Ultrastructural localization of the norepinephrine transporter in superficial and deep layers of the rat prelimbic prefrontal cortex and its spatial relationship to probable dopamine terminals

Abstract

The prefrontal cortex (PFC) is a likely site of action for the therapeutic efficacy of antidepressants that inhibit norepinephrine (NE) reuptake. Moreover, drugs that block the NE transporter (NET) increase extracellular levels of both NE and dopamine (DA), an interaction that may contribute to their therapeutic properties. To examine the subcellular localization of NET and to investigate the spatial relationships between presumed NE and DA axons within the rat prelimbic PFC, we combined immunogold-silver localization of NET with immunoperoxidase staining for the catecholamine synthetic enzyme tyrosine hydroxylase (TH). An additional aim was to quantify the proportion of profiles dually labeled for NET and TH to test the common observation that TH immunolabeling is relatively selective for DA axons. NET-immunoreactive (NET-ir) axonal profiles were typically unmyelinated and occasionally were observed to form symmetric axodendritic synapses. The majority of immunogold NET labeling was unexpectedly observed in the cytoplasm rather than on the plasma membrane. Furthermore, in tissue dually labeled for both NET and TH, only 8-10% of profiles contained both markers. Unlike observations for singly labeled profiles, gold-silver particles for NET in dually labeled axons were localized primarily to the plasmalemma. A systematic survey of terminals labeled only for TH revealed that they were typically separated by at least 1.2 mum from NET-ir varicosities, and the two profile types were not seen to contact common targets. These results suggest that, in the rat PFC, NE axons (1) contain predominantly cytoplasmic NET, (2) infrequently contain TH immunolabeling, and (3) may interact with probable DA afferents by means of extrasynaptic mechanisms.

Activation of β2-adrenoceptor enhances synaptic potentiation and behavioral memory via cAMP-PKA signaling in the medial prefrontal cortex of rats

“…Thus, b2-AR appears to play a distinct role in memory processing via coupling with different downstream signaling, although the mechanism responsible for the recruitment of different signaling by b2-AR is unknown. In the PFC, noradrenergic fibers originating from the brain stem target both deep and superficial layers of the cortex (Lewis and Morrison 1989;Miner et al 2003). Synaptic plasticity occurring in superficial layer 2/3 pyramidal cells of the cortex has been proposed to correspond to the trace fear conditioning (Wu et al 2008;Descalzi et al 2012).…”

Methylphenidate Increases Cortical Excitability via Activation of Alpha-2 Noradrenergic Receptors

“…Studies in humans, non-human primates, and rats have shown that the PFC receives catecholaminergic inputs from the midbrain (Porrino and Goldman-Rakic, 1982;Levitt et al, 1984;Lewis et al, 1987;Lewis and Morrison, 1989;Miner et al, 2003) and a substantial amount of data supports the conclusion that dopamine (DA) and noradrenaline (NE) are involved in aspects of executive function (selective attention, response selection/control), as well as arousal (NE). These actions of DA and NE have been postulated to occur via their effects in the cortex.…”

Amphetamine in Adolescence Disrupts the Development of Medial Prefrontal Cortex Dopamine Connectivity in a dcc-Dependent Manner

“…Varicosities represent sites where neurotransmitter synthesis, packaging, release, and reuptake most often occur (Benes et al, 1996). Furthermore, we and others have shown that the TH antibody used in these studies labels dopamine axons but rarely labels norepinephrine axons within the regions of interest (Miner et al, 2003;Manitt et al, 2011Manitt et al, , 2013. As in all our previous neuroanatomical studies, we obtained counts only from the right hemisphere because of the lateralization of dopamine systems.…”