatal slices. Intrastriatal perfusion of pergolide induced in the awake rat an inhibition of striatal DA release that was antagonized by NT. This action of NT was counteracted by co-perfusion with the NTR1 like antagonist SR48692. These data indicate that there exists in the striatum at the prejunctional level an intramembrane antagonistic NT receptor/DA D2 receptor-receptor interaction where NTR1 like receptor activation reduces the DA D2 autoreceptor function.