Dopamine innervation of monkey entorhinal cortex: Postsynaptic targets of tyrosine hydroxylase-immunoreactive terminals

Abstract

Dopamine (DA) has been demonstrated to play an important role in regulating cortical activity in both neocortical and periallocortical regions. However, marked differences between these two types of cortices in the laminar pattern of DA axons, the types and distribution of DA receptors, and the postnatal development of the DA innervation suggest that DA may have region-specific effects. Such regional specialization may also include the types of cortical cells apposed to DA terminals. In neocortical regions, such as the prefrontal and motor cortices, the majority of structures apposed to DA terminals appear to be the dendritic spines and shafts of pyramidal cells, and a minority are dendrites immunoreactive for gamma-amino butyric acid (GABA). However, the identity of the neural elements apposed to DA terminals in the entorhinal cortex, a periallocortical region, is unknown. In this study, we used immunocytochemical techniques and antibodies against tyrosine hydroxylase (TH) and GABA, visualized with preembedding immunoperoxidase and immunogold-silver labels, respectively, to examine DA terminals and their targets with electron microscopy. In the superficial layers of the monkey entorhinal cortex, TH-immunoreactive (IR) terminals varied greatly in size and formed thin, symmetric synapses. The majority of dendritic structures apposed to these TH-terminals were not GABA-IR, and included both dendritic shafts (64%) and spines (14%). A minority (22%) of the apposed dendrites were GABA-IR. A similar distribution of targets was observed for the subset of TH-IR terminals with identifiable synaptic specializations. In addition, the proportions of GABA-labeled and unlabeled dendrites apposed to TH terminals did not differ from those previously reported for monkey prefrontal cortex. These findings indicate that DA terminals provide direct input to both excitatory and inhibitory cells in the monkey entorhinal cortex and suggest that the effects of DA are mediated through a set of targets that are common to both neo- and periallocortex.

Dopaminergic Regulation of Neuronal Excitability through Modulation ofIhin Layer V Entorhinal Cortex

“…The subcellular localization of DA receptors in the EC is not yet clearly characterized. However, it has been observed that most DAergic synapses appear to contact dendritic shafts or spines (Erickson et al, 2000). Others have observed a laminar distribution of D 1 receptors in the EC consistent with modulation of dendritic inputs (Richfield et al, 1989;Goldsmith and Joyce, 1994).…”

Timing matters in elaborative processing of positive stimuli: Gamma band reactivity in schizophrenia compared to depression and healthy adults

“…In humans, reward is associated with the dopaminergic activity, including gamma activity involving the nucleus accumbens (Cohen et al, 2009). Furthermore, interventions for schizophrenia directed at dopamine-modulated GABA receptor function (Erickson et al, 2000) also alter frontal gamma power (Lewis et al, 2008). Given that the majority of people with schizophrenia are prescribed medications that serve as dopamine antagonists, it is possible that reductions in gamma band activity could be due to medication effects.…”

Abnormal semantic processing in females with fragile X‐associated tremor/ataxia syndrome

“…Hokama et al 2003;Kutas et al 2013;Nestor et al 1997;Salisbury et al 2002). Furthermore, dopamine modulates cortical glutamatergic activity via multiple mechanisms, including D1 receptors on dendritic spines that modulate excitatory inputs to temporal association cortex (Erickson et al 2000;Sesack et al 2003;Smiley et al 1992Smiley et al , 1994. Thus, both glutamatergic and/or dopaminergic neural transmission abnormalities may underlie the altered N400 congruity effect in these women affected by FXTAS.…”