The presence of an active and functioning endocannabinoid (EC) system within cardiovascular tissues implies that this system has either a physiological or pathophysiological role (or both), and there is a substantial literature to support the notion that, in the main, they are protective in the setting of various CVD states. Moreover, there is an equally extensive literature to demonstrate the cardio- and vasculo-protective effects of n-3 long-chain (LC)-PUFA. It is now becoming evident that there appears to be a close relationship between dietary intervention with n-3 LC-PUFA and changes in tissue levels of EC, raising the question as to whether or not EC may, at least in part, play a role in mediating the cardio-and vasculo-protective effects of n-3 LC-PUFA. This brief review summarises the current understanding of how both EC and n-3 LC-PUFA exert their protective effects in three major cardiovascular disorders (hypertension, atherosclerosis and acute myocardial infarction) and attempts to identify the similarities and differences that may indicate common or integrated mechanisms. From the data available, it is unlikely that in hypertension EC mediate any beneficial effects of n-3 LC-PUFA, since they do not share common mechanisms of blood pressure reduction. However, inhibition of inflammation is an effect shared by EC and n-3 LC-PUFA in the setting of both atherosclerosis and myocardial reperfusion injury, while blockade of L-type Ca2+ channels is one of the possible common mechanisms for their antiarrhythmic effects. Although both EC and n-3 LC-PUFA demonstrate vasculo- and cardio-protection, the literature overwhelmingly shows that n-3 LC-PUFA decrease tissue levels of EC through formation of EC–n-3 LC-PUFA conjugates, which is counter-intuitive to an argument that EC may mediate the effects of n-3 LC-PUFA. However, the discovery that these conjugates have a greater affinity for cannabinoid receptors than the native EC provides a fascinating avenue for further research into novel approaches for the treatment and prevention of atherosclerosis and myocardial injury following ischaemia/reperfusion.

A functional role for retinal endocannabinoids has not been determined. We characterized retrograde suppression of membrane currents of goldfish cones in a retinal slice. Whole-cell recordings were obtained from cone inner segments under voltage clamp. IK(V) was elicited by a depolarizing pulse to +54 mV from a holding potential of −70 mV. A fifty-millisecond puff of saline with 70 mM KCl or Group I mGluR agonist DHPG was applied through a pipette directly at a mixed rod/cone (Mb) bipolar cell body. The amplitude of IK(V) decreased 25% compared to the pre-puff control. Retrograde suppression of IK(V) was blocked by CB1 receptor antagonist, SR141716A. The FAAH inhibitor URB597 had no effect on the suppression of IK(V), whereas nimesulide, a COX-2 inhibitor, prolonged the effects of the K+ puff 10-fold. Orlistat, a blocker of 2-AG synthesis, blocked the effect of the K+ puff. Group I mGluR activation of Gq/11 was demonstrated in that a puff with DHPG decreased IK(V) of cones by 32%, an effect blocked by SR141716A. The effect of DHPG was not blocked by the mGluR5 antagonist MPEP, indicating involvement of mGluR1. The suppressive effect of the K+ puff vanished in a Ca2+-free, 2 mM Co2+ saline. TMB-8 or ryanodine, blocked the effect of DHPG, but not that of the K+ puff, showing that calcium influx or release from intracellular stores could mediate retrograde release. We suggest that retrograde suppression of cone IK(V) is mediated by Ca2+-dependent release of 2-AG from Mb bipolar cell dendrites by separate mechanisms: (1) voltage-dependent, mimicked by the K+ puff, that may be activated by the depolarizing ON response to light; (2) voltage-independent, occurring under ambient illumination, mediated by tonic mGluR1 activation. The negative feedback of this latter mechanism could regulate tonic glutamate release from cones within narrow limits, regardless of ambient illumination.

There is evidence for neurodevelopment disturbances in schizophrenia. In rats, a neonatal basolateral amygdala lesion induces behavioural features in adults reminiscent of the symptomatology of schizophrenia. Dopamine plays a key role in the pathogenesis of schizophrenia, and cannabis use has been implicated in the risk for developing schizophrenia. The effects of an excitotoxic, bilateral basolateral amygdala lesion on postnatal days 7 or 21 were compared when the rats were adult. The behavioural response to a novelty challenge and the level of dopamine receptors and cannabinoid receptors in the brain using in-vitro autoradiography was determined. In brain tissue punches concentrations of monoamines and metabolites were determined by high-performance liquid chromatography. The neonatal lesion, but not the later lesion induced behavioural hyperactivity and biochemical effects. The neonatal lesion reduced the density of dopamine D2-like, but not D3-, and less markely D1-like receptors and increased dopamine turnover. These effects were observed in the mesolimbic, but not in the striatal regions. In contrast, density of cannabinoid receptors was increased in the striatal, but not the mesolimbic regions of these animals. Noradrenergic neurotransmission was reduced in both regions. The present findings contribute to the idea that the neonatal basolateral amygdala lesion induces features in adults reminiscent of the neurodevelopmental disturbances in schizophrenia, with a focus on the amygdala–prefrontal cortex–nucleus accumbens circuit.

Goldfish cones contain CB1 receptors at the synaptic terminal, selectively accumulate 3H-anandamide, and contain fatty acid amide hydrolase-immunoreactivity, and voltage-gated calcium and potassium currents are modulated by CB1 ligands (Yazulla et al., 2000; Fan & Yazulla, 2003; Glaser et al., 2005). These data suggest that a retinal mechanism may account for some of the psychophysical effects of cannabis. Here, we studied the effect of a cannabinoid agonist on cone light responses. Whole-cell patch-clamp recordings were made from cones in the isolated goldfish retina. Cones were stimulated with a spot of light of variable wavelength and intensities in combination with voltage-and current-clamp protocols. Pharmacological manipulation was performed using the cannabinoid agonist WIN 55212-2 (10 μM). WIN had no effect on the absolute sensitivity of the cones or on the kinetics of the onset response. However, the light-offset response became faster, and the depolarizing overshoot was enhanced. Time constant of the offset response was reduced from 292 ± 28 ms to 180 ± 11 ms (n = 6) (P < 0.01) in the presence of WIN. Acceleration of the offset response was not affected by flash length from 200 ms to 10 s. This was found under current-clamp as well as under voltage-clamp conditions, indicating that the effect of WIN was mediated directly or indirectly by modulation of the cGMP-gated channels in the outer segment of the cones. The effects of WIN were not blocked by the CB1 antagonist SR141716A. With a train of “dark” flashes from a steady background, the photocurrent recovered toward baseline more quickly with WIN than in Control. In summary, cannabinoids speed up the dynamics of the phototransduction deactivation cascade in the cone outer segments. The functional consequence of this effect is to shorten the recovery time to the offset of bright flashes, perhaps resulting in an increase in contrast sensitivity.

There is much evidence for an endocannabinoid system in the retina. However, neither the distribution of endocannabinoid uptake, the regulation of endocannabinoid levels, nor the role of endocannabinoid metabolism have been investigated in the retina. Here we focused on one endocannabinoid, anandamide (AEA), and its major hydrolyzing enzyme, fatty acid amide hydrolase (FAAH), in the goldfish retina. Immunoblots of FAAH immunoreactivity (IR) in goldfish retina, brain and rat retina, and brain homogenates showed a single band at 61 kDa that was blocked by preadsorption with peptide antigen. Specific FAAH IR (blocked by preadsorption) was most prominent over Müller cells and cone inner segments. Weaker label was observed over some amacrine cells, rare cell bodies in the ganglion cell layer, and in four lamina in the inner plexiform layer. FAAH activity assays showed that goldfish-retinal and brain homogenates hydrolyzed AEA at rates comparable to rat brain homogenate, and the hydrolysis was inhibited by methyl arachidonyl fluorophosphonate (MAFP) and N-(4 hydroxyphenyl)-arachidonamide (AM404), with IC50s of 21 nM and 1.5 μM, respectively. Cellular 3H-AEA uptake in the intact retina was determined by in vitro autoradiography. Silver-grain accumulation at 20°C was most prominent over cone photoreceptors and Müller cells. Uptake was significantly reduced when retinas were incubated at 4°C, or preincubated with 100 nM MAFP or 10 μM AM404. There was no differential effect of blocking conditions on the distribution of silver grains over cones or Müller cells. The codistribution of FAAH IR and 3H-AEA uptake in cones and Müller cells suggests that the bulk clearance of AEA in the retina occurs as a consequence of a concentration gradient created by FAAH activity. We conclude that endocannabinoids are present in the goldfish retina and underlay the electrophysiological effects of cannabinoid ligands previously shown on goldfish cones and bipolar cells.

Cannabinoid CB1 receptor (via Gs) and dopamine D2 receptor (via Gi/o) antagonistically modulate goldfish cone membrane currents. As ON bipolar cells have CB1 and D1 receptors, but not D2 receptors, we focused on whether CB1 receptor agonist and dopamine interact to modulate voltage-dependent outward membrane K+ currents IK(V) of the ON mixed rod/cone (Mb) bipolar cells. Whole-cell currents were recorded from Mb bipolar cells in goldfish retinal slices. Mb bipolar cells were identified by intracellular filling with Lucifer yellow. The bath solution was calcium-free and contained 1 mM cobalt to block indirect calcium-dependent effects. Dopamine (10 μM) consistently increased IK(V) by a factor of 1.57 ± 0.12 (S.E.M., n = 15). A CB receptor agonist, WIN 55212-2 (0.25–1 μM), had no effect, but 4 μM WIN 55212-2 suppressed IK(V) by 60%. If IK(V) was first increased by 10 μM dopamine, application of WIN 55212-2 (0.25–1 μM) reversibly blocked the effect of dopamine even though these concentrations of WIN 55212-2 had no effect of their own. If WIN 55212-2 was applied first and dopamine (10 μM) was added to the WIN-containing solution, 0.1 μM WIN 55212-2 blocked the effect of dopamine. All effects of WIN 55212-2 were blocked by coapplication of SR 141716A (CB1 antagonist) and pretreatment with pertussis toxin (blocker of Gi/o) indicating action via CB1 receptor activation of G protein Gi/o. Coactivation of CB1 and D1 receptors on Mb bipolar cells produces reciprocal effects on IK(V). The CB1-evoked suppression of IK(V) is mediated by G protein Gi/o, whereas the D1-evoked enhancement is mediated by G protein Gs. As dopamine is a retinal “light” signal, these data support our notion that endocannabinoids function as a “dark” signal, interacting with dopamine to set retinal sensitivity.

A number of plasma membrane receptor types originally thought to be specific to neurons have been found in other somatic cells. More surprisingly, the mammalian sperm and neuron appear to share many of these ‘neuronal’ receptors. The morphology, chromosome number, genomic activity, and functions of those two cell types are as unlike as any two cells in the body, but they both achieve their highly disparate goals with the aid of a number of the same receptors. Exocytosis in neurons and sperm is essential to the functions of these cells and is strongly influenced by similar receptors. ‘Neuronal’ receptor types in sperm may also play a role in the control of sperm motility (a function of course not shared by neurons).

This review will consider the evidence for the presence of sperm plasma membrane ‘neuronal’ receptors and for their significance to mammalian sperm function. The persuasiveness of the evidence varies depending on the receptor being considered, but there is strong experimental support for the presence and importance of a number of ‘neuronal’ receptors in sperm.

Dopamine is a light-adaptive signal that desensitizes the retina, while cannabinoids reportedly increase photosensitivity. The presynaptic membrane of goldfish retinal cones has dopamine D2 receptors and cannabinoid CB1 receptors. This work focused on whether dopamine D2 receptor agonist quinpirole and cannabinoid CB1 receptor agonist WIN 55212-2 (WIN) interacted to modulate voltage-dependent membrane currents of cones. A conventional patch-clamp method was used to record depolarization evoked whole-cell outward currents (Iout) and an inward calcium current (ICa) from the inner segment of cones in goldfish retinal slices. WIN had biphasic actions: low concentrations (<1 μM) increased the currents via Gs, while higher concentrations (>1 μM) decreased the currents via Gi/Go. Neither dopamine nor the D2 agonist quinpirole (1–20 μM) had a significant effect on either Iout or ICa. Quinpirole at 50 μM had a mild suppressive (∼20%) effect on Iout. However, quinpirole (<10 μM) completely blocked the enhancement of both currents seen with 0.7 μM WIN. The effect of quinpirole was blocked by sulpiride and by pertussis toxin, indicating that quinpirole was acting via a D2 receptor-Gi/o coupled mechanism. The suppressive action of 50 μM quinpirole (∼20%) was not additive with the suppressive effect of 3 μM WIN (∼40%). D2 agonists via Gi/o oppose the action of low concentrations of CB1 agonists acting via Gs to modulate cone membrane currents, suggesting a role in shaping the cone light response and/or sensitivity to changes in ambient light conditions. The nonadditive effect of high concentrations of WIN and quinpirole suggests that both decrease membrane currents via the same transduction pathway, Gi/Go protein kinase A (PKA).

Endogenous cannabinoids modulate neurotransmitter action and release in the brain. The effects are exerted on membrane permeability to Ca2+ and K+via protein kinase A (PKA). Cannabinoid CB1 receptors are present at the synaptic terminals of cones in goldfish retina. We investigated the effects of CB1 receptor agonist WIN 55212-2 on voltage-gated currents of goldfish cones. Whole-cell currents were recorded with conventional-patch-clamp methods in goldfish retinal slices. Depolarizing pulses elicited inward ICa and Ioutward that contained several components: IK, IA, and ICl. WIN 55212-2 (<1 μM) enhanced IK, ICl, and ICa, while at >1 μM, IK, ICl, and ICa were suppressed. The voltage-activation ranges of these currents were not affected. All effects of WIN 55212-2 were blocked by the CB1 receptor antagonist SR 141716A as well as the PKA inhibitor Wiptide. The enhancing effect of WIN 55212-2 was blocked selectively by 0.5 nM cholera toxin and the suppressive effect was blocked by pertussis toxin. The results obtained from long and short single cones and double cones were basically the same.

Cannabinoid CB1 receptors are distributed throughout the CNS and interact with GABA, glutamate, and dopamine systems. Cannabinoids have effects on the visual system, some of which may have a retinal component, particularly the enhancement of photosensitivity. We used immunocytochemistry and whole-cell recording to study cannabinoids in the goldfish retina. Immunoblots of an antiserum against amino acids (1-14) of the rat CB1 receptor produced a single band in goldfish retina at about 70 kDa. Light microscope immunocytochemistry of CB1 receptor immunoreactivity (CB1R-IR) revealed intense staining of Müller cells and weaker staining of ON bipolar cells (verified with double labeling with PKC-IR) and the outer and inner plexiform layers. Ultrastructural analysis revealed that CB1R-IR was localized intracellularly as well as on the plasma membrane of photoreceptor terminals, bipolar cell terminals and, rarely, amacrine cell boutons. Membrane-associated CB1R-IR was restricted to cone pedicles at sites removed from the synaptic ribbon. Regarding bipolar cells, membrane-associated CB1R-IR was found at 93% of the synaptic terminals in sublamina b (ON-type) and only at 33% of the synaptic terminals in sublamina a (OFF-type). Whole-cell recordings from large ON-type Mb bipolar cells showed that the delayed rectifier (IK(V)) was rapidly and reversibly inhibited by 1 μM of the cannabinoid agonists CP 54490 and (+)-WIN 55212-2, effects blocked completely by the antagonist SR 141716A (1 μM). Inhibition of IK(V) in the Mb bipolar cells by cannabinoids should result in a more tonic ON response to increments of light. As such, cannabinoids may play a role in modulating the temporal aspects of signaling in the retina.