Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2015 Mar 24;112(12):E1498-506.
doi: 10.1073/pnas.1500450112. Epub 2015 Feb 9.

Increased dopamine D2 receptor activity in the striatum alters the firing pattern of dopamine neurons in the ventral tegmental area

Sabine Krabbe  1 , Johanna Duda  2 , Julia Schiemann  1 , Christina Poetschke  2 , Gaby Schneider  3 , Eric R Kandel  4 , Birgit Liss  2 , Jochen Roeper  1 , Eleanor H Simpson  5
Affiliations

Increased dopamine D2 receptor activity in the striatum alters the firing pattern of dopamine neurons in the ventral tegmental area

Sabine Krabbe et al. Proc Natl Acad Sci U S A. .

Abstract

There is strong evidence that the core deficits of schizophrenia result from dysfunction of the dopamine (DA) system, but details of this dysfunction remain unclear. We previously reported a model of transgenic mice that selectively and reversibly overexpress DA D2 receptors (D2Rs) in the striatum (D2R-OE mice). D2R-OE mice display deficits in cognition and motivation that are strikingly similar to the deficits in cognition and motivation observed in patients with schizophrenia. Here, we show that in vivo, both the firing rate (tonic activity) and burst firing (phasic activity) of identified midbrain DA neurons are impaired in the ventral tegmental area (VTA), but not in the substantia nigra (SN), of D2R-OE mice. Normalizing striatal D2R activity by switching off the transgene in adulthood recovered the reduction in tonic activity of VTA DA neurons, which is concordant with the rescue in motivation that we previously reported in our model. On the other hand, the reduction in burst activity was not rescued, which may be reflected in the observed persistence of cognitive deficits in D2R-OE mice. We have identified a potential molecular mechanism for the altered activity of DA VTA neurons in D2R-OE mice: a reduction in the expression of distinct NMDA receptor subunits selectively in identified mesolimbic DA VTA, but not nigrostriatal DA SN, neurons. These results suggest that functional deficits relevant for schizophrenia symptoms may involve differential regulation of selective DA pathways.

Keywords: NMDA receptor; burst activity; dopamine D2 receptor; schizophrenia; ventral tegmental area.

PubMed Disclaimer

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.
Fig. 1.
Electrophysiological in vivo activity of identified DA midbrain neurons in D2R-OE and control mice. (A, Upper) In vivo single-unit activity of a DA VTA neuron from an isoflurane-anesthetized control mouse (Left) and corresponding interspike interval (ISI) histogram (Right, >10-min continuous recording). (Inset) Triphasic extracellular action potential (averaged waveform). (A, Middle) Schematic spike train representation of a longer recording period (Left) and the autocorrelation histogram (ACH; Right) with an initial peak illustrates the bursty activity pattern (>10-min continuous recording; gray lines indicate raw data, and the black line indicates the smoothed ACH fit). (A, Lower) Confocal images confirm that the neurobiotin (NB)-filled neuron (green) expressed TH (blue) and reveal that it was located in the VTA [green dot; schematic coronal plane relative to bregma −3.6 mm (56)]. (Scale bar: 20 μm.) (B) In vivo single-unit recording of a DA VTA neuron from an isoflurane-anesthetized D2R-OE mouse. Data are presented as in A. Note the longer ISIs and absence of burst activity in the neuronal activity compared with the DA VTA neuron from a control mouse in A. (C) In vivo single-unit recording of a DA SN neuron from a control mouse. Data are presented as in A. The recurrent equidistant peaks in the ACH reflect the high regularity of the cellular activity. This neuron was located in the rostral SN (coronal plane relative to bregma −3.16 mm). (D) In vivo single-unit recording of a DA SN neuron from a D2R-OE mouse. Data are presented as in A.
Fig. 2.
Fig. 2.
Analysis of in vivo recordings from DA VTA and DA SN neurons in D2R-OE and control mice. (A) Mean firing frequencies of identified DA VTA and DA SN neurons in control and D2R-OE mice; horizontal lines represent the mean. Note the significantly diminished rate in DA VTA neurons from D2R-OE mice compared with controls (DA VTA in control: n = 28 cells, n = 14 mice; DA VTA in D2R-OE: n = 22, n = 8; DA SN in control: n = 16, n = 8, DA SN in D2R-OE: n = 15, n = 7). (B) Mean burst set rate of DA VTA and SN neurons in control and D2R-OE mice; horizontal lines represent the median. Note the significantly diminished rate in DA VTA neurons from D2R-OE mice compared with controls (DA VTA in control: n = 28 cells, n = 14 mice; DA VTA in D2R-OE: n = 22, n = 8; DA SN in control: n = 16, n = 8, DA SN in D2R-OE: n = 15, n = 7). (C) Accordingly, the % SFB was selectively reduced in DA VTA neurons from mice with striatal D2R overexpression. Horizontal lines represent the median (DA VTA in control: n = 28 cells, n = 14 mice; DA VTA in D2R-OE: n = 22, n = 8; DA SN in control: n = 16, n = 8, DA SN in D2R-OE: n = 15, n = 7). (D) Relative distribution of firing patterns in DA VTA and SN neurons defined by GLO-dependent ACH classification (DA VTA in control: n = 28, DA VTA in D2R-OE: n = 19, DA SN in control: n = 16, DA SN in D2R-OE: n = 12). (E) Functional burst map. DA neurons recorded from control (left side, ●) and D2R-OE (right side, ○) mice are plotted corresponding to their position in the VTA (blue) and SN (green). The symbol size refers to the % SFB. Coronal planes are relative to bregma and are modified from Paxinos and Franklin (56) (also Tables S1–S3). *P < 0.05; **P < 0.005.
Fig. 3.
Fig. 3.
Electrophysiological in vivo characteristics of identified DA midbrain neurons in D2R-OE and control mice after Dox treatment. (A) In vivo single-unit recording of a DA VTA neuron from an isoflurane-anesthetized control mouse after Dox treatment. (B) In vivo single-unit recording of a DA VTA neuron from an isoflurane-anesthetized D2R-OE mouse after Dox treatment. Note the similarity of firing frequency and the persistent absence of bursts in the neuronal activity compared with the DA VTA neuron from a control mouse depicted in A. (C) In vivo single-unit recording of a DA SN neuron from a control mouse after Dox treatment. (D) In vivo single-unit recording of a DA SN neuron from a D2R-OE mouse after Dox treatment. All data are presented as in Fig. 1A.
Fig. 4.
Fig. 4.
Analysis of in vivo recordings from DA VTA and SN neurons in D2R-OE and control mice after Dox treatment. (A) Mean firing frequencies of identified DA VTA and SN neurons in D2R-OE and control mice after Dox treatment; horizontal lines indicate the mean. Normalization of striatal D2R activity restores the in vivo firing rates of DA VTA neurons in D2R-OE mice to control levels (DA VTA in control: n = 15, n = 6; DA VTA in D2R-OE: n = 16, n = 6; DA SN in control: n = 10, n = 5, DA SN in D2R-OE: n = 10, n = 4). (B) Mean burst rate of DA VTA and SN neurons; horizontal lines represent the median. The burst rate is persistently diminished in DA VTA neurons from D2R-OE mice after 5 wk of Dox treatment (DA VTA in control: n = 15, n = 6; DA VTA in D2R-OE: n = 16, n = 6; DA SN in control: n = 10, n = 5, DA SN in D2R-OE: n = 10, n = 4). (C) % SFB is also persistently reduced in DA VTA neurons after normalization of striatal D2R overexpression. Horizontal lines represent the median (DA VTA in control: n = 15, n = 6; DA VTA in D2R-OE: n = 16, n = 6; DA SN in control: n = 10, n = 5, DA SN in D2R-OE: n = 10, n = 4). (D) Relative distribution of firing patterns in DA VTA and SN neurons defined by GLO-dependent ACH classification after Dox treatment (DA VTA in control: n = 12, DA VTA in D2R-OE: n = 14, DA SN in control: n = 8, DA SN in D2R-OE: n = 10). (E) Functional burst map. Data are presented as in Fig. 2E (also Tables S2–S4). *P < 0.05.
Fig. 5.
Fig. 5.
NMDA receptor subunit mRNA levels in mesolimbic DA VTA and nigrostriatal DA SN neurons of D2R-OE and control mice. (A, C, and E) Mesolimbic DA VTA neurons. (B, D, and F) Nigrostriatal DA SN neurons. (A) Mesolimbic DA VTA tracing. (Left) Verification of the injection site of red fluorescent retrobeads in the NAc core and shell. TH counterstaining is shown in green. The section is aligned with diagrams from Paxinos and Franklin (56). (Middle and Right) Schematic mapping of all mesolimbic injection sites [center of injection, coronal planes relative to bregma: 1.70 mm and 1.34 mm; modified from Paxinos and Franklin (56)]. CPu, caudate putamen. (B) Nigrostriatal DA SN tracing. Data are presented as in A. Injection sites of red fluorescent retrobeads were verified to be in the CPu (coronal planes relative to bregma: 0.86 mm and 0.34 mm). GP, globus pallidus. (C) Identification of mesolimbic DA VTA neurons. (Left) Single mesolimbic DA VTA neuron in a coronal fixed midbrain section, identified via fluorescent retrobead labeling, before UV-LMD (white line marks cutting line of the laser). (Scale bar: 25 μm.) (Right) Agarose gel electrophoresis of UV-LMD multiplex-nested RT-PCR products for positive and negative marker genes. CB, calbindin d-28k, GAD, l-gluatamate decarboxylase 65 and 67. Only TH-positive and GFAP- and GAD-negative cDNA pools from mesolimbic DA neurons were included in the NMDA receptor subunit qPCR expression analysis. (D) Identification of nigrostriatal DA SN neurons. Data are presented as in C. Only TH-positive and CB-, GFAP-, and GAD-negative cDNA pools from nigrostriatal DA neurons were included in the NMDA receptor subunit qPCR expression analysis. (E) RT-qPCR results for NMDA receptor α and β subunits from mesolimbic DA VTA neurons. Note the significantly lower mRNA levels of NR1 and NR2B in D2R-OE mice compared with control mice. Details are provided in Table 1. *P < 0.05. (F) RT-qPCR results for NMDA receptor subunits from nigrostriatal DA SN neurons. (G) Schematic mapping of all neurons dissected by UV-LMD and analyzed by RT-qPCR in the VTA (blue) and SN (green) of control (left side, ●) and D2R-OE (right side, ○) mice. Coronal planes relative to bregma [modified from Paxinos and Franklin (56)].
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

See all "Cited by" articles

References

    1. Bleuler E. Dementia Praecox or the Group of Schizophrenias. International Universities Press; New York: 1950. trans Zinkin J.
    1. Kraepelin E. Dementia Praecox and Paraphrenia. Kreiger Publishing Company; Huntington, NY: 1919. trans Barclay RM.
    1. APA . Diagnostic and Statistical Manual of Mental Disorders. 5th Ed American Psychiatric Publishing; Arlington, VA: 2013.
    1. Barch DM. The cognitive neuroscience of schizophrenia. Annu Rev Clin Psychol. 2005;1:321–353. - PubMed
    1. Rabinowitz J, et al. Negative symptoms have greater impact on functioning than positive symptoms in schizophrenia: Analysis of CATIE data. Schizophr Res. 2012;137(1-3):147–150. - PubMed

Publication types

Substances