Chronic Cannabis-Use Increases Intelligence

[beachguy_inthongs]

Natural selection has conserved cannabinoid receptors in various vertebrates and invertebrates that have been evolutionarily separate for 500 million years, indicating the importance of cannabinoid receptors to life.


Particularly important classes of neurons that express high levels of CB1 receptors are GABAergic interneurons in hippocampus, amygdala and cerebral cortex, which also contain the neuropeptides cholecystokinin.


Activation of CB1 receptors leads to inhibition of the release of amino acid and monoamine neurotransmitters.


They may act as retrograde synaptic mediators of the phenomena of depolarization-induced suppression of inhibition or excitation in hippocampus and cerebellum. Central effects of cannabinoids include disruption of psychomotor behaviour, short-term memory impairment, intoxication, stimulation of appetite, antinociceptive actions (particularly against pain of neuropathic origin) and anti-emetic effects.

http://brain.oxfordjournals.org/cgi/...act/126/6/1252

In the mammalian brain, the CB1 receptor is one of the most
abundant G protein-coupled receptors, accounting for most, if not all, of the centrally mediated effects of cannabinoids (Baker, D., Pryce, G., Giovannoni, G., and Thompson, A.J. 2003. The therapeutic potential of Cannabis. Lancet Neurol.).

...we reasoned that if cannabinoids were able to regulate neurogenesis, the NS/PCs capable of producing new neural cells would
contain CB1 receptors.

About 95% of the total neurosphere cells labeled with Hoeschst stain were also labeled with both CB1 and nestin (a marker for NS/PCs) antibodies.


These results suggest that both embryonic and adult hippocampal NS/PCs express CB1 receptors.


...suggesting that HU210 (potent synthetic cannabinoid) specifically acts on CB1 receptors to promote NS/PC proliferation.


HU210 significantly increased NS/PC proliferation


CB1 receptor stimulation activates Gi/o or Gs proteins (Bonhaus, D.W., Chang, L.K., Kwan, J., and Martin, G.R. 1998. Dual activation and inhibition of adenylyl cyclase by cannabinoid receptor agonists: evidence for agonist-specific trafficking of intracellular responses. J. Pharmacol. Exp. Ther. Howlett, A.C., et al. 2004. Cannabinoid physiology and pharmacology: 30 years of progress [review]. Neuropharmacology.


we added pertussis toxin, a selective blocker for Gi/o protein activation, to the culture medium 4 hours prior to HU210 treatment. Again, 10 nM to 1 μM of HU210 significantly increased NS/PC proliferation


It has been shown that HU210 activates Gs proteins when Gi/o proteins are inhibited by pertussis toxin.


These results together suggest the involvement of Gi/o proteins, but not Gs proteins, in HU210-induced NS/PC proliferation.

There was no significant change in phosphorylation of phospho-Akt during the first 1 hour after HU210 application, indicating that the PI3K/Akt signaling pathway is not involved in the action of HU210 on NS/PC proliferation. In contrast, changes in phosphorylation of phospho-ERK1/2 (pERK1/2) during the first 1 hour after HU210 application were dramatic at specific time points, as shown by 1-way ANOVA (with growth factors, F4,15 = 33.698, P < 0.01; without growth factors, F4,15 = 23.513, P < 0.01). As early as 5 minutes after addition of HU210 to culture medium with or without bFGF and EGF (mitogenic growth factors), a 2.5-fold increase in phosphorylation of pERK1/2 was observed (P < 0.05). At 15 minutes after HU210 application, phosphorylation of pERK1/2 reached
the peak level, which was about a 4-fold (with growth factors) or 7-fold increase (without growth factors) relative to control (P < 0.01). By 60 minutes after addition of HU210, phosphorylation of pERK1/2 either significantly decreased (P < 0.05) (Figure 3B) or returned to the pretreatment level (Figure 3C). We did not observe any significant changes in the total ERK1/2 during the first 1 hour after HU210 application. Thus, the significant increase in pERK1/2 in this period suggests an important involvement of ERK signaling pathway in the action of HU210 in promoting NS/PC proliferation.

supported by further experiments in which U0126, a specific inhibitor of the ERK pathway, was employed. Specifically, HU210 profoundly increased phosphorylation of pERK1/2 (P < 0.01), which was almost completely blocked by U0126 (P < 0.01). A parallel experiment demonstrated that U0126 blocked the promoting effects of 100 nM of HU210 on NS/PC proliferation (1-way ANOVA for repeated measures, F1,17 = 6.356, P < 0.05; pairwise comparisons, HU210-treated cells
with or without U0126: P < 0.05).

suggesting that HU210 exerts no significant effects on neuronal differentiation of cultured NS/PCs.

Similarly to HU210, AEA [anandamide] (1 and 5 μM) did not produce significant effects on neuronal differentiation of cultured NS/PCs.

We examined the effects of chronic HU210 injection on cell proliferation in adult hippocampus. Two hours after receiving the last dose of twice-daily injections of vehicle, AM281 (3 mg/kg, i.p.), or HU210 (25 or 100 μg/kg, i.p.) for 10 days, adult Long-Evans rats received BrdU administration and then were perfused 1 day later. Immunohistochemical staining showed an apparent increase in the density of BrdU-labeled cells in the SGZ (dentate gyrus) following chronic administration of 100 μg/kg of HU210.

One-way ANOVA revealed a significant overall difference in the mean plus/minus SEM (All results are expressed as mean plus/minus SEM. Statistical analysis of the data was performed using standard 1-way ANOVA or 1-way ANOVA for repeated measures, followed by the Tukey post-hoc test.) number of BrdU-positive cells in the SGZ. Tukey post-hoc test showed a significant increase (about 40%) in the number of BrdU-labeled cells following 100 μg/kg of HU210 (P < 0.05) but not 25 μg/kg of HU210 (P = 0.979), relative to vehicle.

AM281 injection seemingly decreased the number of BrdU-positive cells in the SGZ, but there was no significant difference relative to control (P = 0.099).

To examine the survival, migration, and differentiation of HU210-induced newborn cells in the SGZ, we injected rats twice daily with HU210 (100 μg/kg, i.p.), AM281 (3 mg/kg), or vehicle for 10 days, followed 12 hours later by 4 BrdU injections at 12 hours intervals.

The number of BrdU-labeled dentate cells in
HU210-treated rats was significantly higher than that in vehicle-treated
rats, indicating that most of chronic HU210 induced newborn cells survived.

Immunofluorescence staining revealed that HU210- and vehicle-treated
rats exhibited a similar proportion of BrdU/neuronal nuclear
antigen (BrdU/NeuN) double-labeling cells to the total BrdUlabeled
cells, suggesting that chronic HU210-induced newborn cells in the SGZ have neuronal differentiation ratio similar to that of vehicle-induced newborn cells in the SGZ. Nevertheless, because chronic HU210 treatment
significantly increased the number of BrdU-labeled newborn cells
in the dentate gyrus, the total number of newborn neurons
doubly labeled with BrdU/NeuN in the dentate gyrus also significantly
increased following chronic HU210.

(continued below)

[beachguy_inthongs]

"No hippocampal neuronal death following chronic HU210 treatment"

We examine the total number of the dentate granule and
CA3 pyramidal neurons following twice-daily injections of HU210
(100 μg/kg) for 10 days. As depicted in Figure 7A, HU210-treated
rats did not show detectable loss of NeuN-immunopositive neurons
in the hippocampus, relative to naive control rats. Stereological
cell counting confirmed that no significant difference in the
total number of the dentate granule cells and CA3 pyramidal neurons between naive and HU210-treated rats. These results, however, do not
exclude the possibility that some of NeuN-stain neurons following
chronic HU210 treatment shown in Figure 7A are dying. Accordingly,
we used TUNEL stain and Fluoro-Jade B stain to examine the
degenerating hippocampal neurons (Zhang, X., et al. 2002. Relations between brain pathology and temporal lobe epilepsy. J. Neurosci.) in rats receiving chronic HU210 treatment, with the naive rats as negative control and kainic acid treated rats as positive control (Zhang, X, et al, 2002)). We failed to detect any TUNEL- or Fluoro-Jade B stained degenerating cells throughout the whole hippocampus in both naive rats and HU210-treated rats, whereas kainic acid injected rats showing epileptic status exhibited numerous dying cells in the CA3 pyramidal cell layer and
even dentate granule cell layer .

We employed the same behavioral tests to examine the effects of chronic HU210 treatment on measures of anxiety and depression.

Cell counting revealed an overall significant difference in the number of BrdU-stained cells in the dentate gyrus

HU210-treated rats displayed a significant increase (P < 0.05)
in the number of BrdU-positive cells in the dentate gyrus, whereas
AM281-treated rats exhibited no significant difference (P = 0.165).

These data together suggest that chronic HU210 treatment
promoted hippocampal neurogenesis and exerted anxiolytic- and
antidepressant-like effects.

To determine the relationship between hippocampal neurogenesis and anxiolytic- and antidepressant-like effects produced by chronic HU210, we examined the effects of a selective destruction of the hippocampal neural
stem cells on the behavioral effects of chronic HU210.

...our results together suggest
that chronic HU210 treatment reduced anxiety and depression,
likely via promoting hippocampal neurogenesis.


http://www.jci.org/cgi/reprint/115/11/3104.pdf

These data together suggest that chronic HU210 treatment
promoted hippocampal neurogenesis and exerted anxiolytic- and
antidepressant-like effects.

To determine the relationship between hippocampal neurogenesis and anxiolytic- and antidepressant-like effects produced by chronic HU210, we examined the effects of a selective destruction of the hippocampal neural
stem cells on the behavioral effects of chronic HU210.

...our results together suggest
that chronic HU210 treatment reduced anxiety and depression,
likely via promoting hippocampal neurogenesis.


http://www.jci.org/cgi/reprint/115/11/3104.pdf