Neocortical choline acetyltransferase (ChAT)-expressing interneurons are a subclass of vasoactive intestinal peptide (ChAT-VIP) neurons of which circuit and behavioural function are unknown. Here, we ...show that ChAT-VIP neurons directly excite neighbouring neurons in several layers through fast synaptic transmission of acetylcholine (ACh) in rodent medial prefrontal cortex (mPFC). Both interneurons in layers (L)1-3 as well as pyramidal neurons in L2/3 and L6 receive direct inputs from ChAT-VIP neurons mediated by fast cholinergic transmission. A fraction (10-20%) of postsynaptic neurons that received cholinergic input from ChAT-VIP interneurons also received GABAergic input from these neurons. In contrast to regular VIP interneurons, ChAT-VIP neurons did not disinhibit pyramidal neurons. Finally, we show that activity of these neurons is relevant for behaviour and they control attention behaviour distinctly from basal forebrain ACh inputs. Thus, ChAT-VIP neurons are a local source of cortical ACh that directly excite neurons throughout cortical layers and contribute to attention.
Summary
Aim
Studies using S‐ and R‐enantiomers of the SSRI citalopram have shown that R‐citalopram exerts an antagonistic effect on the efficacy of the antidepressant S‐citalopram (escitalopram) ...through an interaction at an allosteric modulator site on the serotonin transporter (SERT). Here, we show that protein kinase signaling systems are involved in the allosteric modulation of the SERT in vivo and in vitro.
Methods
We assessed the effects of nonspecific protein kinase inhibitor staurosporine in the action of escitalopram and/or R‐citalopram using electrophysiological and behavioral assays in rats and cell surface SERT expression measures in serotoninergic cells.
Results
Acute administration of R‐citalopram counteracted the escitalopram‐induced suppression of the serotonin (5‐HT) neuronal firing activity and increase of the head twitches number following L‐5‐hydroxytryptophan injection. Importantly, these counteracting effects of R‐citalopram were abolished by prior systemic administration of staurosporine. Interestingly, the preventing effect of staurosporine on 5‐HT neuronal firing activity was abolished by direct activation of protein kinase C with phorbol 12‐myristate 13‐acetate. Finally, in vitro, quantification of the amount of cell surface‐expressed SERT molecules revealed that R‐citalopram prevented escitalopram‐induced SERT internalization that was completely altered by staurosporine.
Conclusion
Taken together, these results highlight for the first time an involvement of protein kinases in the allosteric modulation of SERT function.
Attending the sensory environment for cue detection is a cognitive operation that occurs on a time scale of seconds. The dorsal and ventral medial prefrontal cortex (mPFC) contribute to separate ...aspects of attentional processing. Pyramidal neurons in different parts of the mPFC are active during cognitive behavior, yet whether this activity is causally underlying attentional processing is not known. We aimed to determine the precise temporal requirements for activation of the mPFC subregions during the seconds prior to cue detection. To test this, we used optogenetic silencing of dorsal or ventral mPFC pyramidal neurons at defined time windows during a sustained attentional state. We find that the requirement of ventral mPFC pyramidal neuron activity is strictly time-locked to stimulus detection. Inhibiting the ventral mPFC 2 s before or during cue presentation reduces response accuracy and hampers behavioral inhibition. The requirement for dorsal mPFC activity on the other hand is temporally more loosely related to a preparatory attentional state, and short lapses in pyramidal neuron activity in dorsal mPFC do not affect performance. This only occurs when the dorsal mPFC is inhibited during the entire preparatory period. Together, our results reveal that a dissociable temporal recruitment of ventral and dorsal mPFC is required during attentional processing.
We have recently reported that serotonin(4) (5-HT(4)) receptor agonists have a promising potential as fast-acting antidepressants. Here, we assess the extent to which this property may be optimized ...by the concomitant use of conventional antidepressants.
We found that, in acute conditions, the 5-HT(4) agonist prucalopride was able to counteract the inhibitory effect of the selective serotonin reuptake inhibitors (SSRI) fluvoxamine and citalopram on 5-HT neuron impulse flow, in Dorsal Raphé Nucleus (DRN) cells selected for their high (>1.8 Hz) basal discharge. The co-administration of both prucalopride and RS 67333 with citalopram for 3 days elicited an enhancement of DRN 5-HT neuron average firing rate, very similar to what was observed with either 5-HT(4) agonist alone. At the postsynaptic level, this translated into the manifestation of a tonus on hippocampal postsynaptic 5-HT(1A) receptors, that was two to three times stronger when the 5-HT(4) agonist was combined with citalopram. Similarly, co-administration of citalopram synergistically potentiated the enhancing effect of RS 67333 on CREB protein phosphorylation within the hippocampus. Finally, in the Forced Swimming Test, the combination of RS 67333 with various SSRIs (fluvoxamine, citalopram and fluoxetine) was more effective to reduce time of immobility than the separate administration of each compound.
These findings strongly suggest that the adjunction of an SSRI to a 5-HT(4) agonist may help to optimize the fast-acting antidepressant efficacy of the latter.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A subset of monoamine neurons releases glutamate as a cotransmitter due to presence of the vesicular glutamate transporters VGLUT2 or VGLUT3. In addition to mediating vesicular loading of glutamate, ...it has been proposed that VGLUT3 enhances serotonin (5-HT) vesicular loading by the vesicular monoamine transporter (VMAT2) in 5-HT neurons. In dopamine (DA) neurons, glutamate appears to be released from specialized subsets of terminals and it may play a developmental role, promoting neuronal growth and survival. The hypothesis of a similar developmental role and axonal localization of glutamate co-release in 5-HT neurons has not been directly examined. Using postnatal mouse raphe neurons in culture, we first observed that in contrast to 5-HT itself, other phenotypic markers of 5-HT axon terminals such as the 5-HT reuptake transporter (SERT) show a more restricted localization in the axonal arborization. Interestingly, only a subset of SERT- and 5-HT-positive axonal varicosities expressed VGLUT3, with SERT and VGLUT3 being mostly segregated. Using VGLUT3 knockout mice, we found that deletion of this transporter leads to reduced survival of 5-HT neurons in vitro and also decreased the density of 5-HT-immunoreactivity in terminals in the dorsal striatum and dorsal part of the hippocampus in the intact brain. Our results demonstrate that raphe 5-HT neurons express SERT and VGLUT3 mainly in segregated axon terminals and that VGLUT3 regulates the vulnerability of these neurons and the neurochemical identity of their axonal domain, offering new perspectives on the functional connectivity of a cell population involved in anxiety disorders and depression.
Serotonin (5-HT) exerts its diverse physiological and pharmacological effects through the activation of multiple receptor subtypes. One of the newest members of this family is the 5-HT(7) receptor. ...Increasing investigations on this receptor are currently undertaken to highlight its physiological and physiopathological significance. With the development of selective 5-HT(7) receptor ligands, preclinical studies have started to elucidate the functions of this receptor subtype in more details. Hence, growing body of evidence suggests that the 5-HT(7) receptor is involved in biological processes such as circadian rhythm and thermoregulation, in addition to disorders in which disturbances of the latter are considered to be an important contributing factor. Moreover, preclinical data support the use of 5-HT(7) receptor antagonism as a promising mechanism for the treatment of several dysfunctions such as cognitive deficits and, importantly, have also unveiled anxiolytic and antidepressant-like properties. In this review, we will report major advances in the discovery of 5-HT(7) receptor roles, with special emphasis on the potential application of their antagonists as novel anxiolytic and antidepressant drugs.
The physiological function of 5-HT(7) receptors is not yet fully determined. This study was designed to characterize the involvement of 5-HT(7) receptor in rat body temperature regulation and in ...adrenocorticotropic hormone (ACTH) and corticosterone secretion. In the first part of our study, acute administration of SB-269970 (0.1-1 mg/kg, i.p.), a potent and selective 5-HT(7) receptors antagonist, dose-dependently prevented 5-HT(1A/7) receptor agonist 8-OH-DPAT (0.1 mg/kg, s.c.)-induced hypothermia and when the 5-HT(1A) receptor antagonist WAY-100,635 was co-injected with SB-269970, a reduction of the latter hypothermia was obtained in an additive manner. In contrast, 1 mg/kg (i.p.) of SB-269970 failed to prevent 8-OH-DPAT (0.5 mg/kg, s.c.)-induced increase of ACTH and corticosterone plasma levels. In conclusion, the present results unveil an additive effect of both 5-HT(1A) and 5-HT(7) receptors in core body temperature regulation.
Current antidepressants are clinically effective only after several weeks of administration. Here, we show that serotonin4(5-HT4) agonists reduce immobility in the forced swimming test, displaying an ...antidepressant potential. Moreover, a 3 day regimen with such compounds modifies rat brain parameters considered to be key markers of antidepressant action, but that are observed only after 2-3 week treatments with classical molecules: desensitization of 5-HT1Aautoreceptors, increased tonus on hippocampal postsynaptic 5-HT1Areceptors, and enhanced phosphorylation of the CREB protein and neurogenesis in the hippocampus. In contrast, a 3 day treatment with the SSRI citalopram remains devoid of any effect on these parameters. Finally, a 3 day regimen with the 5-HT4agonist RS 67333 was sufficient to reduce both the hyperlocomotion induced by olfactory bulbectomy and the diminution of sucrose intake consecutive to a chronic mild stress. These findings point out 5-HT4receptor agonists as a putative class of antidepressants with a rapid onset of action.
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